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Integrating Soil Ecological Knowledge into Restoration Management

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Abstract

The variability in the type of ecosystem degradation and the specificity of restoration goals can challenge restorationists' ability to generalize about approaches that lead to restoration success. The discipline of soil ecology, which emphasizes both soil organisms and ecosystem processes, has generated a body of knowledge that can be generally useful in improving the outcomes of restoration despite this variability. Here, we propose that the usefulness of this soil ecological knowledge (SEK) for restoration is best considered in the context of the severity of the original perturbation, the goals of the project, and the resilience of the ecosystem to disturbance. A straightforward manipulation of single physical, chemical, or biological components of the soil system can be useful in the restoration of a site, especially when the restoration goal is loosely defined in terms of the species and processes that management seeks to achieve. These single-factor manipulations may in fact produce cascading effects on several ecosystem attributes and can result in unintended recovery trajectories. When complex outcomes are desired, intentional and holistic integration of all aspects of the soil knowledge is necessary. We provide a short roster of examples to illustrate that SEK benefits management and restoration of ecosystems and suggest areas for future research.
Integrating Soil Ecological Knowledge into
Restoration Management
Liam Heneghan,
1,2
Susan P. Miller,
3
Sara Baer,
4
Mac A. Callaham, Jr.,
5
James Montgomery,
1
Mitchell Pavao-Zuckerman,
6
Charles C. Rhoades,
7
and Sarah Richardson
1
Abstract
The variability in the type of ecosystem degradation and
the specificity of restoration goals can challenge restora-
tionists’ ability to generalize about approaches that lead
to restoration success. The discipline of soil ecology, which
emphasizes both soil organisms and ecosystem processes,
has generated a body of knowledge that can be generally
useful in improving the outcomes of restoration despite
this variability. Here, we propose that the usefulness of
this soil ecological knowledge (SEK) for restoration is
best considered in the context of the severity of the origi-
nal perturbation, the goals of the project, and the resil-
ience of the ecosystem to disturbance. A straightforward
manipulation of single physical, chemical, or biological
components of the soil system can be useful in the restora-
tion of a site, especially when the restoration goal is
loosely defined in terms of the species and processes that
management seeks to achieve. These single-factor manip-
ulations may in fact produce cascading effects on several
ecosystem attributes and can result in unintended recov-
ery trajectories. When complex outcomes are desired,
intentional and holistic integration of all aspects of the soil
knowledge is necessary. We provide a short roster of ex-
amples to illustrate that SEK benefits management and
restoration of ecosystems and suggest areas for future
research.
Key words: ecosystem processes, feedbacks, soil ecology.
Introduction
Restoration ecologists have long recognized the integral
role of soil, particularly in its physical and chemical
aspects, in the successful revegetation of degraded sites
(Jordan et al. 1987). However, explicit incorporation of
soil ecological knowledge (SEK), which acknowledges
interactions among the principal components of the soil
system as well as feedback between the aboveground and
belowground ecosystem processes, into restoration re-
mains in a relatively early stage of development (Aronson
et al. 1993; Harris et al. 2006; Wardle & Peltzer 2007).
Despite earlier attempts to demonstrate the importance of
a soil’s perspective for restoration efforts, a recent and
useful review of research on restoration ecology makes
only scattered references to soil processes and biota (Falk
et al. 2006). Published restoration science in the primary
literature commonly includes soil information associated
with pre-restoration site assessment and the evaluation of
specific soil amendments (Callaham et al. 2008). Recovery
of nutrient capital or biogeochemical processes also moti-
vates restoration activities, but examples where integrated
SEK has been employed are uncommon.
In this article, we discuss restoration practice and re-
search that is informed by SEK. The term ‘‘soil ecological
knowledge’’ is used to indicate perspectives from the disci-
pline of soil ecology that integrate soil physical, chemical,
and biological factors and processes in context of plant–
soil feedback. In particular, it is knowledge from soil
ecology that can be used explicitly to inform restoration
practice. A restoration approach that employs more
sophisticated SEK differs from simpler approaches that
consider soil factors in isolation or that separates above-
ground from belowground ecosystem processes. We dis-
cuss a classification of restoration approaches arrayed
along a gradient of increasing need for knowledge of soil
ecology to attain the ecosystem structure and function of
a particular reference condition. Additionally, we identify
promising new research areas, where restoration projects
may advance our understanding of soil ecology and where,
reciprocally, a deepened knowledge of the soil system
may enhance restoration practice.
The discipline of soil ecology has deep roots in soil sci-
ence and organismal biology. Soil ecologists have merged
1
DePaul University, Environmental Science Program, Chicago, IL 60614, U.S.A.
2
Address correspondence to L. Heneghan, email lhenegha@depaul.edu
3
Millroad Ecological Services, 2200 Three Oaks Court, Fort Collins, CO
80526, U.S.A.
4
Department of Plant Biology, Southern Illinois University, Carbondale,
IL 62901, U.S.A.
5
USDA-Forest Service, Forestry Sciences Laboratory, Athens, GA 30602,
U.S.A.
6
Biosphaere 2, PO Box 210088, University of Arizona, Tucson, AZ 85721,
U.S.A.
7
USDA Forest Service Rocky Mountain Research Station, Fort Collins,
CO 80526, U.S.A.
Ó2008 Society for Ecological Restoration International
doi: 10.1111/j.1526-100X.2008.00477.x
608 Restoration Ecology Vol. 16, No. 4, pp. 608–617 DECEMBER 2008
these traditional disciplines to understand ecosystem pro-
cesses, which have provided tools for elucidating concepts
central to ecology as a whole (Coleman et al. 2004;
Lavelle & Spain 2001; Bardgett 2005). For example, rela-
tionships between biodiversity and ecosystem functioning
have been tested using model soil ecosystems (Lavelle
1996; Bengtsson 1998; Lawton et al. 1998; Setala et al.
1998; Behan-Pelletier & Newton 1999; Heneghan et al.
