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Fact Sheet-02-12
Sagebrush Regions in Nevada: Climate and
Topography influence Species Composition
Brad Schultz, Extension Educator, Central Area
Kent McAdoo, Natural Resource Specialist, Northeast Area
Introduction
Sagebrush (Artemisia spp.) is the primary shrub on
most Nevada rangelands at elevations above 4,500 ft to 5,000
ft. Neil West identifies two distinct sagebrush regions: the
sagebrush semi-desert and the sagebrush steppe. The same
species of sagebrush occur in reach region, but important
differences are present. These include different climatic
patterns, different ratios of shrubs to grasses and forbs (nonwoody flowering plants) in the herbaceous (grasses and forbs)
understory, and different amounts of total vegetation
production each year. These differences result in each
sagebrush type responding differently to disturbances.
Managing sagebrush-grass rangelands in Nevada requires
understanding how the sagebrush species and their associated
shrubs, grasses, and forbs interact with each other,
disturbances, climate, topography, and soils. The potential
relationships are many and complex.
Sagebrush semi-desert
The sagebrush semi-desert covers about 44 million
acres, mostly in Nevada (Figure 1). This area generally is
north of the Nevada Test Site, and south of a diagonal line that
stretches from Reno toward the northeast corner of Nevada.
The sagebrush semi-desert is positioned between the saltdesert shrub vegetation type and the pinyon-juniper (Pinus
monophylla/Juniperus spp.) woodland. These woodlands have
expanded into many areas previously classified as sagebrush
semi-desert. These include the drier mountain slopes, lower
foothills, and gentle slopes above the valley bottoms (i.e.
alluvial fans). The most common sagebrush species are
Wyoming big sagebrush (Artemisia tridentata ssp.
wyomingensis), basin big sagebrush (A. t. ssp. tridentata), and
black sagebrush (A. nova). Less abundant sagebrushes are
mountain big sagebrush (A. t. ssp. vaseyana), low sagebrush
(A. arbuscula), and bud sagebrush (A. spinescens).
After a mature plant community has developed (20 to
30+ years after a fire), the sagebrush semi-desert typically has
a higher ratio of sagebrush to herbaceous species than does the
sagebrush steppe. Many shrub species occur in the sagebrush
semi-desert; however, they are not major components of most
mature sagebrush communities. Associated shrubs are green
Mormon tea (Ephedra viridis), rubber rabbitbrush
(Chrysothamnus
nauseosus),
horsebrush
(Tetradymia
glabrata), spiny hopsage (Grayia spinosa), Prickly gilia
(Leptodactylon pungens), shadscale (Atriplex confertifolia),
four-wing saltbush (Atriplex canescens), and winterfat
(Krascheninnikovia lanata). Toward the sagebrush semidesert’s southern boundary blackbrush (Coleogyne
ramosissima) and Nevada Mormon tea (Ephedra nevadensis)
are common. Mexican cliffrose (Purshia neomexicana) is
common toward the southern and eastern boundary, where
more summer rainfall occurs. The cover, density, and/or
biomass production (pounds of growth) of the associated
shrubs is usually high only on recently disturbed sites, or
where the soil type prevents the presence of sagebrush.
Many species of perennial grasses occur in the
sagebrush semi-desert. They seldom contribute a substantial
amount of biomass in mature sagebrush communities,
regardless of how well the area is managed. Most, but not all,
are cool season species. These include Indian ricegrass
(Achnatherum hymenoides), desert needlegrass (Achnatherum
speciosum), squirreltail (Elymus elymoides), Sandberg’s
bluegrass (Poa secunda), needle-and-thread (Hesperostipa
comata). Thurber's needlegrass (Achnatherum thurberianum),
bluebunch wheatgrass (Pseudoregneria spicatum) and mutton
grass (Poa fendleriana) become more common in the northern
part of the sagebrush semi-desert, and at high elevations
(>6,000 ft). Great Basin wildrye (Leymus cinereus) typically is
limited to landscape positions where runoff accumulates.
Examples include ephemeral (short-lived) streams, meadows,
and bottomlands. Common warm season grasses include
galleta grass (Pleruaphis jamesii), sand dropseed (Sporobolus
cryptandrus) and Fendler’s three-awn (Aristida purpurea).
The warm season grasses have their highest abundance in the
southern and eastern part of the region, where summer rainfall
is more frequent. Some are found in west-central Nevada at
lower elevations. At these sites, winter and spring
precipitation often is sufficient to store substantial amounts of
soil moisture. Adequate soil moisture, spring rainfall, and
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warm spring temperatures coincide with one-another to
promote growth of the warm season grasses.
Forbs are common, but most species are annuals.
These annual forbs are almost completely absent in dry years,
but are abundant in wet years. They can provide important
food for wildlife, but their high variability in forage
production from year-to-year may limit some wildlife
populations. Forbs in the sagebrush semi-desert dry by late
spring and provide almost no summer forage. The shrubs and
perennial grasses provide better continuity for forage from
year-to-year.
The total amount of plant biomass produced each
year varies from about 450 lbs/ac to 1,350 lbs/ac. This is much
less than the sagebrush steppe. Sagebrush in mature
communities typically accounts for about 70% of the relative
plant cover, and as much as 90% of the plant biomass.
Absolute cover from the woody and herbaceous plants ranges
from about 10% to 40%.
The sagebrush semi-desert is significantly warmer
and drier of the two sagebrush regions (Figures 3 and 4).
