Content uploaded by Alan S Weakley
Author content
All content in this area was uploaded by Alan S Weakley on Aug 02, 2016
Content may be subject to copyright.
United States Department of Agriculture
Forest Rocky Mountain General Technical
Service Research Station Report RMRS-GTR-346 August 2016
Classification and Description of
World Formation Types
Don Faber-Langendoen, Todd Keeler-Wolf, Del Meidinger, Carmen Josse,
Alan Weakley, David Tart, Gonzalo Navarro, Bruce Hoagland,
Serguei Ponomarenko, Gene Fults, Eileen Helmer
Faber-Langendoen, D.; Keeler, T.; Meidinger, D.; Josse, C.; Weakley, A.; Tart, D.; Navarro, G.;
Hoagland, B.; Ponomarenko, S.; Fults, G.; Helmer, E. 2016. Classification and
description of world formation types. Gen. Tech. Rep. RMRS-GTR-346. Fort
Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain
Research Station. 222 p.
Abstract
An ecological vegetation classification approach has been developed in which a combi-
nation of vegetation attributes (physiognomy, structure, and floristics) and their response
to ecological and biogeographic factors are used as the basis for classifying vegetation
types. This approach can help support international, national, and subnational classifica-
tion efforts. The classification structure was largely developed by the Hierarchy Revisions
Working Group (HRWG), which contained members from across the Americas. The
HRWG was authorized by the U.S. Federal Geographic Data Committee (FGDC) to devel-
op a revised global vegetation classification to replace the earlier versions of the structure
that guided the U.S. National Vegetation Classification and International Vegetation
Classification, which formerly relied on the UNESCO (1973) global classification (see
FGDC 1997; Grossman and others 1998). This document summarizes the develop-
ment of the upper formation levels. We first describe the history of the Hierarchy
Revisions Working Group and discuss the three main parameters that guide the clas-
sification—it focuses on vegetated parts of the globe, on existing vegetation, and includes
(but distinguishes) both cultural and natural vegetation for which parallel hierarchies are
provided. Part I of the report provides an introduction to the overall classification, focus-
ing on the upper formation levels. Part II provides a description for each type, following
a standardized template format. These descriptions are a first preliminary effort at global
descriptions for formation types, and are provided to give some guidance to our concepts.
Cover photos of Cool Temperate Forests from around the world. Clockwise from
top left:
1. Western Eurasian Forest & Woodland division: European beech (Fagus sylvatica)
forest in Czech Republic (by Scott Franklin)
2. Eastern North American Forest & Woodland division: Eastern Hemlock-Sugar
Maple (Tsuga canadensis-Acer saccharum) forest in central Wisconsin, United States
(by Don Faber-Langendoen).
3. Eastern Asian Forest & Woodland division: Oak-pine / bamboo forest in Foping
National Nature Reserve, Shaanxi Province, China (by Scott Franklin)
4. Valdivian Forest division: Southern beech (Nothofagus spp.) forest in Altos de Lircay
National Reserve, Chile (by Bruce Young)
5. Southeast Australian Cool Temperate Forest & Woodland division: Australian Alps -
mainly Mountain Ash (Eucalyptus regnans) (by Andy Gillison)
Classification and Description of
World Formation Types
Don Faber-Langendoen, Todd Keeler-Wolf, Del Meidinger, Carmen Josse,
Alan Weakley, David Tart, Gonzalo Navarro, Bruce Hoagland,
Serguei Ponomarenko, Gene Fults, Eileen Helmer
Hierarchy Revisions Working Group
FGDC Vegetation Subcommittee
Forest Rocky Mountain General Technical
Service Research Station Report RMRS-GTR-346 August 2016
United States Department of Agriculture
i
ii
Authors
(in order of authorship)
Don Faber-Langendoen: NatureServe, Conservation Science Division,
Arlington, VA
Todd Keeler-Wolf: Biogeographic Data Branch, California
Department of Fish and Game, Sacramento, CA
Del Meidinger: Meidinger Ecological Consultants Ltd., Victoria
BC
Carmen Josse: NatureServe, Conservation Science Division,
Arlington, VA
Alan Weakley: North Carolina Botanic Garden, University of
North Carolina at Chapel Hill, Chapel Hill, NC
David Tart: USDA Forest Service - Intermountain Region,
Natural Resources, Ogden, UT
Gonzalo Navarro: Universidad Católica Boliviana “San Pablo,
Cochabamba, Bolivia
Bruce Hoagland: Oklahoma Biological Survey and Department
of Geography, The University of Oklahoma,
Norman, OK
Serguei Ponomarenko: Ecological Integrity Branch, Parks Canada,
Gatineau, Québec
Gene Fults: Natural Resources Conservation Service - West
National Technology Support Center, Portland,
OR
Eileen Helmer: USDA Forest Service - International Institute of
Tropical Forestry, Fort Collins, CO
iii
Acknowledgments
The work produced here was supported by the U.S. National Vegetation
Classification partnership between U.S. Federal agencies, the Ecological Society
of America, and NatureServe staff, working through the Federal Geographic Data
Committee (FGDC) Vegetation Subcommittee. FGDC sponsored the mandate of the
Hierarchy Revisions Working Group, which included international expertise into the
process. For that reason, this product represents a collaboration of national and inter-
national vegetation ecologists.
We thank Ralph Crawford, chair of the FGDC vegetation subcommittee. We grate-
fully acknowledge the support of the U.S. Federal agencies that helped fund the work
of the Hierarchy Revisions Working Group from 2003 to 2012. We appreciate their pa-
tience with our slow progress on this effort. Most recently, the U.S. Geological Survey,
and in particular Alexa McKerrow, has supported the development of the formation
descriptions that are provided in this document.
We appreciate the support of the Ecological Society of America Vegetation
Classification Panel for their peer review of this document. In particular, we thank the
Panel’s chair, Scott Franklin, for facilitating review among the panel and internation-
ally. Through his efforts, we benefited from international reviewers, including Ken
Baldwin, John Benson, Sara del Río González, Jesus Izco, David Keith, Ángel Penas
Merino, Salvador Rivas-Martínez, Michael Rutherford, and Daniel Sánchez-Mata, and
we thank them for their input. A special thanks to Ángel Penas Merino for creating the
North American and European macrobioclimate maps for this report.
Over the years, various members of the HRWG have participated for a period of
time. We thank Sherm Karl, Otto Huber, Jean-Pierre Saucier, and Andy Gray for their
input at critical stages early on in the development of the formations.
We thank Mary Russo and Kristin Snow, of NatureServe, for maintaining and
editing the classification database and producing the Level 1–Level 3 description
documents for Part II.
iv
v
Executive Summary
An ecological vegetation (EcoVeg) classification approach has been developed in
which a combination of vegetation attributes (physiognomy, structure, and floristics)
and their response to ecological and biogeographic factors are used as the basis for
classifying vegetation types (Faber-Langendoen and others 2014). This approach can
help support international, national, and subnational classification efforts. Support for
many aspects of the development of classification was provided by the U.S. National
Vegetation Classification (USNVC) partnership, in conjunction with development of
the International Vegetation Classification (IVC) (FGDC 2008; Faber-Langendoen
and others 2009; Jennings and others 2009). The classification structure was largely
developed by the Hierarchy Revisions Working Group (HRWG), which contained
members from across the Americas. The group was authorized by the U.S. Federal
Geographic Data Committee (FGDC) Vegetation Subcommittee (chaired by the U.S.
Forest Service), to develop a revised global vegetation classification to replace the
earlier versions of the structure that guided the USNVC and IVC, which relied on the
UNESCO (1973) global classification (see FGDC 1997; Grossman and others 1998).
This document summarizes the development of the upper formation levels.
We first describe the history of the Hierarchy Revisions Working Group and discuss
the three main parameters that guide the classification—it focuses on vegetated parts
of the globe, on existing vegetation, and includes (but distinguishes) both cultural and
natural vegetation for which parallel hierarchies are provided.
For natural vegetation, we define three main physiognomic levels: Formation
Class, Formation Subclass, and Formation; each of the types for all three levels is
also described. For cultural vegetation, we define and describe four main physiog-
nomic levels: Cultural Class, Cultural Subclass, Cultural Formation, and Cultural
Subformation. We use a fourth physiognomic level for cultural vegetation because the
floristic/biogeographic patterns used for natural vegetation at the fourth level are not
nearly as relevant for cultural vegetation. We provide guidance for developing forma-
tion type description and nomenclature.
The upper levels were not developed in a strictly top down manner. Rather, mem-
bers of the HRWG had access to draft mid and lower level units (from Division to
Association) for the United States and parts of Canada and Latin America. A compre-
hensive master spreadsheet of these draft units was organized under the upper levels
and was used to critique the overall “naturalness” of the formation units. The HRWG
reevaluated formation concepts where formations introduced undesirable splits in
lower units that were otherwise ecologically and floristically similar. Our goal was to
make splits between upper level types that had good ecological and vegetation sup-
port for them. Still, inevitably, given the multi-dimensional and continuous gradients
affecting vegetation, some criteria for upper levels require splitting otherwise closely
related floristic and physiognomic types (e.g., open woodland from grassland, flood-
plain forest from upland forest).
vi
Part I of the report provides an introduction to the overall classification, focusing
on the upper formation levels. Appendices provide important information on members
of the working group, a draft set of formation types at all three levels, growth forms
used to describe the types, and comparisons with other formation level classifications.
Appendix I provides a key to Level 1. Appendix J introduces examples of the Division
level, the level immediately below formation. A comprehensive set of Divisions for
all formations is a key next step in the process of establishing an ecological vegetation
classification framework.
Part II provides a description for each type, following a standardized template
format. The HRWG had limited time to develop descriptions, and we focused more
on developing consistent, meaningful concepts than extensive descriptive text. Thus,
these descriptions are a first preliminary effort at global descriptions for formation
types, and are provided to give some guidance to our concepts. Undoubtedly, even
these preliminary descriptions are biased by our western hemisphere perspective. We
look forward to engaging with a broader set of ecologists around the globe to continue
improving both the concepts and the descriptions. We hope such collaboration can
develop, in part, by identifying vegetation types at the Division level around the globe.
vii
Contents
Executive Summary ....................................................v
Part I: Development of the U.S. National Vegetation Classication Hierarchy ...1
Introduction ...........................................................3
Background ...........................................................3
Hierarchy Revisions Working Group .....................................3
Phase I: ......................................................4
Phase II: .....................................................6
Context for the Hierarchy ..............................................6
Vegetated – Non-Vegetated: .....................................7
Existing Vegetation: ............................................7
Natural and Cultural Vegetation: ..................................7
Summary ....................................................8
The Hierarchy .........................................................9
Development of the Upper Levels .........................................9
Ecological Approach to Organizing Formation Class Types: ...........13
Terminology for Formation Names: ...............................13
Zonal and Azonal Vegetation ....................................14
Development of Natural Formations ......................................14
Formation Class ....................................................14
1. Forest & Woodland (Mesomorphic Tree Vegetation) ...............14
2. Shrub & Herb Vegetation (Mesomorphic Shrub & Herb Vegetation). ...16
3. Desert & Semi-Desert (Xeromorphic Woodland, Scrub &
Grassland Vegetation). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Polar And High Montane Scrub & Grassland (Cryomorphic Scrub,
Herb And Cryptogam Vegetation) ..............................17
5. Aquatic Vegetation (Hydromorphic Vegetation) ...................17
6. Open Rock Vegetation (Cryptogam —Open Mesomorphic Vegetation) . 17
Wetlands ....................................................18
Formation Subclass ..................................................19
Formation .........................................................24
Formation Issues ..............................................24
Wetland Formations ...........................................26
viii
Summary of Criteria for Natural Formations ..............................28
Development of Cultural Formations ......................................28
Cultural Class ......................................................29
Cultural Subclass ...................................................29
Cultural Formation ..................................................30
Type Description .....................................................30
Upper Level Nomenclatural Rules ......................................30
Description Template ................................................32
Peer Review .......................................................32
A Key to the Formations ...............................................32
Synopsis ..........................................................33
Part II: Description of World Formation Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
1. Forest & Woodland (C01) .............................................37
1.A. Tropical Forest & Woodland (S17) ..................................40
1.A.1. Tropical Dry Forest & Woodland (F003) .....................42
1.A.2. Tropical Lowland Humid Forest (F020) ......................46
1.A.3. Tropical Montane Humid Forest (F004) ......................49
1.A.4. Tropical Flooded & Swamp Forest (F029) ....................51
1.A.5. Mangrove (F006) ........................................54
1.B. Temperate & Boreal Forest & Woodland (S15) ........................56
1.B.1. Warm Temperate Forest & Woodland (F018) ..................60
1.B.2. Cool Temperate Forest & Woodland (F008) ...................62
1.B.3. Temperate Flooded & Swamp Forest (F026) ..................66
1.B.4. Boreal Forest & Woodland (F001) ..........................68
1.B.5. Boreal Flooded & Swamp Forest (F036) ......................72
2. Shrub & Herb Vegetation (C02) ........................................74
2.A. Tropical Grassland, Savanna & Shrubland (S01) .......................77
2.A.1. Tropical Lowland Grassland, Savanna & Shrubland (F019) .......79
2.A.2. Tropical Montane Grassland & Shrubland (F017) ..............84
2.A.3. Tropical Scrub & Herb Coastal Vegetation (F024) ..............86
2.B. Temperate & Boreal Grassland & Shrubland (S18) .....................88
2.B.1. Mediterranean Scrub & Grassland (F038) .....................89
2.B.2. Temperate Grassland & Shrubland (F012) ....................92
2.B.3. Boreal Grassland & Shrubland (F028) .......................96
2.B.4. Temperate to Polar Scrub & Herb Coastal Vegetation (F005) ......98
ix
2.C. Shrub & Herb Wetland (S44) .....................................100
2.C.1. Tropical Bog & Fen (F002) ...............................102
2.C.2. Temperate to Polar Bog & Fen (F016) ......................103
2.C.3. Tropical Freshwater Marsh, Wet Meadow & Shrubland (F030) ...106
2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow &
Shrubland (F013) .......................................108
2.C.5. Salt Marsh (F035) ...................................... 111
3. Desert & Semi-Desert (C03) ..........................................113
3.A. Warm Desert & Semi-Desert Woodland, Scrub & Grassland (S06) ........115
3.A.1. Tropical Thorn Woodland (F039) ..........................117
3.A.2. Warm Desert & Semi-Desert Scrub & Grassland (F015) ........119
3.B. Cool Semi-Desert Scrub & Grassland (S11) ..........................120
3.B.1. Cool Semi-Desert Scrub & Grassland (F033) .................121
4. Polar & High Montane Scrub, Grassland & Barrens (C04) ..................123
4.A. Tropical High Montane Scrub & Grassland (S16) .....................125
4.A.1. Tropical High Montane Scrub & Grassland (F022) ............127
4.B. Temperate to Polar Alpine & Tundra Vegetation (S12). . . . . . . . . . . . . . . . . . 129
4.B.1. Temperate & Boreal Alpine Vegetation (F037) ................132
4.B.2. Polar Tundra & Barrens (F031) ............................134
5. Aquatic Vegetation (C05) ............................................136
5.A. Saltwater Aquatic Vegetation (S09) ................................138
5.A.1. Floating & Suspended Macroalgae Saltwater Vegetation (F052) ..139
5.A.2. Benthic Macroalgae Saltwater Vegetation (F053) ..............140
5.A.3. Benthic Vascular Saltwater Vegetation (F054) ................142
5.A.4. Benthic Lichen Saltwater Vegetation (F055) ..................143
5.B. Freshwater Aquatic Vegetation (S13) ...............................144
5.B.1. Tropical Freshwater Aquatic Vegetation (F056) ...............146
5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057) .......149
6. Open Rock Vegetation (C06) .........................................151
6.A. Tropical Open Rock Vegetation (S02) ..............................154
6.A.1. Tropical Cliff, Scree & Other Rock Vegetation (F011) ..........156
6.B. Temperate & Boreal Open Rock Vegetation (S04) .....................157
6.B.1. Temperate & Boreal Cliff, Scree & Other Rock Vegetation (F034) 160
7. Agricultural & Developed Vegetation (C07) .............................162
7.A. Woody Agricultural Vegetation (S22) ...............................164
x
7.A.1. Woody Horticultural Crop (F042) ..........................165
7.A.2. Forest Plantation & Agroforestry (F043) ....................166
7.A.3. Woody Wetland Horticultural Crop .........................167
7.B. Herbaceous Agricultural Vegetation (S23) ...........................168
7.B.1. Row & Close Grain Crop (F044) ...........................169
7.B.2. Pasture & Hay Field Crop (F045) ..........................169
7.B.3. Herbaceous Horticultural Crop (F050) ......................170
7.B.4. Fallow Field & Weed Vegetation (F046) .....................171
7.B.5. Herbaceous Wetland Crop (F058) ..........................172
7.C. Herbaceous & Woody Developed Vegetation (S21) ....................172
7.C.1. Lawn, Garden & Recreational Vegetation (F040) ..............173
7.C.2. Other Developed Vegetation (F051) ........................174
7.C.3. Developed Wetland Vegetation (F059) ......................175
7.D. Agricultural & Developed Aquatic Vegetation (S24) ...................175
7.D.1. Agricultural Aquatic Vegetation (F047) .....................176
7.D.2. Developed Aquatic Vegetation (F048) ......................178
References ..........................................................179
Appendix A—Hierarchy Revisions Working Group
2010–2012. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Appendix B. Formation level units, Level 1 to Level 3. .......................191
Appendix C. Glossary Terms ...........................................194
Appendix D. Growth Form Names, Codes, and Denitions ...................200
Appendix E. Growth Forms from Box and Fujiwara (2005) ...................204
Appendix F. Comparisons to Other Formation-Level Classications ............206
Appendix G. Example of Descriptive Methods for Describing
Physiognomy — Structure ........................................212
Appendix H. Key to bioclimatic maps of the world—Rivas
Martinez & Rivas-Saenz ..........................................214
Appendix I. Key to Formation Class (Level 1) ..............................215
Appendix J. Examples of Divisions ......................................220
USDA Forest Service RMRS-GTR-346. 2016. 1
Part I: Development of the U.S. National
Vegetation Classification Hierarchy
2 USDA Forest Service RMRS-GTR-346. 2016.
USDA Forest Service RMRS-GTR-346. 2016. 3
Introduction
There is currently no fully suitable classification framework by which vegetation
ecologists can organize, define, and describe global vegetation patterns at multiple
scales, from broad physiognomic types to narrowly defined floristic types. Some clas-
sification publications provide little more than a name. Others provide very expansive
descriptions but with only some or little consistency to the classification, and others
focus solely on either structural or floristic patterns. What is needed is a compre-
hensive, global vegetation classification approach that is multi-scalar, from broad
global types to local fine scale types. It should be committed to a rigorous plot-based
approach while building on the accumulated work of vegetation ecologists over the
past century, open to ongoing peer review, and able to maintain an authoritative list of
types at all times that can be used for description, inventory, monitoring, and mapping.
Here, we briefly introduce an ecological vegetation (EcoVeg) classification ap-
proach that addresses these needs and then focus on the development and rationale
for the upper formation levels. These formations, both natural and cultural, provide
a basic synopsis of the world’s vegetation that is structured by specific criteria with
sufficient detail to encourage consistent application anywhere in the world and within
a multi-scale hierarchical structure. Details of the scientific basis for the classification
approach are provided in Jennings and others (2009) and Faber-Langendoen and oth-
ers (2014) who build on the integrated “physiognomic-floristic-ecologic,” or EcoVeg,
approach to vegetation classification (Bohn and others 2000-2003; Brown and others
1998; Davies and others 2004; Devilliers and others 1991, 1996; Rodwell and others
2002; Rübel 1930–1931, in Shimwell 1971; Whittaker 1962). Appendices to this
report contain specific descriptions to each formation and a key to the uppermost
formation class level, along with comparisons to other global formation level classifi-
cations. The classification has been developed to support the U.S. National Vegetation
Classification (FGDC 2008), other partner classifications, such as the Canadian and
Bolivian NVC, and constitutes a revision of the International Vegetation Classification
(Grossman and others 1998) that was based on UNESCO (1973).
Background
Hierarchy Revisions Working Group
The U.S. National Vegetation Classification (USNVC) emerged through a partner-
ship between Federal agencies and nongovernmental organizations—NatureServe
and the Ecological Society of America’s Vegetation Classification Panel (hereafter
Panel)—through the auspices of the Federal Geographic Data Committee Vegetation
Subcommittee (FGDC 1997), chaired by the U.S. Forest Service. The USNVC
originally adopted the international structure of UNESCO (1973 see also Appendix
B in Mueller-Dombois and Ellenberg 1974) for its classification. At the same time
NatureServe supported applications of the UNESCO-based structure in other coun-
tries through the International Vegetation Classification (IVC) (Grossman and others
1998). Thus, when the USNVC partners agreed in 2003 to undertake a revision to the
USNVC, an international approach was adopted, reflecting the goals to incorporate
global classification concepts and to avoid an artificial national perspective on units.
Our goal was to concentrate on the natural structuring of vegetation world-wide and to
4 USDA Forest Service RMRS-GTR-346. 2016.
emphasize the physiognomic-structural, floristic and ecological components of vegeta-
tion, without relying on a particular emphasis on any single predominant criterion such
as height, woodiness, cover, environmental schema, or other human uses. To this end,
the partners agreed to form a Hierarchy Revisions Working Group (HRWG) sponsored
by FGDC. The work of the HRWG progressed in two phases, the first phase from
2003–2008, and the second phase from 2010–2013.
Phase I:
The Hierarchy Revisions Working Group (HRWG) was formed in November
of 2003, co-chaired by representatives of the U.S. Forest Service (USFS) and
NatureServe. Members were drawn from State and Federal agencies and organizations
in the United States, Canada, and Latin America. All were chosen based on either their
familiarity with the USNVC, IVC and related classifications or for their expertise in
vegetation classification. Members were also encouraged to have their own “teams”
with which to consult, including the U.S. Forest Service Vegetation Technical Guide
team that developed an existing vegetation classification and mapping manual (Brewer
and others 2005; Tart and others 2005a,b), NatureServe staff who developed meso-
scale classification units called ‘‘terrestrial ecological systems’’ (Comer and others
2003; Comer and Schulz 2007; Josse and others 2003), and California vegetation
ecologists who tested the hierarchy above the alliance level on California’s vegetation
(see Sawyer and others 2009, Appendix 3). The HRWG interacted regularly with the
ESA Panel, Federal agencies, and NatureServe staff.
The HRWG process was somewhat formal, consisting of more or less bimonthly
phone calls between November 2003 and November 2007, and three face-to-face
meetings (May 3–6, 2004 in Denver, Colorado; May 22–25, 2005 in Washington, DC;
March 8–10, 2007 in Mojave, California). The result was a suggested eight-level hi-
erarchy to replace the seven-level hierarchy then in use (FGDC 1997). The lower two
floristic levels, alliance and association, were retained as is, and the top five formation
levels were compressed into three to make way for three new physiognomic-floristic
mid-levels. In 2006, FGDC began the formal process for the USNVC revision,
incorporating both the HRWG suggestions on the full hierarchy and the ESA Panel’s
work on standards for the lower floristic levels. The HRWG continued to advise the
USNVC partners through 2007 and 2008, leading to a formal revised FGDC Standard
(2008). This Standard established the hierarchical framework of the USNVC and the
processes for establishing and revising USNVC types. At that time, a formal report
describing the EcoVeg approach that the USNVC is based on was drafted by the
HRWG (Faber-Langendoen and others 2007), and later published (Faber-Langendoen
and others 2012). Lower floristic level guidelines were published by Jennings and oth-
ers (2009).