1999; Zak et al. 2003; Fitter et al. 2005). Furthermore,
perspectives in soil ecology that focus on the reciprocal
feedback of above- and belowground biota and pro-
cesses have become increasingly central to ecology (e.g.,
Casper & Jackson 1997; Klironomos 2002; Setala 2002;
Wardle 2002; Bardgett & Wardle 2003; Van Der Putten
2003; Wardle et al. 2004). The holistic perspective that
integrates organismic and ecosystem processes at the
core of soil ecology has provided explanations for
patterns in the distribution, abundance, and composi-
tion of species, a fundamental organizing tenet in ecol-
ogy (Tilman 1982; Bever 1994; Bever et al. 1997; Baer
et al. 2005).
Soil biota is directly involved in key ecosystem pro-
cesses (e.g., decomposition and nutrient cycling), and
understanding such interactions has provided one of the
unifying themes of soil ecological research over the past
few decades (Swift et al. 1979; Wardle 2002). Because of
the demonstrated key role in the regulation of ecosystem
processes, application of insights from soil ecology has
been useful in situations where desired outcomes go
beyond simple enhancement of single factors such as pro-
ductivity. For instance, soil ecology has made a substantial
contribution to alternative agricultural practices, such as
no-till cropping systems, by integrating conservation
of physical, chemical, and biological properties of soil
(Coleman et al. 2002). In this case, soil ecologists have
demonstrated the importance of shifts from bacterial to
fungal channels in soil food webs for the development of
soil structure, soil organic matter (SOM) sequestration,
and modulation of soil nutrient availability (Hendrix et al.
1986; Beare et al. 1995). Lessons gained from agroecology
have inspired recent investigations of changes in microbial
community structure following cessation of tillage and
restoration of native vegetation (Allison et al. 2005;
McKinley et al. 2005).
Contribution of Soil Ecology to Restoration—
A Classification
We propose that the relationship between SEK and resto-
ration may be best considered in the context of the sever-
ity of the original perturbation, the goals of the project,
and the resilience of the original ecosystem to disturbance
(Fig. 1). Our conceptual model builds on previous models
of ecosystem restoration (Bradshaw 1987; Whisenant
1999; Hobbs & Harris 2001). We surmise that the utility of
SEK for achieving a restoration goal depends on the
degree to which the restoration intent aims to achieve
characteristics of a specified reference condition. Signifi-
cantly degraded sites generally require active consider-
ation of the soil, e.g., remediating oil spills (Kuyukina
et al. 2003). Site remediation in circumstances where re-
storing pre-disturbance above- and belowground structure
and function is not a priority and may require a mani-
pulation of a single physical, chemical, or biological part
of the soil system to improve a system’s state relative to
the perturbed state. For example, when a system has been
so severely perturbed that plants simply will not grow
(e.g., on soils contaminated by heavy metals, oil spills,
Figure 1. Framework for linking (a) SEK to existing theoretical
models of ecosystem restoration (b and c). (a) When sites are heavily
degraded, improved soil function may be achieved by simple single-
factor manipulations of a given chemical (C), physical (P), or bio-
logical (B) attribute. For greater progress toward a target condition,
an increase in the degree of complex SEK is required (and the
consideration of interactions between P, C, and B components will
be critical). (b) Physical and biological thresholds which must be
overcome if restoration is to be successful (modified from Whisenant
1999). (c) The integral relationship between structural and functional
attributes in ecosystem restoration (modified from Bradshaw 1987).
See text for examples and further illustration.
Integrating Soil Ecological Knowledge
DECEMBER 2008 Restoration Ecology 609
brine scars), the restoration goal may be limited to
reclaiming a specific structure or process to enable revege-
tation. This may be achieved through ripping, tilling, or
contouring compacted substrates to improve aeration,
infiltration, and root growth purposes (Ashby 1997;
Jacinthe & Lal 2007); removing toxic chemicals; or
altering pH (e.g., mine land reclamation). In some cases,
this can involve as little effort as essentially ‘‘waiting’’ for
extant microbial populations to act on the offending tox-
ins. Some soil factors are known to be important in medi-
ating the availability of toxins to the microbes (e.g., soil
porosity, sorption/desorption of toxins to organic matter,
pH, redox potential), and these factors are often targets
for remediation (e.g., Mitsch & Jorgensen 2003). Such
approaches are shown in the lower left-hand part of Fig-
ure 1a: the desired outcome is a relatively general one
(getting some regrowth of vegetation), and the restora-
tionist may manipulate soil factors without requiring
a great deal of knowledge about interactions within
the soil.
Restoration in the sense of returning an ecosystem to
a specified reference condition, e.g., a historical state, both
in terms of a specific community structure and ecosystem
function, will require an increasingly sophisticated under-
standing of the soil and all its physical, chemical, and bio-
logical properties to achieve the desired goal. If a system
is severely degraded, where soil food webs and processes
have been highly altered, an integrated consideration of
physical, chemical, and biological properties of soil and
interactions between plants and soil will be required to
restore all components of the perturbed ecosystem to a ref-
erence condition. This requirement for integrated SEK to
achieve a specific desired system outcome is illustrated in
the upper right-hand side of Figure 1a.
Finally, when the disturbance of a site is not so great as
to overwhelm the resilience of a system (i.e., does not shift
it beyond the self-organized processes and structures of
the system [Gunderson 2000]), the need for management
intervention may be minimal. However, when the distur-
bance is such that the system is degraded to a relatively
stable alternative stable state, the need for SEK will be
considerable.
Our model is summarized with a simple illustration
(Fig. 1) in which an increasingly conscious integration of
physical, chemical, and biological factors is required as the
goal of approaching a specific desired ecological state is
reached. Management options exist along a gradient from
single-factor manipulations of physical, chemical, or
biological elements (shown in Fig. 1a as P, C, and B in
separate circles) to ones where a deliberate regard for
a cascade of interrelated effects of manipulations of soil
factors (maximum SEK) is required to bring about a par-
ticular outcome (shown as P, C, and B linked by arrows
and bound together in a circle). We suggest that there are
intermediate circumstances where a restoration outcome
will require some knowledge of the interaction of effects
(shown as P, C, and B linked by arrows).
Integration of Soil Knowledge: Case Studies
Hobbs and Harris (2001) and Hobbs and Norton (2004)
suggest that abiotic and biotic constraints may stall the
restorative process until thresholds are breached through
human intervention (Fig. 1b; Whisenant 1999; see Fig. 1).
