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Big sagebrush (Artemisia tridentata Nutt.) ecosystems provide habitat for sagebrush-obligate wildlife species such as the Greater Sage-Grouse (Centrocercus urophasianus). The understory of big sagebrush plant communities is composed of grasses and forbs that are important sources of cover and food for wildlife. The grass component is well described in the literature, but the composition, abundance, and habitat role of forbs in these communities is largely unknown. Our objective was to synthesize information about forbs and their importance to Greater Sage-Grouse diets and habitats, how rangeland management practices affect forbs, and how forbs respond to changes in temperature and precipitation. We also sought to identify research gaps and needs concerning forbs in big sagebrush plant communities. We searched for relevant literature including journal articles and state and federal agency reports. Our results indicated that in the spring and summer, Greater Sage-Grouse diets consist of forbs (particularly species in the Asteraceae family), arthropods, and lesser amounts of sagebrush. The diets transition to sagebrush in fall and winter. Forbs provide cover for Greater Sage-Grouse individuals at their lekking, nesting, and brood-rearing sites, and the species has a positive relationship with arthropod presence. The effect of grazing on native forbs may be compounded by invasion of nonnative species and differs depending on grazing intensity. The effect of fire on forbs varies greatly and may depend on time elapsed since burning. In addition, chemical and mechanical treatments affect annual and perennial forbs differently. Temperature and precipitation influence forb phenology, biomass, and abundance differently among species. Our review identified several uncertainties and research needs about forbs in big sagebrush ecosystems. First, in many cases the literature about forbs is reported only at the genus or functional type level. Second, information about forb composition and abundance near lekking sites is limited, despite the fact that lekking sites are an important center of Greater Sage-Grouse activity. Third, there is little published literature on the relationship between forbs and precipitation and between forbs and temperature, thereby limiting our ability to understand potential responses of forbs to climate change. While there is wide agreement among Greater Sage-Grouse biologists that forbs are an important habitat component, our knowledge about the distribution and environmental responses of forb species in big sagebrush plant communities is limited. Our work for the first time synthesizes the current knowledge regarding forbs in sagebrush ecosystems and their importance for Greater Sage-Grouse and identifies additional research needs for effective conservation and management.
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Western North American Naturalist 76(3), © 2016, pp. 298–312
SAGEBRUSH, GREATER SAGE-GROUSE, AND THE
OCCURRENCE AND IMPORTANCE OF FORBS
Victoria E. Pennington1,5, Daniel R. Schlaepfer2, Jeffrey L. Beck3, John B. Bradford4,
Kyle A. Palmquist1, and William K. Lauenroth1
ABSTRACT.—Big sagebrush (Artemisia tridentata Nutt.) ecosystems provide habitat for sagebrush-obligate wildlife
species such as the Greater Sage-Grouse (Centrocercus urophasianus). The understory of big sagebrush plant communities
is composed of grasses and forbs that are important sources of cover and food for wildlife. The grass component is well
described in the literature, but the composition, abundance, and habitat role of forbs in these communities is largely
unknown. Our objective was to synthesize information about forbs and their importance to Greater Sage-Grouse diets
and habitats, how rangeland management practices affect forbs, and how forbs respond to changes in temperature and
precipitation. We also sought to identify research gaps and needs concerning forbs in big sagebrush plant communities.
We searched for relevant literature including journal articles and state and federal agency reports. Our results indicated
that in the spring and summer, Greater Sage-Grouse diets consist of forbs (particularly species in the Asteraceae family),
arthropods, and lesser amounts of sagebrush. The diets transition to sagebrush in fall and winter. Forbs provide cover for
Greater Sage-Grouse individuals at their lekking, nesting, and brood-rearing sites, and the species has a positive rela-
tionship with arthropod presence. The effect of grazing on native forbs may be compounded by invasion of nonnative
species and differs depending on grazing intensity. The effect of fire on forbs varies greatly and may depend on time
elapsed since burning. In addition, chemical and mechanical treatments affect annual and perennial forbs differently.
Temperature and precipitation influence forb phenology, biomass, and abundance differently among species. Our
review identified several uncertainties and research needs about forbs in big sagebrush ecosystems. First, in many cases
the literature about forbs is reported only at the genus or functional type level. Second, information about forb composi-
tion and abundance near lekking sites is limited, despite the fact that lekking sites are an important center of Greater
Sage-Grouse activity. Third, there is little published literature on the relationship between forbs and precipitation and
between forbs and temperature, thereby limiting our ability to understand potential responses of forbs to climate
change. While there is wide agreement among Greater Sage-Grouse biologists that forbs are an important habitat
component, our knowledge about the distribution and environmental responses of forb species in big sagebrush plant
communities is limited. Our work for the first time synthesizes the current knowledge regarding forbs in sagebrush
ecosystems and their importance for Greater Sage-Grouse and identifies additional research needs for effective conser-
vation and management.
RESUMEN.—Los ecosistemas de artemisa (Artemisia tridentata Nutt) son el hábitat de especies silvestres como el
urogallo de las artemisas (Centrocercus urophasianus). El sotobosque de las comunidades de plantas de artemisa grandes
se compone de pastos y malezas que son importantes fuentes de cobertura y alimento para la fauna. El componente de
pastos está bien descrito en la literatura, pero hay un vacío en el conocimiento de la composición, abundancia y el papel que
juega el hábitat de especies herbáceas en estas comunidades. Nuestro objetivo fue sintetizar información sobre las
plantas herbáceas y su importancia para las dietas y los hábitats de los urogallos, cómo las prácticas de manejo de los
pastizales afectan a las plantas herbáceas y cómo éstas responden a los cambios de temperatura y precipitación. También
intentamos identificar las deficiencias en las investigaciones y las necesidades de las plantas herbáceas en comunidades de
plantas de artemisa grandes. Realizamos búsquedas generales en la literatura relevante, incluyendo artículos en revistas
e informes gubernamentales y reportes de agencias federales. Nuestros resultados indican que, durante la primavera y el
verano, la dieta de los urogallos consiste de hierbas, en particular de especies de la familia Asteraceae, artrópodos y, en
menor medida, artemisas. Su dieta cambió a artemisas durante el otoño y el invierno. Las plantas herbáceas ofrecen
cobertura a los urogallos en sus áreas de lek, anidación y lugares de cría, y tienen una relación positiva con la presencia
de artrópodos. Los efectos del pastoreo en las plantas herbáceas nativas pueden agravarse con la invasión de especies no
nativas, y difieren dependiendo de la intensidad del pastoreo. Los efectos del fuego en las plantas herbáceas son muy
variables, y pueden depender del tiempo transcurrido desde la quema. Además, los tratamientos químicos y mecánicos
afectan a las plantas herbáceas anuales y perennes de manera diferente. La temperatura y la precipitación influencian la
fenología, la biomasa y la abundancia de las herbáceas de manera diferente entre especies. Nuestra revisión identificó
varias incertidumbres y la necesidad de estudiar las plantas herbáceas en los ecosistemas de artemisa. En primer lugar, en
muchos casos, la literatura informa sólo a nivel de género o funcional sobre las herbáceas. En segundo lugar, la información
1Department of Botany, University of Wyoming, Laramie, WY.
2Section of Conservation Biology, University of Basel, St. Johanns-Vorstadt 10, CH-4056, Switzerland.
3Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY.
4U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, AZ.
5E-mail: victoria.pennington4@gmail.com
298
Sagebrush (Artemisia L.) ecosystems occur
in portions of western North America where
soil water availability is limiting (Shumar and
Anderson 1986, Schlaepfer et al. 2012) due to
soil properties (Thatcher 1959), topography
(Thatcher 1959), and climate (Daubenmire
1966). Sagebrush plant communities consist
of a shrub overstory and an understory com-
posed of forbs and grasses (Apostol and Sin-
clair 2006). The most widespread species of
sagebrush is big sagebrush (Artemisia triden-
tata Nutt.) (Schultz 2012), and hence the focus
of our paper. Big sagebrush grows mostly in
upland areas (Thatcher 1959) at mean soil
depths of 97–112 cm (Schlaepfer et al. 2012)
and provides habitat for Greater Sage-Grouse
(Centrocercus urophasianus) (Patterson 1952),
Gunnison Sage-Grouse (Centrocercus mini -
mus), and other sagebrush-obligate wildlife
(Knick et al. 2003). There are 3 major big
sagebrush subspecies found in North America:
mountain big sagebrush (A. t. Nutt. ssp. vasey -
ana [Rydb.] Beetle), Wyoming big sagebrush
(A. t. Nutt. ssp. wyomingensis Beetle & Young),
and basin big sagebrush (A. t. Nutt. ssp. tri-
dentata). Mountain big sagebrush grows in
udic soils and primarly at elevations between
2000 and 2800 m, while Wyoming big sage-
brush and basin big sagebrush grow in aridic-
xeric soils, with basin big sagebrush occurring
between 1300 and 2200 m and Wyoming big
sagebrush occurring between 800 and 2200 m
(West 1988, NatureServe 2015).
Greater Sage-Grouse is a sagebrush-obligate
bird that, prior to European settlement in
North America, utilized an estimated 1.2 mil-
lion km2of habitat, of which approximately
668,000 km2remains (Schroeder et al. 2004).
The decrease in habitat is due to large wild-
fires (Nelle et al. 2000, Coates et al. 2015),
overgrazing (Pedersen et al. 2003), human
population expansion (Connelly et al. 2004),
invasive species (Davies 2011), infrastructure
(Braun 1998, Manier et al. 2013), and energy
development (Smith et al. 2014, Holloran et
al. 2015, Kirol et al. 2015). In response to
reduced habitat, Greater Sage-Grouse popula-
tions have declined and are considered at risk
throughout their geographic range in Alberta
and Saskatchewan and in 11 states in the
United States where they occur (Connelly and
Braun 1997, Aldridge and Brigham 2003,
Schroeder et al. 2004). In March 2010,
Greater Sage-Grouse were given a designa-
tion of “warranted but precluded” for listing
under the Endangered Species Act (USFWS
2010); but in September 2015, listing was not
considered warranted (USFWS 2015). How-
ever, Greater Sage-Grouse continues to be a
species of conservation and management con-
cern throughout western North America.