The revised standard was a substantial overhaul of the 1997 standard and the clas-
sification, as summarized by FGDC (2008):
a.
uses vegetation criteria to define all types (de-emphasizing abiotic criteria, such
as hydrologic regimes in wetland types),
USDA Forest Service RMRS-GTR-346. 2016. 5
b. provides a clear distinction between natural (including semi-natural) vegetation
and cultural vegetation wherever these can be observed from broad growth form
patterns (rather than combining natural and cultural vegetation initially and
separating them at lower levels),
c. defines, for natural vegetation, the upper levels of the hierarchy based on broad
growth form patterns that reflect ecological relationships (rather than detailed
structural criteria, which are more effectively used in combination with floristic
criteria in lower levels of the hierarchy),
d.
provides a new set of mid levels for natural vegetation units that bridge the large
conceptual gap between alliance and formation,
e. integrates the physiognomic and floristic hierarchy levels based on ecologic
vegetation patterns, rather than developing the physiognomic and floristic levels
independently and then forcing them into a hierarchy,
f. provides detailed standards for plot data collection, type description and
classification, data management and peer review of natural vegetation,
g. provides a dynamic content standard for the USNVC that allows the FGDC
partner agencies and organizations to revise the classification and its component
vegetation types through a peer review process, and
h. provides, for cultural vegetation, an independent set of levels that addresses the
particular needs of cultural vegetation.
The structure of the revised hierarchy is a substantial revision of the 1997 hierarchy,
which relied heavily on the UNESCO (1973) physiognomic hierarchy for all levels
above the alliance. The newly adopted national vegetation hierarchy consists of eight
levels, organized into three upper levels, three middle levels, and two lower levels
(Table 1). See also Table 3, which provides the details on both the natural and cultural
2008 hierarchies.
Table 1—Comparison of original 1997 USNVC Vegetation Hierarchy (adapted from UNESCO
1973) and the 2008 revision.
1997 FGDC Hierarchy 2008 Revised Hierarchy for Natural Vegetation
Division — Vegetation vs. Non- vegetation Upper Levels
Order — Tree, Shrub, Herb, Nonvascular
Level 1 — Formation Class Level 1 — Formation Class
Level 2 — Formation Subclass
Level 3 — Formation Group Level 2 — Formation Subclass
Level 4 — Formation Subgroup — Natural/Cultural
Level 5 — Formation Level 3 — Formation
Middle Levels Level 4 — Division
Level 5 — Macrogroup
Level 6 — Group
Level 6 — Alliance Lower Levels Level 7 — Alliance
Level 7 — Association Level 8 — Association
6 USDA Forest Service RMRS-GTR-346. 2016.
Phase II:
With the completion of the FGDC standard, USNVC partners began implement-
ing revisions to the classification system, but two important issues remained to be
resolved. First, the 2008 FGDC standard called for a screening/peer review process
to induct proposed types into the revised USNVC. Thus, in June of 2010, FGDC re-
quested the HRWG to take on the task of reviewing, revising, and describing the pilot
upper level units (L1 – L3) provided in the FGDC 2008 standard (see Appendix G in
FGDC 2008). Fortunately, most of the members of the original HRWG stayed with the
project and new members were added (Appendix A).
During this phase of development, the HRWG was able to draw on extensive
testing of the upper level units, which were being used as mid and lower level units
in the USNVC (usnvc.org) and in Canada (cnvc-cnvc.ca). NatureServe and partners
also began applying the same approach to revisions to the International Vegetation
Classification (IVC) through projects in South America (Josse 2011; Navarro 2011)
and Africa. Testing of the hierarchy in Africa led to one major proposed change: move
all wetland formations under an expanded Class V – Hydromorphic and Hydrophytic
Vegetation. This decision was only partly implemented (see below). A draft of world
grassland types from Formation Class to Division was also published (Dixon and oth-
ers 2014; Faber-Langendoen and Josse 2010).
The HRWG completed the initial review of the units in October of 2010, having
found that information from proposed new mid-levels provided good support to the
upper levels (see Division examples in Appendix J). The suggested revisions to move
all wetlands under a single large class in Class V was not adopted. Instead, the deci-
sion was to move all shrub and herb wetlands under a single subclass, while keeping
forested wetlands and aquatic vegetation wetlands in other classes (see “Wetlands”
section below). The HRWG made other modest changes to the 2008 version (e.g., add-
ing a Tropical Thorn Woodland formation, removing cryomorphic and xeromorphic
rock vegetation formations from the “lithomorphic” or open cryptogam class and
placing the vegetation within those formations within existing divisions of hydryomor-
phic and xeromorphic vegetation, modifying various formation names). After further
consultation with the Ecological Society of America Vegetation Classification Panel
(hereafter “ESA Panel”), the HRWG submitted a request to FGDC that the USNVC
partners adopt the 2008 pilot units. FGDC approved the request, based on the process
used to reach those decisions. The set of units is provided in Appendix B.
The HRWG then began writing detailed descriptions of each of the L1 – L3 units,
following the standard description template. In addition, a key to Level 1 was pro-
duced (Appendix I).
Context for the Hierarchy
Several primary categories are helpful in describing the scope of the classification
and placing it within a broader land cover context: vegetated – non-vegetated, existing
vegetation, and natural – cultural vegetation.
USDA Forest Service RMRS-GTR-346. 2016. 7
Vegetated – Non-Vegetated:
The classification includes all vegetated areas with 1 percent or more of their
surface area covered by live vegetation. This includes vegetation found on both
upland environments and in wetlands (rooted emergent and floating vegetation). The
classification excludes non-vegetated (i.e. less than 1 percent vegetation cover) natural
lands (e.g., rock, glaciers, some deserts) and waters (e.g., lakes and rivers) and non-
vegetated cultural lands (e.g., roads, buildings, mines) and waters (e.g., reservoirs,
canals), though it can easily be linked to land cover classifications that do include
these lands to provide a full terrestrial coverage (see “Natural and Cultural Vegetation”
section below).
Existing Vegetation:
This classification includes only existing vegetation types, as described by FGDC
(2008): “Existing vegetation is the plant cover, or floristic composition and vegeta-
tion structure, documented to occur at a specific location and time, preferably at the
optimal time during the growing season.” (see also Jennings and others 2009; Tart and
others 2005a). Abiotic factors, geographic and successional relationships are used to
help interpret the types. Existing vegetation can provide the basis for describing poten-
tial vegetation types.
Natural and Cultural Vegetation:
This classification provides separate categories for natural and cultural vegetation,
a distinction that is consistent with other vegetation and land cover classifications
(e.g., Anderson and others 1976; Di Gregorio2005; Küchler 1969). Although cultural
and natural vegetation are distinguished in the classification, both are subsequently
classified in a hierarchical framework that emphasizes primarily floristics at the lower
levels, both physiognomic and floristics at mid levels, and primarily physiognomy at
upper levels.
Natural (including semi-natural) vegetation is defined as vegetation where
ecological processes primarily determine species composition and stand structure;
that is, the vegetation is comprised of a set of plant species growing spontaneously
(i.e., with little human influence) and is shaped by both abiotic and biotic processes
(Küchler 1969; Westhoff and van der Maarel 1973). Cultural vegetation is defined as
vegetation with a distinctive structure, composition, and development determined by
regular human activity (cultural vegetation sensu stricto of Küchler 1969). The distinc-
tive physiognomy, floristics, and dependence on human activity for its persistence set
cultural vegetation apart from natural and semi-natural vegetation. These distinctive
attributes typically include one or more of the following:
• Dominant herbaceous vegetation is regularly spaced and/or growing in rows,
often in areas with substantial cover of bare soil for significant periods of the
year, usually determined by tillage or chemical treatment.
• Dominant vegetation has highly manipulated growth forms. Structure is rarely
the result of natural plant development, but is usually determined by mechanical
pruning, mowing, clipping, etc.
8 USDA Forest Service RMRS-GTR-346. 2016.
• Dominant vegetation is comprised of species not native to the site or area that
have been intentionally introduced by humans and that would not persist with-
out active management by humans.
Recognition of cultural or “anthromorphic” vegetation classes parallels recent calls
for recognition of an “Anthrosol” order for soils because of intrinsic properties of the
soil caused by farming, fertilizing, irrigation, and tillage (Bryant and Galbraith 2003;
Gong and others 2003).
Summary
We identify these fundamental aspects of vegetation using two categorical levels
(Table 2a). These categories provide the organizing framework for the classification,
beginning with Level 1. The framework allows the vegetation-ecologic approach to
be easily extended to a full terrestrial approach by linking these categories to existing
land cover classification systems, such as FAO Land Cover Classification System
(Di Gregorio 2005) (Table 2b). Further examples of this approach are provided for
the USNVC by FGDC (2008, Appendix B - Relationships to the U.S. National Land
Cover Database (NLCD) (USGS 2001). See also Appendix B.
Table 2a—Conceptual categories and level one of the hierarchy (from FGDC
2008, Table 2.1).
Category 1 Category 2 Level 1
Vegetated Semi-natural vegetation Forest & Woodland (Mesomorphic
Tree Vegetation)
Shrub & Herb Vegetation
(Mesomorphic Shrub & Herb
Vegetation)
Desert & Semi-Desert (Xeromorphic
Woodland, Scrub & Herb Vegetation)
Polar & High Montane Scrub,
Grassland & Barrens (Cryomorphic
Vegetation)
Aquatic Vegetation (Hydromorphic
Vegetation)
Open Rock Vegetation (Cryptogam -
Open Mesomorphic Vegetation)
Cultural vegetation Agricultural & Developed Vegetation
(Anthro-morphic Vegetation)
Nonvegetated Not included (see Table 2b).
USDA Forest Service RMRS-GTR-346. 2016. 9
The Hierarchy
The eight levels of the hierarchy for both cultural and natural vegetation are pro-
vided in Table 3. The EcoVeg approach treats natural vegetation distinct from cultural
vegetation; thus, each has similar but differently defined hierarchical levels. This
allows for a dynamic portrait of all existing vegetation in a way that reflects ongoing
changes driven by land use, climate change, invasive species and natural processes.
Tables 4a and 4b provide examples of natural (4a) and cultural (4b) types across all
levels of the two hierarchies.
Development of the Upper Levels
The upper levels of the classification were based on the formation concept, which
is prominent in the history of vegetation classification (Appendix F). The definition
provided by Whittaker (1962 pg. 150) is typical: “a community type defined by domi-
nance of a given growth form in the uppermost stratum (or the uppermost closed stratum)
of the community or by a combination of dominant growth forms.” The UNESCO (1973)
definition guided much of the earlier work on the EcoVeg approach. The formation is
“basically physiognomic-structural in character with supplementary ecological informa-
tion integrated into its various categories and applicable to natural and semi-natural vegetation.”
Physiognomy can be defined as “the visible structure or outward appearance of a plant
community as expressed by the dominant growth forms, such as their leaf appearance or
deciduousness”(Fosberg 1961). Structure is the horizontal and vertical spatial pattern of
growth forms in a plant community, especially with regard to their height, abundance,
coverage or biomass within the individual layers (Gabriel and Talbot 1984).
Table 2b—Optional non-vegetated categories from land cover classifications
(FAO Land Cover Classification System). See also Appendix B.
Category 1 Category 2 Level 1 FAO (1996)
Non-vegetated Natural Terrestrial: Bare Areas
Aquatic: Natural Waterbodies, Snow & Ice
Cultural Terrestrial: Artificial Surfaces & Associated Areas
Aquatic: Artificial Surfaces & Associated Areas
Table 3—Hierarchy levels for natural and cultural vegetation.
Natural Hierarchy LevelCultural Hierarchy Level
L1 – Formation Class L1 – Cultural Class
L2 – Formation Subclass L2 – Cultural Subclass
L3 – Formation L3 – Cultural Formation
L4 – Division L4 – Cultural Subformation
L5 – Macrogroup L5 – Cultural Group
L6 – Group L6 – Cultural Subgroup
L7 – Alliance L7 – Cultural Type
L8 – Association L8 – Cultural Subtype
10 USDA Forest Service RMRS-GTR-346. 2016.
Table 4a—Hierarchical classification for natural vegetation with examples.
Natural Vegetation Example
Upper Levels
1 – Formation Class Scientific Name: Mesomorphic Shrub & Herb Vegetation
Colloquial Name: Shrub & Herb Vegetation
2 – Formation Subclass Scientific Name: Temperate & Boreal Shrub & Herb Vegetation
Colloquial Name: Temperate & Boreal Grassland & Shrubland
3 – Formation Scientific Name: Temperate Shrub & Herb Vegetation
Colloquial Name: Temperate Grassland & Shrubland
Mid Levels
4 – Division Scientific Name: Andropogon – Stipa – Bouteloua Grassland &
Shrubland Division
Colloquial Name: Central North American Grassland & Shrubland
5 – Macrogroup Scientific Name: Andropogon gerardii – Schizachyrium
scoparium – Sorghastrum nutans Grassland & Shrubland
Macrogroup
Colloquial Name: Central Lowlands Tallgrass Prairie
6 – Group Scientific Name: Andropogon gerardii – Sporobolus heterolepis
Grassland Group
Colloquial Name: Northern Tallgrass Prairie
Lower Levels
7 – Alliance Scientific Name: Andropogon gerardii – Sorghastrum nutans –
Sporobolus heterolepis Grassland Alliance
Colloquial Name: Northern Mesic Tallgrass Prairie
8 – Association Scientific Name: Andropogon gerardii – Hesperostipa spartea –
Sporobolus heterolepis Grassland
Colloquial Name: Northern Bluestem Mesic Tallgrass Prairie
Table 4b—Hierarchical classification for cultural vegetation with
examples.
Cultural Vegetation Example
Upper Levels
1 – Cultural Class Anthromorphic Vegetation
2 – Cultural Subclass Herbaceous Agricultural Vegetation
3 – Cultural Formation Row & Close Grain Crop
4 – Cultural Subformation Graminoid Row Crop
Mid Levels
5 – Cultural Group [optional] Tropical & Temperate Corn Crop
6 – Cultural Subgroup Temperate Corn Crop
Lower Levels
7 – Cultural Type Maize Corn
8 – Cultural Subtype [optional] Corn for silage
USDA Forest Service RMRS-GTR-346. 2016. 11
We define growth form1 as the shape or appearance of a plant reflecting grow-
ing conditions and genetics (see Appendix C for a glossary of terms). Growth form
is usually consistent within a species, but may vary under extremes of environment
(Mueller-Dombois and Ellenberg 1974). A list of growth forms is provided in
Appendix D as a first approximation for defining upper level types.2 This list is
structured into two levels: general growth forms and specific growth forms. These lists
were adapted from Whittaker (1975, pg. 359) and Box (1981), and may reflect a west-
ern hemisphere perspective, but the intent is to provide a method for characterizing the
growth form composition of all formations. For comparison, an extended list of “eco-
physiognomic” growth form types developed by Box and Fujiwara (2005) is presented
in Appendix E. This extended list could provide a stronger basis for the approach
proposed here but needs further review. Introducing a combination of morphological,
anatomical and physiological adaptations could allow for finer classification distinc-
tions. Instead, however, we proposed adding diagnostic species at the mid-levels of the
classification, in addition to growth form descriptors.
By characterizing the growth forms as part of a vegetation plot, it becomes possible
to empirically describe the growth form components of a vegetation type and relate
them to ecological factors. Thus, combinations of growth forms can define xeromor-
phic (desert) vegetation or hydromorphic (aquatic) vegetation. Some growth forms,
however, such as “flowering forb” do not show particularly strong ecological relation-
ships, at least not as currently defined. They may be constant growth forms rather than
diagnostic ones.
As with species in lower level units, a growth form is rarely restricted to one upper
level formation type. Too often, a single physiognomic criteria has been used alone to
define a formation (e.g., defining a formation by 25 to 60 percent tree canopy cover).
Although such criteria may be helpful in a diagnostic key or for particular mapping ap-
plications, we suggest that in an integrated classification, the use of differential growth
forms is more helpful. The same growth forms may appear in multiple units, but it is
the relative abundance of that growth form, in combination with ecological processes
and consideration of broad floristic-biogeographic patterns at lower levels, that define
formation types (Table 5). Thus, tree covered lawns are separated from natural forests
because of differences in the combination of shrub, herb and tree growth forms and
in ecological processes, though both may have 25 to 60 percent tree canopy. Just as a
specified presence and abundance of one or more differential species are primary crite-
ria for defining vegetation types at lower levels, the presence and abundance levels of
one or more growth forms are primary criteria for defining vegetation types at upper
levels.
1
A similar term, life form, is dened as the ecological strategy that a plant uses to complete
its life cycle, e.g., Raunkiaer life forms are dened on the position of the bud or organs from
which new shoots or foliage develop after an unfavorable season. Different life forms may not
always exhibit clear outward structural differences (e.g., hemicryptophytes and geophytes).
2
The growth form list in the FGDC standard is published as a “normative list,” which may
require a formal approval process for amending it. In the mean-time, all additions or changes
could be treated as optional.
12 USDA Forest Service RMRS-GTR-346. 2016.
Finally, growth forms are closely related to plant functional types (PFTs), a group-
ing of organisms that respond in a similar way to a suite of environmental factors
(Gitay and Noble 1997). A comparison of PFTs used for broad scale assessments
shows a very close relationship to the growth forms presented here, and leads to aggre-
gations of functional types that are similar to formations (Leemans 1997). This opens
up the possibility of modeling responses of formations to disturbances and to climate
change (Cramer 1997), as earlier developed by Box (1981) who formulated climatic
envelopes for each of his growth form/plant functional types (Appendix E). See also
Gillison (2013) for a recent treatment of plant functional types.
The upper levels were not developed in a strictly top down manner. Rather, mem-
bers of the HRWG had access to draft mid and lower level units (from Division to
Association) for the United States and parts of Canada and Latin America. In addition,
comparisons were made with other classifications in which physiognomic or forma-
tion types were used to organize floristic types, such as the European vegetation types
published in Rodwell and others 2002 (see other examples in Appendix F). To test
relationships between upper and lower levels, a comprehensive master spreadsheet of
draft units was organized under the upper levels and was used to critique the overall
“naturalness” of the formation units. The HRWG reevaluated formation concepts
where formations introduced undesirable splits in lower units that were otherwise
ecologically and floristically similar. Our goal was to make splits between types that
had good ecological and vegetation support for them. Still, inevitably, given the multi-
dimensional and continuous gradients affecting vegetation, some criteria for upper
levels require splitting otherwise closely related floristic types (e.g., open woodland
from grassland, floodplain forest from upland forest).
Table 5—Characters used to distinguish Tropical Lowland Humid Forest from Tropical
Montane Humid Forest (after Whitmore 1984, Table 18.1).
Formation
Formation Criteria Tropical Lowland Humid Forest Tropical Montane Humid Forest
Canopy height 25-45 m 1.5-33 m
Emergent trees Characteristic, to 60 (80) m tall Often to usually absent, to 37 m tall
Pinnate leaves Frequent Rare to very rare
Principle leaf size class of
woody plantsa
Mesophyll or Macrophyll (or
Megaphyll)
Mesophyll or microphyll
Buttresses Usually frequent and large Uncommon, small or absent
Cauliflory Frequent Rare to absent
Big woody climbers Abundant Usually none
Bole climbers Often abundant Very few to to abundant
Vascular epiphytes Frequent Frequent to abundant
Nonvascular epiphytes Occasional Occasional to abundant
a For definition of leaf-sizes see Mueller-Dombois and Ellenberg (1974, page 453).
USDA Forest Service RMRS-GTR-346. 2016. 13
In summary, the upper levels of the hierarchy are based on dominant and diagnostic
growth forms that reflect ecological and anthropogenic drivers at global and continen-
tal scales, and their concepts are influenced by consideration of vegetation patterns at
lower levels. The comprehensive set of formation types for all 3 levels (L1–L3) are
provided in Appendix B.
Ecological Approach to Organizing Formation Class Types:
Formation Class is a vegetation classification unit of high rank (1st level) defined
by broad combinations of dominant general growth forms adapted to basic ranges of
moisture, temperature, and/or substrate or aquatic conditions (FGDC 2008; cf. Beard
1973; cf. “major physiognomic types” of Whittaker 1975).
A primary concern of the HRWG was to consider the ecological relationships
among vegetation types rather than simply growth forms alone. We asked ourselves
what fundamental ecological/environmental and anthropogenic processes order global
vegetation patterns. Can we identify the characteristics of vegetation that reflect those
processes? Our concern is a familiar one to those seeking an ecological basis for de-
veloping vegetation classifications. For example, Warming (1909, pg. 143) wrote:
“Why not use each growth form [lichen, moss, herb, dwarf-shrub,
shrub, tree] as a foundation upon which to build a special class? The
following classes could then be distinguished: that of forest formations,
of bush-formations of shrub-formations, of dwarf-shrub formations,
or perennial-herb formations, of moss-formations, and of alga-
formations… From a morphological standpoint this would possess a
certain interest, but from a phytogeographical one it must be dismissed,
because it would involve the separation of formations that are oecologi-
cally closely allied.”
He goes on to state that formations can be based on either a single or compound
growth forms, where many growth forms are combined to form a single whole. This
approach has been echoed by others over the years (Box and Fujiwara 2005, 2013;
Whittaker 1962, 1975) and was adopted by the HRWG. Here we rely strongly on
multiple growth forms to define formations types (e.g., including needle-leaved and
cold deciduous broad-leaved trees together within a temperate and boreal forest sub-
formation; aseasonal or drought deciduous herbaceous growth forms with evergreen
or drought-deciduous shrubs to define topical grassland, savanna and shrubland
subformation), wherever these combination of growth forms reflected a more natural
vegetation unit with respect to macro-ecological gradients.
Terminology for Formation Names:
Because our growth forms emphasize primarily morphological adaptations we use
the term “morphic” to name formation types, as in hydromorphic, mesomorphic, xero-
morphic (see also Table 4 in Ellenberg 1988). Other researchers have used terms such
as hydrophyte, mesophyte, and xerophytes (e.g., Warming 1909). But these terms are
often applied to species, where the combination of morphology, anatomy, physiology,
14 USDA Forest Service RMRS-GTR-346. 2016.
and even life history strategy define the forms. These terms may be better applied in
the mid and lower levels of the classification where species are part of the criteria.