The notion is that more degraded environments will
require repairing the physical template (e.g., abiotic com-
ponents) prior to restoring species composition (e.g.,
biotic components) and subsequently, the ecological func-
tions representative of the reference system. Manipula-
tions directed at relieving abiotic filters can be physical
(e.g., reducing soil compaction), chemical (e.g., liming to
alleviate acidity), or biological (e.g., using plants to stabi-
lize and remediate toxic chemical conditions [Shimp et al.
1993; Qadir et al. 2002]).
We suggest that management aimed at fully restoring the
ecosystem structure and function of a reference condition
must integrate the physical, chemical, and biological factors
of that system. We recognize that the soil is a proverbial
‘black box’ where impacts of a given treatment are often
evaluated by specific net outcomes despite the enormous
complexity of interactions that may mediate the response
and therefore determine those outcomes. For instance,
manipulating a physical factor to alleviate compaction and
promote greater plant production will likely simultaneously
alter a suite of aspects of the soil system, such as soil carbon
storage (Jacinthe & Lal 2007). The use of thinning, burning,
and thinning plus burning as treatment variables in Ponder-
osa pine increased total inorganic nitrogen availability in
forest restoration treatments compared with untreated con-
trols (Kaye & Hart 1998) and resulted in higher understory
diversity (Gundale et al. 2006). That is, the manipulation of
the aboveground vegetation has well-characterized impacts
on the cycling and storage of carbon and nutrient in the
soil, and these cascades may be incorporated intentionally
into management. Deliberate manipulation of soil that inte-
grates holistic knowledge of the soil system will be more
likely to achieve the restoration of several system functions
or several aspects of community structure. For the purposes
of illustrating the relative role of SEK in these examples,
we consider both bioremediation and reclamation as types
of ecological restoration. These will be considered along-
side practices such as the manipulation of successional pro-
cesses, which are used to restore community composition
and function to a particular reference condition. The exam-
ples below illustrate a range of potential manipulations of
physical, chemical, and biological factors available to the
restoration. In many cases, single manipulations targeted at
a physical, chemical, or biological component of the soil are
employed; in most cases, these manipulations have conse-
quences for other soil components though these are not
always fully understood.
Physical Manipulations
Soil physical structure influences vegetation growth
(Passioura 1991). When soil structure is degraded, the
Integrating Soil Ecological Knowledge
610 Restoration Ecology DECEMBER 2008
impacts, often mediated by a variety of other related soil
physical characteristics (including those that relate water
availability), can affect both plant growth and community
composition (Burke et al. 1998; Kozlowski 1999). Physical
manipulations to improve soil structure in highly degraded
sites include a variety of tillage practices (e.g., disking, rip-
ping, subsoiling; Scullion & Mohammed 1991; Ashby
1997), incorporation of polyacrylamide beads (Vacher
et al. 2003), and topdressing (e.g., with nitrogenous fertil-
izers or with manure) (Ducsay & Lozek 2004; Johnson
et al. 2006) (Callaham et al. 2008). Management of the
physical soil substrate depth influences the overall quan-
tity of water and nutrients available to support plant
growth (Binkley et al. 1995; Andrews et al. 1998; Bowen
et al. 2005). However, these often-effective practices can
be expensive and time consuming, making them impracti-
cal for many restoration projects.
Manipulation of Soil Chemistry/Fertility
Fertilizers and chemical amendments are commonly used
to improve restoration success (Lu et al. 1997; Jim 2001;
Marrs 2002; Xia 2004). For instance, application of
a phosphorus P fertilizer, N fertilizer, and lime, along
with appropriate pasture seed mix was needed to effec-
tively reestablish pasture in a New Zealand opencast coal
mine reclamation (Longhurst et al. 1999). Restoration of
former agricultural land, with residually high levels of
inorganic nitrogen from long-term fertilization, may re-
quire manipulations to reduce soil fertility that favor the
desired plant species adapted to nitrogen-limited systems
(Wilson & Gerry 1995; Paschke et al. 2000; Suding et al.
2004).
Manipulation of soil chemistry and nutrition as part of
ecosystem restoration is common, but consideration of
the consequences of these practices on physical and bio-
logical soil properties is rare (Callaham et al. 2008). For
instance, the stated goal of treatments where topsoil or
‘topsoil substitute’’ is added is to improve soil nutrient
content and facilitate recovery of plant biomass and com-
munity diversity (e.g., Torbert et al. 1990; Clewell 1999).
However, these amendments also introduce plant seed,
mycorrhizal symbionts, and soil microbes and alter soil
microenvironment and water relations by changing soil
texture, depth, density, and porosity. As such, these ‘‘sec-
ondary’’ mechanisms may have significant influences on
plant performance, the outcome of restoration activities.
We suggest that identification of these soil ecological
mechanisms and interactions will substantially contribute
to understanding of the controls on restoration success.
Manipulation of Soil Organisms
Soil biota, both directly and indirectly, influence soil nutri-
ent dynamics (Verhoef & Brussaard 1990; Lussenhop
1992; Brussaard et al. 1997) and can also influence plant
community development and diversity (De Deyn et al.
2004; Kardol et al. 2005). Soil biota include microflora
(i.e., bacteria and fungi), a wide range of functionally dis-
tinct nematodes and microarthropods, as well as a variety
of macroinvertebrates (i.e., earthworms, beetle larvae,
cicadas). Numerous studies have examined the effects of
disturbance on soil microflora and fauna (e.g., Wardle
et al. 1995; Brussaard et al. 1997), and soil biota are com-
monly employed as indicators of restoration success
(Andersen & Sparling 1997; Todd et al. 2006; Callaham
et al. 2008). However, soil fauna have rarely been
directly manipulated to improve restoration success. One
example of such manipulation is that of introducing
earthworms to improve soil porosity and aggregate
structure but with varying success (Butt 1999). Numer-
ous studies have, however, directly manipulated mycor-
rhizae, either through additions of spores, inoculation
of plants, or addition of soil inocula from undisturbed
communities. The use of mycorrhizal fungi in restora-
tion has attracted considerable attention in recent
years, and increasingly sophisticated knowledge of the
biology and ecology of this group of soil organisms can
influence restoration.