Scientists have described seasonal habitat
requirements for Greater Sage-Grouse for vari-
ous life stages (Patterson 1952, Beck 1977,
Schroeder et al. 1999, Connelly et al. 2000,
Hagen et al. 2007). Herbaceous composition
and structure are particularly important
aspects of Greater Sage-Grouse habitat (Con-
nelly et al. 2000) and can have concomitant
influences on demographic rates, including
nest survival (e.g., Doherty et al. 2014). Habi-
tat guidelines for the breeding season suggest
an understory height >18 cm and understory
canopy cover of 15% at arid sites and 25%
at mesic sites (Connelly et al. 2000). During
brood-rearing, an understory canopy cover
>15% is required by Greater Sage-Grouse,
whereas in the winter, understory height is not
applicable (Connelly et al. 2000), as sagebrush
provides nearly exclusive food and cover to
Greater Sage-Grouse (Eng and Schladweiler
1972, Beck 1977, Remington and Braun 1985,
Smith et al. 2014).
Given that Greater Sage-Grouse are sage-
brush obligates, understanding their habitat
requirements in terms of sagebrush plant com-
munity composition and structure is important
for conservation in the future (Connelly et al.
2016] SAGEBRUSH, SAGE-GROUSE, AND FORBS 299
sobre la composición y la abundancia de las herbáceas cerca de áreas de lek es limitada, a pesar de que los sitios de
lek son una parte importante de la actividad del urogallo. En tercer lugar, tenemos poca literatura sobre la relación entre
las plantas herbáceas y las precipitaciones, así como de las herbáceas y la temperatura, lo cual limita nuestra capacidad
para entender las posibles respuestas de las herbáceas al cambio climático. Nuestra conclusión general es que, si bien
existe un amplio consenso entre los biólogos sobre que las herbáceas son un componente importante en el hábitat del
urogallo, nuestro conocimiento sobre la distribución y las respuestas ambientales de las especies de plantas herbáceas
en las comunidades de grandes plantas de artemisa es limitado. Nuestro trabajo sintetiza, por primera vez, el conoci-
miento actual con respecto a las plantas herbáceas en los ecosistemas de artemisa y su importancia para el urogallo, al
mismo tiempo que identifica la necesidad de continuar investigando para encontrar un manejo y conservación eficaces.
2000, Hagen et al. 2007, Hess and Beck 2012).
Although shrub and grass requirements are
well described, our understanding of the
requirements for forb composition and diver-
sity in big sagebrush communities is limited.
Forbs are herbaceous vascular plants that
are not members of the Cyperaceae, Jun-
caceae, or Poaceae families. They are impor-
tant to Greater Sage-Grouse for 3 reasons:
first, forbs are an important food source for
both juvenile and adult Greater Sage-Grouse
(Klebenow and Gray 1968, Peterson 1970,
Wallestad and Eng 1975, Barnett and Craw-
ford 1994, Drut et al. 1994b); second, although
nesting and brood rearing are likely influ-
enced primarily by grass and sagebrush cover
and structure (Fischer et al. 1996a, Kirol et al.
2012), forbs provide essential cover to conceal
Greater Sage-Grouse eggs, chicks, and adults
from predators (Watters et al. 2002); and
third, Greater Sage-Grouse consume arthro-
pods (Klebenow and Gray 1968, Martin 1970,
Peterson 1970, Wallestad and Eng 1975,
Johnson and Boyce 1990, Drut et al. 1994b),
and forbs are used by arthropods as host
plants (Evans 1984, Porter and Redak 1997).
In the spring and summer, Greater Sage-
Grouse in many areas select for forb and grass
cover that is suitable for nesting and brood
rearing (Klebenow 1969, Peterson 1970,
Wallestad 1971, Kirol et al. 2012). As soils dry
in the summer months and forbs desiccate,
Greater Sage-Grouse may relocate to nearby
mesic areas with abundant green forbs
(Klebenow 1969, Peterson 1970, Wallestad
1971, Fischer et al. 1996b).
Big sagebrush communities have been im -
pacted by range management practices in -
tended to release herbaceous understory. Before
the mid-1970s, approximately 20,000 km2of
sagebrush on federal land had been burned—
or chemically or mechanically treated—and
seeded to exotic grasses, to provide forage for
livestock (Vale 1974). Heavy grazing may
influence the presence of forbs by allowing
nonnative grasses to invade (Branson 1985,
Davies 2011). Additionally, climate change is
an emerging threat to big sagebrush commu-
nities. Global Climate Models (GCMs) suggest
that temperatures in western North America
will likely be warmer (IPCC 2013) and soils
will likely be drier for longer time periods
during the summer (Bradford et al. 2014, Klos
et al. 2014, Palmquist et al. 2016). Climate
change will likely affect the timing of snow -
melt (Bradford et al. 2014), which may affect
forb reproduction, phenology, and mortality
(Inouye 2008). Given these climate projec-
tions and that anthropogenic disturbances will
likely increase in the future, it is important to
understand how forbs might respond to
changes in temperature and precipitation.
Our objective was to compile information
about the importance of forb species to
Greater Sage-Grouse in sagebrush communi-
ties in western North America. Specifically,
we examined (1) which forbs are commonly
used by Greater Sage-Grouse during the
processes of diet and habitat selection, (2) how
rangeland management practices affect forb
composition and biomass, and (3) how forbs
respond to changes in temperature and pre-
cipitation and what implications those forb
responses will have for Greater Sage-Grouse
populations. This work, for the first time,
brings together the currently available knowl-
edge on the relationship between forbs in big
sagebrush ecosystems and the Greater Sage-
Grouse and helps identify knowledge gaps
and important research needs.
METHODS
We conducted a literature search through
Web of Science (Thomson Reuters) and Google
Scholar. On 1 November 2013, we obtained
158 results by searching for the words sage-
grouse and forb in the title, abstract, or subject
fields. Of those 158 articles, 90 were omitted
because they contained only vague informa-
tion about forbs or focused on mining or
restoration methods such as seeding. Most
journal articles were peer reviewed, but we
also included non-peer-reviewed journal arti-
cles, agency reports, conference proceedings,
books, master’s theses, and doctoral disserta-
tions. We classified papers into 4 sections
according to study focus: Greater Sage-Grouse
diet, Greater Sage-Grouse habitat, the rela-
tionship between forbs and rangeland man-
agement practices, and the relationship be -
tween forbs and temperature/precipitation.
Because Greater Sage-Grouse diet and habi -
tat requirements are seasonal, we considered
this information separately for spring, sum -
mer, and fall/winter. Diet studies were selected
and separated by those that were based on
crop dis sections and those that used direct
300 WESTERN NORTH AMERICAN NATURALIST [Volume 76
observations of foraging Greater Sage-Grouse.
Habitat studies were included if they had a
direct asso ciation with Greater Sage-Grouse
and if they evaluated microhabitat characteris-
tics at Greater Sage-Grouse–used sites (e.g.,
nests and brood-rearing locations) compared
to randomly available locations in sagebrush
ecosystems. We report the big sagebrush sub-
species involved in each study, unless the
subspecies was not identified.
Both observational and experimental stud-
ies were grouped together in most sections,
which may have resulted in different conclu-
sions being drawn from these papers due to
differences in methodology. Experimental
studies were differentiated from observational
studies if they had a control and a treatment
group. To address studies with different con-
clusions, we identified conflicting studies that
were in the same section and that had differ-
ent conclusions, and we examined whether
differences in methodology may have caused
them. Although we were ultimately unable
to determine whether differences in methods
or real ecological differences were driving
disparate conclusions, we do identify those
conflicting studies and acknowledge that our
synthesis of them should be interpreted with
caution.
RESULTS AND DISCUSSION
We categorized 68 sources based on
whether the study addressed Greater Sage-
Grouse use of forbs as a diet component
(13 sources), investigated forbs as a habitat
component (23), examined the relationship
between forbs and rangeland management
practices (24), or assessed the relationship
between forbs and temperature/precipitation
(8). There were a total of 22 studies that had
conflicting results possibly due to different
methods, different years, different locations,
or different study areas.
Diet
Thirteen diet studies were included from
Rangeland Ecology and Management, Journal
of Wildlife Management, The Condor, and
various non-peer-reviewed sources (Fig. 1).
Seven (54%) of these studies were published
in the 1990s or later (Fig. 2). There were 12
2016] SAGEBRUSH, SAGE-GROUSE, AND FORBS 301
Fig. 1. Number of studies from journal and nonrefereed articles on Greater Sage-Grouse diet and habitat that contain
information about forbs in big sagebrush plant communities in western North America. Of 158 articles initially obtained,
36 diet and habitat studies were detected from the Web of Science and Google Scholar. (Note: Western North American
Naturalist includes articles from Great Basin Naturalist.)
EcoScience Journal of
Wildlife
Management
Natural
Resources and
Environmental
Issues
PLoSONE Rangeland
Ecology &
Management
The Condor Non-Refereed
Western North
American
Naturalist
Wildlife
Biology
Diet
Habitat
Number of Studies
observational and one experimental study in -
cluded in this section (Supplementary Mater-
ial 1). None of these studies had substantially
conflicting results (e.g., one result was positive
and another result was negative).
SPRING.—Female Greater Sage-Grouse con -
sume a diverse diet in March and April; how-
ever, we found no information about male
diets in spring or about diet effects on male
lekking success. Forbs contain crude protein,
calcium, and phosphorus, which contribute to
nutritional status and reproductive success of
female Greater Sage-Grouse in the spring
(Barnett and Crawford 1994, Gregg et al.
2008). In sagebrush communities in Oregon
and Nevada, adult females ate 21–22 differ-
ent food items, of which 15–16 were different
forb species (Supplementary Material 2; Bar-
nett and Crawford 1994, Gregg et al. 2008).
Females commonly consumed species in the
Asteraceae, Fabaceae, Polemoniaceae, and
Ranunculaceae families (Supplementary Mate-
rial 2; Barnett and Crawford 1994, Gregg
2006, Gregg et al. 2008). Genera commonly
consumed were Agoseris Raf., Antennaria
Gaertn., Arabis L., Astragalus L., Collinsia
Nutt., Crepis L., Delphinium L., Eriogonum
Michx., Lomatium Raf., Phlox L., Ranunculus
L., and Trifolium L. (Supplementary Material
2). In Oregon, forbs were found in 89% of
females’ crop dissections and contributed up
to 35.6% of the aggregate dry mass (Gregg et
al. 2008). In another study, forbs contributed
up to 50% of the weight of the spring diet
(Barnett and Crawford 1994). Less than 1% of
the weight consumed was grass (Barnett and
Crawford 1994).
