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An evidence-based assessment of prescribed grazing practices

Authors:
CHAPTER
1
An Evidence-Based Assessment of
Prescribed Grazing Practices
David D. Briske,1 Justin D. Derner,2 Daniel G. Milchunas,3 and Ken W. Tate4
Authors are 1Professor, Ecosystem Science & Management, 2138 TAMU, Texas A&M
University, College Station, TX 77843-2138; 2Rangeland Scientist and Leader, USDA-ARS
High Plains Grasslands Research Station, Cheyenne, WY 82009; 3Research Scientist,
Forest, Rangeland, and Watershed Stewardship Department, Colorado State University,
Fort Collins, CO 80523-1472; and 4Rangeland Watershed Specialist,
Department of Plant Sciences, 2233 PES, Mail Stop 1,
University of California–Davis, Davis, CA 95616-7323.
Correspondence: Email: dbriske@tamu.edu
Reference to any commercial product or service is made with the understanding
that no discrimination is intended and no endorsement by USDA is implied
21
Experimental grazing
research has produced
consistent relationships
between stocking rate
and plant production,
animal production, and
species composition
of herbaceous plant
communities.
22 Conservation Ben efits of Rangeland Prac tices
1
An Evidence-Based Assessment of
Prescribed Grazing Practices
David D. Briske, Justin D. Derner, Daniel G. Milchunas, and Ken W. Tate
INTRODUCTION
Prescribed grazing is inclusive of many
interrelated management and conservation
activities implemented for purposes of
managing grazed ecosystems. It is supported
by a loosely organized information base that
contains management experience, agency policy
and procedures, and scientific information that
has been developed throughout the history of
the rangeland profession. e components of
prescribed grazing are implemented in various
combinations to achieve multiple management
goals and outcomes under a wide variety of
ecological conditions in diverse rangeland
ecosystems. A fundamental premise of effective
grazing management is that it supports
ecosystem sustainability and restoration of
degraded ecosystems. Management actions
have traditionally emphasized livestock species
and number and their temporal and spatial
distribution on the landscape (Stoddart et
al. 1975; Heitschmidt and Taylor 1991).
e management of grazed ecosystems
involves multiple human dimensions as well
as complex ecological processes, making it
difficult and impractical to attempt to separate
grazing management from overall enterprise
management (Stuth 1991). erefore,
management practices are commonly designed
and applied within the context of specific
landowner operations, management needs,
and natural resource conservation goals.
Consequently, prescribed grazing involves a
continuum of management activities ranging
from extensive management to those that are
much more labor and infrastructure intensive.
Context for the initial development of
prescribed grazing in the United States
originated with management recommendations
to promote sustainable use and recovery of
rangelands damaged by excessive livestock
grazing early in the 20th century (Smith 1896;
Wooten 1916; Sampson 1923, 1951; Hart
and Norton 1988). Excessively high stocking
rates (animal units area−1 time−1) common to
the late 19th and early 20th centuries were
unsustainable, and the negative consequences
of those extreme stocking rates adversely
affected numerous ecosystems throughout the
Great Plains and West. Early rangeland research
advocated use of reduced stocking rates and
simple grazing systems to impose early season
deferment and season-long rest to halt and
potentially reverse ecological damage created
by severe overgrazing. Increased efficiency of
livestock production became an important
objective during the 1980s and was associated
with the introduction of short-duration grazing
to the United States (Savory and Parsons 1980;
Savory 1983). ese management systems
were designed to improve the efficiency of
forage harvest, enhance forage quality, and
promote livestock production. More recently,
prescribed grazing has emphasized broader
conservation goals and ecosystem services.
Biodiversity conservation, water quality and
quantity, woodland encroachment, invasive
species, and carbon sequestration are but a
few of the current high-profile conservation
issues considered within grazed ecosystems.
However, this emphasis is rather recent, and
the amount of experimental information to
date is insufficient to draw valid generalizations
regarding these conservation issues.
Even though the primary objective of this body
of information is to promote effective grazing
management, this is in itself not a sufficient
foundation on which to evaluate this important
land use. It is essential that the underlying
components and processes of effective grazing
management be recognized, understood, and
documented to ensure that this information
base is carefully scrutinized, accurate, and
Prescribed grazing is the
management of vegetation
harvest by grazing or browsing
animals to achieve desired ob-
jectives. (Photo: Derek Bailey)
CHAP TER 1: An Assessment of Grazing Practices 23
effectively promoted. e primary objective of
Rangeland CEAP is to organize and evaluate
the current body of scientific information
supporting the anticipated benefits of
rangeland conservation practices implemented
by the US Department of Agriculture, Natural
Resources Conservation Service (USDA-
NRCS). is assessment is intended to provide
the foundation for the next generation of
planning and assessment procedures that are
to emphasize environmental quality and the
assessment of multiple ecosystem services in
addition to the traditional outcomes of farm
and ranch productivity (Maresch et al. 2008).
is chapter evaluates the ecological
effectiveness of the major purposes and
purported benefits for prescribed grazing
as described in the USDA-NRCS National
Conservation Practice Guidelines. is
standard defines prescribed grazing as managing
the harvest of vegetation with grazing and/
or browsing animals that is often applied as
one component of a broader conservation
management system to achieve one or more of
the following purposes:
Improve or maintain desired species
composition and vigor of plant
communities.
Improve or maintain quantity and quality
of forage for grazing and browsing animals’
health and productivity.
Improve or maintain surface and/or
subsurface water quality and quantity.
Improve or maintain riparian and
watershed function.
Reduce accelerated soil erosion and
maintain or improve soil condition.
Improve or maintain the quantity and
quality of food and/or cover available for
wildlife.
Manage fine fuel loads to achieve desired
conditions.
is definition is very similar to that provided
in the Society for Range Management
(SRM) Glossary of Terms (1998)—“the
manipulation of animal grazing in pursuit of
a defined objective”—and to that of targeted
grazing—“the application of a specific kind of
livestock at a determined season, duration and
intensity to accomplish a defined objective”
(Launchbaugh and Walker 2006). Targeted
grazing emphasizes objectives associated with
landscape dynamics in addition to livestock
production. It is important to note that
prescribed grazing, as defined above, is a much
broader concept than grazing system, which
describes a specialized application of grazing
management based on recurring periods of
grazing, rest, and deferment for two or more
pastures (Heitschmidt and Taylor 1991). e
NRCS National Range and Pasture Handbook
describes prescribed grazing schedules to
recommend appropriate periods of grazing,
rest, and deferment (USDA-NRCS 2003).
e experimental data addressing these
purposes were extracted primarily from
the peer-reviewed literature, summarized
and incorporated into tabular forms to
provide an evidence-based assessment of
how well prescribed grazing achieves these
stated purposes. In some instances, direct
comparisons could be made between intended
conservation outcomes and the experimental
evidence, but in many others, inferences had to
be drawn from the most relevant experimental
data to assess the effectiveness of conservation
outcomes. Constraints of experimental research
have influenced both the type of information
available and the investigations selected for
inclusion in this assessment. For example,
spatial heterogeneity may produce conditions
where most pastures under consideration
possess generally similar topoedaphic
characteristics, but in other cases one or
more pastures may possess distinctly different
characteristics. Only the first condition
characterized by relatively homogeneous site
conditions meets the traditional experimental
requirements of replication and comparison
with experimental controls, while decisions
regarding heterogeneous site conditions can
be assessed only on a case-by-case basis. Given
that the goal of this chapter was to evaluate the
preponderance of evidence supporting major
grazing management practices, investigations
that were unreplicated or that did not have
experimental controls, that applied unequal
treatments, or that contained minimal data
were not included. ese requirements were
relaxed to some extent for the evaluation of
wildlife because investigations addressing
responses of specific wildlife species or groups
to unique management practices were often
limited. Similarly, minor wildlife groups were
24 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
not addressed because of limited research
evidence and space limitations.
is chapter is organized into six major
headings: introduction, evaluation of prescribed
grazing purposes, associated considerations,
recommendations, knowledge gaps, and
conclusions. e evaluation of prescribed
grazing purposes is the largest section, and it
contains seven secondary headings addressing
each of the conservation purposes previously
described. Several of these purposes are
further subdivided into tertiary headings of
stocking rate and grazing system because these
two research themes contain a large portion
of the experimental information associated
with grazing management. In addition to
summarizing the experimental evidence
relevant to prescribed grazing management,
this chapter emphasizes the strengths and
weaknesses of the experimental data, provides
recommendations for improvement of this
conservation practice, and identifies major
knowledge gaps in the experimental literature.
e overarching goal is to describe the current
status of grazing management information
to provide a foundation for development
of the next generation of prescribed grazing
practices. is chapter was commissioned by
and is directed toward the NRCS, but it also
contains important implications to the broader
rangeland profession.
EVALUATION OF PRESCRIBED GRAZING
PURPOSES
Improve or Maintain Desired Species
Composition and Vigor of Plant
Communities
Stocking Rate. Stocking rate has long
been recognized as a fundamental variable
determining the sustainability and profitability
of grazed rangeland ecosystems (Smith 1896;
Wooton 1916; Sampson 1923). e objective
of stocking rate is to balance the forage
demand of grazing animals with that of forage
production over an annual forage production
cycle. e difficulty encountered when
setting and maintaining appropriate stocking
rate on rangelands is the high variability of
forage production associated with annual
and interannual precipitation variation. It
is often recommended that stocking rates
should be conservatively applied to minimize
the detrimental consequences of overstocking
during drought on the economic and ecological
sustainability of grazed ecosystems.
e importance of stocking rate to the
management of grazed ecosystems has attracted
considerable research attention over the past
several decades. is research has produced
consistent relationships between stocking rate
and plant production, animal production,
and species composition of herbaceous plant
communities. Plant production decreases with
increasing stocking rate, as does individual
animal production (Bement 1969; Manley et
al. 1997; Derner and Hart 2007; Derner et
al. 2008). In contrast, animal production per
land area increases with increasing stocking rate
within the limits of ecosystem sustainability.
ese ecosystem responses to stocking rate have
clear production and conservation implications.
e response of several ecosystem variables
indicates that stocking rate is at least indirectly
correlated with ecosystem function and
sustainability. High grazing intensities generally
appear to minimize ecosystem function,
which often has negative consequences for
conservation goals and the provisioning of
ecosystem services. Plant production is the
most consistent response with 69% (25 of
36) of the investigations reporting greater
plant production at lower compared to higher
stocking rates (Fig. 1). Twenty-eight percent
(10 of 36) showed no difference in plant
production with stocking rate. Only four of
FIGURE 1. Number of
investigations reporting
significant effects of
stocking rate on plant
production and cover and
livestock production per
head and per unit land
area.
CHAP TER 1: An Assessment of Grazing Practices 25
FIGURE 2. Number of
investigations reporting
significant effects of grazing
system, categorized as
short-duration and non–
short-duration systems, on
favorable changes in spe-
cies composition of plant
communities.
these investigations considered plant species
diversity or richness in relation to stocking
rate, but the trend is for increasing diversity
and richness with increasing stocking rate,
which is a consistently observed community
response to grazing (Milchunas et al. 1988).
is response is interpreted as a function of the
suppression of grass dominants at high stocking
rates, which increases resource availability for
subordinate species within the community
(Collins 1987; Anderson and Briske 1995;
Knapp et al. 1999). However, cases do exist
where intensively grazed ecosystems are
required to provide specific habitat for flora and
fauna (Milchunas and Lauenroth 2008; Derner
et al. 2009).
Stocking rate has tremendous potential to
modify the species composition of herbaceous
vegetation. Significant change in species
composition was documented to occur in
71% (17 of 24) of the stocking rate studies
evaluated. Plant cover showed a much less
consistent response than did either production
or species composition with 67% (14 of 21) of
the investigations showing no difference with
stocking rate compared to 24% (5 of 21) that
did show a positive response. Compositional
changes largely follow the classical increaser–
decreaser patterns outlined by Dyksterhuis
(1949) and more recently verified in a global
vegetation analysis (Diaz et al. 2007) in which
tallgrasses are replaced by midgrasses and
midgrasses by shortgrasses. Eight of these
studies recorded vegetation responses for ≥ 20
yr and 14 studies for ≥ 10 yr, but significant
vegetation change was also recorded in shorter
time periods. ese vegetation responses also
document the occurrence of equilibrium
dynamics in which grazing modifies the species
composition of plant communities in addition
to weather conditions (Fuhlendorf et al. 2001;
Briske et al. 2003). e potential for recovery
of species composition in response to reduced
stocking rates also documents the high degree
of resilience associated with many rangeland
ecosystems (Milchunas et al. 1988).
Grazing Systems. Although changes in plant
species composition are often more qualitatively
assessed than the plant and animal production
values presented previously, the majority of
investigations have not shown a clear benefit of
rotational grazing over continuous grazing in
promoting secondary succession or improving
community composition on rangelands
(Holechek et al. 1999, 2006). In our survey of
25 grazing experiments, 86% (18) indicated
no difference in species composition for
continuous compared to rotational grazing
at comparable stocking rates. Only 3 of 25
experiments recorded improvements in species
composition, and these were all deferred-
rotation rather than short-duration systems
(Fig. 2).
Experimental data referencing biotic diversity
in grazing systems are limited, especially at
regional scales, so definitive conclusions are
unattainable at this point. However, the limited
experiments addressing plant species diversity
do not show that grazing systems enhance
plant species diversity (Holechek et al. 2006).
In tallgrass prairie, grazing system did not
influence plant richness or diversity, but both
variables increased with increasing stocking rate
(Hickman et al. 2004). Increasing stocking rate
reduced the abundance of the several dominant
C4 grass species and increased the expression
of several subordinate species. Plant diversity
responses to grazing are dependent on the
direct response of various species to grazing
and the indirect response of other species to
grazing-induced release from competition
(Milchunas et al. 1988; Anderson and Briske
1995).