The community and ecosystem consequences of mycor-
rhizal infection vary with mycorrhizal dependency of the
dominant and rare species in a community (Bever et al.
2001, 2002). For example, if dominant species depend on
mycorrhizae, then their presence may be necessary for
restoring ecosystem function (Richter & Stutz 2002). Res-
toration of rare species that are mycorrhizae dependent
may require inoculation for establishment and achieving
the desired community composition (van der Heijden
et al. 1998). Likewise, inoculation may be necessary to
reclaim extremely degraded sites and maximize productiv-
ity of a limited species pool under such circumstances
(Frost et al. 2001). Incorporating mycorrhizae in restora-
tion requires an understanding of cascading ecological
consequences from the relationship between belowground
organisms, aboveground individuals, community structure,
and ecosystem processes.
Restoring mycorrhizae to degraded soils is difficult
(Cardoso & Kuyper 2006), and there is growing interest in
using commercial mycorrhizae inoculums to improve res-
toration success, which prompts a number of research
questions. Are commercial fungi as effective and as viable
as native fungi (Caravaca et al. 2003; Querejeta et al.
2006; Tarbell & Koske 2007)? What are the risks associ-
ated with using non-native fungi in restoration? Under
what circumstance will they benefit invasive plants more
than native plants (Schwartz et al. 2006)?
Applying mycorrhizae requires knowledge about site
conditions. Mycorrhizal fungi, for instance, may not grow
at sites contaminated with heavy metals or where nutri-
ents are very low (Vosa
´tka et al. 1999). Additionally, they
may also be inhibited by high levels of nutrients such as
nitrogen from vehicles and fertilizers (Egerton-Warburton
et al. 2007). Although plants exhibit less dependence on
Integrating Soil Ecological Knowledge
DECEMBER 2008 Restoration Ecology 611
mycorrhizae with increasing nutrient (P) availability in
soil, an unpredictable benefit from sustained populations
is increased infection and plant survivorship during
drought (Gemma et al. 2002; Allen et al. 2003; Walker
et al. 2004; Querejeta et al. 2006).
The use of mycorrhizae illustrates an important part of
the SEK model: in order to effectively incorporate mycor-
rhizae into a restoration strategy, a moderate level of
knowledge about the interactions between the physical,
chemical, and biological factors that prevail at a site is
needed to drive the system along a trajectory leading to
a specific outcome.
Integrated Manipulation
In most of the examples presented above, the manipula-
tion of one component of the soil has implications for
other components. Manipulations based upon an under-
standing of such cascading effects can therefore be per-
formed intentionally to achieve a particular restoration
result. In our model (Fig. 1), we propose that as the com-
plexity and specificity of desired outcomes increase, inten-
tionally integrated strategies become essential. Although
many of the earliest restoration projects aimed at estab-
lishing vegetation of any sort, outcomes which specify
complex species assemblages are now more prevalent
(Bradshaw 2004). As the restoration process approaches
desired functional and compositional attributes, we con-
tend that a more nuanced understanding of SEK will
be required.
Integrated Manipulation of Soil physical, Chemical, and
Biological Properties: An Example Applying SEK to Combat
Invasion
To illustrate what integrated strategies (applying SEK)
may resemble, we discuss efforts to produce resilient res-
toration outcomes in the face of sustained invasion by
exotic species.
SEK has been increasingly applied to prevent and/or
reduce invasion by exotic species in restoration. A sys-
tem’s susceptibility to invasion has been shown to increase
in response to altered disturbance regime (e.g., woody
encroachment in unburned grasslands) and/or soil re-
source availability (Burke & Grime 1996; Davis et al.
2000). For example, restoration of native grasslands on
abandoned agricultural land can be impeded by years of
agricultural fertilizer inputs which have created soil nutri-
ent levels that favor invasive over native plant species
(McClendon & Redente 1992; Morghan & Seastedt 1999;
Maron & Jeffries 2001; Blumenthal et al. 2003; Averett
et al. 2004). The first step in restoring desired native plant
species or communities in such areas may therefore
require ‘‘defertilization’’ to export or sequester excess
nutrients in order to optimize success of native plants that
demand lower soil nutrients. For example, the addition of
carbon, which promotes microbial immobilization of
available and mineralized nitrogen has been shown to
reduce colonization and cover of non-native species in
prairie restorations (Baer et al. 2003). An integrative res-
toration approach may also involve physical and biological
strategies. For example, carbohydrate supplements along
with prescribed fire enhanced native Australian tussock
grass restoration (Prober et al. 2005). Baer et al. (2003)
found reduced colonization and cover of non-native spe-
cies in soil amended with carbon to reduce nitrogen avail-
ability in a prairie restoration. Thus, carbon addition
represents a tool with the potential to alleviate an impor-
tant filter (i.e., soil nitrogen fertility) on community
assembly.
Invasion of a system by exotic species may alter physi-
cal, chemical, and/or biological characteristics of the soil.
Recognizing feedbacks between invading plant species
and soil may be crucial to combating invasion. For exam-
ple, Vinton and Goergen (2006) documented positive
feedback between litter quality and nitrogen mineraliza-
tion in grassland restoration invaded by Smooth brome
(Bromus inermis), a species that demands more nitrogen
than native prairie grasses. Kulmatiski and Beard (2006)
found that soil manipulations (incorporation of activated
carbon) influenced competitive interactions between inva-
sive and native plants in the soil by apparent sequestration
of allelopathic compounds. Although their manipulations
did not result in complete removal of invasive plants from
the system, their work demonstrated that solutions for this
type of complex restoration challenge require consider-
ation of complex soil processes. This type of targeted
manipulation is relatively sophisticated and represents the
most exciting future direction of research for soil ecolo-
gists and restoration ecologists alike.