SUMMER.—Chicks hatch in late spring
(Schroeder 1997) and need access to forbs,
which are more palatable than sagebrush in
summer (Rosentreter 2004). In summer, both
adult and juvenile Greater Sage-Grouse con-
sume forbs (Patterson 1952, Klebenow and
Gray 1968, Klebenow 1969, Martin 1970,
Peterson 1970, Wallestad and Eng 1975, Pyle
1993, Drut et al. 1994b). One study in Oregon
found that juveniles consumed 41 invertebrate
families, 34 forb genera, and 3 grass and shrub
genera (Drut et al. 1994b). In big sagebrush
communities in Idaho, Oregon, and Montana,
adults and juveniles consumed species in the
families Asteraceae, Brassicaceae, Fabaceae,
Liliaceae, and Polemoniaceae in mountain
big sagebrush and Wyoming big sagebrush
302 WESTERN NORTH AMERICAN NATURALIST [Volume 76
Fig. 2. Cumulative number of Greater Sage-Grouse diet and habitat studies that report data on forbs in big sagebrush
plant communities in western North America, 1952 to present. Sources include both journal and nonrefereed articles
obtained from the University of Wyoming libraries and Google Scholar.
(Supplementary Material 2; Patterson 1952,
Klebenow and Gray 1968, Klebenow 1969,
Martin 1970, Peterson 1970, Wallestad and
Eng 1975, Pyle 1993, Drut et al. 1994b). Gen-
era commonly consumed were Achillea L.,
Agoseris, Astragalus, Lactuca L., Taraxacum
F.H. Wigg., and Trifolium (Supplementary
Material 2). Some forb taxa had all above-
ground parts consumed, such as some species
in Asteraceae; whereas other forb species had
only their reproductive parts consumed, such
as some species in Liliaceae (Klebenow and
Gray 1968, Peterson 1970). The seasonal tim-
ing of the consumption of forb species was
likely related to plant phenology or relative
availability; for example, pepperweed (Lepid-
ium L.) pods were low to the ground and
thus eaten by juveniles (Klebenow and Gray
1968, Peterson 1970).
Arthropods are also an important food
source for both adults and juveniles in the
summer. As many as 41 invertebrate taxa
were consumed primarily from the orders
Coleoptera (beetles), Hymenoptera (ants),
and Orthoptera (grasshoppers) in Idaho
(Klebenow and Gray 1968), Montana (Martin
1970, Peterson 1970, Wallestad and Eng
1975), and Oregon (Drut et al. 1994b). In one
experiment, captive-born juvenile Greater
Sage-Grouse 10 days old that were denied a
diet containing insects had a 100% mortality
rate, whereas no juvenile chicks in the con-
trol group (i.e., those fed a diet including
insects and forbs) died during the first 10
days (Johnson and Boyce 1990). An additional
study in Montana found that juveniles con-
sumed more Orthoptera during the summer
when forbs dried up earlier (Peterson 1970).
FALL AND WINTER.—In the fall, the Greater
Sage-Grouse diet transitions from forbs and
insects to big sagebrush foliage (Patterson
1952, Wallestad and Eng 1975, Schroeder et
al. 1999). In October and November, adult
Greater Sage-Grouse in Montana were ob -
served consuming forbs from the Asteraceae
and Fabaceae families, but no insects (Wal -
lestad and Eng 1975). In Montana and Wyo -
ming during December, January, and Febru-
ary, they fed primarily on sagebrush (Patterson
1952, Wallestad and Eng 1975), especially
Wyoming big sagebrush in Colorado (Reming-
ton and Braun 1985) and black sagebrush in
Idaho (Frye et al. 2013).
Habitat
Greater Sage-Grouse use forbs as cover for
life stages including lekking, nesting, and
brood rearing. We identified a total of 23
habitat studies, of which 8 were from the Jour-
nal of Wildlife Management (Fig. 1) and 15
(65%) were from the 1990s or later (Fig. 2).
Habitat studies were based on 22 observa-
tional studies and 1 experimental study (Sup-
plementary Material 1), and 7 of these studies
had conflicting results.
LEKKING AND NESTING.—Forbs provide
herbaceous cover at nesting sites for Greater
Sage-Grouse. Forb cover is important because
it positively influences nest success, most
likely by decreasing nest visibility to preda-
tors (Watters et al. 2002). Forb cover at nesting
sites from 24 studies ranged from approxi-
mately 1% to 21%, and grass cover ranged
from approximately 3% to 58% (Hagen et al.
2007). However, Hagen et al. (2007) is a meta-
analysis paper and therefore synthesized
many different studies with different meth-
ods, which likely explains why there was high
variability in reported forb and grass cover
values. One study suggested that, although
both grass and forb cover contributed to nest
success, forb cover contributed to success
more than grass cover and success could
increase by 4% with an 8%–11% increase in
forb cover in southeastern Alberta (Watters
et al. 2002). By comparison, highest nest suc-
cess is correlated with greater grass height
and shrub cover in the eastern portion of
Greater Sage-Grouse range where sagebrush
is patchier than in areas in the central and
western portion of Greater Sage-Grouse range
(Herman-Brunson et al. 2009, Doherty et al.
2011, 2014).
Greater Sage-Grouse select a variety of
shrubs and forbs at lekking and nesting sites.
Also, Greater Sage-Grouse select nesting sites
with more visual obstruction than random
locations (Dinkins et al. 2016). At a lekking
site in Nevada, tall tumblemustard (Sisym-
brium altissimum L.), an introduced annual/
biennial, averaged 0.5 m in height (Giezentan-
ner and Clark 1974); and in Wyoming, aver -
age visibility from a cover board was 80.2%
and forb species richness was approximately
7 (Klott and Lindzey 1989). At nesting sites
in Alberta, Idaho, Oregon, Washington, and
Wyoming, females used areas dominated by
big sagebrush, threetip sagebrush (Artemisia
2016] SAGEBRUSH, SAGE-GROUSE, AND FORBS 303
tripartita Rydb.), little sage brush (Artemi sia
ar buscula Nutt.), sil ver sage brush (Artemi sia
cana Pursh.), and occasionally dead residual
plants and other cover such as large forbs
(Klebenow 1969, Gregg 1992, Apa 1998, Sveum
et al. 1998, Aldridge and Brigham 2002, Kirol
et al. 2012). Forb families found in the under-
story near nesting sites in Idaho, Oregon,
Utah, and Washington included Asteraceae,
Chenopodiaceae, and Fabaceae (Supplemen-
tary Material 2; Klebenow 1969, Gregg 1992,
Apa 1998, Sveum et al. 1998, Bun nell et al.
2004). In mountain big sagebrush communi-
ties in Utah, forb species diversity averaged
>2 species per 0.25 m2at nesting sites com-
pared to nearby sites that were not selected
for nesting (Bunnell et al. 2004).
BROOD REARING.—Forb cover is important
to Greater Sage-Grouse, both directly for
providing brood-rearing habitat and indirectly
for hosting arthropods which are consumed
by Greater Sage-Grouse broods. In mountain
big sagebrush and Wyoming big sagebrush
communities in Oregon and Nevada, presence
of a single Lepidopteran species (i.e., butter-
flies and moths) decreased the likelihood of
losing an entire brood by 11.8%; and as each
percentage point in the frequency of Phlox
spp. increased at brood-rearing sites, the like-
lihood of losing an entire brood decreased by
2.7% (Gregg and Crawford 2009). Moreover,
in Wyoming, abundance of medium-sized
Coleoptera and Hymenoptera was moderately
(r= 0.68) to strongly (r= 0.81) correlated
with total forb cover in Wyoming big sage-
brush communities (Thompson et al. 2006),
although the relationship between forb cover
and arthropod presence is not always positive
for all orders of arthropods and may depend
on whether there are mainly broad-leaf or
cushion forbs present (Schreiber et al. 2015).
These different conclusions may result from
differing methodology, since Thompson et al.
(2006) grouped all forbs together in their mod-
els, whereas Schreiber et al. (2015) separated
forbs in their models by characteristics such as
leaf type. Woodward et al. (2011) found that
although approximately one-third of initial
nests failed, over half of re-nesting female
Greater Sage-Grouse were successful in a year
when herbaceous cover was higher than in
previous years.
During brood rearing, Greater Sage-
Grouse inhabit sagebrush (8 studies), bitter-
brush (1 study), greasewood (2 studies), grass-
land (1 study), alfalfa fields (Medicago sativa
L.; 1 study), lakebeds/meadows (1 study), and
ditches (1 study); and many of these studies
found that Greater Sage-Grouse use multiple
vegetation types (Klebenow 1969, Peterson
1970, Wallestad 1971, Drut et al. 1994a, Apa
1998, Aldridge and Brigham 2002, Thompson
et al. 2006, Kirol et al. 2012). Plant families
found in brood-rearing habitat include Aster-
aceae, Fabaceae, and Polygonaceae (Supple-
mentary Material 2; Klebenow 1969, Peterson
1969, Martin 1970, Wallestad 1971, Dunn and
Braun 1986, Klott and Lindzey 1990, Apa
1998, Bunnell et al. 2004, Gregg and Crawford
2009). Genera included Achillea, Astragalus,
Lupinus L., Polygonum L., and Taraxacum
(Supplementary Material 2). If forbs are already
abundant, then broods remain at higher eleva-
tions (Wallestad 1971, Aldridge and Brigham
2002). However, Klebenow (1969) found that
53% of broods had dispersed to bitterbrush
communities by July. Peterson (1970) found
that 50% of broods inhabited lower-elevation
greasewood or grassland vegetation types in
September. Wallestad (1971) found that by July
and August, broods occupied approximately
58 ha of alfalfa field and approximately 37 ha
of greasewood. Fischer et al. (1996b) found
that there was a strong negative correlation
(r = 0.83) between Greater Sage-Grouse
migrations and vegetal moisture. Daily move-
ments of broods may also be related to forb
cover. For example, broods preferred areas
with significantly (P< 0.05) lower horizontal
cover during the early and late parts of the
day in Colorado, Wyoming, and Utah (Dunn
and Braun 1986).