Grazing Season and Deferment. Research
addressing the season and length of grazing
deferment is surprisingly limited given its
26 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
importance to grazing management. It is
difficult to draw inferences from the few
investigations specifically addressing season
of grazing, especially given the variability
in production and defoliation responses
associated with precipitation variation within
and among years (Zhang and Romo 1994).
ese authors were unable to make conclusive
recommendations regarding production
responses of northern mixed prairie to the
seasonality and frequency of defoliation
because of weather variation between years.
Plant species with unique growth periods and
production potentials contribute additional
complexity to this assessment (Volesky et
al. 2004). is underscores the difficulty
of making generalizations regarding the
appropriate season of grazing and deferment.
Inferences regarding the appropriate length
of grazing deferment can be derived from
grazing systems research previously evaluated.
Short deferment periods do not yield benefits
in those variables measured, that is, plant
and animal production, species composition,
and soil characteristics. It can be inferred
from this extensive data set that successive
short deferments of 30–45 d are ineffective
in offsetting short, intensive grazing periods
of 2–11 d. Conclusions regarding length of
deferment have been drawn from comparisons
of short-duration and high-intensity, low-
frequency systems using 42- and 84-d
deferment periods, respectively (Taylor et al.
1993). ese authors concluded that 80–90-d
deferment periods were required to maintain
desired species composition on semiarid
rangelands. is interpretation has been
corroborated by research conducted in mesic
tallgrass ecosystems (Reece et al. 1996). Specific
ecological mechanisms limiting increased plant
production and improved species composition
in response to short-term periodic deferment
in rotational systems are not entirely clear,
but they are very likely influenced by the
time required for plant recovery, especially on
semiarid rangelands, and the coincidence of
favorable growth conditions with periods of
grazing deferment (Briske et al. 2008).
Grazing deferment relative to the onset and
recovery from drought has also received
minimal attention given its significance
to grazing management. However, several
conclusions can be drawn from a valuable, but
limited data set. First, grazing deferment during
drought has minimal potential to enhance
plant production or species composition, even
though it is often necessary to destock because
of insufficient forage availability (Eneboe et al.
2002; Heitschmidt et al. 2005; Gillen and Sims
2006). However, deferment is important to
maintain sufficient plant cover and density to
protect soil quality and promote plant recovery
once rainfall resumes (Wood and Blackburn
1981a&b; urow 1991; Dalgleish and
Hartnett 2006). Second, grazing deferment is
not necessarily required for rapid and effective
vegetation recovery from moderate drought
conditions (Eneboe et al. 2002; Heitschmidt
et al. 2005). Investigations demonstrating
the ability of rainfall to override the effects
of stocking rate on forage production and
species composition indirectly support this
interpretation (Milchunas et al. 1994; Biondini
et al. 1998; Gillen et al. 2000; Vermeire et al.
2008). ird, in the cases involving severe,
prolonged drought, 2 yr or more may be
required for recovery of species composition
and productivity. Severe, multiyear drought
can induce mortality of plants and tillers to
retard plant growth following the resumption
of rainfall (Briske and Hendrickson 1998;
Dalgleish and Hartnett 2006; Yahdjian et al.
2006). Consequently, several growing seasons
may to be required for tiller and plant densities
to recover to predrought values. Plant mortality
was found to be approximately twice as great
in heavily compared to more lightly grazed
Great Plains rangelands following the multiyear
drought of the 1950s (Albertson et al. 1957).
Greater plant mortality is likely a consequence
of the suppressed root growth and function
that is known to occur with severe grazing of
individual plants (Crider 1955).
Improve or Maintain Quantity and
Quality of Forage for Grazing and
Browsing Animals’ Health and
Productivity
Stocking Rate. Experimental data confirm the
occurrence of a consistent trade-off between
animal production per head and per land area
with increasing stocking rate. Eighty percent
(16 of 20) of investigations reported greater
animal production per head at low compared
to high stocking rates, while 82% (14 of 17)
Research
addressing the
season and
length of grazing
deferment is
surprisingly
limited given
its importance
to grazing
management.
CHAP TER 1: An Assessment of Grazing Practices 27
Individual plant
production is
most greatly
suppressed by
defoliation during
the middle of the
growing season,
which coincides
with culm elon-
gation and the
early boot stage
of inflorescence
development…
showed greater animal production per land area
at high compared to low stocking rates (Fig. 1).
is trade-off in animal performance is readily
explained by the greater availability of plant
biomass per individual animal with decreasing
stocking rate and greater forage harvest per
unit land area with increasing stocking rate.
Experimental evidence indicates that both
forage quantity and quality decrease with
increasing high compared to low stocking rates.
Forage quality is most likely to decrease during
grazing periods insufficient for appreciable
regrowth, where animals initially select the
highest-quality forage.
Pattern of tiller defoliation research shows that
80% or more of all tillers can be defoliated
in a single grazing period with high stocking
rates or grazing intensities (8 of 11 studies).
is indicates that high harvest efficiencies
and uniform grazing patterns can be obtained
with large livestock numbers in certain cases.
However, these data also indicate that multiple
defoliations occur early within a grazing cycle
(four of six studies). It has been suggested that
repeat defoliations begin to occur at about
the time that 60% of the tillers are initially
defoliated and that very high grazing pressures
and paddock numbers would be required to
minimize the occurrence of multiple grazing
events within individual grazing periods
(Jensen et al. 1990a). ese data challenge
the widely held assumption that rotational
grazing restricts grazing to a single event per
plant during short (5–10-d) grazing periods
while simultaneously promoting high plant
utilization. is may indicate why minimal
differences in plant defoliation patterns have
been found between rotational and continuous
grazing (Hart et al. 1993b). ese detailed
investigations were conducted on very
small pasture sizes (0.2–24 ha), so caution
is warranted when scaling these responses
to larger areas. In addition, frequency of
defoliation may be more detrimental to plants
when defoliation events are separated by
periods of regrowth, as indicated below.
Frequency of tiller defoliation consistently
increases with increasing stocking rate (9 of
10 studies). Defoliation intensity of individual
tillers also increases with increasing stocking
rate, but not as rapidly as defoliation frequency
(four of five studies).
Forage quality decreased with increasing
stocking rate within an individual grazing
period in all four studies evaluated and with
increasing time of grazing for all three studies
that carefully evaluated this relationship. is
clearly indicates that animals compete for
quality forage, and this process establishes the
basis for the negative response of individual
animal performance with increasing stocking
rate.
Season of plant defoliation has unique and
consistent effects on plant production.
Individual plant production is most greatly
suppressed by defoliation during the middle
of the growing season, which coincides with
culm elongation and the early boot stage
of inflorescence development, especially in
bunchgrasses (Olson and Richards 1988). is
was documented in six of nine investigations
and in all three studies specifically evaluating
growth stage responses to defoliation. Early
season defoliation had the least detrimental
effect on subsequent plant production, and
late season defoliation had an intermediate
effect. However, plant production is
increasingly suppressed with increasing
frequency and intensity of defoliation at
any stage of growth (five of six studies),
confirming the interpretation that multiple
defoliations within a growing season are
detrimental to plant growth and function
(Reece et al. 1996; Volesky et al. 2004).
ese patterns of grass production responses
to defoliation at various phenological stages
substantiate the criticism that has been
directed toward early season deferment (i.e.,
range readiness) as a valid conservation
practice.
e occurrence of patch grazing has been well
documented in several investigations, and it
appears to directly relate to the nutritional
intake of animals when other constraints on
animal distribution are absent (e.g., distance
to water and topography). Previously grazed
patches support forage of higher nutritional
quality, including crude protein, fiber, and
digestibility, even though forage quantity
may be less than on previously ungrazed
patches (Cid and Brizuela 1998; Ganskopp
and Bohnert 2006). e primary mechanism
contributing to patch grazing is animal
aversion to consumption of senescent plant
28 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
material, especially current and previous year’s
culms or stems (Ganskopp et al. 1992, 1993).
Consequently, patch grazing may provide
a nutritional benefit to animals at low and
moderate stocking rates (Cid and Brizuela
1998).
Patch structure is relatively consistent within
season and among years, but it is less stable at
higher than at lower stocking rates (Willms et
al. 1988; Cid and Brizuela 1998). At higher
stocking rates, animals begin to selectively
graze previously ungrazed patches to maintain
sufficient forage intake, and they forage greater
distances to achieve this goal (Ring et al. 1985;
Ganskopp and Bohnert 2006). Patch grazing
can be minimized by the removal of senescent
biomass, especially previous year’s biomass
with fire, mowing, or periodic heavy stocking
(Ganskopp and Bohnert 2006). However,
the implications of patch grazing have been
shifting from that of an inefficient use of
forage by livestock to a desirable component of
vegetation heterogeneity capable of promoting
biodiversity in the Great Plains (Fuhlendorf
and Engle 2001, 2004). is is an especially
relevant consideration, both within and among
pastures, in light of the CEAP initiative, which
emphasizes management for environmental
quality and multiple ecosystem services as well
as production goals.
Grazing Systems. Grazing systems represent
a specialization of grazing management that
defines the periods of grazing and nongrazing
(Heitschmidt and Taylor 1991; SRM 1998),
and they have been given tremendous
emphasis by both managers and researchers.
It is important to recognize that constraints
of experimental research, including the need
for relatively homogeneous site conditions
necessary for replication and comparison with
experimental controls, has emphasized the
potential for various periods of grazing and
rest to alter the ecological processes controlling
plant and animal production. ey are unable
to—and therefore do not—address livestock
distribution in heterogeneous landscapes
or livestock movement in response to site
readiness along elevation gradients. However,
these latter considerations are also important
and have been addressed with experimental
data collected with more appropriate
experimental approaches.
e major experimental investigations of
grazing systems have been categorized by
geographic location, ecosystem type, relative
stocking rate, and number and size of pastures
for each of the respective investigations (Briske
et al. 2008). Variables were indicated to differ
between continuous and rotational grazing only
when they were reported as being statistically
significant by the authors. For each experiment,
plant and/or animal production (the most
quantitative data collected) was characterized as
1) greater for continuous grazing (CG > RG),
2) greater for rotational grazing (RG > CG),
or 3) equal if differences did not exist between
continuous and rotational grazing (ND). ese
comparative responses were summarized and
presented as separate histograms for those
investigations that used similar stocking rates
between grazing treatments (Fig. 3A), those
that used greater stocking rates for rotational
than for continuous grazing (Fig. 3B), and for
all stocking rates combined (Fig. 3C). ese
experimental comparisons of rotational systems
included five studies conducted for 9 yr or
more, and four had pasture sizes greater than
300 ha, but only two had greater than eight
pastures per grazing system.
Eighty-nine percent of the experiments (17
of 19; Appendix I) reported no differences
for plant production/standing crop between
rotational and continuous grazing with similar
stocking rates (Fig. 3A). When stocking
rate was less for continuous than rotational
grazing, 75% of the experiments (three of
four) reported either no differences or greater
plant production for continuous grazing (Fig.
3B). Across all stocking rates, 83% of the
experiments (19 of 23; Appendix I) reported
no differences for plant production between
rotational and continuous grazing, 13% (three)
reported greater plant production for rotational
compared to continuous grazing, and 4% (one)
reported greater production for continuous
grazing (Fig. 3C; Briske et al. 2008).
Fifty-seven percent of the experiments (16
of 28; Appendix I) reported no differences
for animal production per head between
rotational and continuous grazing with
similar stocking rates, and 36% (10) reported
greater per head production for continuous
grazing (Fig. 3A). When stocking rate was
less for continuous than rotational grazing,
Grazing is a major land use
on 188 million hectares of
non-federal lands in the Great
Plains and western U.S. (Photo:
Sonja Smith)
CHAP TER 1: An Assessment of Grazing Practices 29
FIGURE 3. Number of published grazing experiments that reported significantly
higher, equal, or lower plant and animal production responses for continuous com-
pared to rotational grazing at (A) similar stocking rates, (B) higher stocking rates for
rotational grazing, and (C) across stocking rates for all experiments. Animal produc-
tion is presented as both a per head and a per land area response (from Briske et
al. 2008).
90% of the experiments (9 of 10) reported
either similar or greater per head animal
production for continuous grazing (Fig. 3B).
Across all stocking rates, 50% (19 of 38;
Appendix I) of the experiments reported no
differences for animal production per head
between rotational and continuous grazing,
8% (three) reported greater production for
rotational grazing, and 42% (16) reported
greater production for continuous grazing
(Fig. 3C). Fifty-seven percent of the
experiments (16 of 28; Appendix I) reported
no differences for animal production per unit
land area between rotational and continuous
grazing with similar stocking rates, and 36%
(10) reported advantages for continuous
grazing (Fig. 3A). When stocking rate
was lower for continuous than rotational
grazing, 75% (three of four; Appendix I)
of the experiments reported greater animal
production per area for rotational grazing
(Fig. 3B). Across all stocking rates, 50%
(16 of 32; Appendix I) of the experiments
reported no differences for animal
production per land area between rotational
and continuous grazing, 16% (five) reported
greater production for rotational grazing,
and 34% (11) reported greater production
for continuous grazing (Fig. 3C; Briske et
al. 2008). A recent ranch-scale investigation
comparing four grazing systems over a
7-yr period that was not included in this
numerical assessment also reported minimal
differences in livestock production among
grazing systems (Pinchak et al. 2010).
No evidence was found indicating that grazing
systems override livestock preference for site
selectivity. Comparisons of continuous season-
long and rotational grazing on five range
sites in northern mixed-grass prairie found
no differences among grass utilization over a
2-yr period (Kirby et al. 1986). is occurred
in spite of the fact that the rotational system
had both a higher stocking rate and a higher
stock density than did the continuous system.