Soil Quality as a Concept Guiding Ecosystem
Restoration
Our conceptual scheme provides an opportunity for link-
ing a soil’s perspective on restoration with monitoring of
restoration progress using soil quality indices. Larson and
Pierce (1991) defined soil quality as the capacity of a spe-
cific kind of soil to function, within natural or managed
ecosystem boundaries, to sustain plant and animal produc-
tivity, maintain or enhance water and air quality, and sup-
port human health and habitation. In the past 10 years,
research on the soil quality concept has proceeded rapidly,
with particular emphasis on understanding the role of the
soil resource in maintaining environmental quality (Glanz
1995; Pickett et al. 2001) and on the application of the soil
quality concept to restoration and management of nonag-
ricultural lands (Sims et al. 1997; Singer & Ewing 2000;
Karlen et al. 2001).
Soil quality is specific to each kind of soil (USDA-
NRCS 2001); however, measuring dynamic soil properties
such as SOM, soil structure, and water-holding capacity
can be used both to compare the efficacy of different soil
Integrating Soil Ecological Knowledge
612 Restoration Ecology DECEMBER 2008
management practices among soils on similar landscape
positions with equivalent inherent properties or to track
temporal changes on the same soil (Singer & Ewing 2000;
Karlen et al. 2001). The results of this assessment can then
serve to guide subsequent soil management decisions
(Karlen et al. 2001). A variety of user-friendly qualitative
and semiquantitative educational materials have been
developed for conducting soil quality assessments, includ-
ing a visual soil assessment procedure (Shepherd 2000),
Soil Quality Information Sheets (Muckel & Mausbach
1996), soil health scorecards (Romig et al. 1996), and com-
mercially available soil quality test kits.
Despite some criticism of the notion of soil quality, it
should be noted that the soil quality concept was con-
ceived merely as an outreach and assessment tool for eval-
uating the sustainability of soil management practices and
for guiding land use decisions. It should be a suitable way
of mediating between research on SEK and managers who
may ultimately apply and evaluate the use of this informa-
tion in restoration projects. Considering the application of
the soil quality concept to restoration, Karlen et al. (2003)
noted that soil quality assessment will be useful in quanti-
fying both the resistance (defined as the capacity of a sys-
tem to continue functioning through a disturbance, Pimm
1984) of a soil to degradation and the resilience of a soil to
recover following degradation. Given its fundamental
grounding in basic principles of pedology and soil ecology,
the soil quality concept is inherently embedded in SEK
and, therefore, it can serve as a useful tool to guide ecosys-
tem restoration.
Conclusions
Restoration aims to overcome constraints on ecosystem
recovery through natural processes to produce resilient
ecosystems that are resistant to invasion, capture and
use resources efficiently, contain biological complexity
needed to function effectively, and provide human-val-
ued services (Ewel 1987; Hobbs 2006). Although the goal
of each restoration is defined by stakeholders, selection
of targets and assessment of success should be guided by
general theory from relevant disciplines and lessons from
practice (Hobbs & Harris 2001). With this understand-
ing, we contend that any attempt to facilitate ecosystem
recovery from degradation will be improved by applying
SEK. Soil ecological perspectives that have emerged in
recent decades are integrative and ecosystem oriented
because they simultaneously consider the influence of
soil physical, chemical, and biological structure on
energy flow and material cycling. SEK can be founda-
tional to restoration across multiple ecological scales
(from population to whole ecosystem restoration). We
propose that the relevance of SEK to restoring degraded
systems is determined by the level of soil degradation
and the specificity of project goals. When a restoration
project aims to restore highly degraded sites to a level of
complexity with all former functions of a specified refer-
ence condition, very targeted or specific SEK is needed.
Success in such instances will require a holistic approach,
as even single-factor manipulations can affect soil physi-
cal, chemical, and biological properties. Variability in
the type of degradation, the specific restoration goals,
the time frame in which results are anticipated, and the
means by which outcomes are assessed challenge our
ability to generalize about approaches that lead to resto-
ration success.
Our conceptual scheme underscores a simple rule of
thumb: when complex ecological outcomes are desired,
incorporating a more comprehensive SEK is critical to
achieve restoration goals. The need for an adequate incor-
poration of SEK into restoration practice may become even
more pressing in future years in the face of global change
(globalization of commerce, increased intercontinental flow
of biota and materials, climate change, etc.). The prospect
of climate change will force difficult decisions on where and
what may be restored in ecosystem restoration projects in
the future (Harris et al. 2006), and soil ecological considera-
tions may ultimately provide guidance for these decisions.
This is evident, given the predicted changes to fundamental
characteristics of and processes in soils under different cli-
mate change scenarios (Bellamy et al. 2005; Saxon et al.
2005). The implications of this for restoration are only now
being investigated (Fox 2007).
Finally, as strong as is the potential for SEK to improve
the practice of ecological restoration, the reciprocal influ-
ences are also promising. Restoration aims to use ecologi-
cal theory to improve practice and apply information from
practice to improve theory (Palmer et al. 2006). Thus, con-
sidering soils in restoration will test our mechanistic
understanding of the ecological structure and function of
soil in altered environments. Most importantly, this will
expose deficiencies in our basic knowledge of soil ecology;
as such, restoration practice provides an ‘‘acid test’’ for soil
ecology (Bradshaw 1987).
Implications for Practice
dKnowledge of soil should routinely be incorporated
into planning and evaluating restoration projects.
The level of sophistication required for incorporating
SEK depends upon the extent of soil degradation,
the goals of the project, and the resilience of the eco-
system, and therefore, all these factors need to be
considered in the execution of restoration work.
dWhen the goals of a restoration project are relatively
general ones—e.g., revegetation of a degraded site,
without a specific target plant community planned—
modest SEK will be needed.
dHowever, restoring a highly degraded site to a very
particular target condition will require extensive
SEK.
Integrating Soil Ecological Knowledge
DECEMBER 2008 Restoration Ecology 613
dThe field of soil ecology which has traditionally com-
bined a strong organismal influence with a focus on
ecosystem processes should provide a source of
knowledge for restoration practitioners, while being
itself influenced by knowledge emerging from resto-
ration practice.
Acknowledgments
We thank two anonymous reviewers for useful comments
on the article. L. Heneghan gratefully acknowledges the
support of National Park Service, Natural Resource Pro-
gram Center during the preparation of this article.