Several studies indicated that broods may
select areas with higher forb cover and diver-
sity. Bunnell et al. (2004) found that forb
diversity at brood sites averaged 3 species per
0.25 m2compared to 2 species per 0.25 m2at
available sites. At brood sites in Oregon, Drut
et al. (1994a) found that forb cover varied from
10% to 27% during early brood rearing (Drut
et al. 1994a); while in Montana, forb canopy
cover averaged between 17% and 27%, with
yellow sweetclover (Melilotus officinalis L.
Lam.) contributing 10%–12% of the total forb
cover (Wallestad 1971). We found 2 studies
where the selection effect for forb cover was
negligible between brood and random sites—
in Alberta (11.2% vs. 12.6%; Aldridge and
304 WESTERN NORTH AMERICAN NATURALIST [Volume 76
Brigham 2002) and in Wyoming (food forbs:
6.7% vs. 5.9%; total forb cover 7.5% vs. 7.1%;
Kirol et al. 2012). Aldridge and Brigham
(2002) suggest that their results may be due to
the amount of precipitation in the area com-
bined with a lack of lowland areas, resulting
in little difference between forb abundance
values. Kirol et al. (2012) also had similar aver-
age forb cover at random plots and brood-
rearing locations. Wallestad (1971) did not
specify forb cover values for the surrounding
area, and Bunnell et al. (2004) and Drut et al.
(1994a) stated that forb cover differed be -
tween used habitat and the surrounding area.
Rangeland Management Practices
LIVESTOCK GRAZING.—Livestock grazing is
prevalent in big sagebrush communities, and
the effects of grazing are important because
an estimated 99% of sagebrush communities
have been grazed at some point (West 1996).
Although the 7 grazing studies we identified
are not experimental research (Supplementary
Material 1), there are no conflicting results.
The lack of experimental studies on this sub-
ject has been recognized before, such as by
Miller et al. (1994), though these researchers
did conclude that grazing results in both indi-
rect and direct losses of perennial forbs. Beck
and Mitchell (2000) in their review paper also
called for more experimental studies to inves-
tigate the effects of grazing on forbs. Grazing
may cause the understory of sagebrush com-
munities to change from being dominated by
native grasses to being dominated by invasive
grasses (Branson 1985), such as cheatgrass
(Bromus tectorum L.; Young and Allen 1997);
and in some areas, invasive plants have been
introduced to increase forage for grazers
(Boyd et al. 2014). Several studies have doc-
umented that increases in invasive species
and decreases in native grasses have resulted
in negative impacts for forbs. Davies (2011)
found that approximately 15% of variation in
perennial forb biomass and 19% of variation
in perennial forb cover was explained by
medusahead (Taeniatherum caput-medusae L.
Nevski) in Wyoming big sagebrush communi-
ties in southeastern Oregon, while Parkinson
et al. (2013) found that the relative growth rate
of native forb shoots decreased by 45% to 81%
when forbs such as hoary aster (Machaeran-
thera canescens Pursh A. Gray), Munro’s
globemallow (Sphaeralcea munroana Douglas
Spach), royal penstemon (Penstemon speciosus
Douglas ex Lindl.), and sulphur-flower buck-
wheat (Eriogonum umbellatum Torr.) were
grown with cheatgrass. Furthermore, in moun-
tain big sagebrush communities in Utah,
Greater Sage-Grouse avoided grazed areas
dominated by smooth brome (Bromus inermis
Leyss.), presumably because forb diversity
was low (Bunnell et al. 2004). Evans (1986)
found that Taraxacum abundance was higher
but overall forb diversity was lower in grazed
areas in Nevada. One study suggested that
Greater Sage-Grouse populations inhabiting
heavily grazed mountain big sagebrush com-
munities may have declined because intense
grazing reduced grasses and forbs necessary
for nesting cover (Pedersen et al. 2003). How-
ever, light and rest-rotation grazing in moun-
tain big sagebrush communities may allow
forbs to recover, and Taraxacum and Achillea
present in lightly grazed areas may be pre-
ferred by Greater Sage-Grouse (Neel 1980).
FIRE.—Fire studies in our synthesis are
based on 2 experimental and 10 observational
studies (Supplementary Material 1) of which
10 studies had conflicting results. Fire is an
important disturbance in sagebrush communi-
ties, and it affects ecosystem functioning such
as nutrient dynamics and understory composi-
tion (Knick et al. 2005). Fire is influenced by
factors such as size and density of sagebrush,
presence of cheatgrass, and climate (Baker
2013). Forb responses to fire may differ
between Wyoming big sagebrush and moun-
tain big sagebrush communities (Beck et al.
2012) because mountain big sagebrush com-
munities are more resilient to disturbance
than Wyoming big sagebrush communities,
possibly as a result of growing in conditions
that are more suitable for plant growth
(Chambers et al. 2007, Davies et al. 2011b,
2012a, Chambers et al. 2014). Some forb
species have higher postfire survival rates
than others. For example, Astragalus purshii
Douglas ex Hook. within 2 years of a fall fire
had seedling survival rates that were double in
burned areas compared to unburned areas in
Wyoming big sagebrush communities in Ore-
gon (Wirth and Pyke 2003). In addition, fire
influences forb abundance differentially across
species. In Wyoming big sagebrush communi-
ties in Oregon, the density, frequency, and rel-
ative abundance of 5 out of 19 forb species sig-
nificantly decreased within one year after a
2016] SAGEBRUSH, SAGE-GROUSE, AND FORBS 305
fall fire (Wrobleski and Kauffman 2003).
Wrobleski and Kauffman (2003) found that
65% of Phlox longifolia plants had reproduc-
tive structures postburn compared to 45% of
plants in control plots; and 41% of Modoc
hawksbeard (Crepis modocensis Greene) plants
had reproductive structures postburn com-
pared to 25% in control plots. However, other
forb species had negative responses to fire in
terms of reproduction. For example, Anten-
naria dimorpha (Nutt.) Torr. & A. Gray had an
approximately 20-cm2smaller crown area per
individual, possibly because it was adapted to
live in unburned areas (Wrobleski and Kauff-
man 2003). In contrast, in mountain big sage-
brush communities in Oregon, frequency of
forbs in the tribe Cichorieae (Asteraceae) sig-
nificantly increased in burned areas (78%)
compared to control areas (50%) within 1–2
years after a fall fire (Pyle and Crawford 1996).
These results may have differed because, in
addition to the studies being conducted at
sites with different sagebrush subspecies,
Wrobleski and Kauffman (2003) conducted fall
burns, whereas Pyle and Crawford (1996) con-
ducted both spring and fall burns. Our synthe-
sis of these results should be interpreted with
caution, and more research is needed on how
the timing of fire influences forbs in big sage-
brush ecosystems.
Forb cover after fire also varies in sagebrush
communities. In mountain big sagebrush
communities in Oregon, forb cover was 8%
on unburned plots compared to 13%–15% on
burned plots (Pyle and Crawford 1996). In
Idaho, burning increased forb production by
61% after an August fire, although this study
did not specify sagebrush subspecies (Mueg-
gler and Blaisdell 1958). One study in Mon-
tana found that forb cover in Wyoming big
sagebrush communities was not different
between control and burn plots; forb canopy
cover averaged approximately 8% for both of
these areas (Cooper et al. 2011). In Wyoming
big sagebrush communities in Montana,
Wambolt et al. (2001) reported that there
was no significant (P0.05) change in peren-
nial forb cover in burned sites. Beck et al.
(2009) reported that the rate of increase for
forb cover and richness was greater in
unburned control plots (0.295 [SE 0.084] and
0.180 [SE 0.032], respectively) compared to
burned sites (0.033 [SE 0.126] and 0.068 [SE
0.024], respectively) in Wyoming big sagebrush
communities in southeastern Idaho after an
August prescribed fire. Another study found
that fall fire did not increase perennial forb
cover except for a Phlox sp. in Wyoming big
sagebrush communities in Oregon (Bates et al.
2011). In contrast, annual forb cover composed
of 90% pale madwort (Alyssum alys soides [L.]
L.) was 5.2 (SE 1.9) after fire, compared to
0.7 (SE 0.4) in control plots in those same
Wyoming big sagebrush communities in Ore-
gon (Bates et al. 2011). Forb cover may have
varied between these studies because they
were conducted over different time frames:
Pyle and Crawford (1996) sampled vegetation
within 2 years of burning, Mueggler and
Blaisdell (1958) conducted their study within
3 years of burning, Rhodes et al. (2010) sam-
pled vegetation within 6 years of a fall fire,
Bates et al. (2011) conducted their study in the
8 years following fire, Beck et al. (2009) con-
ducted their study as much as 14 years after
fire, Wambolt et al. (2001) conducted their
study between 2 and 32 years after fire, and
Cooper et al. (2011) sampled their sites be -
tween 4 and 67 years after fire. As such, these
results may not be directly comparable.
Fire also affects some arthropods. Burning
increased grasshopper abundance 2.3 times in
Wyoming big sagebrush sites burned in the
1990s compared to reference sites or sites
burned or mowed from 2000 to 2006 in north
central Wyoming (Hess and Beck 2014). Fire
did not affect ants in Wyoming (Hess and
Beck 2014) but did negatively affect ant
abundance in Oregon (Rhodes et al. 2010,
Bates et al. 2011) and Idaho (Fischer et al.
1996a). While Hess and Beck (2014) con-
ducted their study at sites treated over a wide
time period (2–19 years postburn) and had the
longest time between burning and sampling,
Rhodes et al. (2010), Bates et al. (2011), and
Fischer et al. (1996a) sampled insects rela-
tively soon (1–8 years) after fire, which may
explain the discrepancy in these results for
ants. Fire did not affect beetles in Idaho
(Fischer et al. 1996a), Oregon (Pyle and Craw-
ford 1996, Rhodes et al. 2010, Bates et al.
2011), or Wyoming (Hess and Beck 2014).
CHEMICAL AND MECHANICAL TREATMENTS.