Heitschmidt et al. (1989) corroborated these
conclusions in mixed-grass prairie in north-
central Texas. Paddocks of 30 and 10 ha were
used to simulate rotational grazing systems
with 14 and 42 paddocks. Livestock selectivity
was not modified by either rotational grazing
system compared to continuous grazing. ese
authors concluded that forage availability,
rather than stocking density or grazing system,
was the primary mechanism that modifies
animal selectivity. However, none of these
investigations specifically addressed the presence
of riparian systems in which livestock frequently
congregate (George et al., this volume).
Only four studies were found that directly
compared forage quality in rotational and
continuous grazing. Forage quality was
30 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
comparable among systems in two of the
investigations (Jung et al. 1985; Heitschmidt
et al. 1987b), and one each favored continuous
(Pfister et al. 1984) and rotational grazing
(Heitschmidt et al. 1987a). Forage quality
was greater for a seven-pasture short-duration
system compared to a seven-pasture high-
intensity, low-frequency system, but similar to
that of a Merrill four-pasture, three-herd system
on the Edwards Plateau of Texas (Taylor et al.
1980). Tiller defoliation patterns in continuous
and rotational grazing have received only
minimal attention, but frequency and intensity
of tiller defoliation was greater for rotational
grazing in only one (Senock et al. 1993) of
four investigations (Hart et al. 1993a; Derner
et al. 1994; Volesky 1994). Collectively, the
small number of investigations reporting mixed
results makes conclusions regarding grazing
systems effects on forage quality and defoliation
patterns equivocal compared to conclusions
addressing plant and animal production, and
species composition.
ree categories of evidence exist to explain
why intensive rotational grazing systems have
not shown greater quantity and quality of
forage and animal production in experimental
research. First, short, periodic deferments
based on established schedules do not always
coincide with favorable growth conditions
in rangeland environments (e.g., Taylor et
al. 1993; Holechek et al. 2001; Gillen and
Sims 2006). e amount and variability of
rainfall and the associated predictability,
duration, and amount of plant growth appear
to override the potential benefit derived
from the redistribution of grazing pressure
in space and time in rotational grazing
systems (O’Reagain and Turner 1992; Ash
and Stafford Smith 1996; Holechek et al.
2001; Ward et al. 2004). Plant growth and
improvement in species composition will be
promoted primarily when deferment coincides
with environmental conditions favorable for
plant growth (Heitschmidt et al. 2005; Gillen
and Sims 2006).
Improper grazing can
detrimentally affect soil surface
characteristics to accelerate
runoff and erosion. (Photo:
Ken Tate)
CHAP TER 1: An Assessment of Grazing Practices 31
These results
refute prior
claims that
animal trampling
associated with
high stocking
rates or grazing
pressures in
rotational grazing
systems enhance
soil properties
and promote
hydrological
function
Second, rotational grazing may not control the
frequency and intensity of plant defoliation
as effectively as often assumed (Gammon and
Roberts 1978a, 1978b, 1978c; Hart et al.
1993a). Investigations of tiller grazing patterns
indicate that it is difficult to achieve a high
percentage of tiller defoliation (> 80%) before
multiple defoliations begin to occur within
a single grazing period (Jensen et al. 1990a;
O’Reagain and Grau 1995). ese data indicate
that grazing management strategies only
marginally modify animal selectivity within the
range of conditions that have been evaluated.
ird, forage quality is not consistently or
substantially increased in intensive systems
compared to continuous grazing (Denny et
al. 1977; Walker et al. 1989; Holechek et al.
2000). e absence of experimental evidence
supporting these three major underlying
assumptions associated with rotational systems
is consistent with the production responses
generated from experimental comparisons of
rotational and continuous grazing. However,
conclusions addressing tiller defoliation patterns
are derived from a small number of experiments
conducted in very small pastures (0.2–24
ha) that may not be entirely representative of
grazing patterns at larger scales.
ese experimental results collectively indicate
that rotational grazing does not promote
primary or secondary production compared
to continuous grazing within rangeland
ecosystems. ese interpretations are consistent
with those of previous reviews over the past 50
yr (Heady 1961; Van Poollen and Lacey 1979;
Holechek et al. 2001), and they clearly support
the long-standing conclusion that stocking rate
and weather variation account for the majority
of variability associated with plant and animal
production on rangelands (Van Poollen and
Lacey 1979; Heitschmidt and Taylor 1991;
Gillen et al. 1998; Holechek et al. 2001;
Derner and Hart 2007).
Improve or Maintain Surface and/or
Subsurface Water Quality and Quantity
Stocking Rate. e response of soil
hydrological characteristics to grazing largely
parallel those of other ecological variables
because stocking rate is the most important
driver regardless of grazing system (Wood and
Blackburn 1981a&b; urow 1991). is
occurs because the removal of large amounts of
plant cover and biomass by intensive grazing
reduces the potential to dissipate the energy of
raindrop impact and overland flow. e erosive
energy of water and the long-term reduction of
organic matter additions to soil detrimentally
affect numerous soil properties, including
the increase of bulk density, disruption of
biotic crusts, reduced aggregate stability, and
organic matter content, which collectively
reduce infiltration rate and increase sediment
yield and runoff. Animal trampling is
another source of mechanical energy that
breaks soil aggregates and is therefore
negatively correlated with maintenance of
soil structure necessary for high infiltration
rates (Warren et al. 1986b; urow 1991;
Holechek et al. 2000). ese results refute
prior claims that animal trampling associated
with high stocking rates or grazing pressures
in rotational grazing systems enhance soil
properties and promote hydrological function
(Savory and Parsons 1980; Savory 1988).
ese hydrological responses to grazing
are strongly contingent on community
composition, with communities that
provide greater cover and obstruction to
overland flow, such as midgrass-dominated
communities having greater hydrological
function, including infiltration rate, than
shortgrass-dominated communities (Wood
and Blackburn 1981b; urow 1991).
Grazing System. Short-duration rotational
grazing systems decreased soil hydrologic
function at heavy to very heavy stocking rates,
compared to continuous and deferred-rotation
grazing systems at moderate to light stocking
rates. e negative changes in vegetation
and soil properties controlling infiltration,
runoff, and soil loss due to heavy stocking
rates generally cannot be overcome by grazing
system. ese collective results strongly refute
claims that animal trampling associated
with high stocking rates or intensities under
intensive rotational grazing systems enhance
hydrological function (Savory and Parsons
1980; Savory 1988).
ere is evidence that soil hydrological
functions degraded by heavy stocking rates can
recover with prolonged rest (i.e., ≥ 1 yr). us,
rotational grazing may maintain higher soil
hydrologic function than continuous grazing
32 Conservation Ben efits of Rangeland Prac tices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
at heavy to very heavy stocking rates if the
deferment period is sufficient (i.e., ≥ 1 yr).
Similarly, moderately stocked continuous or
rotational grazing may maintain a consistently
higher level of hydrologic function compared to
periodic heavy stocking followed by prolonged
deferment for hydrologic recovery.
A few studies have directly examined grazing
systems (deferred rotation, rest rotation, and
rotational deferment) in comparison with
continuous grazing. At moderate stocking
rates, at which most extensive rotational
systems were studied, rotational grazing
systems lead to similar or improved soil
hydrologic function compared to moderate
continuous grazing (Ratliff et al. 1972;
McGinty et al. 1979; Wood and Blackburn
1981b, 1984). As evidenced by Wood and
Blackburn (1981) and urow et al. (1986),
these hydrological responses to grazing
system appear to be strongly contingent
on plant community composition, with
midgrass-dominated communities having
greater hydrological function than shortgrass-
dominated communities. Gifford and
Hawkins (1976) emphasize the importance
that range condition or plant community
composition has on the hydrological function
of a site through time in response to grazing
system.
Improve or Maintain Riparian and
Watershed Function
ere is clear consensus that livestock grazing
can degrade riparian plant communities,
hydrologic function, and associated ecosystem
services. Considerable management attention
has been directed toward prescribed grazing
practices with the intent to restore, enhance,
or maintain rangeland riparian areas. As
with upland habitats, it is clear that grazing
intensity is a major factor determining riparian
response to grazing management. Increased
grazing intensity is generally associated
with detrimental effects on riparian plant
community composition and productivity
as well as physical degradation of riparian
soils and stream channels. ese primary
effects can lead to secondary negative effects
on stream hydrologic functions, which can
cascade to loss of services, such as fish habitat,
flood attenuation, and provisioning of clean
water. Management of grazing intensity is a
viable conservation practice for riparian areas.
Season of grazing also determines livestock
grazing effects on riparian plant communities,
particularly woody plants, and can be
managed to conserve riparian habitats and
their associated services. Livestock distribution
practices such as water developments,
supplement placement, and herding are
effective means of managing the intensity and
season of livestock grazing in riparian areas.
Livestock exclusion is an effective practice
to stimulate immediate recovery for riparian
plant communities degraded by heavy grazing.
While the individual effects of some prescribed
grazing components (e.g., timing, intensity, and
rest) on riparian habitats have been examined,
few studies have rigorously examined the
effects of different grazing systems on
riparian habitats. e effectiveness of grazing
management practices on the conservation
of riparian habitats is covered in depth in the
chapter on riparian herbaceous cover (George
et al., this volume).
Reduce Accelerated Soil Erosion and
Maintain or Improve Soil Condition
Soil vegetative cover is widely recognized as
a critical factor in maintaining soil surface
hydrologic condition and reducing soil
erosion (Gifford 1985). High stocking rates,
regardless of grazing system, that reduce soil
surface vegetative cover below a site-specific
threshold will increase detachment and
mobilization of soil particles due to raindrop
impact, decrease soil organic matter and
soil aggregate stability, increase soil surface
crusting and reduce soil surface porosity, and
thus decrease infiltration and increase soil
erosion and sediment transport (Blackburn
1984). Regardless of grazing system, sufficient
vegetative cover, critical soil cover, or residual
biomass must remain during and following
grazing to protect soil surface condition (e.g.,
porosity, aggregate stability, and organic matter
content) and dependent hydrologic properties
(e.g., infiltration). Site-specific vegetation cover
requirements will vary depending on cover
type (e.g., vegetation, litter, or rock), soil type,
rainfall intensities, and water quality goals
(Gifford 1985).
e majority of research examining soil surface
hydrologic response to grazing has focused
on infiltration or proxies for infiltration, such
Increased
grazing intensity
is generally
associated with
detrimental effects
on riparian
plant community
composition and
productivity as
well as physical
degradation of
riparian soils and
stream channels.
CHAP TER 1: An Assessment of Grazing Practices 33
FIGURE 4. Bird species responses to grazing intensity/management treatments for (A)
shortgrass steppe, (B) mixed-grass prairie, and (C) tallgrass prairie. Drawn from data
in Giezentanner (1970), Skinner (1975), Kantrud (1981), Kantrud and Kologiski
(1982), and Milchunas et al. (1998).
as dry bulk density and soil penetrability. A
handful of studies have examined soil loss.
Increased stocking rates from nongrazed to very
heavy are associated with increased soil loss.
As with infiltration results, light and moderate
stocking rates are generally not different. ere
is no consistent result for the effect of grazing
system on soil loss; in some cases, continuous
systems are reported to have less soil loss, and
in other studies, rotational systems are reported
to have less soil loss. Most of these studies
are confounded by comparisons of different
stocking rates among systems, and several
report that grazing system effect depended on
plant community (e.g., shrub understory vs.
interspace). ere is no compelling evidence
that rotational grazing strategies can reduce
soil loss. Soil vegetative cover (responding to
stocking rate) and inherent soil characteristics
are key variables determining site scale soil loss
(Pierson et al. 2002).
Improve or Maintain the Quantity
and Quality of Food and/or Cover
Available for Wildlife
Stocking Rate. Livestock and wildlife
may directly compete for plant food
resources, and livestock grazing can alter
the composition, productivity, and quality
of plant food resources. Grazing can alter
community structure through removal of
recent production and through longer-term
effects on plant community composition and
productivity. Cover represents an important
component of wildlife habitat for escape and
concealment from predation as well as for
thermal regulation. Cover requirements for
specific wildlife species often vary within a
season and stage of life cycle (e.g., nesting
vs. foraging). Bird (MacArthur 1965; Wiens
1969; Cody 1985), rodent (French et al.
1976; Grant and Birney 1979; Geier and Best
1980; Grant et al. 1982; Kerley and Whitford
2000), lagomorph (Flinders and Hansen
1975), and lizard (Pianka 1966) community
composition and diversity are often closely
correlated with vegetation structure. Direct
behavioral interactions between livestock and
wildlife are another potential means by which
grazing may affect wildlife populations. Social
avoidance can preclude the use of otherwise
suitable habitat, and it can be influenced by
the numbers of livestock present (Roberts and
Becker 1982; Stewart et al. 2002). Trampling
of nests represents another possible mechanism
of negative interaction between livestock
and ground-nesting birds that increases with
stocking rate (Jensen et al. 1990b).
34 Conservation Benefits of Rangelan d Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
ere are fewer studies documenting the
responses of specific wildlife species or groups
to stocking rate or grazing intensity than there
are for plant communities. erefore, studies
published in the gray literature, including
symposia and technical reports, have been
included, but theses, dissertations, or non–
data-based publications have not. Limited
data availability also requires that inferences
be drawn from individual studies rather than
groups of studies, as has been done in other
sections of this chapter. Wildlife responses are
grouped into reptiles, birds, small mammals,
and large ungulates to more effectively
assess their potentially unique responses and
interactions with livestock grazing.