Compounding the issue in North America is use of the term “hydrophyte” or “helo-
phyte” species that depend, to varying degrees, on wet habitats, irrespective of any
obvious morphologic or anatomical adaptations. For example, Tiner (1998) defines
hydrophytes as “plants growing in water or on a substrate that is at least periodically
deficient in oxygen as a result of excessive water content.” Hydrophytic vegetation
is defined as “the sum total of macrophytic plant life that occurs in areas where the
frequency and duration of inundation or soil saturation produce permanently or pe-
riodically saturated soils of sufficient duration to exert a controlling influence on the
plant species present” (U.S. Army Corps of Engineers 1987). By contrast, hydromor-
phic vegetation in our approach is defined by types where rooted and floating aquatic
growth forms are dominant (i.e., aquatic vegetation).
Zonal and Azonal Vegetation
Zonal vegetation refers to vegetation that reflects a close relation to the current cli-
matic conditions of a region and that develop, without significant human interference,
on soils with non-extreme properties (Mueller-Dombois and Ellenberg 1974). For
example, mesic mixed beech-maple forests with Fagus grandifolia (American beech)
and Acer saccharum (sugar maple) in the northeastern United States and southeastern
Canada. Azonal vegetation is found on sites subject to “excessive” moisture or drought
within that climatic region or strong anthropogenic influence; for example, sedge
meadows, forested swamps and rocky woodlands, as well as corn fields and orchards.
From the perspective of existing vegetation, we treat zonal and azonal vegetation to-
gether as part of extended environmental gradients. Thus, although climate is a strong
contributor to global environmental gradients, other factors are also notable, including
substrate (rock, water). The combinations of factors are used when assessing the eco-
logical relationships among formations.
Development of Natural Formations
Formation Class
The formation class is the top level at which users enter the classification; thus, a
small set of clearly defined types is helpful. The six types are defined by broad combi-
nations of dominant general growth forms associated with basic moisture, temperature,
and/or substrate or aquatic conditions, often spanning multiple climatic regions (See
Appendix C for a glossary of terms).
In addition, practical applications of the classification suggest that we be as clear
as possible on specifying criteria for what constitutes forest and woodlands versus
various grassland and shrubland types. Concerns over the precise boundaries of these
classes require careful attention and are noted in the description.
1. Forest & Woodland (Mesomorphic Tree Vegetation)
Concept Summary
Type Concept Sentence: Tropical, temperate and boreal forests, woodlands and
tree savannas characterized by broadly mesomorphic (including scleromorphic) tree
USDA Forest Service RMRS-GTR-346. 2016. 15
growth forms (including broad-leaved, needle-leaved, sclerophyllous, palm, bamboo
trees, and tree ferns), with at least 10 percent cover, irregular horizontal spacing of
vegetation structure, and spanning humid to seasonally dry tropical to boreal and sub-
alpine climates and wet to dry substrate conditions. Includes native forests as well as
managed and some plantation forests where human management is infrequent.
This class contains all mesomorphic tree-dominated vegetation (including sclero-
morphic tree vegetation) down to 10 percent canopy cover. The HRWG followed the
FAO recommendations (FAO 2001), which are satisfactory for ecological and floristic
application in many treed biomes, in both upland and wetland formations. The appro-
priate boundaries for distinguishing forest and woodland vegetation have been defined
in many ways. This is further complicated by use of the term savanna (see below).
However, it is also common to define Forest & Woodland as having greater than 25
percent tree cover, whereas tree savannas, commonly found in grassland regions of the
world, have 10 to 25 percent tree cover (see FGDC 1997; Grossman and others 1998;
UNESCO 1973). Savanna definitions vary widely, from 5 to 30 percent to 10 to 50
percent (Curtis 1959), 10 to 60 percent cover, or even higher, thus spanning the same
range as used by others for woodlands. Given the commonality of a lower threshold
of 10 percent tree cover, we felt it best to initially place tree savannas and woodlands
together, at least in the temperate zone, then separate them at lower levels. The HRWG
recognizes that this is not entirely satisfactory from some rangeland perspectives.
Further review of tropical grasslands, savannas and shrublands by Dixon and others
(2014) suggests some differences in criteria are needed for tropical versus temperate
grasslands and tree savannas, namely:
1. a non-wetland formation with at least 10 percent vascular vegetation canopy
cover;
2. graminoids have at least 25 percent cover (but if less than 25 percent cover,
graminoids exceed that of other herbaceous and shrub cover),
3. broad-leaved herbs (forbs) may have variable levels of cover and dominance,
4. shrubs have less than 25 percent canopy cover, and
5. trees:
i. in temperate regions, typically have less than 10 percent canopy cover, are
less than 5 m tall and are single-layered, or
ii. in tropical regions, typically have less than 40 percent canopy cover, are less
than 8 m tall, and are single layered.
The term “savanna” (let alone its spelling, with or without the “h”) has often engen-
dered confusion and debate. In our work, the term is restricted to two broad vegetation
patterns. For temperate regions, it is applied to grasslands or shrublands with scattered
trees (typically 10 to 30 percent) and primarily limited to fire-maintained upland types,
although these vegetation types are also referred to as woodlands, oak openings and
oak barrens. Temperate grasslands without scattered trees are referred to either as
grasslands or prairies. For tropical vegetation, savanna is applied in the classical sense
as interchangeable with tropical grasslands, with or without scattered trees, but some-
times separating out the treed tropical savanna distinct from non-treed tropical savanna
(tropical grasslands sensu stricto).
16 USDA Forest Service RMRS-GTR-346. 2016.
A final comment on tree growth forms: scleromorphic tree vegetation is treated here
as broadly mesomorphic and is the growth form distinctive to the warm-temperate
formation (level 3) within this class.
2. Shrub & Herb Vegetation (Mesomorphic Shrub & Herb Vegetation).
Concept Summary
Type Concept Sentence: Grasslands, shrublands, open tree savannas, marshes, bogs
and fens dominated by broadly mesomorphic (including scleromorphic) shrub and
herb growth forms (including broad-leaved, needle-leaved, and sclerophyllous shrubs,
and forb and graminoid herbs) with an irregular horizontal canopy structure, typically
less than 10 percent mesomorphic tree cover (but see discussion of tropical grasslands
and savannas above), tropical to boreal and subalpine climates, and wet to dry sub-
strate conditions.
Shrub and herb vegetation is combined here because in many non-forested vegeta-
tion types, these two growth forms may occupy the same upper strata, or in some
cases, grasses may even overtop shrubs (tallgrass prairie, emergent marshes). This can
lead to strong floristic overlap between shrub and grass types, which supports combin-
ing them at the upper levels and separating them at lower levels.
The primary issue with this class is incorporating both upland and wetland types.
See discussion on “Wetlands” below.
3. Desert & Semi-Desert (Xeromorphic Woodland, Scrub & Grassland
Vegetation)
Concept Summary
Type Concept Sentence: Cool and warm semi-deserts dominated by xeromorphic
growth forms, including succulent (e.g., cacti, euphorbias) and small-leaved shrubs
and trees, desert grasses and other xeromorphic growth forms, with an irregular hori-
zontal canopy spacing that is often open to very sparse, including very open sandy and
rocky vegetation with xeromorphic growth forms.
Inclusion of Tropical Thorn Woodland with other warm-desert scrub was a late ad-
dition to the hierarchy. The decision was based on the similarity of xeromorphic trees
to other desert vegetation, although some will prefer that thorn woodland be placed
next to Tropical Dry Forest (indeed some authors include thorn woodlands in that
concept [Pennington and others 2006]). Our logic for the placement of Tropical Thorn
Woodland is based on explicitly defined xeromorophic growth forms (e.g., succulents,
leafless thorn trees, etc.).
Distinguishing non-vegetated and vegetated areas in deserts will also be difficult,
given that on a site where vegetation is about 1 percent cover, there may be patches
that vary between greater than 1 and less than 1 percent, and unbiased plot sampling
of the site could have some plots with no cover. The few plants occurring at such low
percentages may also be generalists and not particularly strong diagnostic species. For
that reason, desert rocky and sandy vegetation are included here, rather than the “Open
Rock Vegetation” class.
USDA Forest Service RMRS-GTR-346. 2016. 17
4. Polar And High Montane Scrub & Grassland (Cryomorphic Scrub,
Herb And Cryptogam Vegetation)
Concept Summary
Type Concept Sentence: Tundra, alpine and tropical high montane habitats domi-
nated by cryomorphic growth forms (including dwarf-shrubs, krummholz, associated
herbs, and cryptograms such as lichens and mosses) with low height and open to
closed canopy.
The name of this formation class emphasizes the cryomorphic nature of the vegeta-
tion. However, in many tropical montane regions that are roughly equivalent with the
temperate “alpine” zone, the vegetation is not truly cryomorphic. That is, the soils
do not experience cryoturbation and the vegetation doesn’t experience frost, strong
winds, and short growing seasons. This is true for parts of the paramo and puna, so
the HRWG placed them under Shrub & Herb Vegetation (class 2) in Tropical Montane
Grassland & Shrubland. However, all temperate alpine vegetation is placed in
cryomorphic. Rocky vegetation dominated by cryptogram and cryomorphic vascular
vegetation (such as Arctic barrens in polar deserts) is included here.
5. Aquatic Vegetation (Hydromorphic Vegetation)
Concept Summary
Type Concept Sentence: Open freshwater and saltwater wetlands dominated by
aquatic vegetation, either rooted with leaves rising up to or near the surface, or floating
freely on the water surface. Stands typically have surface water, generally up to 2 m
in depth, along ocean, lake, pond, and river margins in non-tidal, tidal, and intertidal
habitats.
We include rooted and submerged vegetation in this formation class but treat all
other emergent wetlands under mesomorphic vegetation classes 1 and 2, as many
emergent wetlands share growth forms with upland vegetation. We expect that this
aquatic vegetation class will be most useful in wetland situations such as ponds
(i.e., bodies of water smaller than 8 ha and less than 2 m deep with no wave action;
Cowardin and others 1979). Where aquatic vegetation forms a component of lakes,
rivers, and oceans, other classification schemes can provide a more holistic set of
types, within which various levels of aquatic vegetation types can be included.
Nonetheless, it is possible to include all vegetated habitats, even seagrasses, in this
classification. For example, Den Hartog (2003) developed comprehensive marine
seagrass formations and lower level floristic units for the globe. From a terrestrial per-
spective, wetlands may seem to be sufficiently distinct from upland types in classes 1
and 2 to place them here; but, when viewed from the larger aquatic vegetation perspec-
tive that includes only floating and submerged freshwater and marine vegetation, they
are more closely related to those classes (See Wetlands section below).
6. Open Rock Vegetation (Cryptogam —Open Mesomorphic Vegetation)
Concept Summary
Type Concept Sentence: Lichen, bryophyte, alga or fern-dominated rocky habitats
such as cliffs, talus, scree, pavement, cobble, lava or boulderfields in association with
open or sparse mesomorphic vegetation.
18 USDA Forest Service RMRS-GTR-346. 2016.
This formation class is restricted to cropytogamic dominated vegetation found on
consolidated and unconsolidated rocks where mesomorphic vascular plant cover is
less than 10 percent; there is discussion as to whether non-seed plants such as ferns or
Selaginella spp. should be excluded from the 10 percent vascular cover limit. The typ-
ical habitat is cliff, scree, talus or rock outcrops. Desert rocky or sandy vegetation is
placed in Class 3, and alpine rock, scree and fellfields are placed in Class 4. There are
questions to be resolved regarding placement of sparsely vegetated boulder or cobble
drainages in dry creeks, river beds, or rocky shorelines where nonvascular vegetation
may be a minor component. Scree vegetation may have more direct contact with soil
with higher levels of vascular plant cover. The lack of information on rock vegetation
makes classification and descriptions difficult.
The concept of this class has been narrowed to regions where climates are milder
and mesomorphic vegetation is more typical, and cryptogam vegetation is otherwise
not a typically dominant growth form. Early pilots of this hierarchy included desert,
polar, and alpine rock vegetation in this class. However, given how open the vascular
vegetation can be in those habitats, it created too much of an artificial split between
the very sparse vascular vegetation and the somewhat more open vascular vegetation,
both of which have substantial cryptogam dominance.
Wetlands
Wetlands have international significance due to the variety of human and ecological
values they provide. However, placing wetlands in the hierarchy has been challenging.
Wetlands are handled in various ways by ecological and vegetation classifications.
In various global schemes, they are sometimes only noted incidentally, next to the
main climatically driven types (e.g., Box and Fujiwara 2005; Whittaker 1975). Others
recognized them as wholly distinct from other vegetation (NWWG 1997). The HRWG
integrated them more directly into the hierarchical levels, although we struggled with
their placement, as described below.
Chosen option: Wetlands are placed within various classes, depending on the level
of distinctiveness of growth forms and their ecological drivers, but are always segre-
gated out at Level 3 (formation).
Alternate option: Wetlands are grouped together into a single large hydromorphic
and hydrophytic (or helomorphic) vegetation group. It reflected the perspective of
many who see wetlands as a distinctive set of vegetation types, as well as various wet-
land publications that identify “wetland” as its own higher category (see the National
Wetlands Inventory/Cowardin wetland classification, Cowardin and others 1979; and
the Canadian wetland classification, National Wetlands Working Group 1997).
Rationale for Chosen Option (wetlands initially dispersed among other classes,
then individual wetland types recognized at formation level):
1. It relies more strongly on dominant growth forms rather than diagnostic ones.
2. It more strongly separates the most distinctive vegetation classes (“more
orthogonal vegetation criteria”). That is, it is difficult to class all wetlands
together globally due to their “relative wetness,” because that depends on the
context of surrounding regional climatic and vegetation patterns.
USDA Forest Service RMRS-GTR-346. 2016. 19
3. Wetland distinctions vary even at the species level, because many widespread
species may be considered wetland in some regions but not in other regions;
e.g., definitions of Facultative and Obligate wetlands differ across U.S. wetland
regions.
4. It is less dependent on ecological considerations in defining the class (i.e, a
wetland/non-wetland distinction).
Rationale for Alternative Option (wetlands grouped with aquatic vegetation as a
single class, then individual wetland types recognized at formation level):
1. It identifies the wetland criteria up front, overall, rather than repeatedly across
subclasses.
2. It groups closely related wetland types together.
3. It provides a set of wetland subclasses that are clearly identified in many wetland
classifications (e.g., swamp, bog and fen, marsh).
4. It more strongly integrates ecologically related growth forms, even if not the
dominant ones.
Rationale for either option:
1. Both do a good job of grouping vegetation patterns.
2. Both are equally amenable to mapping approaches.
3. Both provide useful categories for vegetation management.
4. Both recognize the same major wetland types at formation level (Level 3).
The HRWG decided to adopt the chosen option because it was more faithful to the
criteria required for Level 1. Forested wetlands are placed in the “Forest & Woodland”
class; shrub and herb wetlands are placed in the “Shrub & Herb Vegetation” class, but
separated out as a subclass; aquatic wetland vegetation, which has distinctive hydro-
morphic growth forms, is placed in Class 5 under Aquatic Vegetation. As all major
wetland types are separated out at Level 3, most users will find few disadvantages to
the current approach, and they can choose to aggregate all wetlands into their own
category if so desired. Our approach is a classification of all vegetation, not a classifi-
cation of wetland and non-wetland, which is more concerned with legal conservation
and water law issues.
Formation Subclass
Formation Subclass: A vegetation classification unit of high rank (2nd level) defined
by combinations of general dominant and diagnostic growth forms that reflect global
macroclimatic factors driven primarily by latitude and continental position, or that
reflect overriding substrate or aquatic conditions. (cf. Box and Fujiwara 2005, 2013;
FGDC 2008; Walter 1985; Whittaker 1975).
Macroclimatic factors have a strong influence on the development of the formation
subclass, even among substrate-based classes. Few issues arose in developing these
subclasses. The HRWG worked with vegetation patterns that often correspond to
broad bioclimatic classes. The work of Rivas-Martinez and others (Rivas-Martinez
and others 1999a; Rivas-Martinez and Rivas-Sáens 1996–2009) was helpful for global
scale distinctions, particularly the division of bioclimates into Tropical, Temperate,
Mediterranean, Boreal, and Polar (Figure 1). Here we review a few of the subclasses,
where some problems in definition were encountered. In all cases, see additional “clas-
sification comments” in the type descriptions in Part II.
20 USDA Forest Service RMRS-GTR-346. 2016.
Figure 1—Bioclimatic Regions of (a) North America (Rivas-Martinez et al. 1999), (b) Europe (Rivas-Martinez
et al. 2004), and (c) South America (Rivas Martinez, in press). Mapped distribution of these bioclimatic re-
gions should not be used as definitive linework for actual formation distributions. See text for discussion of
Mediterranean bioclimate. Maps used with permission (figure produced by Ángel Penas Merino).
USDA Forest Service RMRS-GTR-346. 2016. 21
Figure 1b
22 USDA Forest Service RMRS-GTR-346. 2016.
Temperate, Boreal and Montane Vegetation
Temperate & Boreal vegetation are combined at the subclass level, because they
share many of the same broad growth forms. They are recognized as distinct at the for-
mation (L3) level based on the simplified set of growth forms and distinctive climate
found in the boreal forests. Montane forests, shrublands, and grasslands in the temper-
ate and boreal regions do not contain distinctive growth forms from lower elevation
vegetation until one reaches the alpine zone. Alpine vegetation shares strong growth
form similarities with polar vegetation, and they are treated together at the subclass
level (4.B. Temperate to Polar Alpine & Tundra Vegetation).
Temperate and Mediterranean Vegetation
The one bioclimate type of Rivas-Martinez and Rivas-Sáens (1996-2009) that
does not correspond as closely to our approach is the Mediterranean bioclimate. They
define this bioclimate to include not only Mediterranean scrub vegetation but also
vegetation that we place in Cool Semi-Desert, (e.g., in North America, the Great Basin
Figure 1c
USDA Forest Service RMRS-GTR-346. 2016. 23
vegetation, in South America the Patagonian vegetation, and in Europe the Eastern
European steppe) (figures 1, 2). In addition, we only use the term “Mediterranean”
in reference to “Mediterranean Scrub & Grassland” (an L3 formation unit), thus
restricting the vegetation concept to sclerophyllous and other Mediterranean type
scrub growth forms within a broadly temperate and boreal subclass. The distinctive
Mediterranean vegetation around the world has been variously treated either narrowly
or broadly; here, we use the term narrowly based on growth forms. The sclerophyllous
and mixed evergreen-deciduous tree growth forms of the European Mediterranean
region are also found in other warm-temperate climates, and are included in the Warm-
Temperate Forest class. That formation includes:
• In Europe, the European Mediterranean cork-oak forests (Quercus suber) of
Spain and Portugal, fir forests (Abies maroccana) and cedar forests (Cedrus at-
lantica) in high-mountain areas in Morocco, oak woodlands broadly distributed
throughout the Mediterranean Basin countries;
• In South America, the warm temperate forests of Nothofagus macrocarpa, N.
glauca, N. alessandrii, Austrocedrus chilensis forests, etc.;
• In Australia, the many Eucalypt forests; and
• In North America, both the Mediterranean California forests and woodlands
and the Southeast U.S. Coastal Plain forests.
Figure 2—Bioclimatic Regions and Formations and Divisions within North America defined by climate. Less-
climatically driven wetland or substrate formations are not as strongly influenced by these patterns. Mapped
distribution of these biogeographic regions should not be used as definitive linework for actual formation,
division or other vegetation type distributions.
24 USDA Forest Service RMRS-GTR-346. 2016.
Our approach here, as throughout, is to emphasize the vegetation patterns, and to
assess their significance through correlations with broad ecological and biogeographic
processes. For example, at the level of formation subclass, we typically combine tem-
perate and boreal units, despite the differences in macroclimate, because of their fairly
strong overlap in dominant and diagnostic growth forms, whereas tropical types are
much more distinctive from either temperate or boreal. Separate temperate and boreal
types are recognized at the formation level.
Formation
Formation: A vegetation classification unit of high rank (3rd level) defined by com-
binations of dominant and diagnostic growth forms that reflect global macroclimatic
conditions as modified by altitude, seasonality of precipitation, substrates, and hydro-
logic conditions. (cf. “formation-type” and “biome-type” of Box and Fujiwara 2005;
FGDC 2008; Walter 1985; Whittaker 1975).
The formation describes vegetation patterns that reflect the combination of macro-
climates and/or substrate and topography. There is no strict parallelism among criteria
in identifying formations; thus, in a few cases, a subclass is not split any further,
because no major patterns of variation are evident with respect to the vegetation or
ecological processes as compared to other types at that level. In addition, bottom-up
information may also be considered from the Division level. For example, a formation
split was avoided if it creates two Divisions with overlapping floristics within broadly
similar growth forms, although tradeoffs are inevitable (e.g., wetland and upland forest
formations may overlap in floristics and dominants).
Formation Issues
Tropical humid forest (1.A.2, 1.A.3)
Commonly called tropical rain forests, we chose this term to ensure that users un-
derstand that both moist and wet, or seasonal evergreen and aseasonal evergreen rain
forests are included in the concept.
Temperate and boreal forest and woodland formations (1.B.1 – 1.B.5.)
The distinctive growth forms and climate relations of major forest formations
draw from a variety of works, including Walter (1985) who separated boreal, cool-
temperate, and warm-temperate forests and woodlands. (See the Formation subclass
discussion under “Temperate and Mediterranean vegetation” for a discussion of warm
temperate and Mediterranean forest vegetation.)
Placement of subalpine forests and woodlands is problematic as to whether they
are more boreal-like or temperate-like in their growth forms and floristics, and corre-
sponding climate. At this time, we treat subalpine forests within the temperate, as they
often take on some of the characteristics of lower elevation forests, and we restrict
boreal forests to the high latitude regions of the globe.
Mediterranean scrub and grassland formation (2.B.1)
See discussion of this vegetation under the Formation Subclass – Warm “Temperate
and Mediterranean “Vegetation.”
USDA Forest Service RMRS-GTR-346. 2016. 25
Coastal upland scrub and herb formations (2.A.3, 2.B.4)
Distinctive ecology and substrate of rocky shores, beaches and dunes, somewhat
reflected in vegetation, are separated out into their own formations. This is one of the
weaker formation distinctions. Note that coastal salt marshes are treated separately as
a wetland formation.
Salt marsh (2.C.5)
The vast majority of salt marshes are temperate, but the formation ranges broadly
enough, both along the coast and inland, that climate regime is identified with it.
Inland salt marshes are typically separated from coastal salt marshes at the Division
level.
Polar tundra and barrens formation (4.C)
Wet Tundra is sometimes defined to include: peaty wet tundra (bogs and poor fens),
tundra meadows, and marshes. But we treat those as wetland types in 2.C. Shrub &
Herb Wetland. Thus a separate “Wet Tundra” is not recognized. Cryptogam dominated
barrens (polar deserts) are also placed here.
Tropical high montane and temperate alpine (4.A.1)
The Tropical Montane Grassland & Shrubland (i.e. paramo and puna) is placed un-
der the Mesomorphic class (2.A.2), differentiating it from the Tropical High Montane
Scrub & Grassland Formation that has been placed within the Cryomorphic Scrub,
Herb & Cryptogam Vegetation Class. This split is a result of the key physiognomic
distinctions such as the ground cover of the formation, which is continuous for the
tropical montane shrubland and grasslands as compared to the low, semi-open cover-
age of the tropical cryomorphic formations, and the predominance of mesomorphic
growth forms (predominantly tussock grasses, large rosette plants, shrubs with
evergreen coriaceous and sclerophyllous – ericoid leaves, and cushion plants). As for
environmental drivers, seasonality is related to rainfall rather than temperature. The
main difference of this formation with its temperate counterpart is the diurnal fluctua-
tion of temperature, which can be 20 °C or more in tropical high mountains (i.e.,
Andes, Africa) with no growth limiting season.