Chemical and mechanical treatments were
examined in 3 observational and 5 experimen-
tal studies (Supplementary Material 1), of
which 5 had conflicting results. Chemical
treatments have been applied to sagebrush
306 WESTERN NORTH AMERICAN NATURALIST [Volume 76
since the 1940s (Miller and Eddleman 2001)
and have had varying effects on forb cover and
composition. Tebuthiuron, an herbicide that
hinders photosynthesis (Crawford et al. 2004),
increased mean forb cover—largely composed
of common dandelion (Taraxacum officinale
F.H. Wigg.)—from 4% to 12% in mountain
big sagebrush communities in Utah (Dahlgren
et al. 2006). This increase in forb cover may
have been due to chemical application which
resulted in “sagebrush skeletons” that altered
wind and moisture conditions for forbs
(Dahlgren et al. 2006). In another study con-
ducted in Wyoming big sagebrush communi-
ties in California, native annual forb cover was
6.5 times higher in plots treated with Imaza-
pic (Kyser et al. 2013).
Another chemical treatment, 2,4-D, which
causes uncontrolled growth and eventual
death in broad-leaf plants, has negative effects
on forbs. In a Montana study, forbs con-
tributed about 20% of canopy cover in the
understory, where only 4% of Greater Sage-
Grouse locations occurred in 2,4-D sprayed
strips, whereas forbs in unsprayed strips con-
tributed about 40% of canopy cover in the
understory (Martin 1970). In Idaho, spraying
2,4-D resulted in a 39% loss of forbs, espe-
cially Lupinus spp. and Erigeron L. spp.
(Mueggler and Blaisdell 1958). Chemical treat-
ments increased nonnative and annual forb
cover in these studies.
Mechanical treatments used to reduce
sagebrush cover also affect forbs and arthro-
pods in sagebrush communities. In mountain
big sagebrush communities in Utah, Dixie
harrow treatments (using a tractor to drag a
harrow with welded railroad spikes) increased
forb cover from 7.6% to 10.7%, but there were
only slight forb cover increases in plots treated
with a Lawson aerator, possibly because more
overstory cover was left after treatment (Dahl -
gren et al. 2006). In Idaho, roto-beating (shred -
ding sagebrush) and railing (using a railroad
rail to thin sagebrush) big sagebrush com -
munities with a healthy herbaceous under-
story increased forb production by 50% and
20%, respectively, especially for Lupinus spp.
(Mueggler and Blaisdell 1958). In Oregon,
mowed Wyoming big sagebrush communities
had more annual forbs and nonnative grasses
(Davies et al. 2011a, 2012b), whereas in Ore-
gon (Davies et al. 2011a) and Wyoming (Hess
and Beck 2014) perennial forb abundance did
not increase after mowing. Mowing did not
increase ant, grasshopper, or beetle abun-
dance in Wyoming (Hess and Beck 2014).
Although Dahlgren et al. (2006) reported in -
creases in overall forb abundance, they did
not distinguish between annual and peren -
nial forbs when collecting field data, whereas
Davies et al. (2011a, 2012b) and Hess and
Beck (2014) examined these groups separately.
Additionally, Davies et al. (2011a, 2012b) and
Hess and Beck (2014) used the same treat-
ment in their methods (mowing), whereas
Mueggler and Blaisdell (1958) used roto-
beating and railing as their methods for study-
ing plant responses.
Temperature and Precipitation
Temperature and precipitation studies
included 2 observational and 6 experimental
studies. None of these studies had results
that conflicted appreciably.
TEMPERATURE.—Adler and Hille Ris Lam-
bers (2008) hypothesized that shrub and grass
functional groups may fare better under future
climate change than forbs because shrubs and
grasses occur in higher densities than forbs.
Increased temperatures will likely cause snow -
melt to occur sooner (Harte and Shaw 1995,
Price and Waser 1998, Palmquist et al. 2016),
with important implications for forb species
because timing of snowmelt and winter pre-
cipitation influences forb phenology (Price
and Waser 1998, Inouye 2008). Warmer tem-
peratures can cause forb species to emerge
sooner and die later (e.g., Munro’s globemal-
low, Sphaeralcea munroana Douglas Spach,
and Lewis flax, Linum lewisii Pursh), emerge
sooner and die sooner (e.g., Palmer’s penste-
mon, Penstemon palmeri A. Gray), or have
lower emergence and higher mortality rates
(e.g., tapertip hawksbeard, Crepis acuminata
Nutt.; Whitcomb 2011). Forbs in heated plots
in Colorado had significantly less aboveground
biomass in 1993 (P= 0.001) and 1994 (P=
0.004) when snowmelt occurred earlier (Harte
and Shaw 1995). Another study found negative
responses to warming in several species. For
example, the number of larkspur (Delphin -
ium L.) in control plots was 4.6 individuals
m2compared to 1.3 individuals m2in
heated plots (de Valpine and Harte 2001). In
addition, the reproductive parts of Erigeron,
Delphinium, and Helianthella (Helianthella
Torr. & A. Gray) plants are susceptible to
2016] SAGEBRUSH, SAGE-GROUSE, AND FORBS 307
frost damage (Inouye 2008). One experiment
documented positive responses of warming for
3 genera: Helianthella because it experienced
less frost damage, Eriogonum because it had
larger flowering stalks, and cinquefoil (Poten-
tilla L.) because it exhibited increases in
above ground biomass (de Valpine and Harte
2001). Therefore, although these studies over-
all suggest that warming may decrease the
biomass of some common forb genera (except
Potentilla), there may be less damage to forb
genera than expected from frost.
PRECIPITATION.—Precipitation affects forbs
in big sagebrush communities because these
communities are already water limited. Long-
term studies in basin big sagebrush and
Wyoming big sagebrush communities indi-
cated that although forb density fluctuated
over 60 years, extreme drought may result in
increased mortality of perennial forbs (Ander-
son and Inouye 2001). In an experiment con-
ducted in a Wyoming big sagebrush commu-
nity in Oregon, areas with shallow soils that
were given precipitation treatments in the
winter and spring had similar soil water con-
tent, but in 1999 perennial forbs in the spring
precipitation treatments had less biomass
(approximately 20 kg ha1 vs. 60 kg ha1)
and cover (approximately 2% vs. 8%) than
those in the winter precipititaion treatements,
suggesting that the timing of precipitation
may be important to forbs (Bates et al. 2006).
In another experiment in Idaho, Tragopogon
dubius seedling survival by August 2007 was
higher in control plots (approximate x
= 60%)
than plots with shelter from winter precipita-
tion (approximate x
= 18%; Prevéy et al.
2010). Overall, the existing literature suggests
that native forbs have low resilience to
changes in precipitation patterns in big sage-
brush communities.
Knowledge Gaps and Research Needs
Our analysis uncovered 3 important uncer-
tainties and research needs. First, information
about forbs was reported at the functional
type level or genus in many studies. Second,
information about forbs at lekking sites and
male Greater Sage-Grouse was limited. Third,
the data linking forbs and temperature/pre -
cipitation were sparse.
Many studies focused their measurements
on the dynamics of shrubs and graminoids,
while information about forbs was vague or
incomplete. Many diet or habitat studies
grouped forbs together as a single functional
group, despite forbs having a high diversity of
traits (e.g., Wallestad 1971, Dunn and Braun
1986, Klott and Lindzey 1989, Drut et al.
1994a, Sveum et al. 1998, Schroeder et al.
1999, Aldridge and Brigham 2002, Watters et
al. 2002, Thompson et al. 2006, Hagen et al.
2007, Beck et al. 2009, Woodward et al. 2011,
Kirol et al. 2012, Schreiber et al. 2015). Other
diet or habitat studies included information
to the family or genus level but did not iden-
tify most or all forbs to the species level (e.g.,
Patterson 1952, Gregg 1992, Barnett and
Crawford 1994, Drut et al. 1994b, Gregg and
Crawford 2009).
Only 3 of 13 diet studies and 2 of 23 habitat
studies discussed the importance of forbs for
Greater Sage-Grouse during lekking (Giezen-
tanner and Clark 1974, Klott and Lindzey
1989, Barnett and Crawford 1994, Gregg 2006,
Gregg et al. 2008), and they focused mostly on
females. Leks are important because they are
where breeding and summer life stage activi-
ties mostly take place (Wallestad and Schlad-
weiler 1974, Schroeder et al. 1999). Therefore,
more information is needed about the role of
forbs at lekking sites.
We found very little information about the
relationship between forbs and temperature /
precipitation. More literature was available
about the effects of rangeland management
practices on forbs than the effects of changes
in temperature/precipitation on forbs, espe-
cially for sagebrush communities. This lack of
information limits our ability to understand
the potential responses of forbs to climate
change in these communities. Although Dum-
roese et al. (2015) reported information about
the importance of forbs and arthropods in the
diet and habitat of Greater Sage-Grouse and
the relationship between forbs and some range-
land management practices, to our knowledge,
this paper is the first to bring all of these com-
ponents, as well as temperature and precipi-
tation, together. This topic is an important
research need because models suggest that
future climate changes will likely affect sage-
brush communities (Homer et al. 2015).
Overall, we conclude that there is wide
agreement among Greater Sage-Grouse biolo-
gists that forbs are an important diet and habitat
component. However, our knowledge about
forbs in sagebrush communities is limited
308 WESTERN NORTH AMERICAN NATURALIST [Volume 76
and additional research is needed to fill key
knowledge gaps.
SUPPLEMENTARY MATERIAL
Two online-only supplementary files accom-
pany this article (scholarsarchive.byu.edu/
wnan/vol76/iss3/6).
SUPPLEMENTARY MATERIAL 1. Observational and
experimental studies by section for forbs used by
Greater Sage-Grouse: diet, habitat, the relation-
ship of forbs to rangeland management practices,
and the relationship of forbs to temperature and
precipitation. Sources were obtained from searches
through Web of Science (Thomson Reuters) and
Google Scholar.
SUPPLEMENTARY MATERIAL 2. Forbs found in
Greater Sage-Grouse diet and habitat studies in
big sagebrush plant communities. Information was
obtained from sources searched through Web of
Science (Thomson Reuters) and Google Scholar.
ACKNOWLEDGMENTS
We thank the U.S. Geological Survey North
Central Climate Science Center (grant G12AC
20504), the U.S. Fish and Wildlife Service
(F13AC00865), and the University of Wyoming
for financial support. We also thank 2 anony-
mous reviewers whose input improved an ear-
lier version of this manuscript. Any use of
trade, product, or firm names is for descriptive
purposes only and does not imply endorse-
ment by the U.S. government.