Reptiles. Ten studies reported on lizard
communities in grazed versus ungrazed
treatments, but only one study assessed lizard
populations over five grazing intensities in
Arizona (Jones 1979, 1981). e largest
negative effect of heavy grazing on lizard
density was found in Sonoran Desert grassland
(−63%), followed by mixed scrub–dry wash
(−54%), chaparral (−41%), and cottonwood–
willow riparian (−20%), with no difference
in desert scrub. Greater species richness was
observed in lightly compared to heavily grazed
desert grassland and cottonwood–willow
riparian habitat, with no difference in the other
three communities. e effects of grazing on
lizard communities were related to differences
in the cover of short (< 0.3 m) vegetation
structure and litter cover, but not necessarily
total vegetation cover. While lizard responses
to grazing may be expected to be more
pronounced than for other groups of organisms
because of their relatively specific microhabitat
requirements, there are insufficient studies over
grazing intensities for generalizations to be
drawn.
Birds. Bird responses to stocking rate are well
recognized as being species dependent and can
be positive, negative, or neutral within any
one location and treatment comparison (Bock
et al. 1993; Saab et al. 1995; Knopf 1996).
Unfortunately, most passerine bird studies
have compared only grazed and ungrazed
communities, and the intensity of grazing is
often not reported. Derner et al. (unpublished
data) reviewed 27 bird studies/habitats from
the literature, and only 10 included more than
FIGURE 5. Bird community (A) dissimilarity (Whittaker [1952] index of community as-
sociation), (B) abundance (% difference between grazing intensity differential), and (C)
diversity (H) across grazing intensity gradients for North America studies. Dissimilarity
index values range from 0.0 to 1.0, with a value of 0 indicating both treatments hav-
ing all species in common and in the same proportions (0% dissimilar) and a value
of 1.0 indicating no species in common (100% dissimilar). Data from Giezentanner
(1970), Johnson and Springer (1972), Skinner (1975), Grzybowski (1980, 1982),
Kantrud (1981), Kantrud and Kologiski (1982), and Milchunas et al. (1998).
one grazing intensity in addition to the long-
term ungrazed community. e abundance of
individual species within a site can be strongly
affected by grazing intensity. For example,
CHAP TER 1: An Assessment of Grazing Practices 35
·
TABLE 1. Bird community dissimilarity, abundance (numbers), diversity, richness, and dominance in response to grazing averaged by region,
evolutionary history of grazing, plant community life form, and plant community type. Forests were not included in region or evolutionary
history categories. Plant community types are for major groupings or those with more than one comparison (from Derner et al., unpublished
data).
Birds
Precipitation
(average mm yr−1)
Dissimilarity
(index)
Abundance (high
grazed % low
grazed)
Diversity (high
grazed /low
grazed)
Richness (high
grazed/low
grazed)
Dominance (high
grazed/low
grazed) N
By region
Great Plains 487 0.40 38 1.18 1.02 1.12 38
Southwest1 362 0.54 3 0.91 0.90 1.29 4
Northwest1 154 0.54 −22 1.25 1.14 0.83 6
Other grasslands 2 0.54 −33 1.10 0.93 0.96 10
By evolutionary history
Short history 617 0.53 −27 1.06 0.90 0.98 21
Long history 487 0.40 38 1.18 1.02 1.13 37
By life form
Grassland 483 0.43 30 1.18 1.02 1.09 40
Shrubland 291 0.45 −5 1.10 1.03 1.01 11
Forest 1 182 0.52 −45 0.96 0.68 1.06 7
By community type
Shortgrass steppe 357 0.29 36 0.94 0.83 1.13 6
Mixed-grass prairie 416 0.35 −2 0.91 0.90 1.25 23
Tallgrass prairie 988 0.61 217 2.52 1.71 0.59 6
Fescue grassland 383 0.60 −31 1.06 1.00 1.09 2
Coastal prairie 2 0.42 −9 0.96 0.54 0.72 2
Southwest grassland 362 0.54 3 0.91 0.90 1.29 4
Shadscale shrubland 154 0.42 −31 1.49 1.43 0.62 2
1Northwest includes the Great Basin and all communities west of the Rocky Mountains, except for Arizona, New Mexico, and southern California, which are considered Southwest.
2Number of sites reporting precipitation too few to provide a reasonable mean.
horned larks respond positively to increasing
grazing intensity in shortgrass steppe, while
lark buntings respond negatively (Fig.
4A). Chestnut-collared long-spurs respond
positively to increasing grazing intensity in
mixed-grass prairie, while savannah sparrows
respond negatively (Fig. 4B). e greatest
abundance of bird species in tallgrass prairie
occurred at intermediate intensities of grazing
(Fig. 4C). While species within a site respond
differently to grazing intensity, a particular
species may also have a varied response among
sites. Knopf (1996) suggested that birds may
not be generally classified as increasers or
decreasers in response to grazing, but that
individual species responses to grazing may
vary over gradients of potential vegetation
structure or aboveground primary production.
Although there are examples for regional
differences in bird species response to grazing,
Derner et al. (unpublished data) concluded
that data over gradients of grazing intensity
and regional gradients of primary production
are too limited to produce good models of bird
preferences for particular grazing intensities
at particular levels of primary production.
Reviews by Bock et al. (1993) and Saab et
al. (1995) provide tables of bird species by
region within the western United States that
show general positive, negative, primary
productivity–dependent, or neutral/mixed/
uncertain responses to grazing.
36 Conservation Benefits of Rangeland Practices
CHAP TER 2: Assessment of Prescribed Fire as a Conservation Practice 37
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
At the community level, the change in bird
community composition relative to the
ungrazed or lightly grazed condition usually
increased with increasing grazing intensity
(Fig. 5A; Table 1). However, dissimilarity was
generally greater when the communities were
ungrazed compared to lightly or moderately
grazed than when grazing intensity further
increased to moderate or heavy. Total bird
community abundance showed both positive
and negative responses with increasing grazing
intensity across and within community types as
anticipated (Fig. 5B). Bird community diversity
was generally slightly negative with increasing
grazing intensity (Fig. 5C). Exceptions were
observed for one tallgrass prairie study and
some mixed-grass prairie sites where slightly
greater diversity occurred at intermediate levels
of grazing intensity. In addition to these general
diversity patterns, management decisions need
to explicitly evaluate the specific habitat needs
of bird species of concern.
Most studies of grazing effects on upland game
birds (gallinaceous birds) addressed ungrazed
versus grazed conditions rather than grazing
intensity gradients, much like research for all
other wildlife groups. Based on two studies,
wild turkeys prefer ungrazed/lightly grazed
vegetation and avoid moderately/heavily
grazed areas. Similarly, heavy grazing was
consistently detrimental to sharp-tailed grouse
(three subspecies) because of a loss of nesting
cover and tree and shrub density (based on 10
studies reviewed in Kessler and Bosch 1982).
ere are contrasting positive and negative
results from ungrazed/grazed studies for sage
grouse and prairie chickens, but sage grouse
appear to prefer light/moderate grazed areas
over heavy grazed areas, but very high cover in
some ungrazed habitat may be avoided as well
(some reviewed in Beck and Mitchell 2000).
Historical evidence suggests that grazing is
detrimental to quail species in the southwestern
United States, but recent studies indicate
that light to moderate grazing intensities may
be beneficial to Mearn’s quail by increasing
availability of food resources. Montezuma
quail prefer high grass cover and tree density,
while scaled quail prefer high grass cover and
low tree density. In contrast, five studies of
bobwhite quail in Texas (see Bryant et al. 1982)
suggest that grazing is beneficial if intensities
are not too high. In summary, heavy grazing
most often results in loss of cover below some
optimal level for gallinaceous birds, although
light grazing may be beneficial under some
circumstances.
Small Mammals. Small mammals can be
sensitive to changes in vegetation structure,
but they may also be affected by grazing
FIGURE 6. Rodent species abundance across grazing intensities in (A) shortgrass steppe and (B) mixed-
grass prairie. Drawn from data in McCulloch (1959) and Grant et al. (1982).
CHAP TER 1: An Assessment of Grazing Practices 37
TABLE 2. Rodent community dissimilarity, abundance (numbers), diversity, richness, and dominance in response to grazing averaged by
region, evolutionary history of grazing, plant community life form, and plant community type. Forests were not included in region or evolution-
ary history categories. Plant community types are for major groupings or those with more than one comparison (from Derner et al., unpub-
lished data).
Rodents
Dissimilarity
(index)
Abundance
(high grazed
% low grazed)
Diversity (high
grazed/low
grazed)
Richness (high
grazed/low
grazed)
Dominance
(high grazed/
low grazed)
Unique species
(high grazed/low
grazed) N
By region
Great Plains 0.35 −27 0.99 0.89 1.11 −2.0 14
Southwest1 0.34 24 0.89 0.85 1.41 −1.0 6
Northwest1 0.43 8 0.81 0.95 1.60 −0.8 19
By evolutionary history
Short history 0.41 12 0.83 0.93 1.55 −0.9 25
Long history 0.35 −27 0.99 0.87 1.11 −2.0 14
By life form
Desert 0.18 −43 0.85 0.73 1.40 −1.5 2
Grassland 0.34 13 0.73 0.92 1.30 −1.4 4
Shrubland 0.38 −0 0.73 0.76 1.62 −1.7 12
Savanna 0.43 14 0.92 1.51 1.53 1.0 3
Forest 0.30 −55 0.82 0.75 0.96 −1.0 2
By community
Shortgrass steppe 0.19 −9 1.24 1.0 0.68 0.0 1
Mixed-grass prairie 0.32 −18 0.81 0.78 1.29 −2.9 9
Grassland 0.47 −13 0.79 0.62 1.53 −5.8 4
Sand sage shrub 0.19 −23 0.82 0.91 1.10 −0.6 5
Tallgrass prairie 0.48 −50 1.34 1.1 0.80 −0.5 4
Desert grassland 0.41 58 0.91 0.92 1.41 −0.8 4
Shadscale shrubland 0.53 1 0.57 0.6 2.36 −2.0 2
Atriplex shrubland 0.52 −27 0.63 0.96 1.81 0.0 2
Sagebrush shrubland 0.30 30 0.76 0.86 1.49 −1.5 6
Northwest grassland
2 0.34 13 0.73 0.95 1.30 −0.3 4
1Northwest includes the Great Basin and all communities west of the Rocky Mountains, except for Arizona, New Mexico, and southern California, which are considered Southwest.
2See Savanna for Northwest savannas.
induced modification of seed and arthropod of individual species of small mammals to
food resources. Derner et al. (unpublished grazing intensities are similar to birds, but
data) reviewed 24 rodent studies/habitats they differ from birds at the community level.
from the literature, and only six included Like birds, some rodent species are favored by
more than one grazing intensity in addition to grazing, some decline, and others are relatively
long-term ungrazed exclosures. e responses neutral (Fig. 6 A and B). e response of some
38 Conservation Ben efits of Rangeland Prac tices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
FIGURE 7. Rodent community (A) dissimilarity (Whit-
taker [1952] index of community association), (B)
abundance (% difference between grazing intensity
differential), and (C) diversity (H) across grazing
intensity gradients for North America studies. Dis-
similarity index values range from 0.0 to 1.0, with
a value of 0 indicating both treatments having all
species in common and in the same proportions
(0% dissimilar) and a value of 1.0 indicating no
species in common (100% dissimilar). Data from
Frank (1940), Smith (1940), McCulloch (1959),
Grant et al. (1982), Rice and Smith (1988), and
Bich et al. (1995).
species to grazing intensity can be substantial.
Generalizations concerning rodent responses
to livestock grazing intensity are less developed
than those for birds, in part because of fewer
studies but also because of less consistent
population responses.
Derner et al. (unpublished data) assessed the
number of rodent species unique to various
grazing intensities to evaluate the general
patterns of declining rodent diversity with
increasing grazing intensity. Greater numbers
of species were likely to be captured on
ungrazed or lightly grazed communities than
on moderately or heavily grazed communities.
However, 19 of 41 cases also displayed
species unique to the more intensively grazed
communities as well, but in only five cases
was the total number of unique species greater
on the more intensively grazed community.
e net effects by region and evolutionary
history were unique and unexpected. e
numbers of unique species associated with
heavy grazing were smaller in the Great
Plains than in the Southwest or Northwest
and in ecoregions with long rather than short
evolutionary histories of grazing (Table 2).
Deserts, grasslands, and shrublands displayed
somewhat similar reductions in rodent species
with increasing grazing intensity, and the
losses were greater compared to savannas and
forests. e greatest reductions in rodent
species with increasing grazing intensities
occurred in mixed-grass prairie. In general,
no consistent trends could be discerned for
changes in rodent species composition with
grazing intensity relative to ungrazed or
lightly grazed condition (dissimilarity; Fig.
7A) or abundance; Fig. 7B). Rodent diversity
generally declines or is unchanged with
increasing grazing intensity, with the exception
of a shortgrass steppe study (Fig. 7C). Declines
in rodent diversity with grazing intensity
were only small to moderate when they were
observed.
CHAP TER 1: An Assessment of Grazing Practices 39
Bird responses to grazing are
highly species specific and
positive, negative and neutral
outcomes occur. (Photo: USDA:
Gary Kramer)
Other Small Mammals. Heavily grazed
or “overgrazed” communities are generally
preferred over ungrazed or lightly grazed
communities by black-tailed jackrabbits in
eastern Texas (Taylor and Lay 1944), the
Mojave Desert in California (Brooks 1999), the
sand hills of Colorado (Sanderson 1959), and
southern Arizona (Taylor et al. 1935) and by
Great Plains jackrabbits in mixed-grass (Smith
1940) and tallgrass prairie (Phillips 1936) of
Oklahoma. Schmutz et al. (1992) observed
that rabbits became more abundant as range
conditions deteriorated in desert grassland.