Cliff, scree and rock formations (6.A.1-6.B.1)
Climate and substrate combinations are used for these formations, but there is little
literature available to guide us. Vascular components of these rock formations are of-
ten helpful. That is, one might find bromeliads on tropical cliffs, deciduous broadleaf
shrubs on temperate cliffs, and sclerophyllous evergreen shrubs on Mediterranean
cliffs. We are not aware of how the nonvascular growth forms might differ among
these formations.
In early pilots of this hierarchy, additional formations existed for desert, polar, and
alpine rock vegetation but these have now been moved under those classes and sub-
classes (see discussion above under “6. Open Rock Vegetation”).
26 USDA Forest Service RMRS-GTR-346. 2016.
Wetland Formations
Our approach to defining wetland formations follows a widely used set of
physiognomic-ecological types and terms that provide a set of wetland units cor-
responding to broad climatic and edaphic factors. We drew, in particular, on the
Canadian Wetland Classification system for types and definitions (National Wetlands
Working Group 1997; see also Mackenzie and Moran 2004) and from Mitsch and
Gosselink (2000) for ecological processes and functions. The major wetland types
that inform our formation distinctions are described in Table 6. Most of the wetland
types are divided into tropical versus temperate wetlands based on the different kinds
of dominant growth forms (e.g., broad-leaved evergreen trees and palms in tropical
swamps) (see Appendix B).
Table 6—Major wetland types used to guide formation distinctions. Types, definitions, environmental
features and growth forms are adapted from the Canadian National Wetlands Working Group (1997) and
Mackenzie and Moran (2004), with linkage to major wetland types described by Mitsch and Gosselink
(2000).
Wetland type Definition
Environmental
features Growth forms
Mitsch &
Gosselink
(2000) Type
Forest &
Woodland (1)
Flooded
& Swamp
Forest
A swamp is a wooded
mineral (or less often peat)
wetland on sites with a
flowing/flooded or fluctuating
semi-permanent, near
surface water table. Forested
swamps have trees occurring
on elevated microsites.
Flooded forests occur on
sites where flooding varies
from temporary (<7 days)
to semi-permanent (>180
days). Trees >2 m have >10
percent cover. We place
shrub swamps with marsh
and wet meadow in Class 2.
Mineral
soils or well-
humified peat.
Temporary to
semi-permanent
flooding (0.1 to
2 m deep), or
freshwater or
oligohaline tidal
inundation
Tall shrub,
broad-leaved
tree, needle-
leaved
tree, forb,
graminoid,
hydromorphic
herb (rarely)
Freshwater
swamps;
Riparian
ecosystems
(wetland,
tree)
Mangrove Mangroves occur in the inter-
tidal and brackish backwater
of estuarine areas in tropical
regions. Mangroves include
tree and shrub forms of
mangrove of all heights.
Intertidal and
supratidal zones,
semi-diurnal to
diurnal, flooding
by brackish or
saltwater
Mangrove,
halophytic
shrub,
halophytic
(succulent)
forb,
graminoids
Mangrove
swamps
(continued)
USDA Forest Service RMRS-GTR-346. 2016. 27
Wetland type Definition
Environmental
features Growth forms
Mitsch &
Gosselink
(2000) Type
Shrub & Herb
Wetland (2.C.)
Bog Bogs are shrubby, nutrient-
poor peatlands with
distinctive communities
of ericaceous shrubs
and hummock-forming
Sphagnum species,
sometimes with sedges,
adapted to high acid and
oxygen-poor soil conditions.
Trees >5 m typically have
<10 percent cover (raised
bogs may contain some
forested stands).
+/-
ombrotrophic,
pH < 5.5,
>40 cm fibric/
mesic peat
Stunted
needle-
leaved tree,
low shrub,
dwarf shrub
(ericaceous),
sphagnum
Peatland
Fen Fens are peatlands where
groundwater or stream inflow
maintains relatively moderate
to high mineral content
within the rooting zone. Sites
are characterized by non-
ericaceous shrubs, sedges,
grasses, reeds, and brown
mosses. Trees >5 m typically
have <10 percent cover.
Forested fen is included
under Swamp Forest.
Groundwater-fed
pH > 5.0
>40 cm fibric/
mesic peat
Low shrub
(often non-
ericaceous),
sedge (often
fine), grass,
reed, and
brown moss,
with or without
sphagnum
Peatland
Freshwater
Marsh, Wet
Meadow
& Shrub
Swamp (non-
tidal and
tidal)
A marsh-wet meadow is
a shallowly flooded or
saturated wetland dominated
by emergent grass-like
vegetation. A fluctuating
water table is typical in
marshes and wet meadows,
with early season high water
tables and some flooding
dropping through the
growing (or dry) season, and
exposure of the substrate or
drying of the profile possible
in late (or dry) season
or drought years. Shrub
wetlands (shrub swamps,
shrub carrs) occupy similar
sites to wet meadows. Trees
>5 m have <10 percent
cover.
Mineral soils or
well-humified
peat. Protracted
shallow flooding
(0.1 to 2.0 m)
or prolonged
soil profile
saturation, or
freshwater or
oligohaline tidal
inundation.
Grass, sedge
(often coarse),
forb, low
shrub, tall
shrub
Freshwater
marshes -
emergent;
Tidal
freshwater
marshes;
Riparian
ecosystem
(wetland,
herb/shrub)
Saltwater
Marsh
Saltwater marshes are
intertidal to supratidal
ecosystems that are flooded
diurnally (or less), sometimes
with freshwater inputs, and
are dominated by salt-
tolerant emergent graminoids
and succulents. Trees >5 m
have <10 percent cover.
Intertidal and
supratidal zones,
semi-diurnal to
diurnal, flooding
by brackish or
saltwater [n.b.
inland non-
tidal saline wet
meadows may
also be placed
here]
Grass,
sedge, forb,
halophytic
(succulent)
forb,
halophytic
shrub.
Tidal salt
marshes
Table 6—(Continued).
(continued)
28 USDA Forest Service RMRS-GTR-346. 2016.
Wetland type Definition
Environmental
features Growth forms
Mitsch &
Gosselink
(2000) Type
Table 6—(Continued).
Aquatic Aquatic
Vegetation
(non-tidal
and tidal)
Aquatic wetlands are shallow
waters dominated by rooted,
submerged and floating
aquatic plants. They are
associated with permanent
still or slow-moving waters,
such as shallow potholes,
ponds, rivers and lakes.
Aquatic plants may occur in
mineral or in well-humified
sedimentary peat. Emergent
growth forms <10 percent
cover, hydromorphic growth
forms >1 percent cover.
+/-Permanent
deep flooding
(0.5 – 2 m),
substrate can
be muck, sand,
marl or rocky
substrates
Hydromorphic
(aquatic) herb,
Emergents
< 10 percent
cover
Freshwater
marshes -
aquatic
Summary of Criteria for Natural Formations
We summarize the criteria for these three formation levels in Table 7, and compare
them with the Division level, which introduces the use of both physiognomic and
floristic criteria.
Development of Cultural Formations
As with the natural vegetation, physiognomic criteria represent the primary prop-
erties of cultural vegetation at the upper levels but are assessed in light of human
activities that govern these properties. Thus, the arrangement and organizing criteria
for these units is quite different from natural units, being largely constructed from
physiognomic and structural considerations driven by human management activities.
Excluded from these criteria are properties from outside the current vegetation, such as
explicit habitat factors (e.g., climate, soil type) or land use activities (e.g., grazed pas-
ture versus ungrazed pasture), except as these are expressed in the vegetation growth
forms and structures. Some types are difficult to classify as natural or cultural vegeta-
tion (e.g., forest plantation, pastures), and the user may need to compare both parts of
the hierarchy to determine the type’s location.
The upper levels of the hierarchy are based on dominant and diagnostic growth
forms that reflect anthropogenic drivers at global to continental scales. A compre-
hensive set of cultural vegetation units are available in pilot form for most levels of
the hierarchy, based on the U.S. Natural Resources Conservation Service’s National
Resources Inventory (NRI) (FGDC 2008; Appendix I); thus, we deferred to that
classification for most of the units but organized them into a hierarchical structure
consistent with the overall framework.
USDA Forest Service RMRS-GTR-346. 2016. 29
Table 7—Brief summary of criteria for formation units and division.
Criteria Formation Class
Formation
Subclass Formation Divisiona
Diagnostic
Species
-- -- -- Very large set. Many
character spp., often
endemic to the division.
At least some of the
character species are
dominant in parts of the
range of the type.
Growth Forms Broad combinations
of dominant general
growth forms and
specific growth forms
Combinations
of general and
specific dominant
and diagnostic
growth forms
Combinations of
dominant and diagnostic
growth forms, sometimes
based on individual
diagnostic growth forms
(e.g. mangrove)
The same combination
of growth forms as at the
formation level
Range of
Variation
Overlapping general
growth forms
(tree, shrub), but
combinations of
diagnostic growth
forms generally non-
overlapping (e.g.,
xeromorphic)
Combinations of
diagnostic growth
forms partially non-
overlapping (e.g.,
warm temperate
forests and tropical
forests
Combinations of
diagnostic growth
forms more strongly
overlapping (e.g.,
temperate and boreal
forests), relative
abundances more
important
Essentially non-
overlapping floristics
Ecological
Gradients
Basic moisture,
temperature, and/or
substrate or aquatic
conditions
Global
macroclimatic
factors driven
primarily by latitude
and continental
position, or that
reflect overriding
substrate (rock
vegetation) or
water salinity
(aquatic
vegetation)
Global macroclimatic
conditions in combination
with landmass and
edaphic factors, such as
altitude, seasonality of
precipitation, substrates,
and hydrologic conditions
Continental scale
biogeographic
differences in
composition, reflecting
macroclimate patterns
modified by the
continents. Divisions
within a formation are
often geographically
separated.
aA character species in a Division shows a distinct maximum concentration, either in constancy and/or abundance, in one well-defined
vegetation type as compared to all others and recognizable at general/global geographic scales (Mueller-Dombois and Ellenberg
1974).
Cultural Class
Cultural Class: A vegetation classification unit of high rank (1st level) defined by
broad combinations of dominant general growth forms determined by global scale
human activities
Cultural Subclass
Cultural Subclass: A vegetation classification unit of high rank (2nd level) defined
by combinations of general dominant and diagnostic growth forms that reflect global
scale human activities.
30 USDA Forest Service RMRS-GTR-346. 2016.
Cultural Formation
Cultural Formation: A vegetation classification unit of high rank (3rd level) defined
by combinations of dominant and diagnostic growth forms that reflect global scale
human activities.
Type Description
Many details of type description especially for natural vegetation, are provided in
FGDC (2008) and Jennings and others (2009), including from plot data preparation
and data collection, data analysis, interpretation, documentation and archiving, and
type description, nomenclature, and peer review. That work, however, was focused on
the lower floristic levels of the natural types, alliances and associations. Additional
guidance is needed for application across all levels of the hierarchy. Here we sum-
marize our approach to type description of the formations (See also Faber-Langendoen
et al. 2014).
Upper Level Nomenclatural Rules
The HRWG has adopted and advocated for the approach taken in FGDC (2008) and
Jennings and others (2009), whereby a scientific name, a translated scientific name
(from the vernacular plant names available from widely accepted standard taxonomic
references), and a colloquial name are all provided. Translated names and colloquial
names are provided in English and a variety of other common languages. The names
can include both physiognomic terms (forest, grassland, bog, tundra) and species
names, and may also include a biogeographic term. The HRWG recommends develop-
ment of a glossary of nomenclatural terms to guide ongoing naming of types.
Formation types at Levels 1-3 are named, defined, and organized by vegetation
structure and physiognomy, as these are reflected in broad climatic and site factors.
A convenient aid for naming the formations, and consistent with the goal of using
common terminology (FGDC 2008), is to use terms based on the habitats that they
occupy; it should be re-emphasized that habitat factors are not typically used in defin-
ing formations (Whitmore 1984, pg. 155). To avoid tendencies towards making the
name too descriptive, we also provide a one-sentence descriptive summary of the type.
The result is a set of easily recognized formations with memorable colloquial names
that communicate the most distinctive vegetation and ecological characteristics of the
formation. Currently, we apply only English terms to the three formation levels, and
distinguish scientific and common names only for Level 1.3
Overall Style
All first letters of English words in a vegetation type name are capitalized and, as
needed, additional words are separated by either a hyphen with spaces ( - ), a comma
and space (, ) or the “and” symbol with spaces ( & ).
3
These approaches to nomenclature do not rule out the option of adding a formal Latinized
name for types at these three levels, as done by Rübel (1930-1931, see Appendix B in Shimwell
1971). For example, following Rübel, the scientic names for the Desert and Semi-Desert class
could be “Deserta,” the Warm Semi-Desert subclass could be named “Siccadeserta,” and the
Cool Semi-Desert subclass named “Frigorideserta.”
USDA Forest Service RMRS-GTR-346. 2016. 31
Level 1 (Formation class)
Class names are based on the very broad growth forms that correspond to global
moisture/temperature regimes. The single name helps identify the broad grouping of
growth forms that correspond to particular moisture/temperature conditions. A paren-
thetical set of names is included to guide general users to the main kind of vegetation
included in the class. The class level is organized by decreasing complexity and cover
of the vegetation, reflecting increasingly stressful site factors. Given the wide overlap
in use of the terms “Forest” and “Woodland” we use both terms to indicate that the
class definition encompasses all mesomorphic (i.e. broad-leaved or needle-leaved)
trees of varying height and canopy spacing.
Examples:
• Mesomorphic Tree Vegetation (Forest & Woodland)
• Mesomorphic Shrub & Herb Vegetation (Shrub & Herb Vegetation)
• Xeromorphic Woodland, Scrub & Herb Vegetation (Desert & Semi-Desert)
• Hydromorphic Vegetation (Aquatic Vegetation)
Level 2 (Formation subclass)
The subclass name reflects the structure, physiognomy and environmental factors
that characterize the subclass. The primary environmental factor is macroclimate.
Physiognomic terms are sometimes more specific than the class name (e.g., scrub ver-
sus shrubland where the vegetation may include tall xeromorphic tree-like plants such
as tall cacti). All such terms, if used, should be defined.
Examples:
• Tropical Forest & Woodland
• Temperate & Boreal Grassland & Shrubland
• Cool Semi-Desert Scrub & Grassland
• Saltwater Aquatic Vegetation
Level 3 (Formation)
The formation name reflects the structure, physiognomy and environmental factors
that characterize the formation. The primary environmental factors are macroclimate
in combination with soil moisture conditions, elevation and substrate. Physiognomic
terms are sometimes more specific than the class or subclass name. All physiognomic
terms should be defined in the vegetation type description.
Examples:
• Tropical Lowland Humid Forest
• Mediterranean Scrub & Grassland
• Cool Semi-Desert Scrub & Grassland
• Marine & Estuarine Saltwater Aquatic Vegetation
32 USDA Forest Service RMRS-GTR-346. 2016.
Description Template
The official template for describing types is provided in FGDC (2008) and Jennings
and others (2009), and is appropriate to all levels of the hierarchy (see also FGDC
2008, Section 3.2.3). An expanded set of instructions on completing the template is
available on request from the authors. Following are a few general observations on the
format of these descriptions:
• A standard template is used, supplemented with a few additional fields.
• Concepts for Level 1 types were developed from the expertise of the HRWG
members. Other levels are more commonly used by other classifications and ap-
propriate citations and synonyms are provided (See Appendix F).
• A standard set of growth forms is used (see Appendix D; see also Appendix E in
FGDC 2008). Growth forms types are placed in italics to remind the reader that
the terms have specific meanings. Additional growth forms that may be useful
to add to the list and that are included in the descriptions can also be placed in
italics, with an asterisk.
These descriptions are a first preliminary effort at global descriptions for formation
types, and are provided to give some guidance to our concepts. Undoubtedly even
these preliminary descriptions are biased by our western hemisphere perspective. We
look forward to engaging with a broader set of ecologists around the globe to continue
improving both the concepts and the descriptions. We hope such collaboration can
develop, in part, by identifying vegetation types at the Division level around the globe.
Peer Review
We follow the approach of FGDC (2008) and Jennings and others (2009) for peer
review. Those documents outline a process based on a dynamic classification standard,
whereby peer review is an open process conducted by professional organizations in
collaboration with other interested parties. It is administered by a peer review board
under the aegis of an institution capable of providing independent reviewers of ap-
propriate experience in vegetation classification. In this case, the ESA Vegetation
Classification Panel will solicit review of the current set of formations. It is desirable
to have a panel of international vegetation ecologists oversee the ongoing peer review
of these global formation types.
A Key to the Formations
An introduction and key to the Formation Class (Level 1) is provided in Appendix
I. We note in the introduction to the key, that keying out formations requires attention
to vegetation strata and growth forms. Many species have only a single or primary
growth form. Therefore, if a species list and vegetation strata or general growth forms
are part of the plot description, detailed recording of specific growth forms may not be
needed (e.g., Mucina and others 2000; Peet and others 1998; Tart and others 2005b).
If a flora or species list for a state, province, or nation also identifies the species
growth form(s), then a rollup of species to growth forms will simplify the standard
field methods. The user need only be aware of those species that have multiple growth
USDA Forest Service RMRS-GTR-346. 2016. 33
forms, and which growth form is present on the plot. In the United States, the U.S.
Department of Agriculture (USDA) PLANTS database (2002 version; see http://
plants.usda.gov) lists the general growth form (“growth habit”) of all plant species
in the United States This list could be supplemented with the specific growth forms
(Appendix D) of each species.
Synopsis
We have introduced an ecological vegetation classification approach (the EcoVeg
approach) by which vegetation ecologists can organize global vegetation patterns at
multiple scales (Faber-Langendoen and others 2014), and also provide rationale and
detailed descriptions for each of the upper level units. We believe this framework is
an important contribution to what is currently available to vegetation ecologists, land
managers, and conservationists. Many global classifications deal with only broad
structural patterns, others with only floristics. We provide an introduction to forma-
tions, along with the descriptions and key, as a basic synopsis of the world’s vegetation
structured by specific growth form criteria. Sufficient detail is given to encourage
consistent application anywhere in the world and within a hierarchical structure that
includes both floristic and growth form criteria, ultimately at the levels of alliance and
association. The formations descriptions are not detailed; they rely on a large tradition
of description and classification for their support, and they seek to provide as concise
an overview as possible. They are presented here in draft form, and we are aware
that we have not been able to invest as much effort across all of them. More work is
needed to reference the many publications that support or improve these concepts.
In addition, our work is only one, among many, and so establishing crosswalks to
other classification will increase our understanding of how others have defined and
described the vegetation.
A real test of these concepts is whether they provide any value in moving to
the next step, which is supporting description and classification of Divisions and
Macrogroups within the formations. It is these types that force us to specify very
clearly in which continents and regions these formations are found and whether the
summaries of variability so simply described here can account for the variation ob-
served around the globe. Our expertise has primarily come from Western Hemisphere
vegetation ecologists, though we have also considered vegetation in Africa and
Europe. We look forward to helping vegetation ecologists achieve consensus on
these “mid-level” units (see Appendix J for examples of Cool Temperate Forest and
Grassland Divisions). Such collaboration can help us better understand the ecological
processes, biogeographic and historical relationships, current threats, and conservation
status of vegetation types.
34 USDA Forest Service RMRS-GTR-346. 2016.
USDA Forest Service RMRS-GTR-346. 2016. 35
PART II: DESCRIPTION OF WORLD
FORMATION TYPES
36 USDA Forest Service RMRS-GTR-346. 2016.
USDA Forest Service RMRS-GTR-346. 2016. 37
1. Forest & Woodland (C01)
Overview
Database Code: 1 (C01)
Scientific Name: Mesomorphic Tree Vegetation Class
Common Name (Translated Scientific Name): Mesomorphic Tree Vegetation Class
Colloquial Name: Forest & Woodland
Hierarchy Level: Class
Lower Level Hierarchy Units:
1.A. Tropical Forest & Woodland (S17)
1.B. Temperate & Boreal Forest & Woodland (S15)
Concept Summary
Type Concept Sentence: Tropical, temperate and boreal forests, woodlands and
tree savannas characterized by broadly mesomorphic (including scleromorphic) tree
growth forms (including broad-leaved, needle-leaved, sclerophyllous, palm, bamboo
trees, and tree ferns), typically with at least 10 percent cover (but tropical tree savan-
nas up to 40 percent cover, when trees are less than 8 m tall), irregular horizontal
spacing of vegetation structure, and spanning humid to seasonally dry tropical to
boreal and subalpine climates and wet to dry substrate conditions. Includes native
forests, as well as managed, and some plantation forests where human management is
infrequent.
Classification Comments: Plantations, ruderal, and native forest and woodland
stands are typically placed in this class. Some plantation forests can be placed here
rather than in the Agricultural & Developed Vegetation Class (C07) despite having a
canopy layer that may be very regular (spaced in planted rows), if the tree regenera-
tion, shrub and ground layers develop spontaneously with irregular horizontal spacing,
similar to native forests (i.e., regular human intervention does not occur for these
layers). However, where plantations have highly regular horizontal structure, with
regular human intervention in all layers (e.g., through cutting, spraying, ground-layer
mowing), they may better be placed in the Agricultural & Developed Vegetation Class
(C07).
Similarly, tree-dominated vegetation that has a natural, irregular horizontal spacing
in the tree layer, but highly regular shrub or herb layers because of human interven-
tion, should be placed in the Agricultural & Developed Vegetation Class (C07). For
example, shade coffee, cacao, and other woody agricultural crops grown under native
(or exotic) tree species and in which all non-treed strata layers are subject to regular
human intervention should be placed in that class.
Included in this class are low-statured trees that overtop other growth forms. These
include tree sapling and seedling stands with trees less than 2 m, where the tree growth
form is at least 10 percent cover and overtops other growth forms. These include
subarctic woodlands, and coastal dwarf-tree woodlands that are less than 2 m but
are single-stemmed with definite crowns. Conversely, treed bogs and fens, with low
stunted trees and conical canopies, and otherwise sharing the moss and dwarf-shrub
layers of open bogs and fens, are placed with those types. Where trees share the same
strata as grasslands and shrublands (e.g., tallgrass brush prairie of 1 to 3 m, with trees
less than 2 m), the vegetation is placed in the shrub- and herb-dominated classes.
38 USDA Forest Service RMRS-GTR-346. 2016.
Tree cover ranges from 10 to 100 percent, and is inclusive of what are called for-
ests, woodlands, and tree savannas, at least in the non-tropical regions. The class limit
of 10 percent tree cover (for mesomorphic tree growth forms) follows that of FAO’s
Global Forest Resources Assessment 2000 (FAO 2001). We exclude stands of trees
planted primarily for agricultural production (such as fruit tree or forest plantations)
and typically agroforestry, as well as those in developed lands, such as cities and road-
sides (they are placed in Class 7, formation 7.A.2). However, unlike FAO, we do not
include what FAO calls “temporarily unstocked areas” (such as clearcuts, burnt areas)
unless the tree growth form is actually present at 10 percent cover—even if in seedling
or sapling form—and exceeds the height of other growth forms.