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Supplementary resources (2)

... If herbaceous production is limiting, big sagebrush reduction treatments may be beneficial if they increase the availability of forbs and invertebrates necessary for adults and juveniles. Information regarding the response of forbs and invertebrates to treated sagebrush habitats is often conflicting and depends largely on the sagebrush community and time period of study (Pennington et al., 2016). Furthermore, there is little information available about the response of forbs and invertebrates following chemical treatments in Wyoming big sagebrush communities. ...
... Environmental variation may influence how dietary items for sage-grouse respond after treatment. Annual weather influences total herbaceous production in sagebrush communities (Noy-Meir, 1973); however, the relationship between annual weather and forb production is less understood (Pennington et al., 2016). ...
Article
Treatments in big sagebrush (Artemisia tridentata Nutt.) are often implemented to improve habitat conditions for species such as greater sage-grouse (Centrocercus urophasianus). These treatments aimto increase the availability of forbs and invertebrates critical to juvenile and adult sage-grouse during the breeding season. However, information regarding the response of forbs in treated sagebrush are often conflicting, dependent on the type of sagebrush community treated and time after treatment. In addition, there is little information on the response of invertebrates to treatments, particularly herbicide treatments inWyoming big sagebrush (A.t. ssp. wyomingensis Beetle & Young) communities.We evaluated the response of forbs and invertebrates in Wyoming big sagebrush that had been mowed or aerially treated with tebuthiuron compared with untreated reference areas. We also compared forb and invertebrate dry matter (DM) between treated plots and locations used by brood-rearing females. Forb and invertebrate DMinmowed and tebuthiuron treatments did not differ fromuntreated plots up to 4 yr after treatment and were equal to or less than locations used by brood-rearing grouse up to 2 yr after treatment. Our findings corroborate best available science that suggest treating Wyoming big sagebrush may not increase food availability for sage-grouse.
... This congregation of animals and associated heavy grazing pressure can result in changes to the structure and composition of mesic meadow vegetation ( Bullock et al. 2001 ;Boyd et al. 2014 ) and soils ( Naeth et al. 1991 ), which may influence the ability of mesic meadows to provide wildlife habitat ( Krausman et al. 2009 ). The complexities of grazing management systems require controlled experiments to document how variation in the application of grazing affects mesic habitats that support vital preferred forb communities for sage-grouse during late brood rearing ( Beck and Mitchell 20 0 0 ;Pennington et al. 2016 ). ...
Article
Full-text available
Mesic meadows provide valuable water and forage resources for wildlife and livestock in the arid western United States. Greater sage-grouse (Centrocercus urophasianus), a species of conservation concern, rely on these habitats because they support forb species of high importance to broods during late brood rearing. Because mesic meadows comprise a small fraction of the landscape, identifying grazing strategies compatible with maintenance and production of mesic resources is vital to balancing livestock production with suitable conditions for sage-grouse. We evaluated relationships between short-duration grazing treatments and habitat components important to sage-grouse in mesic meadows. In 2019 and 2020, we implemented short-duration (16 d) grazing treatments that varied by season (Early: early June; Late: early August) and intensity (control: 0%, moderate: 30−40%, high: 70−80% relative use). We evaluated cover and biomass percentages of high importance forbs (HIF), soil moisture, and noxious weed cover before and after grazing and again after pasture regrowth (Early: ≈13 wk, Late: ≈6 wk). Short-duration treatments did not reduce HIF cover or biomass. Early-season (P = 0.018) and high-intensity (P = 0.04) grazing increased HIF cover during the pregrazing sample period from 2019 to 2020, suggesting positive effects of these treatments on HIF cover during the pregrazing sample period. Postgrazing HIF cover and biomass percentages remained similar across treatments. Percentages of HIF biomass after regrowth were greater (P = 0.04) in early-season than late-season treatments in 2020. Seasonal declines in soil moisture from pregrazing to regrowth sample periods were greater (P < 0.001) in early-season treatments than late-season treatments but not associated with grazing intensity (P = 0.60). Cover of noxious weeds remained unchanged under short-duration treatments. Our study emphasizes the potential of early-season, high-intensity grazing to increase HIF cover and biomass for brood-rearing sage-grouse in mesic meadows over short time intervals.
... the Gunnison sage-grouse (Centrocercus minimus), the greater sagegrouse (Centrocercus urophasianus), and pygmy rabbits (Brachylagus idahoensis). Habitat components for these and other sagebrush obligates consist of three plant functional types: big sagebrush, perennial grasses, and perennial forbs (Connelly et al., 2004;Connelly et al., 2011;Knick et al., 2003;Manier et al., 2013;Pennington et al., 2016;Rachlow et al., 2021). For example, sage-grouse brood-rearing sites are characterized by a higher-than-average abundance of perennial grasses and forbs, which provide food sources for hens and chicks (Connelly et al., 2004;Schroeder et al., 1999). ...
Article
Plant community response to climate change will be influenced by individual plant responses that emerge from competition for limiting resources that fluctuate through time and vary across space. Projecting these responses requires an approach that integrates environmental conditions and species interactions that result from future climatic variability. Dryland plant communities are being substantially affected by climate change because their structure and function are closely tied to precipitation and temperature, yet impacts vary substantially due to environmental heterogeneity, especially in topographically complex regions. Here, we quantified the effects of climate change on big sagebrush (Artemisia tridentata Nutt.) plant communities that span 76 million ha in the western United States. We used an individual‐based plant simulation model that represents intra‐ and inter‐specific competition for water availability, which is represented by a process‐based soil water balance model. For dominant plant functional types, we quantified changes in biomass and characterized agreement among 52 future climate scenarios. We then used a multivariate matching algorithm to generate fine‐scale interpolated surfaces of functional type biomass for our study area. Results suggest geographically divergent responses of big sagebrush to climate change (changes in biomass of ‐20% to +27%), declines in perennial C3 grass and perennial forb biomass in most sites, and widespread, consistent, and sometimes large increases in perennial C4 grasses. The largest declines in big sagebrush, perennial C3 grass and perennial forb biomass were simulated in warm, dry sites. In contrast, we simulated no change or increases in functional type biomass in cold, moist sites. There was high agreement among climate scenarios on climate change impacts to functional type biomass, except for big sagebrush. Collectively, these results suggest divergent responses to warming in moisture‐limited vs. temperature‐limited sites and potential shifts in the relative importance of some of the dominant functional types that result from competition for limiting resources.
... Hook. & Arn., all of which are widely distributed throughout the region and considered a high priority for restoration (Dumroese et al., 2016;Pennington et al., 2016). Seeds were collected from wild stands in summer between June and July 2015 (Table 1). ...
Article
In degraded drylands, post-disturbance native plant community re-establishment is almost exclusively conducted using seeds. These restoration efforts are challenging, in large part as a result of a limited understanding of seed dormancy and germination traits. In this paper, we characterize these traits for four herbaceous perennials (Asteraceae) that are widely distributed and highly desired in the restoration of ecologically imperiled drylands of North America. We assess baseline germination and the effects of chemical stimulants across a suite of temperatures and quantify the influence of (1) cold stratification, (2) dry after-ripening, and (3) dry cold storage on germination. Three months of cold stratification achieved near-maximum dormancy alleviation for all species. Exposure to warmer temperatures following stratification increased germination further, reducing the required stratification length. Across all species, at least a third of seeds maintained at 3 ± 2 °C germinated, suggesting that in situ germination occurs in late winter or early spring. Changes in the thermal germination envelope were species dependent, indicating different germination niches and strategies for population persistence. Dry after-ripening and cold storage improved germination, but responses were highly variable across species, temperature, and time. Chemical stimulants promoted germination in three species and may be an alternative to cold stratification or after-ripening.
... Although big sagebrush and bluebunch wheatgrass are arguably two of the most important plant species in sagebrush steppe ecosystems, intact (i.e., uninvaded) sagebrush steppe plant communities can be highly diverse and forb diversity especially has been implicated as an important aspect of habitat quality for sage-grouse (see Pennington et al., 2016). Early studies of AMF in sagebrush steppe focused on identifying colonization of, and AMF species associated with, plants in the community (see Wicklow-Howard, 1994), but few studies have attempted to gain a broad understanding of mycorrhizal responsiveness of sagebrush steppe plants. ...
Technical Report
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USGS sage-grouse and sagebrush ecosystem research is aligned with priority needs outlined in the “Integrated Rangeland Fire Management Strategy Actionable Science Plan” (Integrated Rangeland Fire Management Strategy Actionable Science Plan Team, 2016). The list of 116 research projects is organized into five thematic areas: fire (16 projects); invasive species (7 projects); restoration (23 projects); sagebrush, sage-grouse, and other sagebrush-associated species (60 projects); and weather and climate (10 projects). Individual projects often overlap multiple themes (for example, effects of wildfire and invasive annual grasses on greater sage-grouse habitat); therefore, project descriptions are organized according to the main focal theme.
Technical Report
Full-text available
USGS sage-grouse and sagebrush ecosystem research is aligned with priority needs outlined in the “Integrated Rangeland Fire Management Strategy Actionable Science Plan” (Integrated Rangeland Fire Management Strategy Actionable Science Plan Team, 2016). The list of 116 research projects is organized into five thematic areas: fire (16 projects); invasive species (7 projects); restoration (23 projects); sagebrush, sage-grouse, and other sagebrush-associated species (60 projects); and weather and climate (10 projects). Individual projects often overlap multiple themes (for example, effects of wildfire and invasive annual grasses on greater sage-grouse habitat); therefore, project descriptions are organized according to the main focal theme.