MacMahon and Wagner (1985) suggested that
many areas of the Chihuahuan and Sonoran
deserts initially altered by fire suppression and
livestock grazing do not return to previous
conditions when large herbivores are excluded
because lagomorphs and rodents, favored by
the initial changes, maintain the vegetation
at early seral stages. In contrast, Flinders and
Hansen (1975) found that cottontail rabbits
were more abundant in moderately than in
either lightly or heavily grazed shortgrass
steppe, white-tailed jackrabbits showed no
preference, and black-tailed jackrabbits were
more abundant in lightly and moderately
compared to heavily grazed communities.
Changes beneficial to rabbits with increasing
grazing intensity include increased rabbit
mobility and improved forage due to increases
in annuals.
Wild Ungulates. ere is a large body of
research addressing dietary and habitat use
overlap between livestock and deer and elk.
In general, high dietary overlap is observed
between cattle or sheep and elk, compared
with much lower overlap between cattle or
sheep and deer (Skovlin et al. 1968; Mackie
1970; MacCracken and Hansen 1981; Berg
and Hudson 1982; Loft et al. 1991). However,
dietary overlap between deer and cattle can
increase with increasing intensity of cattle
grazing (Mackie 1981; Vavra et al. 1982;
Severson and Medina 1983). Habitat use is
often separated in time because of seasonal
migrations of deer and elk and in space
because of topography or cover requirements
(Skovlin et al. 1968; Mackie 1970; Berg and
Hudson 1982). For example, mule deer, elk,
and cattle observations on slopes steeper than
10 degrees averaged 50%, 42%, and 18%,
respectively. Dietary overlap between domestic
and native herbivores is generally greatest
during the period in which the herbivores are
most nutritionally stressed (Olsen and Hansen
1977; Mackie 1981), and habitat overlap is
most likely to occur when wildlife are at lower
elevations during winter, which often represents
the period of greatest nutritional stress (Wallmo
et al. 1981).
Increasing grazing intensities by livestock are
likely to create a bottleneck in the quantity
and quality of forage for wild ungulates during
nutritionally stressed periods (e.g., winter
or drought). More generalist, large-rumen
livestock are better able to utilize dormant grass
forage than deer under conditions of low forage
availability in heavily compared to moderately
or lightly stocked pastures (MacMahan and
Ramsey 1965). Dietary overlap between cattle
40 Conservation Ben efits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
and pronghorn is low, and Schwartz et al.
(1977) found that pronghorn were able to
maintain seasonal diet qualities on long-term
pastures heavily grazed by cattle similar to what
they did on lightly grazed pastures in shortgrass
steppe under nondrought conditions. In
contrast, a pronghorn die-off was attributed to
very heavy grazing by domestic animals during
a drought (Hailey et al. 1966). Other studies
of livestock grazing effects on pronghorn
populations also show mixed responses.
In contrast, habitat overlap is a prerequisite
to facilitation of one herbivore by another.
Positive or facilitative effects of livestock
grazing on associated wildlife species may
result from a reduction in the amount of
unpalatable, standing dead material (Short
and Knight 2003) or increased protein content
and digestibility of forage available late in
the season (Clark et al. 2000; see below).
Both competition and facilitation can act
simultaneously, and competition can be the
strongest factor (Hobbs et al. 1995). Longer-
term facilitative relationships may be based on
a dichotomy in diet preference of grass versus
forbs and shrubs. For example, grazing by deer
and livestock can potentially shift community
composition toward a composition favored by
other species of herbivores.
Grazing can potentially be used as a tool to
enhance wildlife populations, and this may
be particularly true when season of grazing or
deferment of grazing is used to meet specific
wildlife goals. In some situations, wildlife
and livestock may overlap in habitat use
only during particular times of the year. For
examples, breeding birds may nest only during
spring/early summer and require specific
conditions during that time. Elk and deer
may move down from forested mountainous
habitat during the winter to occupy foothills
and plains more likely to be used for livestock
grazing. Grazing may be imposed or deferred,
depending on cover and foraging requirements
of specific species. Some waterfowl or some
upland game species require dense nesting
cover, whereas some birds, such as mountain
plover or curlews, choose nesting sites with
very little cover and will not nest in ungrazed
or lightly grazed habitat. Many of the examples
of season-of-use studies come from wildlife
refuges or experimental sites where livestock
FIGURE 8. Responses of nine wildlife categories to rotational compared to continuous
livestock grazing systems summarized as neutral, negative, or positive. Each wildlife
category is subdivided into a population (upper) and a habitat (lower) section to indi-
cate the mechanism of livestock impact. The large dark bars represent studies without
confounding experimental designs, and the small lightly shaded bars represent stud-
ies with design problems. Each study may have one to four response variables, so
each bar does not represent a single study.
use is optional and management options are
flexible.
Successful use of season of grazing may result
from a facilitation effect of grazing by livestock
on forage for other ungulates. Alpe et al. (1999)
showed that early summer grazing improved
forage quality for wild ungulates in autumn and
winter if livestock was removed in time to allow
sufficient regrowth, but that late season livestock
grazing decreased forage quality for wild
CHAP TER 1: An Assessment of Grazing Practices 41
ungulates. Successful use of season/deferment of
grazing may also be possible when pastures that
are not frequently used by wildlife are available;
otherwise the removal of livestock from one
pasture must outweigh the effects of increased
stocking rate in adjacent pastures. Even in these
cases, experimental outcomes can be neutral,
positive, negative, or mixed, depending on
wildlife species or timing of grazing (Medin
1986; Alpe et al. 1999; Mathis et al. 2006).
Grazing Systems. Wildlife responses to
rotational and continuous grazing at relatively
similar grazing intensities and within similar
plant communities are evaluated in this section.
Studies investigating different pastures within
the same grazing system are also considered
separately and clearly identified when used.
Studies are organized by wildlife taxonomic
groups and summarized across all groups and
mechanisms for positive, neutral, or negative
responses to grazing system.
Birds. Although passerine birds represent the
most studied group of wildlife in response to
grazing intensity (see section above), only two
published studies of rotational compared to
Ungulate responses to grazing
are equivocal so that no broad
conclusions can be drawn.
(Photo: USDA: Gary Kramer)
continuous grazing were located. However,
there are a number of unpublished theses,
studies within pastures of an individual
system or that compare rotational grazing
with ungrazed communities that were not
considered here. e dissertation of Kempema
(2007) was unique because it assessed several
grazing periods of increasing duration, so it
is summarized here. ese studies report that
passerine responses to grazing systems compared
to continuous grazing were most often neutral
(Fig. 8). e rotational systems had the least
vegetative heterogeneity at both small and large
spatial scales because of the reduced capacity for
selective grazing at the bite and patch scale by
livestock compared to continuous grazing. is
was accompanied by a decrease in bird species
richness with decreasing duration of grazing
(long-continuous richest). In contrast, the
short-duration system had the highest densities
of the most species. For most bird species (11),
there was no significant grazing system effect on
density, and for the three species that showed
significant density effects, the responses were
both positive and negative. Nest success was also
similar among the three grazing systems. e
small number of passerine studies specifically
conducted in grazing systems precludes the
development of general conclusions.
Grazing systems studies on gallinaceous birds
frequently evaluated nest trampling or nest
predation, often conducted with artificial
nests. All studies without confounded designs
show neutral responses to grazing system (Fig.
8). Larger densities of livestock in smaller
pastures of rotational systems do not appear to
increase trampling losses under the densities
and in the habitats studied. A higher density
of livestock in some pastures and longer rests
in others appears to produce a similar mean
effect. Trampling of nests is often found
to increase linearly with stocking density
(Bientema and Müskens 1987; Paine et al.
1996; Kempema 2007), and the ecological
significance of nest trampling is greater in more
productive ecosystems that support greater
stocking density. In contrast, Koerth et al.
(1983) found trampling losses of nests to be
similar between short-duration and continuous
grazing, even though the short-duration
system was stocked at a higher rate (5.3 vs.
8.0 ha · steer−1). Nest trampling may not be
linear with stocking density because livestock
42 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
may travel less in smaller pastures (Koerth et
al. 1983 and citations therein). Alternatively,
a reduction in diet selection may increase
search time exploring new pastures during
repeated rotations (Spalinger and Hobbs 1992;
Wilmshurst et al. 1999), and large herd size
may result in more temporally constant activity
levels among livestock (Paine et al. 1996).
Direct studies of population or habitat
responses between grazing systems are few,
but positive responses have been reported
for rotational grazing systems compared to
continuous grazing for bobwhite quail in
response to increased bare ground and greater
forb densities (Fig. 8). ere are too few studies
for sharptail or turkey to draw any meaningful
conclusions concerning the effect of grazing
system. No grazing systems studies were found
for prairie chickens or sage grouse, but some
management recommendations have been
made, including multiyear periods of rest to
restore vegetative cover (Hagen et al. 2004).
Vegetative cover is an important habitat
requirement for waterfowl, although very
dense vegetation can be detrimental to nest-
site selection (Kantrud 1990). Ignatiuk and
Duncan (2001) observed no difference in duck
nest success in an extensive study of once-over
rest-rotation or deferred-rotation systems and
continuous grazing, while additional studies
compared only pastures within grazing systems
or conditions following changes in grazing
regime (Fig. 8). When rest periods were
from 1 to 3 yr, Gilbert et al. (1996) observed
increasing duck nest densities with increasing
years of rest, and regression analyses suggested
that a 6- to 7-yr rest would be necessary for
recovery to that of an ungrazed condition.
Other waterfowl studies with confounding
experimental designs also suggest that long rest
periods may be beneficial, but there are too few
waterfowl studies of grazing systems to form
robust conclusions.
Large Ungulates. Grazing systems research has
been conducted with elk, deer, and pronghorn
antelope, but the pronghorn study compared
rest-rotation only with ungrazed pastures. Eight
studies that included 18 response variables
were found comparing grazing systems
with continuous grazing for deer. e most
common deer response to grazing system was
negative, followed by neutral and then positive
responses (Fig. 8). However, population-level
responses for deer were equally split between
positive and neutral for rotational compared to
continuous grazing. Studies assessing habitat
characteristics important to deer were most
often negative in rotational grazing systems
compared to continuous. Only one grazing
system study reported on social avoidance by
deer, and it showed deer–livestock competition
in the short-duration system compared to
continuous grazing that was attributed to
habitat modification rather than deer leaving
the pasture (Cohen et al. 1989). Responses of
deer to rotational systems are generally mixed
so that no clear trends can be established.
Only one study was located that directly
compared elk responses in a deferred-rotation
grazing system compared to season-long
grazing and found no significant response
when averaged over grazing intensities (Fig. 8)
but did find a highly significant interaction of
grazing system with grazing intensity (Skovlin
et al. 1968, 1975, 1983). Elk preferred season-
long to deferred rotation at the light grazing
intensity, but preferred deferred to season-long
rotation at the high grazing intensity. Elk
utilized individual plants that had not been
grazed by cattle, and cattle use of numbers of
individual plants at the low grazing intensity
was greater under the rotation system. Forage
quantity and preference for areas receiving little
or no prior current-year use by livestock can
regulate elk movement across larger landscapes
as well (Mackie 1970). ese results and
the observation that elk preference strongly
increased with decreasing grazing intensity
even from light to ungrazed treatments are
in accordance with the within-system studies
showing a high degree of elk sensitivity to
livestock grazing intensity and selection for
ungrazed units or treatments, unutilized/
little utilized areas within grazed pastures,
and ungrazed individual plants. However,
the studies within various pastures of a single
rotational grazing system are often cited to
support rotational grazing as benefiting elk
populations. ree of these studies found no
social avoidance between elk and livestock for
selection of ungrazed pastures. Livestock grazing
facilitated use by elk the year following grazing
in two studies, and elk avoided currently and
previously grazed pastures in the other study.
…the most
frequent wildlife
response was
no differences
between
continuous and
rotational grazing
systems, with the
remaining cases
equally divided
among positive
and negative.
CHAP TER 1: An Assessment of Grazing Practices 43
The response
of soil organic
carbon to
stocking rate is
equivocal, based
partially on the
limited number
of investigations
that have been
conducted.
Summary of Wildlife and Grazing Systems.
e limited number of available studies does
not permit generalizations concerning wildlife
responses to grazing systems and when or
where or for which species positive, negative,
or neutral responses may be predicted. ere
appear to be many false claims and few valid
studies in the literature (Kirby et al. 1992),
and this assessment applies to the literature
addressing wildlife responses to grazing
systems. Collectively, comparative wildlife
responses to rotational and continuous grazing
were that 17 showed no difference, eight
were negative, and eight were positive (Fig.
8). ese experimental data indicate that
the most frequent wildlife response was no
differences between continuous and rotational
grazing systems, with the remaining cases
equally divided among positive and negative.
However, most wildlife groups showed mixed
responses to grazing system, and it is clear that
there are conditions where rotational grazing
systems benefit a wildlife species or group, but
the opposite response is documented as well.
Much more is known about wildlife responses
to grazing intensities than grazing systems, but
even here the majority of studies assess grazed
and long-term ungrazed communities, which
are generally not relevant to prescribed grazing
management (Krausman et al., this volume).
Manage Fine Fuel Loads to Achieve
Desired Conditions
Grazing does reduce fine fuel loads, and it
can therefore modify both fire frequency and
intensity (Belsky and Blumenthal 1997; Briggs
et al. 2002; Fuhlendorf and Engle 2004).
is interpretation is supported by the well-
documented inverse relationship between
stocking rate and aboveground herbaceous
standing crop (Bement 1969; Milchunas and
Lauenroth 1993; Manley et al. 1997; Derner
and Hart 2007). It is often hypothesized
that woody plant encroachment is partially a
consequence of reduced fire regimes associated
with livestock grazing (Scholes and Archer
1997; Swetnam and Betancourt 1998;
Briggs et al. 2005). However, beyond these
broad generalizations, there are only limited
experiential data to support grazing as a means
of fuel management (Belsky and Blumenthal
1997; Davies et al. 2010). is is perhaps
not that surprising given that fire–grazing
interactions are strongly influenced by site,
year, season, and specific fire conditions (Davies
et al. 2009).