Other classifications may limit forests and woodland to a narrower range of tree
cover. For example, forests and woodlands are sometimes defined as 25 to 100 percent
cover, and distinguished from tree savannas with 10 to 25 percent cover, which includ-
ed under broadly defined grassland and shrubland classes (Driscoll and others 1984;
FGDC 1997; Grossman and others 1998; Minnesota DNR 2005). UNESCO (1973) re-
quired that tree savannas also have a strong herbaceous layer (greater than 50 percent
graminoid cover). Still, a variety of definitions of tree savanna have been published,
from the 10 to 25 percent cover noted above, to 10 to 30 percent cover in Nelson
(2005), 10 to 40 percent in UNESCO (1973), and 10 to 50 percent cover in Curtis
(1959). Blue oak, Engelmann oak, and other woodlands in California Mediterranean
woodlands are typically between 10 and 60 percent cover, and California State ecolo-
gists place these in the Forest & Woodland (Barbour and others 2007). However,
apart from tree savannas, there are many other forest and woodland types and regions
where the degree of canopy closure plays less of a role in defining types, for example,
forested swamps and bogs, longleaf pine woodlands (Peet 2006), eastern pine barrens,
and subarctic woodlands.
Thus, given the variety of situations, we have chosen a more inclusive definition of
forest and woodland that encompasses most tree savanna concepts, and rely on lower
levels of the hierarchy to make distinctions based on a combination of biogeography,
ecology, and floristics. For example, in the context of the eastern Great Plains tall-
grass prairie-forest border, it is common to recognize oak savannas, based on open
tree cover levels (e.g., 5 to 30 percent tree cover in Nelson 2005), as separate from
oak woodlands (30 to 80 percent cover) and oak forests (80 to 100 percent cover).
Savannas may be distinguished from forests or woodlands, but these structural distinc-
tions often correspond to lower level units of the NVC hierarchy (e.g., group, alliance,
and association). Still, Dixon and others (2014) suggest that there may be good eco-
logical reasons to treat upland tropical tree savannas, with 10 to 40 percent tree cover,
trees less than 8 m tall, and a substantial graminoid layer as part of 2. Shrubland &
Grassland (C02), and we allow for that option here.
Similar NVC Types:
2. Shrubland & Grassland (C02): When grasses and shrubs dominate the ground
layer and tree cover is near but greater than 10 percent, is clumped, or over-
topped by grasses and shrubs, there may be cases where assignment to this
class is preferable. Short mesomorphic trees that do not overtop shrubs and
USDA Forest Service RMRS-GTR-346. 2016. 39
herbs are placed in this class. However, in tropical upland savanna regions,
stands may have 40 percent tree cover, where trees are less than 8 m tall, tree
regeneration is sparse to absent, and there is a substantial graminoid layer.
3. Desert & Semi-Desert (C03): Occasionally xeromorphic trees may be
sufficiently dense to form woodland stands (e.g., saguaro, Joshua tree,
microphyllous-leaved mesquite woodlands, tropical thorn woodlands). The
dominance of xeromorphic growth forms places these stands in the Desert &
Semi-Desert class rather than Forest & Woodland.
7. Agricultural & Developed Vegetation (C07): Forests found in urban parks and
lawns may have an irregular horizontal spacing but a highly regular or mowed
understory and are placed in this developed vegetation class. Forests, such as
orchards and forest plantations, typically have either a very regularly spaced
tree canopy (often pruned or trained) and/or plowed or regularly manipulated
ground layer (e.g., tree-shaded shrub or herb crops).
Diagnostic Characteristics: Mesomorphic tree growth forms (broad-leaved, nee-
dle-leaved, and sclerophyllous trees, palms, bamboo trees, and tree ferns) have greater
than 10 percent canopy cover, a spontaneous, irregular horizontal canopy spacing, and
overtop other growth forms, except in tropical upland regions, where trees typically
have greater than 40 percent cover, are greater than 8 m tall, and the vegetation lacks a
substantial graminoid layer.
Vegetation
Physiognomy and Structure: Growth Forms: Stands are dominated by me-
somorphic trees, including broad-leaved deciduous (including mostly deciduous,
winter-deciduous, facultatively deciduous), broad-leaved evergreen (including mostly
evergreen), needle-leaved (deciduous and evergreen), sclerophyllous trees, palms,
bamboo trees, and tree ferns. Tree growth forms generally have a single main stem
and more-or-less definite crowns, and may be as low as 2 m (scrub trees) (e.g., tropical
cloud elfin forest, mesquite woodland). Where growth forms are not easily defined,
woody plants equal to or greater than 5 m at maturity are considered trees (FGDC
2008).
Structure: Typical stands have one or more of the tree growth forms exceeding 5 m
in height, and the canopy has irregular horizontal tree stem spacing, with a minimum
of 10 percent canopy cover (8 m in height and minimum of 40 percent in tropical
forests and woodlands, as low as 2 m in subarctic woodlands). A tree regeneration
layer is often present, along with various associated growth forms (shrubs, herbs,
nonvasculars). Stands of trees where the tree growth form is short (<5 m) in height but
overtopping shrub and herb growth forms, may also be placed in this class.
Environment
Environmental Description: Climate: Climates range from humid tropical to
boreal and subalpine, with fairly moderate moisture and temperature conditions. See
details under the various forest and woodland subclasses.
Soil/substrate/hydrology: Dry to wet soils, including those found in swamp forests
and mangroves.
40 USDA Forest Service RMRS-GTR-346. 2016.
Distribution
Geographic Range: Forest and Woodland occurs on all continents, mostly in the
following ecoregions (Bailey 1989, 1996): the Humid Tropical and Humid Temperate
Domains, the Subarctic Division of Polar Domain, and Mountain Divisions of Dry
Domain. It is less common in other divisions of Polar and Dry domains.
Citations
Synonymy:
= Forest (FAO 2001) [Approximately equivalent. Xeromorphic scrub woodlands are
probably included here, but otherwise the concepts are very similar.]
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: Hierarchy Revisions Working Group
Acknowledgments:
Version Date: 26 Aug 2014
1.A. Tropical Forest & Woodland (S17)
Overview
Database Code: 1.A (S17)
Scientific Name: Tropical Forest & Woodland Subclass
Common Name (Translated Scientific Name): Tropical Forest & Woodland
Subclass
Colloquial Name: Tropical Forest & Woodland
Hierarchy Level: Subclass
Placement in Hierarchy: 1. Forest & Woodland (C01)
Lower Level Hierarchy Units:
1.A.1. Tropical Dry Forest & Woodland (F003)
1.A.2. Tropical Lowland Humid Forest (F020)
1.A.3. Tropical Montane Humid Forest (F004)
1.A.4. Tropical Flooded & Swamp Forest (F029)
1.A.5. Mangrove (F006)
Concept Summary
Type Concept Sentence: Tropical forests found at lowland and montane elevations
including tropical dry forests, and lowland to montane humid forests (tropical rainfor-
ests) and tropical forested wetlands, where frost is essentially absent at sea level.
Classification Comments: Review of tropical monsoon forests is needed, as they
can vary from dry to moist.
Similar NVC Types:
1.B. Temperate & Boreal Forest & Woodland (S15): Broad-leaved evergreen trees
may be common in warm temperate forests, comparable to tropical dry forests
(i.e., evergreen leaves are typically small), but deciduousness is caused by frost,
and types are found where a hard frost occurs annually.
USDA Forest Service RMRS-GTR-346. 2016. 41
2.A. Tropical Grassland, Savanna & Shrubland (S01): Where tree cover exceeds
10 percent, stands are typically placed in the Tropical Forest & Woodland
(S17). However, in tropical upland savanna regions, stands may have 40 per-
cent tree cover, where trees are less than 8 m tall, tree regeneration is sparse to
absent, and there is a substantial graminoid layer.
3.A. Warm Desert & Semi-Desert Woodland, Scrub & Grassland (S06): Thorn
woodlands, with xeromorphic characteristics (aphyllous or very small-leaved
trees, with succulents), are placed in this subclass, and rainfall is more typically
between 25 and 100 cm.
7.A. Woody Agricultural Vegetation (S22): Tropical Forest & Woodland (S17) long-
rotation plantations or woody restoration plantings with an irregular structure
and a largely spontaneous ground layer may initially be similar to Woody
Agricultural Vegetation (S22) in their early stages of development, especially if
planted in rows and the understory is strongly manipulated.
Diagnostic Characteristics: Tropical Forest & Woodland is dominated by
broad-leaved, often megaphyll, evergreen trees, broad-leaved drought-deciduous
or semi-deciduous trees, or small-leaved (micro- to mesophyll evergreen trees).
Evergreen needle-leaved trees may occur in association with these other growth forms.
Climates are consistently warm (seasonal daily temperatures with minimal variation),
and annual rainfall is typically greater than 100 cm.
Vegetation
Physiognomy and Structure: Tropical Dry Forest (typically called Tropical Dry
Forest or Tropical Seasonally Dry Forest) range in canopy types, including evergreen,
semi-evergreen (needle-leaved or broad-leaved), or largely or wholly deciduous
Canopy heights decrease and canopy coverage tends to decrease as the climate dries
until the forests are reduced to open, short-statured (5 - 15 m) woodlands (Whittaker
1975). Tree growth forms predominate, with micro- to mesophyll leaves, but succulent
species may be present. They occur in humid dry tropical climates, typically with a
pronounced dry season, during which some or all of the trees may lose their leaves, or
leaves may be moderately small and evergreen sclerophyllous. Some tropical forests
have a more sustained dry period, with less seasonality.
Tropical humid forests (including moist and wet forests) occur in the humid tropics
where rainfall varies from abundant and well-distributed throughout the year to some-
what seasonal. Tree growth forms predominate, are tall, often of numerous species,
some with buttressed bases, often smooth bark, and evergreen meso- to macrophyll
leaves. Also present may be tree ferns, large woody climbers or lianas, and both vascu-
lar and nonvascular epiphytes, often of greater diversity than the ground layer. Heights
may exceed 30 m (Whittaker 1975).
Tropical forested wetlands include swamps and mangroves, with hydrophytic plants
and, in the case of mangrove, distinctive hydromorphic growth forms adapted to saline
conditions.
42 USDA Forest Service RMRS-GTR-346. 2016.
Environment
Environmental Description:
Climate: In general, the tropical humid forest has a fairly consistent average annual
temperature, ranging from 26 to 27 degrees C, and a more variable daily temperature,
with changes up to 5 degrees C. In the tropical dry forest, average annual temperatures
range between 20 and 30 degrees C, and daily temperatures change from between
26 to 28 degrees C. At sea level, frost is essentially absent from the Tropical Forest &
Woodland (Holdridge 1967). Rainfall ranges from 100 to 450 cm (400 to 180 inches),
with the rainfall becoming increasingly more seasonal in tropical dry climates, where
the dry season may extend for 4 to 7 months (Holzman 2008).
Soil/substrate/hydrology: Soils in humid regions are often highly weathered ancient
soils with high acidity and low nutrient and organic matter content; however, many
tropical forests occur on rich volcanic or limestone soils. The major soil orders in the
U.S. system include Oxisols, Ultisols, Inceptisols, and Entisols (Soil Survey Staff
1999) (see Brady and Weil 2002 for comparison of U.S. soil orders with Canadian
and FAO systems). Younger and richer soils are found in alluvial habitats or in areas
influenced by ashes from volcanic activity (Holzman 2008).
Distribution
Geographic Range: Tropical Forest & Woodland is concentrated around the
equator with tropical humid forest most common between 0 and 10 degrees N and S
latitude, and tropical dry forest between 10 and 23 degrees N and S, with latitudinal
limits shaped by frost and drought. Tropical Forest & Woodland is found in three
major regions: South and Central America and the Caribbean Islands; Africa (west,
central, and interior) and Madagascar; and the Indo-Asian Pacific (India, Southeast
Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia).
Citations
Synonymy:
= Tropical Forest & Woodland (Holzman 2008)
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: D. Faber-Langendoen and E. Helmer
Acknowledgments:
Version Date: 26 Aug 2014
1.A.1. Tropical Dry Forest & Woodland (F003)
Overview
Database Code: 1.A.1 (F003)
Scientific Name: Tropical Dry Forest & Woodland Formation
Common Name (Translated Scientific Name): Tropical Dry Forest & Woodland
Formation
Colloquial Name: Tropical Dry Forest & Woodland
USDA Forest Service RMRS-GTR-346. 2016. 43
Hierarchy Level: Formation
Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Tropical Dry Forest & Woodland is dominated by
broad-leaved drought-deciduous, semi-deciduous, and small-leaved or sclerophyllous
evergreen trees where rainfall is lower, often associated with more strongly seasonal,
tropical climates, rainshadows, or drying winds. At continental scales, the largest areas
occur between 10 and 23 degrees N and S latitude.
Type Concept: Tropical Dry Forest & Woodland, including most monsoon forests,
occurs in extensive areas near the equator around the globe between about 10 and
23 degrees N and S latitude, though it is also be found near windward coasts and on
the leeward sides of mountains or islands. These forests are dominated by broad-
leaved drought-deciduous trees or small-leaved (micro- to mesophyll) evergreen trees
or broad-leaved (meso- to macrophyll) sclerophyllous-leaved trees. Evergreen needle-
leaved trees may occur in association with these other growth forms. It is a medium to
high forest varying on average from 15 to 25 m tall, typically with several structural
levels as complex upper canopy, several subcanopy levels of treelets and shrubs,
woody vines, and an irregular low herbaceous plant stratum. Canopy heights decrease
and canopy coverage tends to decrease as the climate dries until the forests are reduced
to open, short-statured (5 - 15 m) woodlands (more rarely shorter). Included are semi-
evergreen, partially sclerophyllous, semi-deciduous and deciduous, mostly dense to
semi-dense forests adapted for a distinct period of seasonal winter drought, resulting
in 4 to 7 months of drought (rainfall 60 mm or less), during which some or all of the
trees lose their leaves. Annual rainfall ranges from 100 to 200 cm. The considerable
diversity of dry tropical forests and woodland types are related to the topographic,
hydric and edaphic variations as well as with the floristic composition and different
biogeography.
Classification Comments: Mooney and others (1995) suggest that Tropical Dry
Forest & Woodland may be defined as forest occurring in tropical regions character-
ized by pronounced seasonality in rainfall distribution, resulting in several months
of drought. The forests that develop under such climatic conditions share a broadly
similar structure and physiognomy; they mainly occur on oligotrophic, reddish soils
(Oxisols, Ultisols), but may also occur on mesotrophic soils. Beyond that, they note
that these shared characteristics are difficult to define with precision. They may
either be deciduous or evergreen, though typically small-leaved, and either open- or
closed-canopy. There are sclerophyllous evergreen broad-leaved (mesophyllous to
macrophyllous-leaved) Tropical Dry Forest & Woodland in the Brazilian-Bolivian
Cerrado. But we include here only the most closed form of cerrado (i.e. the cer-
radão) and the more typical cerrado is placed in 2.A. Tropical Grassland, Savanna &
Shrubland (S01).
Many authors include thorn woodlands as part of a broadly defined “tropical
dry forest” or “seasonally dry tropical forest” (SDTF). For example, Pennington
and others (2006) use a wide interpretation of SDTF in the Neotropics, including
44 USDA Forest Service RMRS-GTR-346. 2016.
formations as diverse as tall forest on moister sites to cactus scrub on the driest, but
they exclude the Chaco of Argentina, Paraguay and Bolivia because it receives frost.
See also Oliveira-Filho and others (2006) who include caatingas and carrascos within
their broad definition of SDTF, but exclude cerrados and chaco. Here we treat 3.A.1
Tropical Thorn Woodland Formation (F039) as a separate xeromorphic growth form-
based formation that includes, in the Neotropics, caatingas, carrascos, and chaco.
Tropical monsoon forests are sometimes grouped with 1.A.2 Tropical Lowland
Humid Forest Formation (F020) as “tropical moist forest,” but being deciduous with
pronounced drought periods, they are better included here with 1.A.1 Tropical Dry
Forest & Woodland Formation (F003) (Whitmore 1998). Further review of the range
of variation in tropical monsoon forests is needed, to clarify the transition to Tropical
Lowland Humid Forest.
Similar NVC Types:
1.A.2. Tropical Lowland Humid Forest (F020): As seasonality increases, the abun-
dance of drought-deciduous trees increases, and semi-evergreen humid forests
more closely resemble Tropical Dry Forest & Woodland (F013). Tropical monsoon
forests are sometimes grouped with Tropical Lowland Humid Forest as “tropical
moist forest” (Whitmore 1998), but they are here included with Tropical Dry Forest
& Woodland.
1.B.1. Warm Temperate Forest & Woodland (F018): Broad-leaved evergreen trees may
be common in this formation, comparable to Tropical Dry Forest & Woodland
(i.e., evergreen leaves are typically small), but deciduousness is caused by frost,
and types are found north or south of around 23 degrees N and S latitude.
3.A.1. Tropical Thorn Woodland (F039): Thorn woodlands, with xeromorphic char-
acteristics (aphyllous or very small-leaved trees, with succulents) are placed in
this xeromorphic woodland formation (F039). Rainfall is between 25 and 100 cm.
Tropical Dry Forest & Woodland grades to Tropical Thorn Woodland in areas with
lower annual rainfall and increasing period of seasonal drought (in xeric warm
bioclimates), while the trees and shrubs become fully deciduous and with a con-
siderable increase of distinct xeromorphic adaptations such as thorns, succulency
and clearly microphyllous species that instead are scarce or absent in Tropical Dry
Forest & Woodland.
7.A.2. Intensive Forestry Plantation & Agroforestry Crop (F043): Tropical Dry Forest
& Woodland (F003) long-rotation plantations or woody restoration plantings with
an irregular structure and a largely spontaneous ground layer may initially be
similar in their early stages of development, especially if planted in rows and the
understory is strongly manipulated.
Diagnostic Characteristics: Tropical Dry Forest & Woodland is dominated
by broad-leaved drought-deciduous trees or, more rarely, small-leaved (micro- to
mesophyll) evergreen trees or broad-leaved (meso- to macrophyll) sclerophyllous-
leaved trees. Thorn forest scrub, and scrubby cerrado are excluded. Evergreen
needle-leaved trees may occur in association with these other growth forms. Climates
USDA Forest Service RMRS-GTR-346. 2016. 45
are consistently warm (seasonal daily temperatures with minimal variation), and an-
nual rainfall is strongly seasonal, but average annual rainfall is typically greater than
100 cm.
Vegetation
Physiognomy and Structure: Tropical Dry Forest & Woodland is dominated
by broad-leaved drought-deciduous trees or, more rarely, small-leaved (micro- to
mesophyll) evergreen trees or broad-leaved (meso- to macrophyll) sclerophyllous-
leaved trees (Lugo and others 2006). Evergreen needle-leaved trees may occur in
association with these other growth forms. It is a medium to high forest varying on
average from 15 to 25 m tall, typically with several structural levels as complex upper
canopy, several subcanopy levels of treelets and shrubs, woody vines, and an irregular
low herbaceous plant stratum. Canopy heights decrease and canopy coverage tends
to decrease as the climate dries until the forests are reduced to open, short-statured
(5 - 15 m) woodlands (more rarely shorter). Included are semi-evergreen, partially
sclerophyllous, semi-deciduous and deciduous, mostly dense to semi-dense forest
(Whittaker 1975).
In the Neotropics the lower forest level is often dominated by colonies of clumping
terrestrial bromeliads. Overall, there is predominance in the canopy of medium-sized
leaves (mesophyllous) that fall partially or almost completely in the dry season. Tall
arborescent cacti can be frequent in dry semi-deciduous forest of the Neotropics and
physiognomically similar arborescent succulent euphorbias in the Paleotropics. In
western Brazil, eastern Bolivia, and Paraguay, this formation includes large stands
of medium-low and partially sclerophyllous semi-evergreen forests or “cerradão,”
with characteristic adaptations to drought and fire, such as very corky bark on twisted
trunks and xylopodiums (but we exclude the more typical cerrado, which is placed
with 2.A. Tropical Grassland, Savanna & Shrubland (S01).
Environment
Environmental Description: Climate: Tropical Dry Forest & Woodland occurs
in areas where the air subsides near the tropics of Cancer and Capricorn and the
Intertropical Convergence Zone (ITCZ) migrates north and south seasonally, produc-
ing the alternating pattern of rainfall and dryness. The average drought season varies
in length from 3 to 6 months and is generally coincident with the annual lowest
temperatures. Annual rainfall ranges from 100 to 200 cm (Whitmore 1998), or where
the annual rainfall is less than 160 cm, with a period of at least 5 to 6 months receiving
less than 10 cm, during which some or all of the trees lose their leaves (Pennington
and others 2006). The climate is warm tropical pluviseasonal, subhumid to humid.
Soil/substrate/hydrology: The substrate often includes large areas of highly weath-
ered reddish soils with high iron and aluminum content and low mineral nutrients
content, as well as frequent development of laterization. The main soil orders in the
U.S. system associated with Tropical Dry Forest & Woodland are Oxisols, Ultisols and
Alfisols (Soil Survey Staff 1999) [see Brady and Weil (2002) for comparison of U.S.
soil orders with Canadian and FAO systems]. More rarely, they occur on mesotrophic
soils. This type also occurs on limestone substrates in the Caribbean and Mesoamerica
(Lugo and others 2006).
46 USDA Forest Service RMRS-GTR-346. 2016.
In most areas, Tropical Dry Forest & Woodland supports seasonal regimes of
fire, both natural and characteristically human induced, which can cause frequent
pyrogenic secondary savannized or woodland physiognomies. Fires, in conjunction
with climate, are likely to partially explain the distribution of Tropical Dry Forest &
Woodland (Bond and others 2005).
Tropical Dry Forest & Woodland tends to occur at lower elevations. However, in
South America, large more-or-less isolated pockets occur in several valleys of the
eastern slopes of the Andes, particularly in southern Peru and Bolivia, where they can
reach altitudes up to approximately 1,200 m.
Distribution
Geographic Range: Tropical Dry Forest & Woodland is concentrated near the
equator, primarily between 10 and 23 degrees N and S latitude. It is found in three
major regions: South and Central America and the Caribbean Islands; Africa (west,
central and interior) and Madagascar; and the Indo-Asian Pacific (India, Southeast
Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia).
In the Neotropics, this formation occupies large areas in central South America,
mainly in eastern Bolivia, central and western Brazil, and eastern Paraguay. Also, in
the Neotropics, these forests extend across northern South America (Venezuela) and in
western Mesoamerica (Mexico to Panama), with minor extensions in western Ecuador
and Peru.
In the Paleotropics, Tropical Dry Forest & Woodland potentially occupies large
areas in Africa (Sudano-Zambezian and Madagascan regions), India and Southeast
Asia (Indochinese region), northeastern Australia, and the Pacific Islands, but gener-
ally has been extensively degraded by human activity to semi-open woodlands and
treesavannas.