Article
Dryland ecosystems may be especially vulnerable to expected 21st century increases in temperature and aridity because they are tightly controlled by moisture availability. However, climate impact assessments in drylands are difficult because ecological dynamics are dictated by drought conditions that are difficult to define and complex to estimate from climate conditions alone. In addition, precipitation projections vary substantially among climate models, enhancing variation in overall trajectories for aridity. Here, we constrain this uncertainty by utilizing an ecosystem water balance model to quantify drought conditions with recognized ecological importance, and by identifying changes in ecological drought conditions that are robust among climate models, defined here as when >90% of models agree in the direction of change. Despite limited evidence for robust changes in precipitation, changes in ecological drought are robust over large portions of drylands in the United States and Canada. Our results suggest strong regional differences in long‐term drought trajectories, epitomized by chronic drought increases in southern areas, notably the Upper Gila Mountains and South‐Central Semi‐arid Prairies, and decreases in the north, particularly portions of the Temperate and West‐Central Semi‐arid Prairies. However, we also found that exposure to hot‐dry stress is increasing faster than mean annual temperature over most of these drylands, and those increases are greatest in northern areas. Robust shifts in seasonal drought are most apparent during the cool season; when soil water availability is projected to increase in northern regions and decrease in southern regions. The implications of these robust drought trajectories for ecosystems will vary geographically, and these results provide useful insights about the impact of climate change on these dryland ecosystems. More broadly, this approach of identifying robust changes in ecological drought may be useful for other assessments of climate impacts in drylands and provide a more rigorous foundation for making long‐term strategic resource management decisions.
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The Great Basin Desert is among the most difficult places for successful ecological restoration due to the repeated effects of fire, aridity and invasive plants. The goal of this research was to determine whether four local populations of two native annual forb species, Microsteris gracilis and Layia glandulosa, differed in the capacity to survive competition with cheatgrass (Bromus tectorum) and whether soil nutrients affected outcomes. Seeds were collected in the spring of 2016 and planted in two phases in the fall, allowing for maximum germination. Factorial treatments included a competition treatment, with either a single forb or cheatgrass seed sown alone or together, and a soil nutrient treatment, with either no nutrient addition (low) or the addition of fertilizer pellets (high). Plants were harvested, dried and weighed in March of 2017. Biomass and flower production were compared across treatments. The two forb species had declining performance in competition with cheatgrass, especially under high nutrient conditions, where cheatgrass grew larger. Neither species exhibited population-level variation in reproductive response to any treatment, but L. glandulosa populations varied in biomass responses to soil nutrient availability. Though the presence of cheatgrass competition and high soil nutrients affected all forb populations negatively, one L. glandulosa population was able to respond to increased soil nutrients, indicating that some populations may serve as better sources for restoration.
Technical Report
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The sagebrush (Artemisia spp.) ecosystem extends across a large portion of the Western United States, and the greater sage-grouse (Centrocercus urophasianus) is one of the iconic species of this ecosystem. Greater sage-grouse populations occur in 11 States and are dependent on relatively large expanses of sagebrush-dominated habitat. Sage-grouse populations have been experiencing long-term declines owing to multiple stressors, including interactions among fire, exotic plant invasions, and human land uses, which have resulted in significant loss, fragmentation, and degradation of landscapes once dominated by sagebrush. In addition to the sage-grouse, over 350 species of plants and animals are dependent on the sagebrush ecosystem. Increasing knowledge about how these species and the sagebrush ecosystem respond to these stressors and to management actions can inform and improve strategies to maintain existing areas of intact sagebrush and restore degraded landscapes. The U.S. Geological Survey (USGS) has a broad research program focused on providing the science needed to inform these strategies and to help land and resource managers at the Federal, State, Tribal, and local levels as they work towards sustainable sage-grouse populations and restored landscapes for the broad range of uses critical to stakeholders in the Western United States. USGS science has provided a foundation for major land and resource management decisions including those that precluded the need to list the greater sage-grouse under the Endangered Species Act. The USGS is continuing to build on that foundation to inform science-based decisions to help support local economies and the continued conservation, management, and restoration of the sagebrush ecosystem. This report contains descriptions of USGS sage-grouse and sagebrush ecosystem research projects that are ongoing or were active during 2018 and is organized into five thematic areas: Fire, Invasive Species, Restoration, Sagebrush, Sage-Grouse, and Other Sagebrush-Associated Species; and Climate and Weather.
Article
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Degradation, fragmentation, and loss of native sagebrush (Artemisia spp.) landscapes have imperiled these habitats and their associated avifauna. Historically, this vast piece of the Western landscape has been undervalued: even though more than 70% of all remaining sagebrush habitat in the United States is publicly owned, <3% of it is protected as federal reserves or national parks. We review the threats facing birds in sagebrush habitats to emphasize the urgency for conservation and research actions, and synthesize existing information that forms the foundation for recommended research directions. Management and conservation of birds in sagebrush habitats will require more research into four major topics: (1) identification of primary land-use practices and their influence on sagebrush habitats and birds, (2) better understanding of bird responses to habitat components and disturbance processes of sagebrush ecosystems, (3) improved hierarchical designs for surveying and monitoring programs, and (4) linking bird movements and population changes during migration and wintering periods to dynamics on the sagebrush breeding grounds. This research is essential because we already have seen that sagebrush habitats can be altered by land use, spread of invasive plants, and disrupted disturbance regimes beyond a threshold at which natural recovery is unlikely. Research on these issues should be instituted on lands managed by state or federal agencies because most lands still dominated by sagebrush are owned publicly. In addition to the challenge of understanding shrubsteppe bird-habitat dynamics, conservation of sagebrush landscapes depends on our ability to recognize and communicate their intrinsic value and on our resolve to conserve them. ¿Tambaleando en el Borde o Demasiado Tarde? Asuntos de Conservación e Investigación para la Avifauna de Ambientes de Matorral de Artemisia spp Resumen. La degradación, fragmentación y pérdida de paisajes nativos de matorrales de Artemisia spp. han puesto en peligro a estos ambientes y su avifauna asociada. Históricamente, esta vasta porción del paisaje occidental ha sido subvalorada: aunque más del 70% de todo el hábitat de matorral de Artemisia de los Estados Unidos es de propiedad pública, <3% de éste es protegido por reservas federales o parques nacionales. En este artículo revisamos las amenazas a las que se enfrentan las aves de los matorrales de Artemisia para enfatizar la urgencia de emprender acciones de conservación e investigación, y sintetizamos la información existente que constituye la base para una serie de directrices de investigación recomendadas. El manejo y conservación de las aves de los matorrales de Artemisia necesitará más investigación en cuatro tópicos principales: (1) la identificación de prácticas primarias de uso del suelo y su influencia sobre los ambientes y las aves de Artemisia, (2) un mejor entendimiento de las respuestas de las aves a componentes del hábitat y a procesos de disturbio de los ecosistemas de Artemisia, (3) el mejoramiento de diseños jerárquicos para programas de censos y monitoreos y (4) la conexión de los movimientos de las aves y los cambios poblacionales durante la migración y en los períodos de invernada con la dinámica en las áreas reproductivas de matorrales de Artemisia. Estas investigaciones son esenciales porque ya hemos visto que los ambientes de Artemisia pueden ser alterados por el uso del suelo, la diseminación de plantas invasoras y la disrupción de los regímenes de disturbio más allá de un umbral en el que la recuperación natural es poco probable. La investigación en estos asuntos debe instituirse en tierras manejadas por agencias estatales o federales porque la mayoría de las tierras aún dominadas por Artemisia son de propiedad pública. Además del desafío de entender la dinámica aves-hábitat en las estepas arbustivas, la conservación de los paisajes de matorral de Artemisia depende de nuestra habilidad de reconocer y comunicar su valor intrínseco y de nuestra decisión para conservarlos.
Article
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We revised distribution maps of potential presettlement habitat and current populations for Greater Sage-Grouse (Centrocercus urophasianus) and Gunnison Sage- Grouse (C. minimus) in North America. The revised map of potential presettlement habitat included some areas omitted from previously published maps such as the San Luis Valley of Colorado and Jackson area of Wyoming. Areas excluded from the revised maps were those dominated by barren, alpine, and forest habitats. The resulting presettlement distribution of potential habitat for Greater Sage-Grouse encompassed 1 200 483 km2, with the species' current range 668 412 km2. The distribution of potential Gunnison Sage-Grouse habitat encompassed 46 521 km2, with the current range 4787 km2. The dramatic differences between the potential presettlement and current distributions appear related to habitat alteration and degradation, including the adverse effects of cultivation, fragmentation, reduction of sagebrush and native herbaceous cover, development, introduction and expansion of invasive plant species, encroachment by trees, and issues related to livestock grazing. Distribución de Centrocercus spp. en América del Norte Resumen. Revisamos los mapas de distribución potencial precolombino y de poblaciones actuales de Centrocerus urophasianus y C. minimus en América del Norte. El mapa modificado de hábitat potencial precolombino incluyó algunas áreas omitidas de mapas anteriormente publicados, como el Valle San Luis de Colorado y el área de Jackson, Wyoming. Las áreas excluídas de los mapas modificados fueron las dominadas por hábitats forestales, alpinos y estériles. La distribución precolombina resultante para C. urophasianus abarcó 1 200 483 km2, con un territorio actual de 668 412 km2. La distribución de habitat potencial para C. minimus abarcó 46 521 km2, con un territorio actual de 4787 km2. Estos contrastes tan marcados parecen estar relacionados con la modificación y degradación del hábitat, incluyendo los efectos nocivos de la agricultura, la fragmentación de hábitat, la disminución de Artemisia spp. y otras coberturas herbáceas nativas, el desarollo, la introducción y la expansión de especies de plantas invasoras, la invasión de árboles y cuestiones relacionadas con pastoreo de ganado.
Article
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In the western US, Greater Sage-Grouse (Centrocercus urophasianus Bonaparte [Phasianidae]) have become an indicator species of the overall health of the sagebrush (Artemisia L. [Asteraceae]) dominated communities that support a rich diversity of flora and fauna. This species has an integral association with sagebrush, its understory forbs and grasses, and the invertebrate community dependent on that flora. Adult birds and their growing chicks consume a wide variety of understory species, and the invertebrates that develop on this flora are an important source of protein, especially for developing broods. Restoration plans for degraded sagebrush communities must consider outplanting the correct species and seed source of sagebrush and its diverse array of native forbs. Changes in climate and the problem with invasive species, especially annual grasses that spawn large-scale fires, will need to be addressed so that restoration efforts can succeed.