Patterns of fire and grazing appear to be
critically linked on the landscape (Fuhlendorf
and Engle 2004). Grazing may increase the
variability on fire occurrence by reducing the
amount and increasing the heterogeneity of fine
fuel distribution (Holdo et al. 2009). Grazed
patches have less fine fuel that is less likely to
burn than ungrazed patches that contain larger
amounts of combustible fine fuel (Collins and
Smith 2006; Kirby et al. 2007). However,
grazing increased fuel homogeneity in a
bunchgrass-dominated rangeland by reducing
biomass of individual plants to a greater extent
than biomass in the plant interspaces (Davies et
al. 2010).
Weather and fuel conditions further increase
the complexity of the relationship between
fuel load and fire frequency and intensity. For
example, fine fuel load is strongly correlated
with fire intensity when fuel moisture is held
constant, but when fuel moisture is low,
intense fires can be carried by much lower
fuel loads (Twidwell et al. 2009). is will
be influenced by the season, time of day, and
specific weather conditions associated with
individual fires. It is no coincidence that most
wildfires occur during extreme fire conditions;
during these extreme conditions, fire can
be carried by a wide range of fuel loads.
erefore, it should not be assumed that fire
frequency and intensity decrease linearly with
decreasing fuel loads resulting from greater
grazing intensities.
e relative proportions of fine and coarse fuel
loads can also influence the relationship between
grazing and fire frequency and intensity. Woody
plant encroachment is often associated with
a reduction in the amount of fine fuel, but
coarse fuel loads often increase substantially
(Hibbard et al. 2001; Norris et al. 2001; Briggs
et al. 2002). Although coarse fuels have higher
ignition temperatures, closed-canopy woodlands
can be highly flammable during extreme fire
conditions. erefore, the role of grazing as a
tool for fuel management is generally supported,
but it should be cautiously evaluated on a case-
by-case basis because fire potential in influenced
by interactions among several ecosystem
variables (Fuhlendorf et al., this volume).
44 Conservation Ben efits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
ASSOCIATED CONSIDERATIONS
Livestock Distribution
Animal selectivity and foraging behavior
within landscapes has received considerable
attention on rangelands (Bailey et al. 1996;
Launchbaugh and Howery 2005). Herbivores
naturally select preferred plants and landscape
positions over others (Van Soest 1994),
resulting in differential patterns of species
use within communities and management
units when stocking rates are not excessive
and pastures are of sufficient size (Bailey et
al. 1996; Launchbaugh and Howery 2005).
Rangelands have traditionally been managed
to increase uniformity of vegetation use by
livestock and maximize livestock gains within
the limits of individual animal performance
and long-term ecosystem sustainability
(Bement 1969). is management approach
has been effective and sustainable from the
standpoint of livestock and forage production
(e.g., Hart and Ashby 1998), but it often
does not mimic the pattern of historic
disturbance regimes (Fuhlendorf and Engle
2001) or create habitat structure required for
many grassland bird species (Knopf 1996;
see Deferment and Rest section below).
Livestock distribution and grazing behavior
can be modified by adjusting the location of
supplemental feed and water, implementation
of patch burns, and herding (Williams 1954;
Ganskopp 2001; Fuhlendorf and Engle 2004;
Bailey 2005) in addition to the traditional
practice of fencing.
Experimental data evaluating the most critical
variables associated with livestock distribution
were evaluated from 51 studies and two
reviews. Treatment responses were categorized
into 1) general distribution effects, 2) steep-
slope use, 3) high-elevation use, 4) distance
from water, 5) plant preferences, 6) uniformity (e.g., fences, salt, and water placement) to
of grazing, and 7) riparian use. All 51 studies the modification of animal behavior (e.g.,
were short term (< 5 yr), and the vast majority attractants, genetic selection, breeds, and type
of them used cattle as the livestock species of animal) over the past two decades. Livestock
(41). Pasture sizes used in these investigations distribution in response to specific conservation
were generally large (22 > 200 ha). Recent practices have received relatively little attention
investigations have incorporated technological with the exception of prescribed burning (see
advances involving GPS devices (e.g., collars) to Fuhlendorf et al., this volume).
track individual animal movement to provide
spatial- and temporal-explicit use patterns. e experimental data verify that many of
Strategies for modifying patterns of livestock the common assumptions regarding livestock
distribution have shifted from specific practices distribution and preferences for specific sites
Rangelands play an important
role in the global carbon cycle
because of the large reservoirs
of organic and inorganic
carbon they contain. (Photo:
Brandon Bestelmeyer)
CHAP TER 1: An Assessment of Grazing Practices 45
Prescribed grazing must
balance the forage demand of
animals with the physiological
requirements of plants to be
sustainable. (Photo: USDA:
Lynn Betts)
and conditions are valid. Water distribution
(11 of 15 studies), steep slopes, and high
elevations (13 of 17 studies) unequivocally
influenced livestock distribution. Livestock by
and large prefer riparian to upland areas (e.g.,
Bowns 1971; Smith et al. 1992; Howery et
al. 1996, 1998), burned to nonburned areas
(Coppedge and Shaw 1998; Biondini et al.
1999), previously grazed compared to ungrazed
areas (Ganskoppp and Bohnert 2006), and
fertilized to nonfertilized areas (Samuel et al.
1980). Range riding and/or herding of animals
also effectively modified livestock distribution
(Skovlin 1957; Bailey et al. 2008). A clear
exception to these generalizations is that salt
location has only a minor influence on grazing
distribution within a growing season (five
of seven studies; Ganskopp 2001). Standard
approaches to modifying livestock distribution
are warranted, but it appears that they can only
minimize animal selection and preferences
rather than completely eliminate them (Jensen
et al. 1990a).
Grazing and Soil Organic Carbon
Rangelands play an important role in the global
C cycle because of 1) an extensive land area,
2) large reservoir of sequestered C that could
be released back into the atmosphere with
improper management, 3) potential for high
rates of soil organic carbon (SOC) accumulation
by restoration of degraded rangelands, and 4)
a vast pool of soil inorganic C as carbonates in
semiarid and arid rangeland soils that may allow
sequestration or release of CO2 (Schuman et
al. 1999; Derner and Schuman 2007; Svejcar
et al. 2008). SOC sequestration is influenced
by climate (Derner et al. 2006), biome type
(Conant et al. 2001), management (grazing, N
inputs, restoration, and fire; Follett et al. 2001;
Mortenson et al. 2004; Derner and Schuman
2007; Bremer and Ham 2010; Pineiro et al.
2010), and environmental conditions (drought
and climate change; Jones and Donnelly
2004; Ingram et al. 2008; Svejcar et al. 2008).
Rangelands are typically characterized by short
periods of high C uptake (2–3 mo · yr−1), long
periods of C balance or small losses (Svejcar
et al. 2008), and climate-driven interannual
variability in net ecosystem exchange (Zhang et
al. 2010). ree main drivers that will control
the fate of C sequestration in rangelands are 1)
long-term changes in production and quality
of above- and belowground biomass; 2) long-
term changes in the global environment, such
as rising temperatures, altered precipitation
patterns, and rising CO2 concentrations, that
affect plant community composition and forage
quality; and 3) effects of short-term weather
conditions (e.g., droughts) and interannual
variability in climate on net C exchange (Ciais
et al. 2005; Soussana and Lüschert 2007;
Ingram et al. 2008; Svejcar et al. 2008; Zhang
et al. 2010).
46 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
Application of appropriate management
practices, such as proper stocking rates, adaptive
management, and destocking during drought
conditions on poorly managed rangelands
(113 M ha), could result in sequestration of
11 Tg C · yr−1, and continuation of sustainable
management practices on the remaining
rangelands would avoid losses of 43 Tg C · yr−1
(Schuman et al. 2001).
SOC sequestration rates decrease with
longevity of the management practice
(Derner and Schuman 2007), indicating
that ecosystems reach a “steady state” and
that changes in inputs would be required to
sequester additional C (Conant et al. 2001,
2003; Swift 2001). e response of SOC to
stocking rate is equivocal, based partially on
the limited number of investigations that have
been conducted. Sixty-two percent (five of
eight) of the investigations showed no response
of SOC to stocking rate (Smoliak et al. 1972;
Wood and Blackburn 1984; Warren et al.
1986a; Biondini et al. 1998; Schuman et al.
1999) with one showing a decrease (Ingram
et al. 2008) and two showing an increase in
response to increasing stocking rate (Manley
et al. 1995; Reeder and Schuman 2002). e
two investigations showing an increase in SOC
with increasing stocking rate occurred in the
northern mixed-grass prairie during a relatively
wet period (Manley et al. 1995; Reeder and
Schuman 2002). It has been demonstrated
that increasing SOC in these grasslands may
partially result from increasing dominance
of the shallow-rooted, grazing-resistant
species blue grama (Bouteloua gracilis), which
incorporates a larger amount of root mass in
the upper soil profile than do midgrass species
that it replaces (Derner et al. 2006). In a global
analysis, Milchunas and Lauenroth (1993)
found that in 19 of 34 comparisons, SOC was
less in grazed than ungrazed communities, and
results were similarly mixed for root biomass.
Contributions of Individual Plant
Research to Grazing Management
Many of the assumptions on which grazing
management is founded originated from
defoliation experiments conducted with
individual plants. Suppression of plant
photosynthesis, root growth cessation, support
of regrowth by carbohydrate reserves, and
regulation of tillering by apical dominance
represent several of the major assumptions
(Briske and Richards 1995). e relevance
of these individual plant-based assumptions
to grazing management has recently been
questioned in an assessment of plant and
animal production responses to grazing systems
(Briske et al. 2008). In several instances, these
plant-based assumptions have shown little
correspondence with the outcomes observed
in grazing systems. Since the development of
these plant-based assumptions in the mid-20th
century, some have been substantiated, but
others have been refuted from the vantage point
of greater scientific understanding derived from
more sophisticated experimental techniques.
Several plant-based assumptions that have been
validated and invalidated are summarized below.
Unfortunately, these assumptions often prevail
long after they have been refuted by substantial
experimental evidence.
Valid Plant-Based Interpretations. Numerous
plant-based interpretations were developed
early in the profession to cope with widespread
overgrazing and rangeland degradation
that prevailed in the late 19th and early
20th centuries. ese were often based on
observation and general inference because
knowledge of plant physiology was very limited
during this period and did not substantially
improve until the mid-20th century. Several of
the more important plant-based interpretations
that have been supported by current science are
summarized below.
Leaf Removal and Subsequent Growth.
Photosynthetic leaf area provides the energy
source for plant growth and reductions in leaf
area suppress both plant photosynthesis and
growth (Sampson 1923). is interpretation
has been well supported with additional
insights addressing the various contributions
of leaf canopy position and leaf age (Caldwell
et al. 1981; Gold and Caldwell 1989). e
validity and consequences of this well-
established process are reflected in the adverse
effects of severe and multiple defoliations on
plant growth within a growing season.
An important caveat associated with
plant defoliation experiments, even when
conducted with field-grown plants, is that
the defoliation intensities imposed are often
very severe compared to actual defoliation
CHAP TER 1: An Assessment of Grazing Practices 47
…grazing
management
recommendations
should not be
developed
exclusively
from processes
derived at the
individual plant
level without
at least partial
verification of
the anticipated
response within
communities or
ecosystems.
patterns documented in the field. Eight of 12
defoliation studies evaluated defoliated plants
at ≤6 cm, and three of these eight defoliation
intensities were imposed on large tallgrass
species. is suggests that while this research
is valuable for understanding mechanisms of
plant response to defoliation, caution should
be used in translating these responses to actual
grazing management applications.
Root Growth and Function. Root growth
and function are increasingly suppressed
with increasing intensity and frequency of
defoliation because they are entirely dependent
on energy derived from photosynthesis (Crider
1955). is interpretation has also been well
supported by subsequent research investigating
specific physiological mechanisms, including
root respiration and nutrient absorption
kinetics (Ryle and Powell 1975; Macduff et
al. 1989). However, even though suppression
of root growth following severe defoliation
of individual plants is well established, the
evidence that intensive defoliation suppresses
root biomass within plant communities
remains equivocal (Milchunas and Lauenroth
1993; McNaughton et al. 1998; Johnson
and Matchett 2001). A specific mechanism
has not been provided for this inconsistency,
but it likely has to do with compensating
root growth by less intensively grazed
plants within the community or a shift
in species composition to species that
allocate a greater proportion of biomass
belowground. Contrasting grazing responses
between individual plants and communities
demonstrates that caution should be used
when extrapolating individual plant responses
to communities and ecosystems.
Defoliation-Induced Competitive
Interactions. e ability of disproportionate
defoliation intensity among adjacent plants
to modify intra- and interspecific competitive
interactions to favor less severely grazed plants
was initially proposed by Mueggler (1972).
is interpretation has been substantiated
with more recent and sophisticated research
using isotopes of phosphorous (Caldwell et al.
1985, 1987) and nitrogen (Hendon and Briske
2002) demonstrating that both the frequency
and intensity of defoliation can modify
belowground competition. is series of
physiological effects on competitive interactions
is partially reflected in the widely observed
patterns of increaser and decreaser plant species
and grazing-induced changes in the species
composition of plant communities.