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... In ecological restoration, it is important to take into account both vegetation and soil when restoring ecosystems Heneghan et al. 2008). This is because the two interact, and because each may respond differently after disturbance and/or after restoration. ...
Thesis
L’objectif principal de la thèse a été d’expérimenter de nouvelles techniques en ingénierie écologique afin de restaurer le sol et la végétation d'une pelouse sèche méditerranéenne sub-steppique, détruite suite à une fuite d'hydrocarbures (plaine de La Crau, Bouches-du-Rhône, France). Après évacuation des terres polluées en décharge, un transfert de sol a été réalisé au printemps 2011 en procédant à une translocation directe, selon un ratio 1/1 avec respect ou non de l’organisation verticale des principaux horizons du sol. Après trois années de suivis, nous avons pu mettre en évidence l’importance de prendre en considération différentes composantes (sol, végétation, myrmécofaune) de l'écosystème, et surtout leurs interactions, pour mieux évaluer à l'avenir la réussite d'opérations de restauration écologique. Ainsi, nous avons mesuré que la régénération du sol en ce qui concerne les paramètres physico-chimiques et biologiques pouvait être rapide pour certains d'entre eux, comme c’est le cas pour la biodégradation du carbone et de la biomasse bactérienne, mais beaucoup plus lente pour d'autres comme c’est le cas pour le rétablissement des échanges verticaux entre les horizons dans le profil de sol. De même, la régénération de la végétation steppique a été atteinte à très court terme (trois années) concernant sa richesse, sa diversité spécifique, et sa similarité de composition avec la steppe de référence mais au prix d'interventions de restauration à fort coût économique et environnemental (destruction du milieu donneur). C'est pourquoi, la fourmi moissonneuse Messor barbarus est apparue comme un ingénieur des écosystèmes potentiel pour compléter le travail entrepris en accélérant la redistribution des graines viables, et ainsi en restaurant la structuration de la végétation qui fait encore défaut. En effet, cette fourmi concentre localement certaines graines par la construction de dépotoirs aux entrées de leur nid et d’augmente la richesse spécifique de la végétation dans l’écosystème de référence lorsque les dépotoirs sont naturellement détruits au cours de l’hiver. Un suivi de la recolonisation naturelle des fourmis et une expérimentation originale de transfert de reines fondatrices, de l'écosystème de référence vers l'écosystème à restaurer, ont également montré, que lorsque l’habitat n’était pas favorable à la recolonisation naturelle de Messor barbarus, la transplantation permettait d'obtenir d’excellents résultats sur le taux de survie des fourmis transférées. Il sera cependant encore nécessaire de poursuivre ces suivis pendant quelques années pour valider in fine le rôle positif des fourmis vis-à-vis de la restauration de la structuration spatiale de la communauté végétale steppique.
... Given the crucial role of soil biota in driving key ecosystem functions and development , it is essential to ensure facilitation of soil communities when selecting and applying restoration treatments. A limited, but growing number of papers, emphasize the importance of above-and belowground linkages for restoration ecology (Eviner and Hawkes 2008;Heneghan et al. 2008;Kardol and Wardle 2010;Van der Putten et al. 2013). ...
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Several restoration methods have been developed to aid ecosystem development from highly degraded Icelandic deserts into fully vegetated functional ecosystems. Despite the critical role of soil biota in many key ecosystem processes, the effect of restoration efforts on soil biota has rarely been explored. We took advantage of a large-scale restoration field experiment, to study the effect of distinct revegetation treatments on the taxonomic and functional composition of Collembola communities. Soil samples were taken from plots (one ha. each), that had received functionally distinct revegetation treatments; i: grass + fertilizer, ii: birch seedlings, iii: willow cuttings, iv: lupine and v: control. We were able to show that different revegetation treatments led to the establishment of distinct collembola communities in terms of density and taxonomic and functional composition, 20 years after the revegetation process had started. Life-forms were responsive to revegetation treatment, which suggests that the treatments had induced successional trajectories that lead to distinct habitat conditions, especially with respect to abiotic stress. In contrast to literature, eu-edaphic species were dominating in plots, which were exposed to high levels of disturbance and fluctuations in abiotic conditions. Further research is needed to unravel, to which extent resource supply and abiotic habitat conditions steer Collembola community development across successional trajectories.
... Hardwood floodplain forests in the lower middle Elbe have been severely degraded and intensively used for hundreds of years. When an ecosystem undergoes such severe degradation, successful restoration processes require a sophisticated understanding of the physical, chemical and biological properties of soils (Heneghan et al., 2008). In the case of forest restoration, physical and chemical parameters of soils as for example soil texture, pH, cation exchange capacity and others, are indicators of water availability and nutrient cycling, respectively (Lozano-Baez et al., 2021;Schoenholtz et al., 2000). ...
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The analyses of soil properties and processes under the consideration of the spatial complexity of floodplains is a key step in the preparation of floodplain restoration measures. In that context, we analyzed how hydro-geomorphology influences soil physicochemical properties and formation processes in hardwood floodplain forests at the local scale. Our analyses are based on, 44 mixed topsoil samples, 135 soil drillings (2.0 m depth) and 18 reference pits (1.6 m depth) distributed in 44 hardwood floodplain forests along 150 km of the middle Elbe River. We considered four hydrogeomorphic units (HGUs) along a lateral floodplain gradient. Two HGUs located in the active floodplain and defined by their morphology Active High (AH), and Active Low (AL), and two located in the former floodplain: seepage water influenced (FS), and disconnected from the river hydrology (FD). Our results indicate that the HGUs in the active floodplain benefit from a stronger connection to the river hy-drology. Higher pH CaCl2 values in the active HGUs as well as expected higher total P contents due to river deposition result in increased phosphorous availability. Physicochemical parameters as lower pH CaCl2 and predominance of iron mottling found in the FD indicate increased P sorption, therefore lower P sol availability. However, HGUs in the former floodplain, particularly those disconnected from the river hydrology, are characterized by higher total carbon and nitrogen content. These results improve our understanding of the soil physicochemical dynamics and their interactions in the different hydrogeomorphic units, and could allow the evaluation of floodplain restoration measures based on soil nutrient distribution to increase the potential of restored forests to develop on the selected geographic setting.