Article
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Declines in Greater Sage-Grouse (Centrocercus urophasianus, hereafter sage-grouse) populations could be attributed to low chick survival, which may be influenced by the availability of food and cover at sites used by females rearing broods. Habitat attributes important to broods may vary regionally; thus, it is necessary to understand factors affecting regional sage-grouse brood-rearing site selection, especially when estimating the impacts of development. We monitored brood-rearing female sage-grouse equipped with solar Argos Global Positioning System Platform Transmitter Terminals from 2011 to 2013 to assess microhabitat selection by broods in Carbon County, Wyoming. We measured vegetation and arthropod characteristics at diurnal sites used by broods (n = 42 in 2011, n = 31 in 2012, n = 32 in 2013) and at 3 paired-random sites associated with each used site (n = 315), located 50 m, 250 m, and 500 m from the used site. We fit conditional logistic models within an information-theoretic framework to identify vegetation and arthropod characteristics associated with microsite selection of brood-rearing sites. Sage-grouse selected brood-rearing sites with greater visual obstruction (0-45.7 cm in height), higher numbers of arthropods in the order Diptera, and lower numbers of arthropods in the order Coleoptera. There was an interaction effect between the number of arthropods in the order Hymenoptera and the canopy cover of broad-leaf forbs; the relative probability of selection increased with increasing number of Hymenoptera when there was low cover (<20%) of broad-leaf forbs, but decreased with increasing number of Hymenoptera when there was high broad-leaf forb cover (>20%). We also found a quadratic relationship between selection of brood-rearing sites and total vegetation canopy cover; the relative probability of selection increased until approximately 75% cover and then decreased with increasing cover. Sage-grouse rearing broods selected a diverse array of vegetation types, but greatest use occurred within mesic communities. Our results could be used to identify vegetation communities with high relative probabilities of use by sage-grouse rearing broods, which will help guide management decisions and provide reference conditions for future research that evaluates the effects of wind energy development on sage-grouse.
Technical Report
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Greater sage-grouse (Centrocercus urophasianus; hereinafter, sage-grouse) are a sagebrush obligate species that has declined concomitantly with the loss and fragmentation of sagebrush ecosystems across most of its geographical range. The species currently is listed as a candidate for federal protection under the Endangered Species Act (ESA). Increasing wildfire frequency and changing climate frequently are identified as two environmental drivers that contribute to the decline of sage-grouse populations, yet few studies have rigorously quantified their effects on sage-grouse populations across broad spatial scales and long time periods. To help inform a threat assessment within the Great Basin for listing sage-grouse in 2015 under the ESA, we conducted an extensive analysis of wildfire and climatic effects on sage-grouse population growth derived from 30 years of lek-count data collected across the hydrographic Great Basin of Western North America. Annual (1984–2013) patterns of wildfire were derived from an extensive dataset of remotely sensed 30-meter imagery and precipitation derived from locally downscaled spatially explicit data. In the sagebrush ecosystem, underlying soil conditions also contribute strongly to variation in resilience to disturbance and resistance to plant community changes (R&R). Thus, we developed predictions from models of post-wildfire recovery and chronic effects of wildfire based on three spatially explicit R&R classes derived from soil moisture and temperature regimes. We found evidence of an interaction between the effects of wildfire (chronically affected burned area within 5 kilometers of a lek) and climatic conditions (spring through fall precipitation) after accounting for a consistent density-dependent effect. Specifically, burned areas near leks nullifies population growth that normally follows years with relatively high precipitation. In models, this effect results in long-term population declines for sage-grouse despite cyclic periods of high precipitation. Based on 30-year projections of burn and recovery rates, our population model predicted an overall 43-percent reduction in population size across the Great Basin by 2044. Further, example management scenarios that may help offset adverse wildfire effects are provided by models of varying levels of fire suppression and post-wildfire restoration that focus on areas especially important to sage-grouse populations. These models illustrate how sage-grouse population persistence likely will be compromised as sagebrush ecosystems and sage-grouse habitat are degraded by wildfire, especially in a warmer and drier climate, and by invasion of annual grasses that can increase wildfire frequency and size in the Great Basin.
Article
Fire is a dominant and highly visible disturbance in sagebrush (Artemisia spp.) ecosystems. In lower elevation, xeric sagebrush communities, the role of fire has changed in recent decades from an infrequent disturbance maintaining a landscape mosaic and facilitating community processes to frequent events that alter sagebrush communities to exotic vegetation, from which restoration is unlikely. Because of cheatgrass invasion, fire-return intervals in these sagebrush ecosystems have decreased from an historical pattern (pre-European settlement) of 30 to >100 yr to 5-15 yr. In other sagebrush communities, primarily higher elevation ecosystems, the lack of fire has allowed transitions to greater dominance by sagebrush, loss of herbaceous understory, and expansion of juniper-pinyon woodlands. Response by birds living in sagebrush habitats to fire was related to the frequency, size, complexity (or patchiness), and severity of the burns. Small-scale fires that left patchy distributions of sagebrush did not influence bird populations. However, large-scale fires that resulted in large grassland expanses and isolated existing sagebrush patches reduced the probability of occupancy by sagebrush-obligate species. Populations of birds also declined in sagebrush ecosystems with increasing dominance by juniper (Juniperus spp.) and pinyon (Pinus spp.) woodlands. Our understanding of the effects of fire on sagebrush habitats and birds in these systems is limited. Almost all studies of fire effects on birds have been opportunistic, correlative, and lacking controls. We recommend using the large number of prescribed burns to develop strong inferences about cause-and-effect relationships. Prescribed burning is complicated and highly contentious, particularly in low-elevation, xeric sagebrush communities. Therefore, we need to use the unique opportunities provided by planned burns to understand the spatial and temporal influence of fire on sagebrush landscapes and birds. In particular, we need to develop larger-scale and longer-term research to identify the underlying mechanisms that produce the patterns of bird responses to fire in sagebrush ecosystems.
Article
In the coming century, climate change is projected to impact precipitation and temperature regimes worldwide, with especially large effects in drylands. We use big sagebrush ecosystems as a model dryland ecosystem to explore the impacts of altered climate on ecohydrology and the implications of those changes for big sagebrush plant communities using output from 10 Global Circulation Models (GCMs) for two representative concentration pathways (RCPs). We ask: (1) What is the magnitude of variability in future temperature and precipitation regimes among GCMs and RCPs for big sagebrush ecosystems, and (2) How will altered climate and uncertainty in climate forecasts influence key aspects of big sagebrush water balance? We explored these questions across 1980-2010, 2030-2060, and 2070-2100 to determine how changes in water balance might develop through the 21st century. We assessed ecohydrological variables at 898 sagebrush sites across the western US using a process-based soil water model, SOILWAT, to model all components of daily water balance using site-specific vegetation parameters and site-specific soil properties for multiple soil layers. Our modeling approach allowed for changes in vegetation based on climate. Temperature increased across all GCMs and RCPs, whereas changes in precipitation were more variable across GCMs. Winter and spring precipitation was predicted to increase in the future (7% by 2030-2060, 12% by 2070-2100), resulting in slight increases in soil water potential (SWP) in winter. Despite wetter winter soil conditions, SWP decreased in late spring and summer due to increased evapotranspiration (6% by 2030-2060, 10% by 2070-2100) and groundwater recharge (26% and 30% increase by 2030-2060 and 2070-2100). Thus, despite increased precipitation in the cold season, soils may dry out earlier in the year, resulting in potentially longer, drier summer conditions. If winter precipitation cannot offset drier summer conditions in the future, we expect big sagebrush regeneration and survival will be negatively impacted, potentially resulting in shifts in the relative abundance of big sagebrush plant functional groups. Our results also highlight the importance of assessing multiple GCMs to understand the range of climate change outcomes on ecohydrology, which was contingent on the GCM chosen.
Article
The purpose of our study was to identify microhabitat characteristics of greater sage-grouse (Centrocercus urophasianus) nest site selection and survival to determine the quality of sage-grouse habitat in 5 regions of central and southwest Wyoming associated with Wyoming's Core Area Policy. Wyoming's Core Area Policy was enacted in 2008 to reduce human disturbance near the greatest densities of sage-grouse. Our analyses aimed to assess sage-grouse nest selection and success at multiple micro-spatial scales. We obtained microhabitat data from 928 sage-grouse nest locations and 819 random microhabitat locations from 2008-2014. Nest success was estimated from 924 nests with survival data. Sage-grouse selected nests with greater sagebrush cover and height, visual obstruction, and number of small gaps between shrubs (gap size ≥0.5 m and
Article
Increasing demands on and and semiarid ecosystems, which comprise one-third of Earth's terrestrial environment, create an urgent need to understand their biodiversity, function, and mechanisms of change. Sagebrush (Artemisia) steppe, the largest semiarid vegetation type in North America, is endangered because of losses to agriculture, excessive grazing, and invasive species. Establishment in 1950 of what is now designated as the Idaho National Engineering and Environmental Laboratory (southeastern Idaho, USA) created the largest existing reserve of this extensive vegetation type. We used cover, density, and frequency data for vascular plants sampled on 79 permanent plots nine times during 45 years to (1) assess long-term changes in abundance and distribution of major species and life forms, (2) assess changes in species richness and plot similarity, and (3) test the hypotheses that plant cover and stability of cover are positively associated with species richness and that invasibility is inversely related to native plant cover and richness. From 1933 through 1957 the area was subject to severe drought, with annual precipitation exceeding the long-term mean only four times. Cover of shrubs plus perennial grasses was 18% in 1950, and the vegetation was heavily dominated by sagebrush. Perennial grass cover was only 0.5%. With elevated precipitation after 1957, shrub cover increased to 25% by 1965, and by 1975 cover of perennial grasses had increased 13-fold. Subsequent fluctuations in cover did not track precipitation closely. Cover and density of major species were often out of phase, and correlation analyses indicated lags of 2-5 yr in responses of species or functional groups to precipitation. Aggregate species richness of the area has not changed appreciably, but richness of shrubs, perennial grasses, and forbs per plot steadily increased from 1950 to 1995. Vegetative heterogeneity also increased, with mean similarity among plots declining from 72% to 40%. Plots having higher species richness tended to maintain higher levels of cover and to vary less in cover relative to their mean level, indicating links between species richness and function. Abundance of normative species was negatively correlated with cover, but not with richness of native species. Thus, adequate cover of native species can render these semiarid communities more resistant to invasion. Maintaining richness and cover of native species should be a high management priority for these ecosystems.