Invalid Plant-Based Interpretations. Several
well-established interpretations derived from
individual plant response to defoliation have
been invalidated with the advent of more
sophisticated experimental procedures. is
brief summary of refuted interpretations is
intended not to criticize this early work, but
merely to indicate that the knowledge base
supporting grazing management has and
will continue to advance as more research
information is obtained.
Apical Dominance and Tillering. Apical
dominance was promoted as the primary
mechanism controlling tiller initiation
following defoliation of perennial grasses. It
was based on the direct hypothesis of auxin
action indicating that removal of the apical
meristem terminated supply of the growth
inhibitor auxin to the axillary buds near the
base of the tiller and thereby allowed their
outgrowth into new tillers (Leopold 1949).
Physiologists considered this concept invalid
in the 1950s, Jameson (1963) concluded
that this interpretation of apical dominance
was not supported by evidence for rangeland
grasses, and this conclusion was corroborated
by a larger data synthesis of perennial grasses
(Murphy and Briske 1992). e traditional
concept of apical dominance as applied in
grazing management was a partial and overly
restrictive interpretation of tiller initiation in
perennial grasses. A complete understanding
of the mechanisms contributing to tiller
initiation is yet to be developed, but it is
likely a multivariable processes regulated
by several interacting physiological and
environmental variables (Tomlinson and
O’Connor 2004).
Carbohydrate Reserves as Indicators
of Regrowth. Carbohydrate reserves were
proposed as an index of potential plant
regrowth, and this concept was frequently
applied in grazing management during the
latter half of the 20th century and is still
applied in limited cases. Since carbohydrate
reserves decrease following plant defoliation,
it was widely assumed that they must be
48 Conservation Ben efits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
a major source of carbon supporting leaf
regrowth (Briske and Richards 1995). A more
thorough evaluation of plant carbon balance
indicated that root carbohydrates were used
primarily within root systems rather than being
allocated aboveground to support regrowth
and that reserve pools of perennial grasses
contained very small amounts of carbon that
contributed to regrowth for only 1–3 d before
leaf photosynthesis once again became the
primary carbon source (Richards and Caldwell
1985). Moreover, it appears that a consistent,
positive relationship between the size of the
carbon reserve pools and grass regrowth had
never been established in support of this
widely used interpretation (Busso et al. 1990).
In retrospect, the concept of carbohydrate
reserves was founded on an oversimplified
interpretation of carbohydrate patterns in
grasses, and it never had great relevance to
grazing management. Residual leaf area and
the availability of meristems, in the presence of
favorable environmental conditions, are now
recognized to provide more reliable indicators
of plant regrowth following defoliation (Briske
and Richards 1995). Ironically, emphasis on
the maintenance of carbohydrate reserves in
perennial grasses inadvertently applied these
valid indicators of plant growth and thereby
indirectly contributed to efficient grazing
management.
e hierarchical structure of ecological
systems describes the nested levels of
ecological organization that coincide with
increasing complexity and interaction among
components within systems. is hierarchical
structure determines why it is possible for
even well-established processes at the level of
individual plants to not directly translate to
communities and ecosystems. For example,
recall that the well-established reduction in
root growth following intensive defoliation
of individual plants is not consistently
expressed as a reduction of root biomass
within grazed communities (Milchunas
and Lauenroth 1993; McNaughton et al.
1998). is inconsistent response suggests
that processes and interactions within
populations or communities are overriding
or mitigating the negative root response of at
least some of the plant species. Reductionist
investigations of individual plants produce
valuable mechanistic insights, but they may
be too narrow in scope to identify important
interactions and trade-offs at higher scales to
make them relevant for direct management
application (Briske 1991). Plant-based
research over the past century indicates that
grazing management recommendations should
not be developed exclusively from processes
derived at the individual plant level without
at least partial verification of the anticipated
response within communities or ecosystems.
is is a rather sobering conclusion after
nearly a century of individual plant-oriented
research, but it does provide evidence of
maturation and progress within the rangeland
profession.
RECOMMENDATIONS
e following recommendations have
emerged from our evaluation of the benefits
of NRCS prescribed grazing practices with
the relevant experimental literature. ey
are presented to enhance the effectiveness
of the current conservation planning
standard and to emphasize the CEAP goals
addressing environmental quality of managed
lands, including the assessment of multiple
ecosystem services.
Priorities and Approaches to
Conservation Planning
Conservation planning would benefit from a
substantial shift in priorities that deemphasize
the independent development of facilitating
practices (e.g., fencing, roads, and pipelines)
and reemphasize integration of these practices
with adaptive management decisions (e.g.,
stocking rate, drought management, and
monitoring) to promote environmental quality
of rangelands as recommended by CEAP.
With the clear exception of improved livestock
distribution, there is no indication that
facilitating practices alone directly promote
effective environmental conservation. e
function of grazed ecosystems is similarly
controlled by several dominant environmental
variables, albeit over diverse social and
environmental conditions, that are expressed
in dynamic forage production patterns within
and among years establishing that management
decisions, especially during critical periods, can
have profound effects on grazed ecosystems.
e environmental variables and many of the
social variables cannot be directly managed, but
Conservation
planning would
benefit from a
substantial shift
in priorities that
deemphasize
the independent
development
of facilitating
practices (e.g.,
fencing, roads,
and pipelines)
and reemphasize
integration of
these practices
with adaptive
management
decisions…
CHAP TER 1: An Assessment of Grazing Practices 49
Renewed
emphasis
on drought
contingency
planning must
integrate both
economic and
ecological
considerations
to effectively
encourage
managers to
adopt and
implement
destocking
options…
recognition and planning for their occurrence
with effective adaptive management plans at
both the tactical and the strategic level can
minimize their detrimental consequences
to both production and conservation goals.
Increased development and delivery of
contingency planning protocols are required to
effectively cope with these variable conditions
common to most grazing enterprises. ese
tools should emphasize dynamic stocking
rate determinations and provisions to support
flexible management strategies, including
effective destocking and restocking tactics and
the potential to develop reserve forage supplies
(e.g., Sharrow and Seefeldt 2006; Hanselka et
al. 2009; Torell et al. 2010).
We recommend that additional decision
support tools and guidelines be developed to
inform adaptive grazing management decisions,
especially during critical events and seasons.
Current information and technology will
support development of novel, comprehensive
approaches for implementing dynamic stocking
rate determinations that can be effectively
incorporated into management plans and
monitored by landowners. An undertaking
of this magnitude will require investment
of considerable intellectual and financial
capital, but the experimental evidence strongly
confirms that site-appropriate stocking rates
represent the very foundation of sustainable
grazing management and associated
conservation benefits. ese tools could target
specific landowners via conservation planning
or be more generally accessible through AFGC,
(American Forage and Grassland Council),
GLCI (Grazing Lands Conservation Initiative),
SRM (Society for Range Management), or
SWCS (Soil and Water Conservation Society)
publications and venues or made available on
NRCS websites. Incentives could be variously
structured to encourage use and adoption of
these tools and approaches. Conservation plans
may even require participation in a set number
of instructional activities to attain and maintain
program eligibility.
Forage Inventory Assessment and
Monitoring
Development and implementation of forage
inventory and monitoring protocols in grazed
ecosystems requires greater emphasis. is will
require that the process of balancing forage
production with animal demand be placed in
the broadest possible context to include forage
inventory, seasonal plant growth dynamics,
and drought management over both short- and
long-term periods (e.g., Sharrow and Seefeldt
2006; Hanselka et al. 2009). Static seasonal or
annual stocking rates provide a broad reference,
but they are insufficient to addresses wide
seasonal and interannual variation in forage
production common to most rangelands.
Consequently, emphasis on static stocking rates
results in systems being over- or understocked
the majority of the time (Hart and Ashby
1998). Spatial variability of forage production,
associated with variation in soils, landscape
position, and local precipitation patterns, also
minimizes the value of static, regional stocking
rates. Use of the grazing pressure index,
describing animal units per unit of forage mass
over a period of time, has been recommended
to standardize stocking rates and improve
clarity of animal–forage relationships (Smart et
al. 2010).
Stocking rates based on residual forage,
determined as a percentage of site-specific
annual forage productivity, minimizes the
probability of over- and undergrazing at both
spatial and temporal scales (Bement 1969;
Clary and Leininger 2000). Management based
on residual forage ensures sufficient vegetative
cover to protect soils during drought and
dormant seasons, enhances the capacity for
plant regrowth, and provides food and cover
for wildlife during stress periods. Stocking
rates established to promote environmental
quality on rangelands may also promote
heterogeneity in structure and diversity of flora
and fauna because livestock are less likely to
graze uniformly across local topographic–plant
community gradients within pastures.
Experimental information and available
technology support development of a
comprehensive approach for implementing
dynamic stocking rate determinations that can
be effectively incorporated into management
plans with landowner participation. An
undertaking of this magnitude will require
investment of considerable intellectual
and financial capital, but the experimental
evidence directly confirm that site-appropriate
stocking rates represent the very foundation
of sustainable grazing management and
50 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
associated conservation benefits. Management
for appropriate stocking rates not only supports
conservation goals, but it also forms the basis
for effective drought management strategies
and sustainable long-term economic returns
(Manley et al. 1997; Hart and Ashby 1998;
Torell et al. 2010).
Alternative approaches are required to more
directly and effectively incorporate dynamic,
site-specific stocking rate assessments into
overall management strategies and conservation
planning. Landowner incentives could be
provided to encourage adoption of forage
inventory and monitoring as well as the grazing
adjustments suggested by these protocols.
ese tools and guidelines are required to more
closely estimate actual forage utilization or
grazing intensity so that this information can
be integrated into an adaptive management
framework that emphasizes and supports
flexible grazing management. Existing
annual forage production curves emphasizing
specific reference points that are critical to
the attainment of various management and
conservation goals (e.g., midpoint and end of
growing season, critical wildlife requirements,
and sensitivity of riparian zones) require greater
attention and user friendly access. Readily
accessible monthly and seasonal precipitation
probabilities derived from long-term regional
climatic records would also support forage
inventory decisions (Andales et al. 2006). ese
tools may represent simple, direct measures of
forage availability as well as more complicated
procedures to forecast drought and forage
production that could be implemented in
various combinations at various temporal and
spatial scales. Specific recommendations to
support dynamic stocking rate determinations
and promote adaptive management are
summarized below.
Estimation of Residual Biomass to
Determine Grazing Intensity. Estimates of
residual forage could be used as a means to
determine site- and period-specific stocking
rates and grazing intensities, especially during
drought conditions. is is a well-established
management procedure that has a strong
ecological basis focused on soil protection,
continued surface hydrological function,
and maintenance of sufficient residual plant
material to provide a source of regrowth when
rainfall occurs (Bement 1969; Bartolome et al.
1980; Blackburn 1984; Gifford 1985; Clary
and Leininger 2000). Recommendations could
be incorporated within conservation plans
requesting that land managers periodically
monitor residual biomass, at intervals and
locations relevant to management objectives,
following a prescribed set of procedures. ese
residual biomass records could be maintained
as part of the ongoing conservation plan to
support longer-term stocking rate adjustments
and overall adaptive management (Bement
1969; Clary and Leininger 2000).
Forage Production and Drought
Forecasting. Major technical advances have
occurred in the forecasting of forage production
and drought that could be used to support
both tactical (within the growing season) and
strategic (multiple growing seasons) grazing
management decisions at regional levels.
Forage production models such as GPFARM
(Great Plains Framework for Agricultural
Resource Management; Andales et al. 2006)
could be linked with 6–14-d, 1-mo, and 3-mo
precipitation and temperature forecasts through
the NOAA Climate Prediction Center (http://
www.cpc.noaa.gov/index.php) to provide
regional projections of forage availability.
Drought projections are also provided by US
Drought Monitor (http://www.drought.unl.
edu/DM/monitor.html) and the Vegetation
Drought Response Index (http://drought.
unl.edu/vegdri/VegDRI_Main.htm). is
index integrates satellite-based (MODIS)
observations of vegetation conditions based
on NDVI, climate data, and other biophysical
information, such as land cover/land use type
and soil characteristics. Maps of the Vegetation
Drought Response Index have been produced
every 2 wk beginning in 2009 throughout
the conterminous United States that deliver
continuous geographic coverage over large
areas, provide regional to subcounty-scale
information of drought effects on vegetation,
and have inherently finer spatial detail (1-km2
resolution) than other commonly available
drought indicators, such as the US Drought
Monitor. Incorporation of soil water forecasts
(http://www.cpc.ncep.noaa.gov/products/
Soilmst_ Monitoring/US/Soilmst/Soilmst.
shtml) could further promote the accuracy
of these forage production projections.
Forage projections could be developed for
The vast majority
of experimental
results indicate
that there is no
clear advantage
of any one
grazing system
over another
in terms of
ecological
benefits.
CHAP TER 1: An Assessment of Grazing Practices 51
The importance of effective
tactical and strategic decisions
to successful grazing manage-
ment is widely acknowledged,
but only poorly documented.
(Photo: Alexander Smart)
specific periods of management interest and
provide probabilities for forage responses to
dry, average, and wet conditions to ascertain
various levels of management risk. Forecast
information could interface with existing forage
production curves previously developed by the
NRCS to generate various forage inventory
projections to inform management planning.
Drought Contingency Planning. It is essential
that monitoring protocols be linked to drought
contingency planning and management actions.
It is widely recognized that the commonly
employed strategy of “optimistic inaction”
regarding stocking rate adjustments in response
to developing drought is a major contributor to
long-term rangeland degradation (Stafford Smith
and Foran 1992; urow and Taylor 1999;
Torell et al. 2010). However, it is irresponsible to
delay or fail to implement drought contingency
planning based on the unpredictability of
drought given its frequent occurrence on most
rangelands (urow and Taylor 1999). Renewed
emphasis on drought contingency planning
must integrate both economic and ecological
considerations to effectively encourage managers
to adopt and implement destocking options in
relation to drought.