Citations
Synonymy:
= Seasonally Dry Tropical Forests (Mooney and others 1995)
= Tropical Dry Forest (Miles and others 2006)
= Tropical Seasonal Forest (Holzman 2008)
= Tropical broadleaf woodland: biome type 8 (Whittaker 1975)
= Tropical seasonal forest: biome type 2 (Whittaker 1975)
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: G. Navarro, D. Faber-Langendoen and E. Helmer
Acknowledgments:
Version Date: 26 Aug 2014
1.A.2. Tropical Lowland Humid Forest (F020)
Overview
Database Code: 1.A.2 (F020)
Scientific Name: Tropical Lowland Humid Forest Formation
Common Name (Translated Scientific Name): Tropical Lowland Humid Forest Formation
Colloquial Name: Tropical Lowland Humid Forest
USDA Forest Service RMRS-GTR-346. 2016. 47
Hierarchy Level: Formation
Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)
Lower Level Hierarchy Units
See examples in Appendix J
Concept Summary
Type Concept Sentence: Tropical Lowland Humid Forest is dominated by
broad-leaved evergreen trees, often with multiple complex strata and growth forms
in lowland to submontane or premontane elevations with aseasonal to moderately
seasonal rainfall and warm temperatures.
Classification Comments: Heath forests are a striking variant within this forma-
tion, as described by Richards (1996) and Whitmore (1998). They occur on podsolized
soils developed from siliceous sand, either coastal alluvium or weathered sandstones.
Although typically found in a rainforest climate and retaining basic growth forms
characteristic of 1.A.2 Tropical Lowland Humid Forest Formation (F020), the
nutrient-poor, acidic conditions produce a strikingly distinct physiognomy. Here are
found dense, often pole-sized trees, a stronger predominance of microphylls over
mesophylls, with some sclerophylly, and woody climbers that are more often slender.
The most extensive heath forests are found in the upper reaches of the Rio Negro and
Rio Orinoco of South America, also in Guyana (wallaba forests of Eperua falcata),
coastal forests of southeastern Madagascar, Gabon, Cameroon and Ivory Coast, and
in Kalimantan, Sarawak and Brunei in Borneo (referred to as kerangas), and parts of
Malaya (Whitmore 1998).
Tropical montane forests may resemble heath forests to some degree (Whitmore
1998). Tropical monsoon forests are sometimes grouped with Tropical Lowland
Humid Forest as “tropical moist forest” (Whitmore 1998), but by and large, they are
included with 1.A.1 Tropical Dry Forest & Woodland Formation (F003). Further
review is needed of the transition between monsoon forests and humid forests or
rainforests.
Similar NVC Types:
1.A.1. Tropical Dry Forest & Woodland (F003): As climate becomes more seasonal,
increasing numbers of deciduous trees are found. Stands are placed in Tropical
Dry Forest & Woodland when greater than 25 percent cover of trees are decidu-
ous during a dry period, or where small-leaved (micro- to mesophyll) trees
dominate. These forests also share some characteristics with the heath forest
variant of Tropical Lowland Humid Forest.
1.A.3. Tropical Montane Humid Forest (F004): Montane rainforests at highest
elevations are considerably smaller and heavily covered with bryophytes,
but lower elevation montane forests (towards 1000 m) share similarities with
Tropical Lowland Humid Forest.
1.A.4. Tropical Flooded & Swamp Forest (F029): Soils are typically saturated
to flooded, but many of the growth forms are shared with Tropical Lowland
Humid Forest.
Diagnostic Characteristics: Tropical Lowland Humid Forest is dominated by
meso- to megaphyll, broad-leaved evergreen trees (up to 25 percent deciduous trees),
with a complex multi-layer structure, often exceeding 30 m in height. Climates are
48 USDA Forest Service RMRS-GTR-346. 2016.
consistently warm (seasonal daily temperatures with minimal variation), and annual
rainfall is relatively aseasonal and typically greater than 100 cm, with any given month
rarely less than 60 mm.
Vegetation
Physiognomy and Structure: Tropical Lowland Humid Forest is a dense, multi-
layered forest, with broad-leaved evergreen trees that can exceed 45 m in height. The
tree layer is minimally divided into a top stratum with giant emergent trees, over a
main stratum between 25 and 35 m tall, under which a stratum of shorter trees between
10 and 25 m occurs. Ground vegetation may be sparse, commonly with small trees
(treelets). Herbs may be patchy. Individual trees may be deciduous or semi-deciduous,
but overall comprise less than 25 percent of the main stratum. Evergreenness varies
from completely evergreen to evergreen seasonal forest (which is mainly evergreen
but individual trees may lose their leaves) to semi-evergreen seasonal forest (in
which up to about 25 percent of the main canopy may be deciduous) (Richards 1996).
Whitmore (1998) notes the following features: buttresses are common, cauliflory
and ramiflory are occasional to common, pinnate leaves are frequent, leaf blades of
mesophyll size predominate, big woody climbers (mostly free-hanging) are frequent
to abundant, bole climbers, shade and sun epiphytes are occasional to frequent, and
bryophytes are rare (Table 5). These characteristics are lost as forests become drier or
as elevation increases.
Environment
Environmental Description: Climate: Tropical Lowland Humid Forest (including
semi-evergreen rainforest) occurs in aseasonal, humid climates where water stress
is low to absent, with no regular annual dry season (Whitmore 1998). In general, a
tropical rainforest climate can be defined as one with monthly mean temperatures of
at least 18 degrees C throughout the year, and an annual rainfall of at least 170 cm
(and usually above 200 cm) and either no dry season or a short one of fewer than 4
consecutive months with less than 10 cm rainfall (Richards 1996; Whitmore 1998).
African rainforests are primarily semi-evergreen (where deciduous trees may com-
prise up to 25 percent of the main canopy), as are Australian rainforests, and various
parts of other regional rainforest blocks (Whitmore 1998).
Soil/substrate/hydrology: These forests generally occur from sea level to approxi-
mately 1,200 m elevation, but the boundary between lowland and montane forests
occurs at different elevations depending on the “Massenerhebung effect” (Collins
1990; Richards 1996). This is a phenomenon whereby large mountains and the central
parts of large ranges are warmer at given elevations than small mountains and outlying
spurs. Thus Collins (1990) mapped the boundaries in the Caribbean, Central America,
Madagascar, Australia and Southeast Asia at 910 m, whereas in West Africa the bound-
ary was set at 1200 m, in New Guinea at 1,400 m and in South America at 1800 m.
Soils are often ancient and deeply weathered, with little organic darkening of the
topsoil and with bright reddish or yellowish colors throughout the subsoil. Few of the
original rock minerals remain in the upper horizon. Organic content may vary. Soils
are often clay-like, but weathered sands also occur. Other more recent soils include
those found on recent volcanic deposits, colluvial and alluvial soils (Richards 1996).
USDA Forest Service RMRS-GTR-346. 2016. 49
Distribution
Geographic Range: Tropical Lowland Humid Forest is concentrated around the
equator, between the Tropic of Cancer (23 degrees N latitude) and Tropic of Capricorn
(23 degrees S latitude). It is found in three major regions: South and Central America;
Africa (west, central and interior) and Madagascar; and the Indo-Asian Pacific (India,
Southeast Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia).
In the United States, it is found in Hawaii and in several territories, including Puerto
Rico and many of its Pacific island territories.
Citations
Synonymy:
= Lowland tropical rain forest: biome type 1 (Whittaker 1975)
= Tropical Rain Forest (Richards 1996)
> Tropical heath forest (Whitmore 1998) [Heath forests occur on podsolized soils
developed from siliceous sand, either coastal alluvium or weathered sandstones. The
nutrient-poor, acidic conditions produce a strikingly different physiognomy of dense,
often pole-sized trees, stronger predominance of microphylls over mesophylls, with
some sclerophylly. Woody climbers are more often slender.]
> Tropical lowland evergreen rain forest (Whitmore 1998) [Whitmore separates out
tropical semi-evergreen rainforest, which is here combined at the formation level.]
> Tropical semi-evergreen rain forest (Whitmore 1998) [Whitmore separates out tropi-
cal lowland evergreen rainforest, which is here combined at the formation level.]
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: D. Faber-Langendoen
Acknowledgments:
Version Date: 26 Aug 2014
1.A.3. Tropical Montane Humid Forest (F004)
Overview
Database Code: 1.A.3 (F004)
Scientific Name: Tropical Montane Humid Forest Formation
Common Name (Translated Scientific Name): Tropical Montane Humid Forest
Formation
Colloquial Name: Tropical Montane Humid Forest
Hierarchy Level: Formation
Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Tropical Montane Humid Forest is dominated by
broad-leaved evergreen trees, with increasingly small leaves and stems, often gnarly,
with dense crowns as elevations increase. These forests are generally found within
23 degrees N and S latitude of the equator between 1,000 and 3,500 m in elevation.
50 USDA Forest Service RMRS-GTR-346. 2016.
Classification Comments: The proportion of precipitation that is from clouds is a
defining factor, but is difficult to assess. Tropical Montane Humid Forests resemble
heath forests to some degree (Whitmore 1998), with their wet climate, but have
smaller stems and leaves.
Similar NVC Types:
1.A.2. Tropical Lowland Humid Forest (F020): These rainforests are typically much
taller, with multiple strata and growth forms, but as elevations increase (up
to 1,000 m), a transition occurs to lower elevation Tropical Montane Humid
Forest.
Diagnostic Characteristics: Tropical Montane Humid Forest is dominated by
micro- to mesophyll, broad-leaved evergreen trees (up to 25 percent deciduous trees),
with a simple or two-layer structure, ranging from 5 to 30 m in height. Climates are
more often cool, but without frost, with seasonal daily temperatures with minimal
variation. Annual rainfall is relatively aseasonal and typically greater than 100 cm,
with any given month rarely receiving less than 60 mm. The proportion of precipita-
tion that is from clouds is a defining factor, but is difficult to assess. Better defining
characteristics are the amounts of epiphytes and ferns and where the epiphytes occur
as well as canopy structure.
Vegetation
Physiognomy and Structure: Tropical Montane Humid Forest is dominated by
broad-leaved evergreen trees, with increasingly small leaves and stems, often gnarly,
with dense crowns as elevations increase. Lower elevations represent a transition from
1.A.2 Tropical Lowland Humid Forest Formation (F020) [see Table 5]. At the highest
elevations, the trees may be less than 10 m tall (sometimes referred to as elfin wood-
land), and covered in bryophytes, ferns, and other epiphytic plants. Peat may form,
sometimes with sphagnum mosses (Sphagnum spp.). These in turn may be replaced
by a kind of “tropical subalpine forest” with very tiny leaves (nanophylls), as found in
New Guinea and the Andes (Whitmore 1998). Treeline is typically reached between
3500 and 4000 m, where the vegetation transitions to “tropical high montane grassland
and shrubland” (tropical “alpine” vegetation).
Environment
Environmental Description: Climate: Climates are more often cool, but without
frost, with seasonal daily temperatures with minimal variation. Annual rainfall is
relatively aseasonal and typically greater than 100 cm, with any given month rarely
receiving less than 60 mm. The proportion of precipitation that is from clouds is a
defining factor, though this is difficult to know in the field. Better defining character-
istics are the amounts of epiphytes and ferns and where the epiphytes occur as well as
canopy structure.
Soil/substrate/hydrology: Tropical Montane Humid Forest is typically found
between elevations of 1,000 to 3,500 m, with the treeline typically reached between
3,500 and 4,000 m. But the boundary between lowland and montane forests occurs
at different elevations depending on the “Massenerhebung effect” (Collins 1990;
Richards 1996). This is a phenomenon whereby large mountains and the central parts
USDA Forest Service RMRS-GTR-346. 2016. 51
of large ranges are warmer at given elevations than small mountains and outlying
spurs. Thus Collins (1990) mapped the boundaries in the Caribbean, Central America,
Madagascar, Australia, and Southeast Asia at 910 m, whereas in West Africa the
boundary was set at 1,200 m, in New Guinea at 1,400 m, and in South America at
1,800 m.
Distribution
Geographic Range: Tropical Montane Humid Forest is generally found around the
globe within 23 degrees N and S latitude of the equator, typically between 1000 and
3500 m in elevation. It is found extensively in Central and South America, especially
the Andes and parts of the Caribbean, and is uncommon in Africa (Cameroon and the
eastern fringe of the Congo basin) and many mountain regions throughout the Indo-
Malayan region.
Citations
Synonymy:
= Elfinwoods: biome-type 7 (Whittaker 1975)
= Tropical montane rain forests (Whitmore 1998) [Whitmore (Table 2.2) discusses the
range of variation between lower and upper montane rainforests.]
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: D. Faber-Langendoen, E. Helmer and J. Sawyer
Acknowledgments:
Version Date: 26 Aug 2014
1.A.4. Tropical Flooded & Swamp Forest (F029)
Overview
Database Code: 1.A.4 (F029)
Scientific Name: Tropical Flooded & Swamp Forest Formation
Common Name (Translated Scientific Name): Tropical Flooded & Swamp Forest
Formation
Colloquial Name: Tropical Flooded & Swamp Forest
Hierarchy Level: Formation
Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Tropical Flooded & Swamp Forest is a forested or
wooded wetland and peatland found in margins of freshwater lakes, alluvial plains,
rivers and depressions around the globe.
Classification Comments: Forests may vary from deciduous to evergreen. Further
review is needed of the degree of variation in evergreen versus deciduous-leaved trees
between floodplains and swamps in tropical dry versus moist-wet climates.
52 USDA Forest Service RMRS-GTR-346. 2016.
Similar NVC Types:
1.A.2. Tropical Lowland Humid Forest (F020): Overall dominant growth forms
are similar, but forest structure is more complex in Tropical Lowland Humid
Forest, and the soils are not saturated or inundated. Tree palms and lianas are
more common.
1.A.5. Mangrove (F006): As concentrations of salts decline, Mangrove (F006) may
grade into Tropical Flooded & Swamp Forest.
Diagnostic Characteristics: This formation is dominated by mesophyll, broad-leaved,
evergreen trees, with soils saturated to flooded for all or parts of the year, varying from
peat to mineral soil textures. Climates are consistently warm (seasonal daily tempera-
tures with minimal variation).
Vegetation
Physiognomy and Structure: Tropical Flooded & Swamp Forest is a forested or
wooded wetland and peatland. Structural characteristics that recur in flooded forests
are presence of monospecific stands such as palm swamp, even-canopied forests, and
sharp vegetation zonations. It is common to find that trees in flooded tropical forests
develop sclerophylly (firm, thickened leaves) due to poor nutrition or water limita-
tions, or gas exchange structures (e.g. pneumatophores, lenticels, knees, aerial roots,
swelling of base of trees, surface or aerial roots) in order to overcome poor soil aera-
tion, or support structures (e.g. plank buttresses and stilt roots) to provide stability in
muddy or steep conditions. Tree heights can vary greatly, from 1 to 50 m.
Based on the type of dominant species, swamp forests can be conveniently divided
into two types: forests dominated by broad-leaved evergreen hardwood species and
those dominated by palms. Dominance by palms becomes stronger with increasing
hydroperiod or soil moisture conditions. Species richness generally decreases with
increasing hydroperiod. One formation that covers large areas in western Amazonia
and in the Orinoco River basin is the often monodominant “aguajales” or Mauritia
flexuosa stands. These palm swamps may be regularly affected by riverine floods,
but they mostly occur farther from current river channels, the water-logged condition
then being maintained by a combination of high precipitation and poor drainage in
depressional terrain. Other palm-associated (Raphia, Manicaria) swamps are typical
of the coastal regions of Central America and northern South America along estuarine
channels, sometimes in mixed stands with a few mangrove species.
Environment
Environmental Description: Soil/substrate/hydrology: Tropical swamp forests can
be divided into freshwater or brackish swamp or floodplain forest (along rivers and
lakes) and peat swamp forest (formed behind natural floodplain levees), where peat
layers may be well in excess of 1 m thick (Whitmore 1984). The floodplain forests are
found along rivers, streams, coasts and lakes. They have a dynamic water table, with
seasonal flooding inundating the vegetation for short (<7 days) to long (>1 month)
periods, leading to an influx of sediment and mineral enrichment during high water
periods. Information about underlying soils is scarce.
USDA Forest Service RMRS-GTR-346. 2016. 53
Many floodplain swamp forests are potentially peat-accumulating, but, although
studies on this subject exist in Southeast Asia, they have apparently never been pub-
lished for the Amazon basin (Whitmore 1998). Swamps and other types of wetlands in
the Neotropics have been described in terms of their vegetation composition, structure,
and geomorphology, but studies have failed to deal with peat formation or detailed de-
scriptions of the underlying soils. There is evidence that at least the Mauritia swamps
frequently accumulate peat of some kind.
The lowland tropical peat swamps are formed from layers of woody debris too
waterlogged to fully decompose. Slowly deposited over thousands of years, the
carbon-rich peat strata have been known to reach a thickness of up to 20 m. In
Indonesia the ombrogenous peatlands are mostly formed on the inward edge of the
mangroves. They are usually dome-shaped and several meters thick overlying the
mangrove mineral soil; the whole sequence taking several thousand years. Periods
with rising sea levels promote the formation of very deep peat layers up to 20 m
thickness with the alluvial soil far below present sea levels. Peat domes younger than
3,000 years do have the alluvial soil at about present mean sea level.
The initial rate of vegetation growth and peat build up is rapid, as the alluvial man-
grove soils are nutrient rich. As the peat accumulates, it builds up above the level of
the nutrients in the alluvial soils that are accessible for the plant roots. In that case, the
mineral supply to the vegetation depends on the minerals in the rainwater and avail-
able nutrients of the decaying vegetation in the surface layer. As the swamp ages and
the peat layer increases, nutrients become increasingly scarce, tree growth and litter
production are reduced, and growth of the whole formation slows down.
Besides its association with mangroves, the lowland Neotropical peatlands are
associated with palm swamps and open herbaceous marshes. The latter apparently
are relatively nutrient rich, since surface runoff water easily reaches all parts of the
swamps. Furthermore, the layer of organic material is usually thin enough for the roots
of the plants to have direct contact with the underlying mineral soil. In the case of
palm swamps, they may be regularly affected by riverine floods, but for most of their
extent they occur farther from current river channels, the water-logged condition then
being maintained by a combination of high precipitation and poor drainage, which
makes them ombrogenous types of peatlands.
Distribution
Geographic Range: Flooded forest systems are a regular feature of the low-lying
coastal areas in the West Indies, southern Mexico, Central America, and northern
South America. In South America, the greatest extent of flooded forest occurs in
Amazonia, and in the basins of other important rivers, such as the Orinoco and the
Atrato. However, the most complex mosaics of wetlands, savannas, and flooded
forests are maybe those of the Beni in Bolivia and the Brazilian Pantanal, on very
extensive flat basins subject to a strong seasonality in the precipitation. Some of the
extensive floodplains of South America include treed and shrub swamps that are lo-
cated off the direct influence of the main river channels, usually occupying past, silted
up river arms or depressed areas with inflows product of runoff and seepage or only
sporadic, extreme river floods.
54 USDA Forest Service RMRS-GTR-346. 2016.
Citations
Synonymy:
> Freshwater swamp forest (Whitmore 1998) [Whitmore divides the Tropical Swamp
& Flooded Forest into two formations based on peat or mineral soils.]
> Peat swamp forest (Whitmore 1998) [Whitmore divides the Tropical Swamp &
Flooded Forest into two formations based on peat or mineral soils.]
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: C. Josse and G. Navarro
Acknowledgments:
Version Date: 26 Aug 2014
1.A.5. Mangrove (F006)
Overview
Database Code: 1.A.5 (F006)
Scientific Name: Mangrove Formation
Common Name (Translated Scientific Name): Mangrove Formation
Colloquial Name: Mangrove
Hierarchy Level: Formation
Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Mangroves are dominated by broad-leaved evergreen
trees, with complex aerial root systems, found in estuarine and coastal marine habitats
that form a typically narrow fringe along the coasts of tropical latitudes worldwide.
Similar NVC Types:
1.A.4. Tropical Flooded & Swamp Forest (F029): As concentrations of salts de-
cline, Mangrove (F006) may grade into this formation.
2.C.5. Salt Marsh (F035): Dwarf mangroves may grade into tropical salt marshes.
Diagnostic Characteristics: Broad-leaved evergreen trees, with complex aerial
root systems (including aerial “stilt” roots and pneumatophores), found in tropical
estuarine and coastal marine habitats.
Vegetation
Physiognomy and Structure: Physiognomically, mangroves vary in size from
shrubby dwarf trees to tall trees, with mesophyll, evergreen leaves. They have a com-
plex set of aerial roots. Roots may diverge from the tree as much as 2 m above ground
and penetrate the soil away from the main stem. Secondary roots may branch off,
creating a “stilt root” structure. They also may contain pneumatophores (root exten-
sions growing up above the water surface) emerging 30 cm or more above the muddy
surface. Their adaptations to cope with seawater include methods of salt secretion,
exclusion and accumulation.
USDA Forest Service RMRS-GTR-346. 2016. 55
Environment
Environmental Description: Soil/substrate/hydrology: Mangroves (mangal,
mangle) are tidal, estuarine forested wetlands that occur along the (sheltered) coasts
of tropical latitudes of the Earth. They are commonly found on the intertidal mudflats
along the shores of estuaries, usually in the region between the salt marshes and sea-
grass beds. Where tidal amplitude is relatively low, they form narrow bands along the
coastal plains, and rarely penetrate inland more than several kilometers along rivers.
Where tidal amplitude is greater, mangroves extend farther inland along river courses
forming extensive stands in the major river deltas. Mangrove cays occur also within
the lagoon complex of barrier reefs (Stoddart and others 1982). In general, mangroves
fall within two categories: mangroves of oceanic islands and inland mangroves.
The latter need to adapt to a pronounced variation in salinity due to the variations in
freshwater carried from the interior streams, while the former owe the salinity gradient
to the rate of evaporation in the shallow ponds and mudflats and the rainfall on site,
especially in the case of small to very small islands.
Gilmore and Snedaker (1993) described five distinct types of mangrove forests
based on water level, wave energy, and pore water salinity: (1) mangrove fringe
forests, (2) overwash mangrove islands, (3) riverine mangrove forests, (4) basin
mangrove forests, and (5) dwarf mangrove forests. Dwarf forests are most commonly
observed in south Florida, around the vicinity of the Everglades, but occur in all
portions of the range where physical conditions are suboptimal, especially in drier
transitional areas.
Rainfall plays an important role in distribution and species composition because
rainfall regulates salt concentrations in soils and plants, as well as providing a source
of freshwater for the mangroves. This is an important factor when propagules begin to
take root and when mature individuals bloom and fruit. If high rainfall occurs over a
short period and other months of the year are prone to drought, the conditions can be
considered unfavorable for the growth and distribution of mangroves.