... The reestablishment of a key soil component as organic matter in restoration processes is an effective strategy to induce positive cascading effects on related soil properties, and consequently on soil health and ecosystem functions recovery (Heneghan et al., 2008;Larney and Angers, 2012;Hueso-González et al., 2018). In a context in which the recovery of ecosystem functionality could be hampered, the correct application of organic amendments would help to regain C and N pools, and thus essential soil microbial functions (Cellier et al., 2014;Luna et al., 2018). ...
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Understanding how soil chemical/physical and biological parameters behave after the increasingly common fires in Mediterranean Chilean ecosystems is critical to boost their recovery. Incorporating organic amendments in soil to support its post-fire recovery is promising; however, there are important gaps regarding the seasonal responses of soil parameters following such additions. This study aimed to identify the effects of different organic amendments (compost, poultry, and swine manure) and methods of plant establishment (sowing or plantation), through the seasons observed in a sclerophyll Mediterranean Chilean forest over one year. Season over organic amendments and plant establishment method had a very strong effect on most of the twelve soil parameters evaluated. Across seasons, soil pH, electrical conductivity, water content, and aggregate stability were less variable than C and N pools, colony forming units (CFUs) of heterotrophic and free-living N 2 fixing microorganisms, and urease and ammonia monooxygenase activities. Manure-based amendments increased NO 3 and heterotrophic CFUs during fall and summer, respectively. The use of compost resulted in greater soil organic matter and carbon, mostly in summer. Different responses of soil abiotic and biotic properties after fire and organic amendments can likely influence differently processes related to ecosystem recovery, particularly those related to C and N cycles.
... However, if the ecosystem is more disturbed, restoration of the biotic component will be necessary besides removal of the disturbance. If the disturbance has degraded both abiotic and biotic components, the priority is to restore the physical and chemical properties of the soil (Heneghan et al., 2008) by identifying the ecological functions of interest, and then the biotic component. In all cases community and population changes should be monitored to ensure that all target functions have been restored (Holl and Aide, 2011). ...
Article
Ecological engineering of degraded ecosystems often manipulates plants, with positive outcomes for their restoration or ecosystem services production. The importance of soil biota for successional plant communities has prompted consideration of direct inoculation (active) or attraction (passive) of soil organisms as a relevant restoration strategy. However, few attempts have manipulated soil invertebrates as part of nature based solutions for ecosystem restoration, despite their major role in many soil ecological processes and in plant-soil feedback processes. In addition, while ecological restoration and ecological engineering approaches successfully incorporate plant traits, soil invertebrate traits remain underused. Exploiting the functional diversity of soil communities by adopting a trait-based approach could enhance restoration of soil chemical, biological and physical properties. Here, we conduct a narrative review and identify a set of soil invertebrate functional traits with great potential in ecosystem restoration. We focus on traits related to four main ecological functions that are often at the core of restoration plans: nutrient cycling and carbon cycling, pollutant detoxification, soil structure arrangement, and biological control agent by prey/pest regulation. This paper further proposes guidelines for stakeholders that need to be addressed to successfully integrate soil organism traits into ecological engineering. Finally, we highlight main knowledge gaps and limitations currently impeding the use of soil invertebrate traits in ecological engineering, and identify avenues for future research. We especially bring out (i) that few studies still use soil invertebrates in restoration, so even fewer are based on traits, (ii) a lack of data about soil inver�tebrate species role in ecosystems, (iii) a lack of data about attributes from specific traits and groups in existing soil functional trait databases, (iv) the complex relationships between functions and traits and (v) that future studies are needed to demonstrate the benefits of such trait-based approaches compared to approaches relying on emblematic species.
... Farrell et al. (2020) suggested that research focused on the role that soil microbial communities play during ecological restoration is not generally routine. However, we found numerous examples of research focused on manipulating biotic soil conditions (e.g., inoculating with soil microbes) to promote restoration outcomes (Heneghan et al. 2008;Beyhaut et al. 2014;Grman et al. 2020;Vahter et al. 2020). Including restoration of soil microbial communities into ecosystem restoration can create conditions that ultimately increase successful establishment of a desirable plant community and the additional ecosystem services microbial communities can provide (Farrell et al. 2020). ...
Article
With global efforts to restore grassland ecosystems, researchers and land management practitioners are working to reconstruct habitat that will persist and withstand stresses associated with climate change. Part of these efforts involve movement of plant material potentially adapted to future climate conditions from native habitat or seed production locations to a new restoration site. Restoration practice often follows this plant-centered, top-down approach. However, we suggest that restoration of belowground interactions, namely between plants and arbuscular mycorrhizal fungi or rhizobia, is important for restoring resilient grasslands. In this synthesis we highlight these interactions and offer insight into how their restoration might be included in current grassland restoration practice. Ultimately, restoration of belowground interactions may contribute to grassland habitat that can withstand and respond to future climate uncertainties.
Article
Soil aggregation and organic carbon (OC) content are important indicators of soil quality that can be improved with plant residue amendments. The extent of the effects of plant residue amendments on soil aggregation and OC content across different plant residue and soil types is not fully understood. In this meta‐analysis, we evaluated the effects of plant residue amendments on soil aggregation and OC content for different plant residues (fresh, charred) and soil types varying in clay content, initial OC content, and pH. Our meta‐analysis included 50 published studies (total of 299 paired observations). We estimated the response ratios of mean weight diameter (MWD) and separate aggregate size classes, total soil OC (TSC), and aggregate‐associated OC. We also considered the effect of experimental factors (study duration, residue type, residue amount, initial soil OC, clay content, and pH). The benefit of plant residue amendment on soil aggregation was larger in soils with initially low OC content and neutral pH. Initial soil OC content and pH were more important than soil clay content for OC storage in soil aggregates. Both fresh and charred plant residue amendments were effective in forming aggregates, whereas charred residues were more effective in increasing TSC. We found only a weak positive relationship between the response ratio of TSC and MWD indicating that other factors besides soil aggregation contributed to the increase in soil C storage. While plant residue amendments can enhance soil aggregation and TSC, these effects are likely governed by the type of plant residue and soil properties such as the initial soil pH and OC content.