Conservative stocking rates and the formation
of reserve forage or grass banks are well-
established strategies for contending with
economic and environmental aversion to
drought risk (urow and Taylor 1999).
During normal or wet years, these grass
banks could serve as restoration programs to
support prescribed burning or to promote
critical ecosystem services (i.e., biodiversity
and carbon sequestration). Flexible stocking
is also an effective means to cope with
variable precipitation and forage production
(Stafford Smith and Foran 1992; Torell et al.
2010). Cow-calf herds should represent only
a conservative component of total livestock
holdings because of the high cost of adjusting
cow numbers relative to the potential for
short-term gain. Equal forage allocation to
cow-calf and stockers has been recommended
for ranching operations in the western United
States (Torell et al. 2010). It is important
to recognize that flexible stocking conveys
additional costs and financial risks that
will require specific decision-making tools
to expand its adoption, and it may not be
appropriate for risk-averse managers (Tanaka et
al., this volume).
The Role of Grazing Systems
It is extremely difficult to experimentally mimic
livestock movements and defoliation patterns
associated with various applications of grazing
strategies used by managers. However, grazing
systems research has carefully evaluated the
ecological responses of individual plants and
communities, including wildlife populations,
soils and surface soil hydrology, and their
feedbacks on livestock performance, including
forage intake and weight gain per animal and
per unit area. ese major ecological variables
integrate numerous ecosystem processes
sufficiently well to provide reliable guidance
for the implementation and evaluation of the
ecological consequences associated with grazing
systems. e vast majority of experimental
results indicate that there is no clear advantage
of any one grazing system over another in terms
of ecological benefits. Conclusions derived from
these experimental data provide a sufficient
basis to establish ecological guidelines for the
evaluation and application of grazing systems
in conservation planning and ecosystem
assessment. ese data directly corroborate
the long-standing conclusions that weather
52 Conservation Benefits of Rangeland Practices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
variability and stocking rate account for the
majority of variation associated with plant and
animal production and species composition
changes on rangelands (Heitschmidt and
Taylor 1991; Holechek et al. 2001; Derner
and Hart 2007). is interpretation further
emphasizes the importance of effective adaptive
management to the successful operation of
grazed ecosystems, including the establishment
of clear goals, monitoring of resource
conditions, and the ability to make appropriate
and timely management adjustments. Stated in
another way, there is no indication that grazing
systems possess unique properties that enable
them to compensate for poor management
(Briske et al. 2008).
is interpretation also emphasizes that it is
not sufficient to evaluate only whether grazing
management is effective; we also need to
determine why it is effective. is information
is essential to guide development of effective
conservation practices by determining whether
emphasis should be focused on facilitating
practices or on adaptive management skills.
Although largely undocumented, the importance
of effective adaptive management to successful
grazing management is widely acknowledged,
and it requires much greater emphasis than
it has received (Stuth 1991; Brunson and
Burritt 2009; Hanselka et al. 2009). Both
research and monitoring are required on
ranch-scale operations to more clearly evaluate
the contribution of adaptive management to
the success of conservation practices and to
investigate the interaction between adaptive
management and various grazing systems at the
ranch level (e.g., Jacobo et al. 2006).
Deferment and Rest
Few evidence-based conclusions can be drawn
regarding the appropriate season for grazing
deferment and the benefits of long-term rest.
is is partially illustrated by the inconsistent
vegetation responses associated with the
application of rest-rotation systems (Holechek
et al. 2001). Minimal advantages may have
resulted because one season of complete rest
may not have been sufficient to compensate
for more intensive use of grazed pastures in
previous years. Vegetation responses to season
of grazing and deferment are highly dependent
on 1) the timing and amount of precipitation
received during the growing season, 2) the
intensity of defoliation, and 3) the opportunity
for regrowth following defoliation. Research is
required to quantify the benefits of long-term
rest (> 1 yr) and alternating seasons of pasture
use in successive years. Limited evidence suggests
that exclusion of livestock is not necessary
for recovery from moderate drought on well-
conditioned rangeland (Heitschmidt et al. 2005;
Gillen and Sims 2006), but it may be beneficial
following severe drought that has induced
substantial tiller and plant mortality (Dalgleish
and Hartnett 2006; Yahdjian et al. 2006). Plants
subject to light and moderate grazing often
show less drought-induced mortality than plants
that have been severely grazed prior to drought
(Albertson et al. 1957).
Grazing can potentially be used as a tool to
manage wildlife populations, and this may be
particularly true when season of grazing or
deferment of grazing is used to meet specific
wildlife goals. Seasonal livestock use may
especially benefit wildlife where only part of
the range is desirable wildlife habitat and social
avoidance or seasonal migration are important
considerations, facilitation through improved
forage quality has been demonstrated, or
specific nesting requirements are an issue. In
these cases livestock grazing may be imposed
or deferred, depending on cover and foraging
requirements of specific wildlife species. For
example, some waterfowl or some upland
game species require dense nesting cover,
whereas some birds, such as mountain plover
or curlews, choose nesting sites with very little
cover and will not nest in ungrazed or lightly
grazed habitat. Successful use of seasonal and
deferred grazing may also be possible when
pastures with limited wildlife value are available
to minimize livestock use in adjacent pastures
that contain critical wildlife habitat.
Stronger Linkages between Science and
Management
NRCS Conservation Practice Standards
should be routinely informed by both
scientific and management knowledge
external to the agency to ensure that the most
current and vetted information available is
incorporated into the conservation planning
process. is represents a formidable challenge
because science and management are not
directly comparable endeavors (Provenza
1991), and this may partially explain why
The knowledge
gaps identified
in this synthesis
need to be at
least partial
addressed to
promote the
development
and adoption of
more effective
conservation
practices
in grazed
ecosystems.
CHAP TER 1: An Assessment of Grazing Practices 53
The diverse ecosystem services
originating from rangelands
require greater recognition and
valuation. (Photo: USDA: Gary
Kramer)
stronger science–management linkages have
not been forged in the rangeland profession.
Experimental research has focused on specific
aspects of grazing management, including
stocking rate, grazing system, and livestock
distribution, in a static and independent
manner, rather than on their dynamic
interaction within adaptively managed
ecosystems. e critical but poorly defined
contribution of adaptive management to
grazed ecosystems is a major impediment
to the development of linkages between
research and management because decision
making is often excluded from experimental
research even though it is central to grazing
management (Briske et al. 2008; Brunson
and Burritt 2009). Research requires
systematic collection of information to
document outcomes of various grazing
strategies, while the outcomes of conservation
practices standards are seldom monitored
and documented. is often results in the
difficult task of comparing quantitative
research results with qualitative and often
anecdotal management information. New
organizational structures are needed to bridge
the gap between research and management to
support and incentivize a more comprehensive
framework for conservation planning (Boyd
and Svejcar 2009; Svejcar and Havstad 2009).
e NRCS may wish to adopt a more formal
research–management framework to address
conservation programming that could be
convened each time a conservation practice
standard undergoes reevaluation.
Substantial differences between rangeland
science and management have presented barriers
to their integration throughout the history
of the rangeland profession. e extensive
54 Conservation Ben efits of Rangeland Prac tices
D. D. Briske, J. D. Derner, D. G. Milchunas, and K. W. Tate
synthesis of experimental information provided
in this document and the science–management
partnership forged by this 3.5-yr undertaking
represents an important initial step in attaining
this goal. Greater integration and information
exchange among researchers and managers
would create a “win–win” situation for the
profession by facilitating development of
evidence-based conservation practices. is
represents a necessary step if Conservation
Practice Standards are to effectively adopt CEAP
recommendations to provide regular assessments
of the societal benefits of taxpayer investments
in conservation practices. It would also enable
the management community to play a more
direct role in establishing the rangeland research
agenda, as suggested in the following section.
Effective monitoring of conservation practice
outcomes will be crucial for enhancement of
science–management linkages by providing a
quantitative source of information exchange
between these two groups.
KNOWLEDGE GAPS
e following knowledge gaps were identified
in the process of summarizing and interpreting
the experimental literature associated with
prescribed grazing. It is anticipated that by
highlighting these poorly understood issues,
they may receive additional research attention
and funding to promote greater understanding.
It is critical that these knowledge gaps be
at least partially addressed to promote the
development and adoption of more effective
conservation practices in grazed ecosystems.
Ecosystem Processes and Services in
Grazed Ecosystems
Traditionally, grazing research has focused on
several ecological variables, including plant
and animal production and, to a lesser extent,
patterns of species composition change and
wildlife responses and habitat. ese variables
provide a valuable, but admittedly narrow
foundation on which to assess ecosystem
services and environmental quality in grazed
ecosystems. Research programs designed to
increase our understanding of ecosystem
processes and the provisioning of ecosystem
services are desperately needed. Relevant
topics include plant functional groups, soil
health and sustainability, biodiversity, carbon
sequestration, greenhouse gas emissions,
drought and drought recovery, and spatial
heterogeneity of ecosystem and landscape
structure.
Ecosystem Restoration and
Conservation Strategies
Even though grazing management was
initiated to halt and reverse the adverse effects
of overgrazing on rangeland ecosystems,
restoration of grazed ecosystems has received
limited research attention in the past several
decades. Research has been focused primarily
on optimization of livestock production
during the past 30 yr with use of intensified
grazing systems. Consequently, experimental
information regarding the season of utilization
or deferment that is most appropriate to
restore degraded ecosystems or to promote
various conservation strategies is limited.
Research addressing individual bunchgrass
responses to defoliation in the field indicates
that mid-growing season is the most sensitive
period for defoliation. However, we are
unaware of community-level field studies
that corroborate this conclusion. Similarly,
individual plant research has imposed very
severe defoliation intensities compared to
observed utilization rates in grazed ecosystems
so that the direct application of these results
to management is limited. Plant, community,
and ecosystem responses to realistic grazing
patterns would benefit from further
documentation.
Contributions of Adaptive Management
Management goals, abilities, and
opportunities as well as personal goals
and values (e.g., human dimensions) are
inextricably integrated within grazing
management, and they are likely to interact
with the adoption and operation of grazing
systems to an equal or greater extent than the
underlying ecological processes (Briske et al.
2008). erefore, research and monitoring
approaches need to explicitly document
the contribution of adaptive management
within ecosystems to promote a more
comprehensive understanding of successful
grazing management (Brunson and Burritt
2009; Budd and orpe 2009). e potential
synergistic effects of grazing systems and
adaptive management inputs have not been
examined experimentally at the level of the
ranch enterprise (Briske et al. 2008; Brunson
Research and
monitoring
approaches
need to explicitly
document the
contribution
of adaptive
management
within
ecosystems to
promote a more
comprehensive
understanding
of successful
grazing
management.
CHAP TER 1: An Assessment of Grazing Practices 55
Current NRCS grazing
practices are appropriate in
many respects, but multiple
opportunities exist to improve
their effectiveness. (Photo:
Sonja Smith)
and Burritt 2009). Successful research in
this area will require direct involvement of
social and political scientists addressing these
critical human dimensions issues and their
interactions with ecological systems. A novel
experimental approach used by Jacobo et al.
(2006) compared adjacent ranches that had
employed unique grazing systems to achieve
the optimal production outcome. e strength
of this approach is that it enables researchers
to evaluate outcomes reflecting the entire
ranch enterprise, including the capacity
to adaptively manage for the best possible
outcomes, within the context of the respective
grazing system. is approach simultaneously
evaluates ecological and managerial responses,
but it has yet to be determined whether it will
be possible to distinguish between these two
responses. Similarly, incentives and barriers
of various social institutions influencing
the adoption of conservation practices have
received minimal research emphasis given
their importance to the management of
complex adaptive systems (Stafford Smith et
al. 2007).
Evaluation of Large-Scale Ecosystem
Responses
Grazing research has not adequately assessed
the effects of grazing at large scales (Bailey et
al. 1996; Archibald et al. 2005), which often
demonstrate the occurrence of patch- and area-
specific grazing. Smaller experimental pastures
usually result in more uniform distribution of
grazing intensity, which may not appropriately
describe how domestic grazing animals utilize
large landscapes or, in the case of native
ungulates, how they migrate regionally. e
direct application of research results obtained
in small-scale experiments (< 200 ha) to
large ranch enterprises may not be entirely
appropriate because the ecological processes of
interest often do not scale in a linear fashion
(Fuhlendorf and Smeins 1999; Peters et al.
2006). Investigations of the potential benefits
of grazing systems at large scales require further
evaluation, and the evaluation metrics should
involve a variety of ecosystem services, such as
firm-level production, biodiversity concerns,
watershed function, and wildlife habitat.
Integration of Complex Ecosystem
Components
e complexity of grazed ecosystems resides in
the broad array of interacting variables associated
with both ecological and human systems. A wide
range of ecological variation is associated with
rainfall regime (i.e., amount, seasonality, and
intra- and interannual variability), vegetation
structure, composition, and productivity
and soils, prior land use, and livestock
characteristics (i.e., breeds, prior conditioning,
and previous experience). is tremendous
ecological variability is paralleled by large, but
unappreciated variability associated with the
commitment, ability, goals, and opportunities of
managers and associated stakeholders dependent
on the services of these ecosystems (Briske et al.
2008; Brunson and Burritt 2009). e success
and benefits that accrue from conservation
practices within these complex systems is
dependent on three unique activities. First, the
conservation practices must be based on sound
managerial and ecological principles; second,
practices must be effectively incorporated into
the overall conservation plan; and, third, they
must be appropriately applied, maintained, and
monitored by ecosystem managers. e third
component addressing manager or