Mangroves provide habitats for commercially important crustaceans; are important
nursery grounds for juvenile fish; filter and trap pollutants and sediments from land
runoff thus maintaining estuarine water quality; provide barriers and buffer zones to
stabilize shorelines and prevent coastal erosion; and are also a major producer of or-
ganic material. Mangroves protect the coast against erosion, but monsoons and storms
cause large waves and winds to erode the coast, destroying many mangrove areas. Sea
level rise, together with monsoons or hurricanes and storms, accelerates the speed of
mangrove coastal erosion.
Mangroves cannot tolerate frost, especially in the seedling stage, but mangroves
are also regulated by sea temperatures, rarely occurring outside the range delimited
by the winter position of the 20 degree C isotherm (Hogarth 2007). It is not entirely
clear why mangroves are limited to the tropics. Given their pan-tropical distribution
and the wide availability of muddy, saline habitats in temperate regions, there would
seem to be many suitable opportunities to spread into these latitudes. Hogarth (2007)
suggests that perhaps the combination of being a tree, tolerating salt, and coping with
waterlogging creates a metabolic cost that is difficult to sustain in lower temperatures
and shorter day lengths.
56 USDA Forest Service RMRS-GTR-346. 2016.
Distribution
Geographic Range: Mangroves occur along the (sheltered) coasts of tropical
latitudes of the Earth, typically between the equator and 23 degrees N and S, but man-
groves occur considerably southward in southeastern Australia. Mangrove distribution
appears to be limited by both frost and sea temperatures, rarely occurring outside the
range delimited by the winter position of the 20 degree C isotherm (Hogarth 2007).
They are estimated to cover 18 million ha (Spalding and others 1997, in Hogarth
2007).
Citations
Synonymy:
= Mangrove vegetation (mangal) (Richards 1996)
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: C. Josse
Acknowledgments:
Version Date: 26 Aug 2014
1.B. Temperate & Boreal Forest & Woodland (S15)
Overview
Database Code: 1.B (S15)
Scientific Name: Temperate & Boreal Forest & Woodland Subclass
Common Name (Translated Scientific Name): Temperate & Boreal Forest &
Woodland Subclass
Colloquial Name: Temperate & Boreal Forest & Woodland
Hierarchy Level: Subclass
Placement in Hierarchy: 1. Forest & Woodland (C01)
Lower Level Hierarchy Units:
1.B.1. Warm Temperate Forest & Woodland (F018)
1.B.2. Cool Temperate Forest & Woodland (F008)
1.B.3. Temperate Flooded & Swamp Forest (F026)
1.B.4. Boreal Forest & Woodland (F001)
1.B.5. Boreal Flooded & Swamp Forest (F036)
Concept Summary
Type Concept Sentence: Temperate & Boreal Forest & Woodland is typically
dominated by broad-leaved deciduous and needle-leaved trees, with some broad-
leaved evergreens in warmer regions, and a climate that varies from warm temperate
with only rare frosts to very cold subarctic conditions. It is found across the globe
in the mid latitudes, typically between 25 and 60 to 70 degrees N and S latitude, and
includes boreal, cool temperate, and warm temperate/Mediterranean forests.
Classification Comments: Warm temperate forests and woodlands are defined
here to include both the classic Mediterranean forests and woodlands and the more
humid warm temperate forests. Both share increasing levels of broad-leaved evergreen
trees, including sclerophyllous-leaved trees, as well as evergreen shrubs and herbs,
USDA Forest Service RMRS-GTR-346. 2016. 57
as compared to other temperate forests and woodlands. Walter (1985) recognizes two
warm temperate biomes, the “Zonobiome of the Winter-Rain Region with an Arid-
Humid Climate and Sclerophyllic Woodlands” (Zone IV) and the “Zonobiome of the
Warm-Temperate Humid Climate” (Zone V), distinct from the cool-temperate biome
“Zonobiome of the Temperate-Nemoral Climate” (Zone VI) and the boreal biome
“Zonobiome of the Cold-Temperate Boreal Climate” (Zone VIII). Schultz (1995) also
recognizes the two warm-temperate regions, which he refers to as: “Mediterranean-
Type subtropics” (with world distribution shown in his Figure 129) and “Humid
subtropics” (with world distribution shown in his Figure 171).
Similar NVC Types:
1.A. Tropical Forest & Woodland (S17): There is a strong dominance by broad-
leaved evergreen trees, and deciduousness is caused by drought rather than
forest composition.
2.B. Temperate & Boreal Grassland & Shrubland (S18): Tree cover is less than 10
percent.
7.A. Woody Agricultural Vegetation (S22): Long-rotation plantations or woody
restoration plantings of Temperate & Boreal Forest & Woodland (S15) with
an irregular structure and a largely spontaneous ground layer may initially be
similar in their early stages of development to Woody Agricultural Vegetation
(S22), especially if planted in rows and the understory is strongly manipulated.
Diagnostic Characteristics: Temperate & Boreal Forest & Woodland is typi-
cally dominated by broad-leaved deciduous and needle-leaved trees, with some
broad-leaved evergreens in warmer regions (See Table 8). Climate varies from warm
temperate with only rare frosts and snow to cold subarctic conditions. It is found
across the globe typically between 25 and 60 to 70 degrees N and S latitude.
Table 8—Characteristics of Boreal and Temperate Forests.
Criterion
Boreal Forest &
Woodland
(upland and wetland)
Cool Temperate Forest &
Woodland
(upland and wetland)
Warm Temperate Forest &
Woodland
(upland and wetland)
Dominant
Growth Forms
Needle-leaved (usually
evergreen) conifer, often
strongly conical-shaped,
and simple, broad-leaved,
small mesophyll deciduous
hardwoods.
Broad-leaved deciduous or
evergreen needle-leaved conifer,
alone or in mixes, variable leaf
and crown shapes, and leave
sizes typically mesophyll with
a seasonal green understory
of herbs. The tall-shrub layer
is variable, and is often broad-
leaved deciduous, but the
short-shrub layer may be heath.
The moss layer is often sparse,
but more dominant in cold, rainy
and/or high montane needle-
leaved evergreen stands.
Broad-leaved evergreen trees,
microphyll to small mesophyll
leaves, sometimes dwarfed
stems, sclerophyllous or small-
leaved trees (e.g., eucalypts,
sclerophyllous oaks); or various
combinations of broad-leaved
deciduous, broad-leaved
evergreen or evergreen needle-
leaved conifer trees.
(continued)
58 USDA Forest Service RMRS-GTR-346. 2016.
Criterion
Boreal Forest &
Woodland
(upland and wetland)
Cool Temperate Forest &
Woodland
(upland and wetland)
Warm Temperate Forest &
Woodland
(upland and wetland)
Table 8—(Continued).
Location Northern Hemisphere
south of the arctic treeline.
Middle latitudes of North
America, western and far-
eastern Eurasia, and an isolated
small area in the middle latitude
of South America.
Mediterranean Basin and
Mediterranean and warm
temperate regions in North
America (California, Southeast
Coastal Plain), Chile, South
Africa, Australia, India and
Southeast Asia.
Climate Type Cold snow climates, with
extended cold winters and
short mild summers, frozen
soils in winter.
Humid temperate climates with
distinctive spring, summer,
autumn, and cool to cold
winter seasons, with freezing
temperatures.
Mild (mostly frost-free) winter,
temperate humid spring, hot-dry
summer, and mild, often dry
autumn seasons. Rainy season
in winter and dry summers
(Mediterranean).
Temperature Lengthy periods of
freezing temperatures
with the coldest month
isotherm –3 oC, with
the growing season
generally averaging
less than 100 days,
occasionally interrupted by
nights of below-freezing
temperatures.
Freezing temperatures usually
of moderate duration, although
of frequent occurrence during
winter months. Potential growing
season generally from 100
to 200 days and confined to
late spring and summer when
freezing temperatures are
infrequent or absent.
Freezing temperatures of short
duration but generally occurring
every year during winter months.
Potential growing season more
than 200 days with less than
an average of 150 days a year
subject to temperatures below
0 oC or chilling fog.
Precipitation
Controls
Seasonal shift of polar
front.
Summer convectional storms,
Atlantic hurricanes, Asian
monsoons.
Stationary high-pressure cells in
summer.
Precipitation
(annual)
38–50 cm (15–20 inches) 50–125 cm (20–50 inches). 25–100 cm (10–40 inches)
(Mediterranean).
Dominant Soil-
Forming Process
Podzolization Podzolization. Severe weathering.
Major Soil
Orders (Soil
Survey Staff
1999)
Gelisols, some Spodosols
in south.
Alfisols and Ultisols, some
Spodosols in north.
Various, Ultisols and Alfisols
common.
Soil
Characteristics
Sandy ash-colored A
horizon; accumulation
of minerals in B horizon;
generally low in natural
fertility.
Gray forest soils with
accumulated silicate clay
minerals in B horizon; some
(Alfisols) with relatively high
natural fertility; more leached
soils in southern areas (Ultisols)
due to higher precipitation levels.
Naturally productive soils, some
regions worn by thousands of
years of human use.
Biogeographic
History
Recent-post Pleistocene
migration of plants and
animals.
Recent-post Pleistocene to
ancient Tertiary origins.
Recent to more ancient, some
regions influenced by thousands
of years of human use.
USDA Forest Service RMRS-GTR-346. 2016. 59
Vegetation
Physiognomy and Structure: Temperate forests and woodlands include temper-
ate rainforest, temperate deciduous forest, and temperate evergreen forests and
woodlands. They are dominated by broad-leaved or needle-leaved growth forms.
Trees typically range in height from 10 to 30 m, but rainforest trees may attain great
height, exceeding 50 m. Temperate broad-leaved deciduous and needle-leaved forests
and wooodlands grow in cool temperate continental climates, with summer rainfall
and cold winters, during which the broad-leaved trees lose their leaves, extending to
high montane regions, where they resemble boreal forests and woodlands. Temperate
broad-leaved evergreen forests and woodlands, often mixed with broad-leaved de-
ciduous and needle-leaved trees, occur in warm-temperate climates, with either mild
winters and moist, warm summers, or winter-rain winters and dry, warm summers
(Mediterranean). Tree species diversity is low in temperate forests and woodlands
(Whittaker 1975).
Boreal Forest & Woodland contains primarily needle-leaved evergreen trees,
with or without boreal broad-leaved deciduous trees. Structure varies from tall,
closed canopy (but rarely exceeding 15 m) to open, low (<5 m) subarctic woodlands.
Nonvascular mosses and lichens may predominate in the ground layer. Winters are
very cold and vary from arid to moist. Temperate high montane forest may resemble
Boreal Forest & Woodland (Whittaker 1975).
Environment
Environmental Description: Soil orders in Table 8 are described using the U.S.
soil orders (Soil Survey Staff 1999). See Brady and Weil (2002) for comparison of
U.S. soil orders with Canadian and FAO systems.
Distribution
Geographic Range: Temperate forests and woodlands range from the giant forests
of the Pacific Coast of North America, or the Australian temperate rainforests, to New
Zealand and Chile, to montane forests in various locations. Temperate forests and
woodlands occur across much of the United States and southern Canada, in limited
parts of Mesoamerica, Western Europe, Mediterranean regions, Southeast Asia, south-
ern Australia, and limited parts of Chile. Boreal forests and woodlands occur in the
northern regions of North America and Eurasia. A few isolated areas may occur in the
Southern Hemisphere.
Citations
Synonymy:
= Temperate Forest Biomes (Kuennecke 2008) [Kuennecke includes boreal, cool
temperate, and warm temperate (Mediterranean) formations as part of his “temperate
forest biomes” concept.]
= Temperate and boreal woodlands & scrub (Mucina 1997) [Mucina created this type
as an organizational category for Braun-Blanquet classes and did not define it as a
formal type.]
> Temperate broad-leaved forests and scrub (Rodwell and others 2002) [European
cool and warm temperate forests and floodplain forests are included in the subclass,
but boreal forests are excluded.]
60 USDA Forest Service RMRS-GTR-346. 2016.
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: D. Faber-Langendoen
Acknowledgments:
Version Date: 26 Aug 2014
1.B.1. Warm Temperate Forest & Woodland (F018)
Overview
Database Code: 1.B.1 (F018)
Scientific Name: Warm Temperate Forest & Woodland Formation
Common Name (Translated Scientific Name): Warm Temperate Forest & Woodland
Formation
Colloquial Name: Warm Temperate Forest
Hierarchy Level: Formation
Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Warm Temperate Forest & Woodland is dominated by
broad-leaved evergreen trees, sometimes with dwarfed stems and small, sclerophyllous
leaves (in Mediterranean climates), or various combinations of broad-leaved decidu-
ous, broad-leaved evergreen and needle-leaved evergreen conifer trees. Winters are
mild (mostly frost free) and may be the rainiest season, springs are temperate-humid,
summers are hot-dry, and autumn is often dry.
Classification Comments: The warm-temperate Mediterranean regions around the
world typically contain both the classic Mediterranean scrub (2.B.1. Mediterranean
Scrub & Grassland Formation (F038)), and the forests and woodlands included
here. Cool-temperate and warm-temperate forests may be difficult to distinguish,
but cool-temperate forests are more strongly dominated by broad-leaved deciduous
trees, and broad-leaved evergreen trees are essentially absent. Braun (1950) includes
at least parts of these warm-temperate forests in her “Deciduous Forest Formation”
(the “Southeastern Evergreen Forest Region”), but briefly notes a “Subtropical Broad-
leaved Evergreen Forest” that includes central Florida southward.
Various ecoregional treatments recognize the distinct vegetation and climate of
the warm-temperate region, e.g., Brown and others (1998) separates cool-temperate
from warm-temperate vegetation. Walter (1985) recognizes two warm-temperate
biomes, the “Zonobiome of the Winter-Rain Region with an Arid-Humid Climate and
Sclerophyllic Woodlands” (Zone IV) and the “Zonobiome of the Warm-Temperate
Humid Climate” (Zone V), distinct from the cool-temperate biome “Zonobiome of
the Temperate-Nemoral Climate” (Zone VI) and the boreal biome “Zonobiome of the
Cold-Temperate Boreal Climate” (Zone VIII). Similarly, Schultz (1995) recognizes
the two warm temperate regions, which he refers to as: “Mediterranean-Type subtrop-
ics” (with world distribution shown in his Figure 129) and “Humid subtropics” (with
world distribution shown in his Figure 171). We prefer the term warm temperate to
USDA Forest Service RMRS-GTR-346. 2016. 61
subtropics. Schultz states that “apart from the driest sites and those with lowest nutri-
ent contents, all the regions of the Mediterranean Type subtropics were originally
covered by forests of mostly evergreen sclerophyllous species of trees” and in the
European Mediterranean region, these were mostly evergreen oak, such as Quercus
ilex. Today, many of these regions are more typically dominated by sclerophyllous
shrub formations, as described in 2.B.1 Mediterranean Scrub & Grassland Formation
(F038).
Similar NVC Types:
1.A.1. Tropical Dry Forest & Woodland (F003): Broad-leaved evergreen trees may
be common in Warm Temperate Forest & Woodland (F018), comparable to
Tropical Dry Forest & Woodland (F003) (i.e., evergreen leaves are typically
small), but deciduousness in Warm Temperate Forest & Woodland is caused by
frost, and types are found north or south of 23 degrees N and S latitude.
1.B.2. Cool Temperate Forest & Woodland (F008): More strongly dominated by
broad-leaved deciduous trees; broad-leaved evergreen trees essentially absent.
Frost regularly occurs, with snow common in the northern parts of the regions.
1.B.3. Temperate Flooded & Swamp Forest (F026): Warm Temperate Forest &
Woodland (F018) typically contains well-drained soils and lacks any aquatic
vegetation, peat or muck layer.
2.B.1. Mediterranean Scrub & Grassland (F038): The vegetation is more
commonly scrub-shrub, typically sclerophyllous, or with open (sometimes an-
nual-dominated) grasslands and forb meadows. Combinations of dwarf scrubby
trees less than 2 m tall with low shrubs may grade into Warm Temperate Forest.
2.B.2. Temperate Grassland & Shrubland (F012): Open woodlands or tree savan-
nas, with grassy or shrubby understories, and with trees 10 percent cover or
more, are placed in Warm Temperate Forest & Woodland (F108), but may have
strong floristic similarities to grasslands.
Diagnostic Characteristics: Broad-leaved evergreen trees, sometimes with
dwarfed stems, microphyll to small mesophyll leaves, sclerophyllous (Mediterranean);
or various combinations of broad-leaved deciduous, broad-leaved evergreen or needle-
leaved evergreen conifer trees. Mild (mostly frost-free) winter, temperate humid
spring, hot-dry summer, and mild, often dry autumn seasons. Rainy season in winter
and dry summers (Mediterranean).
Vegetation
Physiognomy and Structure: The vegetation varies from (a) dominance by
broad-leaved evergreen trees, sometimes with dwarfed stems, and microphyll to small
mesophyll leaves, with varying levels of sclerophylly (Mediterranean) to (b) various
combinations of broad-leaved deciduous, broad-leaved evergreen or needle-leaved
evergreen conifer trees. Natural disturbances include wind and fire.
Environment
Environmental Description: Climate: Freezing temperatures of short duration are
expected, generally occurring every year during winter months. The potential growing
season is more than 200 days with less than an average of 150 days a year subject to
temperatures below 0 degrees C or chilling fog (Brown and others 1998). Spring is
62 USDA Forest Service RMRS-GTR-346. 2016.
mild, summers are hot-dry, and autumns are mild and often dry. Rainy season in win-
ter is most strong in Mediterranean climates. Average annual precipitation varies from
25 to 100 cm (10 to 40 inches).
Soil/substrate/hydrology: Soils are often strongly weathered. Soils are various, with
Ultisols and Alfisols most common, and productive, but in some regions the soils are
worn by thousands of years of human use (Soil Survey Staff 1999) (see Brady and
Weil, 2002, for comparison of U.S. soil orders with Canadian and FAO systems).
Distribution
Geographic Range: Warm Temperate Forest & Woodland is found in the
Mediterranean Basin and Mediterranean and warm temperate regions in North
America (California, Southeast Coastal Plain), Chile, South Africa, Australia, India
and Southeast Asia.
Citations
Synonymy:
= Warm Temperate Forest and Woodland (Brown and others 1998)
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: D. Faber-Langendoen
Acknowledgments:
Version Date: 26 Aug 2014
1.B.2. Cool Temperate Forest & Woodland (F008)
Overview
Database Code: 1.B.2 (F008)
Scientific Name: Cool Temperate Forest & Woodland Formation
Common Name (Translated Scientific Name): Cool Temperate Forest & Woodland
Formation
Colloquial Name: Cool Temperate Forest
Hierarchy Level: Formation
Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Cool Temperate Forest & Woodland includes temperate
deciduous forest and woodland, temperate needle-leaved forest and woodland, and
temperate rainforest, dominated by broad-leaved or needle-leaved tree growth forms.
Classification Comments: This formation includes a range of conifer and broad-
leaved hardwood growth forms. The formation is sometimes restricted to “temperate
broadleaf forest regions,” but even there, pure conifer stands can occur, (e.g., in
temperate eastern North America, there are pure conifer stands of Tsuga canadensis
and Pinus strobus). Inclusion of western North American conifer forests in this
cool-temperate formation rather than the Boreal Forest & Woodland follows that of
Brandt (2009) and others. Warm-temperate and cool-temperate forest and woodland
USDA Forest Service RMRS-GTR-346. 2016. 63
formations are very similar, but differences are driven by broad climatic patterns.
Overlap with boreal forests in the western montane region also presents conceptual
challenges.
Various ecoregional treatments recognize the distinct vegetation and climate of
the cool-temperate region, e.g., Brown and others (1998) separate cool-temperate
from warm-temperate vegetation. Walter (1985) recognizes the cool-temperate biome
“Zonobiome of the Temperate-Nemoral Climate” (Zone VI) distinct from two warm-
temperate biomes, the “Zonobiome of the Winter-Rain Region with an Arid-Humid
Climate and Sclerophyllic Woodlands” (Zone IV) and the “Zonobiome of the Warm-
Temperate Humid Climate” (Zone V), and from the boreal biome “Zonobiome of the
Cold-temperate Boreal Climate” (Zone VIII).
Our approach treats the subalpine forests of the Rocky Mountain region as part of
1.B.2 Cool Temperate Forest & Woodland Formation (F008), rather than as part of
1.B.4 Boreal Forest & Woodland Formation (F001), such as done by Whittaker (1975)
and Brown and others (1998). Our decision is in line with a more biogeographic ap-
proach for divisions, and corresponds to that of Rivas-Martinez and others (1999b),
but is debatable from a structural and climatic perspective. As Chris Lea (pers. comm.
2012) notes, one could retain lowland and lower montane western coniferous forests
in Cool Temperate, but move high montane and subalpine to the Boreal formation, to
which they also have strong floristic and environmental similarities (this would require
a name change of the latter to something like “Boreal & High Montane” or “Boreal
& Subalpine” formation). This would have minimal impact on lower level units,
requiring only a transfer of two current western North America groups (G020 and
G025) to F001, under a new (western North American) division of F001 and eastern
North America group G024 (requires a new macrogroup and division, but the descrip-
tion of these would be identical with the existing group description). The only major
new description for Forests and Woodlands would be a new division description for
“Western North America High Montane & Subalpine Forest,” within formation F001.
These forests, fairly simply, contain quaking aspen and lodgepole pine on up through
the Engelmann spruce-fir types. In the Sierra Nevada, Ponderosa pine, Douglas-
fir, “mixed conifers” (white fir, etc.) represent the upper limits of 1.B.3 Temperate
Flooded & Swamp Forest Formation (F026). The Shrubland & Grassland class needs
no formation-level adjustments, but some lower level adjustments might be needed for
consistency. We will continue to review this issue as we compare our work with that of
Eurasian treatments of boreal and cool temperate (nemoral) forests.
Similar NVC Types:
1.B.1. Warm Temperate Forest & Woodland (F018): Has increasing prominence
of evergreen broad-leaved trees, and shrubs, and evergreen herb ground layer.
Snow virtually absent, frost is relatively rare.
1.B.3. Temperate Flooded & Swamp Forest (F026): Cool Temperate Forest &
Woodland (F008) typically contains well-drained soils and lacks any aquatic
vegetation, peat or muck layer.
1.B.4. Boreal Forest & Woodland (F001): Greatly simplified set of growth forms,
primarily more conical-shaped spruce, fir and larch, and simple-leaved boreal
hardwoods of Betula spp. and Populus spp. Moss layer often very prominent.
Persistence of snow typically greater than 5 months of the year. Frost possible
64 USDA Forest Service RMRS-GTR-346. 2016.
in almost any season. These conditions also closely describe North American
subalpine and high montane forests, but those are treated here with Cool
Temperate Forest & Woodland because of the floristic, biogeographic and eco-
logical similarities with lower elevation forests. See Brown and others (1998)
who recognize a “Boreal and Subalpine Forest & Woodland” type.
2.B.2. Temperate Grassland & Shrubland (F012): Open woodlands or tree savan-
nas, with grassy or shrubby understories, and with trees 10 percent cover or
more, are placed in Cool Temperate Forest & Woodland (F008), but may have
strong floristic similarities to grasslands.
7.A.2. Intensive Forestry Plantation & Agroforestry Crop (F043): Long-rotation
plantations or woody restoration plantings of Cool Temperate Forest &
Woodland (F008) with an irregular structure and a largely spontaneous ground
layer may initially be similar in their early stages of development, especially if
planted in rows and the understory is strongly manipulated.