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Training the next generation of applied ecologists is critical for combatting ongoing ecosystem degradation and meeting the rising demand for professionals in the ecological restoration economy. Despite growing interest, relatively few undergraduate programs are explicitly focused on restoration ecology. To adequately prepare students for future careers in restoration, educators should incorporate lessons on the science and practice of restoration into curricula of broader ecology courses. Given the interdisciplinary nature of restoration ecology, projects grounded in restoration science can be used by instructors to explore a broad range of topics. Course‐based research aimed at solving local restoration problems is one powerful way to enhance students’ ecological literacy and professional development as well as promote diversity in the field. In this paper, I describe an initiative in which undergraduates in my ecology course conducted their own experiments evaluating the effects of soil amendments on the performance of native plant species that are targets for restoration on our campus nature preserve. Students worked in groups to independently design and execute experiments, analyze data, and communicate their results in formal reports and presentations. Student projects represent useful case studies that highlight the influence of soil conditions on restoration outcomes. Results of assessment surveys also illustrate the tremendous benefits of student‐led research on participants’ scientific skills, learning experiences, and appreciation for applied science. A greater emphasis on restoration and inquiry‐based learning in undergraduate ecology courses will ensure students pursuing careers in ecological restoration have the training necessary to meet the complex challenges of such endeavors. This article is protected by copyright. All rights reserved.
Article
Forest restoration is considered among the most affordable and effective practices to address ecosystem and biodiversity loss and mitigate the impacts of human‐induced global change. Soils are intrinsically complex systems that mediate and regulate multiple processes and functions vital for forest ecosystem restoration. Although monitoring soil attributes are critical for evaluating the success of forest restoration projects, research and development of soil function indicators are still limited. Here we have reviewed the most commonly reported soil indicators in forest restoration research and their recovery trajectory on a global scale. We also identified and discussed less frequently used indicators that have the potential for monitoring ecosystem recovery. We found that soil indicators have considerably increased in the literature. However, research is regionally concentrated, and a significant proportion of publications neither considered reference ecosystems (41%) nor provided basic information about soil types (<21%). The most reported indicator types were chemical (76%) (e.g., soil carbon, nitrogen, and pH). A significant proportion of the studies (46%) performed long‐term evaluations (>15 years) of indicators. The majority of the indicators tended to resemble the levels of the reference ecosystem in the long‐term, with a few exceptions (e.g., water content and bulk density). We identified several less used but more integrative indicators with great potential for monitoring forest ecosystem recovery (e.g., aggregate stability, oxidizable carbon, soil respiration, and enzyme activity). Our results emphasize the need to effectively develop standardized soil health indicators to monitor ecosystem recovery under different conditions and expand their use in underrepresented regions. This article is protected by copyright. All rights reserved.
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A number of excellent textbooks on general ecology are currently available but‚ to date‚ none have been dedicated to the study of soil ecology. This is important because the soil‚ as the ‘epidermis’ of our planet‚ is the major component of the terrestrial biosphere. In the present age‚ it is difficult to understand how one could be interested in general ecology without having some knowledge of the soil and further‚ to study the soil without taking into account its biological components and ecological setting. It is this deficiency that the two authors‚ Patrick Lavelle and Alister Spain‚ have wished to address in writing their text. A reading of this work‚ entitled ‘Soil Ecology’‚ shows it to be very complete and extremely innovative in its conceptual plan. In addition‚ it follows straightforwardly through a development which unfolds over four substantial chapters. Firstly‚ the authors consider the soil as a porous and finely divided medium of b- organomineral origin‚ whose physical structure and organisation foster the development of a multitude of specifically adapted organisms (microbial communities‚ roots of higher plants‚ macro-invertebrates).
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Small-plot field experiments were established in the first decade of October at the Plant Breeding Station of Sládkovičovo-Nový dvor with winter wheat (Triticum aestivum L.), variety Astella. There was investigated an effect of topdressing with nitrogen on the yield of winter wheat grain and its quality characteristics in the experiment. Nitrogenous fertilizers were applied at the growth phase of the 6th leaf (Zadoks = 29). Soil of the experimental stand was analysed for inorganic nitrogen content (Nan) down to the depth of 0.6 m of soil profile. Productive nitrogen fertilizing rate was computed to ensure Nan content in soil on the level of 120 and 140 kg N/ha, respectively. Three various forms of fertilizers were examined, urea solution, ammonium nitrate with dolomite, and DAM-390. Different weather conditions statistically highly, significantly influenced grain yield in respective experimental years. Topdressing with nitrogen caused a statistically highly significant increase of grain yield in all fertilized variants ranging from +0.35 to +0.82 t/ha according to respective treatments. Average grain yield in unfertilised control variant represented 7.23 t/ha. Nitrogen nutrition showed a positive effect on the main macroelements offtake (N, P, K, Ca, Mg, S) by winter wheat grain in all fertilized variants. Nitrogen fertilizing to the level of 140 kg/ha N in soil positively influenced formation of wet gluten and crude protein with highest increment in variant 5 (solution of urea) representing +12.8 and +10.7%, respectively in comparison to control unfertilised variant as well as to variant 2 (solution of urea and fertilizing on the level of 120 kg N/ha) where increments represented +8.8 and 9.7%, respectively. Thousand-kernel weight, volume weight and portion of the first class grain were not markedly influenced by nitrogen fertilizing.
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The interesting approach to ecological restoration described in this book will appeal to anyone interested in improving the ecological conditions, biological diversity, or productivity of damaged wildlands. Using sound ecological principles, the author describes how these ecosystems are stabilised and directed toward realistic management objectives using natural recovery processes rather than expensive subsidies. An initial emphasis on repairing water and nutrient cycles, and increasing energy capture, will initiate and direct positive feedback repair systems that drive continuing autogenic recovery. This strategy is most appropriate where landuse goals call for low-input, sustainable vegetation managed for biological diversity, livestock production, timber production, wildlife habitat, watershed management, or ecosystem services. Providing a comprehensive strategy for the ecological restoration of any wildland ecosystem, this is an invaluable resource for professionals working in the fields of ecological restoration, conservation biology and rangeland management.