Diagnostic Characteristics: This formation contains pure or mixed stands of
broad-leaved deciduous or needle-leaved evergreen tree growth forms, with a seasonal
green understory of herbs. The tall shrub layer is variable, and is often broad-leaved
deciduous, but the short shrub layer may be heath. The moss layer is often sparse, but
more dominant in cold, rainy and/or high montane needle-leaved evergreen stands.
Snow may be on the ground between 1 to 6 months of the year (8 months in high
montane temperate examples).
Vegetation
Physiognomy and Structure: In moist climates and habitats, there are commonly
five strata: (1) a tree stratum, 15 to 35 m (60 to 100 feet) tall, dominated by broad-
leaved deciduous and/or needle-leaved evergreen forest, often with a substratum of
small trees (5 to 15 m tall); (2) a small tree and tall sapling layer (between 2 to 5 m);
(3) a short shrub layer (<2 m); (4) an herb layer of perennial forbs, including an eco-
logical group that bloom primarily in early spring (in deciduous broadleaf-dominated
examples); and (5) a ground layer of lichens, clubmosses, and true mosses. Lichens
and mosses also grow on the trunks of trees. Woody vines (lianas) are not common.
In dry, and fire-dependent climates and regions, the structure may be simple, with a
tree layer (>10 percent) and a strong grassy or shrubby ground layer. In western North
America, structure is more variable, reflecting the range of ecological sites, from high
mountains and valleys, to coastal rainforests with a variety of mesoclimates. Structural
variability ranges from short-statured conifers, with a sparse understory and heavy
duff layer, to the tallest and largest trees in the world in moist to wet climates, with
shrub, herb and moss growth forms prominent (Whittaker 1975).
Many of the genera, previously part of an Arcto-Tertiary Geoflora, are common
to all three of the disjunct Northern Hemisphere broadleaf expressions of this biome.
Included among these genera are Quercus (oak), Acer (maple), Fagus (beech),
Castanea (chestnut), Carya (hickory), Ulmus (elm), Tilia (basswood or linden),
Juglans (walnut), and Liquidambar (sweetgum). Different species of these genera oc-
cur on each continent. In the Southern Hemisphere different sets of genera and species
are found. Western North America contains a much reduced set of hardwood genera
and expanded conifer diversity (Abies, Picea, Pinus, Pseudotsuga, Thuja, Tsuga).
Transitions to the boreal forests are also apparent.
USDA Forest Service RMRS-GTR-346. 2016. 65
The temperate regions of the Southern Hemisphere differ from their northern
counterparts. Distinctions between warm temperate and cool temperate are much
contracted (e.g., in parts of the evergreen southern beech Nothofagus forests in South
America, Australia and New Zealand).
Environment
Environmental Description: Climate: This formation is associated with cooler
continental and oceanic temperate climates (Koeppen Dca, Dcb, and Do, and Cfb).
There is a growing season of approximately 100 to 200 days, confined to late spring
and summer when freezing temperatures are infrequent or absent. The 50 to 250 cm
(20 to 100 inches) of precipitation are distributed evenly throughout the year. The non-
growing season is due to temperature-induced drought during the cold winters.
Soil/substrate/hydrology: Soils are sometimes referred to as “gray forest soils,”
where silicate clay minerals accumulate in the B horizon. Some soils (Alfisols) have
relatively high natural fertility; others are more leached, due to higher precipitation
levels (Ultisols) and more common in the warmer parts of the region. Other orders in
the U.S. system include Spodosols in the more northern regions and Inceptisols (Soil
Survey Staff 1999) (see Brady and Weil 2002 for comparison of U.S. soil orders with
Canadian and FAO systems).
Distribution
Geographic Range: This formation is most prominent in the Northern Hemisphere,
where it occurs in four major, disjunct expressions in (1) western and central
Europe, (2) eastern Asia, including Korea and Japan, (3) eastern North America, and
(4) western North America. Cool temperate forests may occur as minor components
of southern and montane New Zealand and in Australia, especially Tasmania. Cool
temperate forests also occur in Chile.
Citations
Synonymy:
> Cool Temperate Forest (Brown and others 1998) (Brown and others place the
subalpine forests of the montane regions in their “Boreal and Subalpine Forest
and Woodland” type.)
< Taiga or Subarctic - Subalpine needle-leaved forests (biome type 6) (Whittaker
1975) [Whittaker combines the subalpine forests of the temperate region with
boreal forests.]
> Temperate deciduous forests (biome type 4) (Whittaker 1975)
> Temperate evergreen (needle-leaved) forest (biome type 5) (Whittaker 1975)
[Whittaker includes both temperate evergreen broadleaf and temperate ever-
green needle-leaved forest in this biome type, but notes the distinction between
the two in Plate 4.]
> Temperate rain forests (biome-type 3) (Whittaker 1975)
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012) after R.H. Whittaker (1975)
Author of Description: D. Faber-Langendoen
Acknowledgments: Todd Keeler-Wolf, Ken Baldwin, Chris Lea
Version Date: 26 Aug 2014
66 USDA Forest Service RMRS-GTR-346. 2016.
1.B.3. Temperate Flooded & Swamp Forest (F026)
Overview
Database Code: 1.B.3 (F026)
Scientific Name: Temperate Flooded & Swamp Forest Formation
Common Name (Translated Scientific Name): Temperate Flooded & Swamp Forest
Formation
Colloquial Name: Temperate Flooded & Swamp Forest
Hierarchy Level: Formation
Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Temperate Flooded & Swamp Forest is a tree-dominated
wetland influenced by minerotrophic groundwater, either on mineral or organic (peat)
soil, found in mid latitudes of the globe.
Classification Comments: No distinction is made between warm versus cool
temperate floodplain and swamp forests, because they do not have the same degree of
change from broad-leaved evergreen to broad-leaved deciduous trees observed in up-
lands. Separation of temperate wetland from upland forests requires consideration of
soils, vegetation and hydrology. At the wettest extremes, these forests are continuously
flooded and aquatic vegetation growth forms may dominate the herb or field layer.
Otherwise, these forests may be saturated and a peat layer may form. There are also
practical user and ecological benefits to distinguishing wetland forests from upland
forests at the formation level.
Similar NVC Types:
1.B.1. Warm Temperate Forest & Woodland (F018): These typically contain well-
drained soils, and lack any aquatic vegetation, peat or muck layer.
1.B.2. Cool Temperate Forest & Woodland (F008): These typically contain well-
drained soils, and lack any aquatic vegetation, peat or muck layer.
1.B.5. Boreal Flooded & Swamp Forest (F036): Temperate Flooded & Swamp
Forest (F026) less often contains a sphagnum peat layer and is more commonly
dominated by hardwood species.
2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland (F013):
Tall shrub swamps share many structural and habitat similarities to hardwood
tree swamps, especially during the tree regeneration stage.
Diagnostic Characteristics: Temperate Flooded & Swamp Forest is defined as
a tree-dominated wetland in a temperate climate that is influenced by minerotrophic
groundwater, either on mineral or organic soils. The vegetation is dominated by broad-
leaved or needle-leaved trees, generally over 10 percent cover, and the substrate is
either a wood-rich peat or a mineral soil on floodplains.
Vegetation
Physiognomy and Structure: Temperate Flooded & Swamp Forest is a forested
wetland and peatland. These swamps are defined as tree-dominated wetlands that
USDA Forest Service RMRS-GTR-346. 2016. 67
are influenced by minerotrophic groundwater. The vegetation is dominated by either
broad-leaved or needleleaved trees generally over 10 percent cover, and a wood-rich
peat or a mineral soil on floodplains (National Wetlands Working Group 1997).
There are three general physiognomic variants of forested swamps: coniferous
swamps, broad-leaved deciduous (hardwood) swamps, and broad-leaved evergreen
(hardwood) swamps. Mixtures of the above can also be described. Shading of the
understory tends to favor shade-tolerant species. In cool-temperate regions, hardwood
swamps generally occur in somewhat richer conditions, giving way to shrub swamps
and marshes in somewhat wetter locations. Coniferous swamps occur across a wider
range of trophic levels from rich to poor (National Wetlands Working Group 1997).
Environment
Environmental Description: Soil/substrate/hydrology: In swamp forests, the water
table is often below the major portion of the ground surface, and the dominant ground
surface is at the hummock ground surface, that is; 20 cm or more above the average
summer groundwater level. It is the aerated (or partly aerated) zone of substrates
above the water that is available for root growth of trees. These temperate swamps
are not as wet as marshes, fens and the open bogs. The drier treed swamps grade into
upland forest on mineral soil, and the wettest treed swamps grade into scrubby treed
fen, which is wetter with less tree canopy cover. Scrubby tree fens may grade into tall
shrub swamps, but they are somewhat drier and have at least 10 percent tree canopy
cover (National Wetlands Working Group 1997).
Flooded forests (sometimes called riverine or riparian swamps) have a more
dynamic water table, with seasonal flooding inundating the vegetation for short
(<7 days) to long (>1 month) periods. They are found along rivers, streams, and lakes.
They are subject to dramatic water fluctuations, seasonal flooding, and an influx of
sediment and mineral enrichment during high water periods. Peat accumulation is
usually shallow, often less than 40 cm, but depths of 1 m can exist (National Wetlands
Working Group 1997).
The temperate flooded and swamp forest occurs on mineral soils as well as on peat.
In the cool temperate regions, the texture of underlying mineral soils is variable, rang-
ing from clays to sands, and they frequently are Gleysols. On sands, iron-rich ortsteins
or fragipans are often present, acting as impermeable layers that impede water drain-
age. Swamps on mineral soils tend to accumulate peat by paludification. When organic
soils develop, they are Histosols (U.S. system) or Mesisols or Humisols (Canadian
system) that are rich in woody peat, at least in the surface layers [see Brady and Weil
(2002) for a comparison of U.S. soil orders with Canadian and FAO systems]. Swamps
on peat have developed either by a basin-filling process or by paludification of previ-
ously drier mineral soils. In the basin-filling process, the previous ecosystem was a
marsh or fen, whereas in paludification the swamp has developed over an older, dry
upland forest on mineral soil (National Wetlands Working Group 1997).
The nutrient regime in swamps is highly variable, ranging from base-rich conditions
with pH above 7.0, to base-poor conditions where pH can be in the range of 4.5 or
lower. Temperate swamp forms may be recognized based on the base-rich/pH gradient,
i.e., calcareous rich (eutrophic), intermediate (mesotrophic), and poor (oligotrophic)
(National Wetlands Working Group 1997).
68 USDA Forest Service RMRS-GTR-346. 2016.
Distribution
Geographic Range: These forested wetlands are widely distributed throughout the
mid-latitudes around the globe.
Citations
Synonymy:
> Cold Temperate Swamp & Riparian Forest (Brown and others 1998) [Cool- and
warm-temperate forested wetlands are distinguished, based on climate.]
>< Swamp (National Wetlands Working Group 1997) [This type includes tree swamps
with greater than 30 percent cover, boreal and temperate swamps, and both tree and
tall-shrub (>1 m) swamps.]
> Warm Temperate Swamp & Riparian Forest (Brown and others 1998) [Cool- and
warm-temperate forested wetlands are distinguished, based on climate.]
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: D. Faber-Langendoen, after National Wetlands Working
Group (1997)
Acknowledgments:
Version Date: 26 Aug 2014
1.B.4. Boreal Forest & Woodland (F001)
Overview
Database Code: 1.B.4 (F001)
Scientific Name: Boreal Forest & Woodland Formation
Common Name (Translated Scientific Name): Boreal Forest & Woodland
Formation
Colloquial Name: Boreal Forest
Hierarchy Level: Formation
Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Boreal Forest & Woodland (or taiga) is dominated by
needle-leaved (usually evergreen, conical-shaped) conifers, and broad-leaved decidu-
ous hardwoods that cover the northern regions of North America and Eurasia, with
extended cold winters and short mild summers.
Classification Comments: The Braun-Blanquet approach generally recognizes
the Vaccinio-Piceetea class of vegetation as synonymous with Eurasian and North
American boreal and sub-boreal coniferous forests, including both upland boreal
forests and forested swamps (Peinado and others 1998; Spribille and Chytrý 2002;
Kolbek and others 2003); however, Rivas-Martinez and others (1999b) separated the
North American Boreal Forest & Woodland into a separate class, distinct from both
European boreal forests and western temperate forests.
USDA Forest Service RMRS-GTR-346. 2016. 69
Various ecoregional treatments recognize the distinct vegetation and climate of the
boreal region, compared to the temperate region. Brown and others (1998) separates
arctic-boreal from both cool-temperate and warm-temperate vegetation. Walter (1985)
recognizes the boreal biome “Zonobiome of the Cold-temperate Boreal Climate”
(Zone VIII), distinct from the cool-temperate biome “Zonobiome of the Temperate-
Nemoral Climate” (Zone VI) and two warm-temperate biomes, the “Zonobiome of
the Winter-Rain Region with an Arid-Humid Climate and Sclerophyllic Woodlands”
(Zone IV) and the “Zonobiome of the Warm-Temperate Humid Climate” (Zone V).
Some authors extend the North American Boreal Forest & Woodland southward
into the southern Rocky Mountains and/or Appalachian Mountains (e.g., Brown and
others 1998; Kuennecke 2008; Whittaker 1975), primarily because of the spruce-fir
zones that occur in those ranges. But the more temperate climate, increasingly diverse
conifer and hardwood growth forms, biogeographic patterns and distinctive species
suggest that they can satisfactorily be placed in a temperate formation, where they
extend up to the treeline in the subalpine regions (see also Rivas-Martinez and oth-
ers 1999b). However, biogeographic comparisons across larger regions, including
biome or formation scales, and which can be done at the genus level and above (e.g.,
McLaughlin 2007), suggest a greater similarity of high-elevation Engelmann spruce-
fir in the Rocky Mountains with that of the boreal. But similarities are less strong in
the eastern deciduous region, where red spruce-fir forests share more species with the
eastern temperate region. Chris Lea (pers. comm. 2012) notes that there are a number
of subdominant species common to North American high montane/subalpine forests,
North American boreal forests, and Eurasian boreal forests (a number of Vaccinium
spp., Linnaea borealis, Carex aquatilis, Carex utriculata, etc.), and at least one
dominant tree species (Populus tremuloides) that is common to North American high
montane/subalpine and North American boreal forests. Additionally, many fauna spe-
cies (lynx, pine marten, pine grosbeak, golden-crowned kinglet, crossbills, etc.) show
similar species distribution patterns. But many of these species also have consider-
able overlap in the temperate zone. We will continue to review this issue with North
American and Eurasian colleagues.
Similar NVC Types:
1.B.2. Cool Temperate Forest & Woodland (F008):
1.B.5. Boreal Flooded & Swamp Forest (F036):
7.A.2. Intensive Forestry Plantation & Agroforestry Crop (F043): Long-rotation
plantations or woody restoration plantings of Boreal Forest & Woodland (F001)
with an irregular structure and a largely spontaneous ground layer may initially
be similar in their early stages of development, especially if planted in rows and
the understory is strongly manipulated.
Diagnostic Characteristics: Boreal Forest & Woodland is dominated by needle-
leaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous
hardwoods, with extended cold winters and short mild summers. Tree height rarely
exceeds 15 m, and may be as low as 2 m in subarctic conditions. Lichens and mosses
frequently dominate the ground layer.
70 USDA Forest Service RMRS-GTR-346. 2016.
Vegetation
Physiognomy and Structure: Boreal Forest & Woodland is dominated by needle-
leaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous
hardwoods. Lichens and mosses often dominate the ground layer. The structure of
Boreal Forest & Woodland varies from closed forest to lichen woodland and forest-
tundra. Closed forests dominate the southern boreal zone; lichen woodlands dominate
the northern regions; and isolated forest-tundra patches occur in the tundra zone near
or just above treeline (Elliott-Fisk 2000). Boreal forests are a disturbance-based forest,
with fires and insect outbreaks as primary disturbances. Tree species diversity is very
low. Evergreen spruce (Picea), fir (Abies), and deciduous larch (Larix) are common
distinctive genera, as are broad-leaved deciduous aspen (Populus) and birch (Betula)
(Whittaker 1975).
Environment
Environmental Description: According to Brandt (2009), the boreal zone’s north-
ern boundary in both North America and Eurasia is generally the southern limit of the
tundra; its southern boundary generally coincides with the northern limit of temperate
forests, or grasslands (steppes).
Climate: There are lengthy periods of freezing temperatures with the coldest
month isotherm of 3 degrees C, and the growing season generally averaging less than
100 days, occasionally interrupted by nights of below freezing temperatures. Snow
may be present for extended periods (7 to 10 months) and soils are typically frozen in
winter. Annual precipitation is 38 to 50 cm (15 to 20 inches). In North America, the
northern boundary of the forest corresponds to the July isotherm of 13 degrees C, with
departures due to montane or maritime influences (Elliott-Fisk 2000). The southern
boundary in central and eastern Canada corresponds approximately with the 18 degree
C July isotherm, but in the west the forest border shifts to slightly cooler regions with
higher precipitation (Elliott-Fisk 2000). These broad-scale climatic factors are modi-
fied by local and regional topography, climates and soils.
Brandt (2009, and Table 2 therein) characterizes the limits of boreal forests based
on their dominance by “cold-tolerant” trees species, i.e., tolerant of temperatures of
minus 80 degrees C or lower (primarily within Abies, Larix, Picea, or Pinus but also
Populus and Betula). Temperate forests are characterized by “cold-intolerant” species,
i.e., they require temperatures above minus 45 degrees C to survive. A number of
temperate species have “intermediate cold-tolerance,” common to the cool-temperate
forest. Regions of the landscape where both species co-occur is sometimes referred
to as the “hemiboreal subzone,” that is, the northern parts of the cool-temperate
zone where cold-intolerant tree species, cold-tolerant tree species, and species with
intermediate cold-tolerance co-occur, and with the cold-tolerant species contributing
substantially to the forest cover. Brandt’s information provides the cold-tolerance
limits of these species, but equally valuable in understanding the temperate versus
boreal distinction would be the warm-tolerance limits. For example, in North America,
Picea mariana appears to be less warm tolerant than Pinus banksiana, but both have
the same cold tolerance.
USDA Forest Service RMRS-GTR-346. 2016. 71
Soil/substrate/hydrology: Most boreal soils were subject to extensive glaciations
(excluding parts of the Yukon Territory, the Northwest Territories, and Alaska). Soils
are somewhat poorly to excessively drained. They are the result of podzolization,
which is a consequence of low temperatures and excess precipitation above that of
evapotranspiration. Soils often contain a sandy ash-colored A horizon, with an ac-
cumulation of iron and aluminum with organic matter in the B horizon. Soils are
generally of low fertility, as nutrients are also removed from the upper horizons.
With the low temperatures, organic matter decomposes slowly, resulting in acidic soil
conditions and low nitrogen and mineral levels (Elliott-Fisk 2000; Kuennecke 2008).
Permafrost is absent or typically occurs less than 100 cm below the surface in the
Boreal Forest & Woodlandzone. Spodosols are most common; Inceptisols, Histosols,
and Entisols occasional (Soil Survey Staff 1999) (see Brady and Weil 2002 for a com-
parison of U.S. soil orders with Canadian and FAO systems).
Distribution
Geographic Range: Boreal Forest & Woodland is found in North America from
Greenland to Newfoundland and across northern Canada into Alaska, and in Eurasia,
throughout most of Scandinavia and Russia, and parts of China, Kazakhstan, and
Mongolia (Brandt 2009). It is absent from the Southern Hemisphere.
Citations
Synonymy:
= Linnaeo americanae-Piceetea marianae (Rivas-Martínez and others 1999b) [The
concept of Boreal Forest & Woodland as applied within North America closely
corresponds to the concept here. The authors also appear to be the first in the Braun-
Blanquet tradition to recognize a distinct North American Boreal Forest & Woodland
class.]
< Vaccinio-Piceetea (Peinado and others 1998) [The authors discuss the full diagnos-
tic floristic composition of boreal forests across the Northern Hemisphere, and then
focus on North America. They extend the Boreal Forest & Woodland further south
(into the temperate-montane and cool-temperate regions of western and eastern North
America) than the concept provided here.]
< Boreal Forest & Woodland Biome (Kuennecke 2008) [The author provides a gen-
eral introduction to the entire boreal forest, but in North America extends the concept
into the Southern Rockies and Appalachian Mountains.]
= Taiga and Boreal Forest & Woodland (Elliott-Fisk 2000) [The treatment is restricted
to North America.]
< Taiga or Subarctic-Subalpine needle-leaved forests (biome-type 6) (Whittaker 1975)
[Whittaker combines the subalpine forests of the temperate region with boreal forests.]
Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic
Data Committee (Faber-Langendoen and others 2012)
Author of Description: D. Faber-Langendoen
Acknowledgments: Ken Baldwin, Chris Lea
Version Date: 26 Aug 2014
72 USDA Forest Service RMRS-GTR-346. 2016.
1.B.5. Boreal Flooded & Swamp Forest (F036)
Overview
Database Code: 1.B.5 (F036)
Scientific Name: Boreal Flooded & Swamp Forest Formation
Common Name (Translated Scientific Name): Boreal Flooded & Swamp Forest
Formation
Colloquial Name: Boreal Flooded & Swamp Forest
Hierarchy Level: Formation
Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)
Lower Level Hierarchy Units:
See examples in Appendix J
Concept Summary
Type Concept Sentence: Boreal Flooded & Swamp Forest is a tree-dominated
wetland influenced by minerotrophic groundwater (rarely ombrotrophic), either on
mineral or organic (peat) soil, found in northern, high latitudes of North America and
Eurasia, with extended cold winters and short mild summers.
Classification Comments: Subarctic and arctic (polar) flooded and swamp forests,
including willow swamps (though these may not exceed 2 m), belong in this forma-
tion. Forested bogs and fens (>10 percent canopy) are also included here.
Similar NVC Types:
1.B.3. Temperate Flooded & Swamp Forest (F026): These forests less often con-
tain a sphagnum peat layer and are more commonly dominated by hardwood
species.
1.B.4. Boreal Forest & Woodland (F001): These typically contain better drained
soils, lack any aquatic vegetation or muck layer, and, if a peat layer is present,
it is shallow (<40 cm).
2.C.2. Temperate to Polar Bog & Fen (F016): Boreal Flooded & Swamp Forest
(F036) includes forested bogs with greater than 10 percent tree cover, along
with poor swamps.
Diagnostic Characteristics: Boreal Flooded & Swamp Forest is defined as a
tree-dominated wetland in a boreal climate that is influenced by minerotrophic
groundwater, either on mineral or organic (peat) soils; less commonly, they occur in
transitional floodplain habitats. The vegetation is dominated by over 10 percent cover
from needle-leaved trees and the wood-rich (less commonly sphagnum-rich) peat that
this vegetation lays down.
Vegetation
Physiognomy and Structure: These swamps are defined as tree-dominated wet-
lands that are influenced by minerotrophic groundwater, either on mineral or organic
soils. The vegetation is dominated by over 10 perce