Average annual precipitation ranges from as little as 6 in to
over 12 in. Most precipitation occurs in the winter and early
spring (November-April). The variation among years for both
total annual precipitation and winter-spring precipitation is
much higher in the sagebrush semi-desert, than for the
sagebrush steppe.
Sagebrush steppe
The sagebrush steppe covers over 11 million acres in
Nevada (Figure 2). In Nevada, it occurs in two distinct areas:
one loosely defined by latitude and the other by elevation.
North of the sagebrush semi-desert, the sagebrush steppe
occupies the mountains, hills, plateaus and mesas above the
valley bottoms, where the soil often has a high salt content.
Farther south, it occupies the upper elevations of mountain
ranges where a sagebrush zone occurs above the pinyonjuniper woodland. This situation resembles islands of
sagebrush steppe at high elevations, surrounded by rings of PJ
woodland at intermediate elevations, and vast expanses of
sagebrush semi-desert on the lower mountain slopes, foothills,
and valley slopes. The lower elevation limit for the sagebrush
steppe in extreme northern, and northwestern Nevada is about
4,500 feet to 5,000 feet. In central and eastern Nevada it
typically occurs in the mountains above 6,500 feet to 7,500
feet, depending on aspect.
All of the sagebrush species found in the sagebrush
semi-desert also occur in the sagebrush steppe. Wyoming
sagebrush is most common at the lower elevations on
droughty soils. Mountain sage is typical where annual
precipitation is more than about 12 inches. Low sagebrush
typically inhabits shallow soils with high clay content.
Lahontan sagebrush (A. arbuscula ssp. longicaulis), a
subspecies of low sagebrush, is restricted to northwestern
Nevada near the historic shorelines of Lake Lahontan. Soils
are typically shallow and have a clay layer (horizon) at
shallow depths. Black sagebrush is most common in the high
elevation varient of the sagebrush steppe, where soils are
shallow and calcium content is high. These areas are most
common in eastern Nevada. Less common sagebrush species
include silver sagebrush (A. cana), alkali sagebrush (A.
arbuscula var longiloba), and three-tip sagebrush (A.
tripartita).
The sagebrush steppe either has, or has the potential
to have a high abundance of herbaceous species in mature
sagebrush communities. Roughly equal amounts of shrubs and
herbaceous species occur on undisturbed and/or properly
managed sites. Also, herbaceous species are common in the
interspaces between sagebrush and other shrubs. In contrast
with the sagebrush semi-desert, the sagebrush steppe often has
a high abundance of other shrubs in mature plant
communities. These include bitterbrush (Purshia tridentata),
snowberry (Symphoricarpos spp.), mountain mahogany
(Cercocarpus
ledifolius),
Douglas
rabbitbrush
(Chrysothamnus viscidiflorus), currant (Ribes spp.), and
serviceberry (Amelanchiar spp.). These species often occupy
areas that accumulate drifting snow.
Common, widespread grasses include bluebunch
wheatgrass, beardless wheatgrass (Pseudoregneria inerme)
Sandberg=s bluegrass, Canby bluegrass (Poa canbyi = Poa
secunda), Thurber=s needlegrass, Idaho fescue (Festuca
idahoensis), squirreltail, western needlegrass (Achnatherum
occidentale), Columbia needlegrass (Achnatherum nelsonii),
Letterman=s needlegrass (Achnatherum lettermanii), mutton
grass, mountain brome (Bromus marginatus) and Cusick=s
blue grass (Poa cusickii). Indian ricegrass is more limited in
distribution here than in the sagebrush semi-desert, often
occurring where soils are sandier. Great Basin wild rye has a
broader distribution than in the sagebrush semi-desert. In
addition to playas and bottomland locations with deep soils, it
often inhabits slopes and swales up to about 9,000 ft in
elevation, particularly where snowdrifts occur. These areas
provide soil moisture well into the summer.
Forbs are a much more common component of the
sagebrush steppe. Many are perennial and provide forage for
wildlife every year. During wetter years many remain green
well into the summer or fall. Important perennial forbs include
Arrowleaf balsamroot (Balsamorhiza sagittata), buckwheats
(Eriogonum spp.), Penstemon (Penstemon spp.), lupines
(Lupinus spp) wild onions (Allium spp.), desert parsley
(Lomatium spp.), phlox (Phlox spp.), loco weeds (Astragalus
spp.), daisy (Erigeron spp and Townsendia spp.), evening
primrose (Oenothera spp.), rosy everlasting (Antennaria
rosea), false dandelion (Agoseris glauca), tapertip hawksbeard
(Crepis acuminatus), and waterleaf (Phacelia spp.).
Aboveground biomass production ranges from about
700 lbs/acre to over 2,200 lbs/acre. The proportion of the
annual biomass that comes from grasses and forbs is variable
and depends on the growing potential of the specific site, the
length of time from prior burning, and grazing history.
Locations where fire has recently burned (e.g. 1-15 years
before present) generally have more grasses and forbs, and
fewer shrubs. Site potential depends on interactions among
total and seasonal precipitation, redistribution of precipitation
due to winds and topography, aspect (north, south, east, west),
and the soil=s water holding capacity (a function of depth,
texture, and gravel/rock content).
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Role of Climate
Climate, as reflected by average high temperatures
and average precipitation (annual and monthly), appears to
play an important role in determining whether the vegetation
on sagebrush sites resembles the sagebrush steppe or the
sagebrush semi-desert. The mean high temperature in the
sagebrush steppe, from March through June (i.e., period of
peak plant growth), is 5°F to 6°F cooler than in the sagebrush
semi-desert (Figures 3 and 4). In the sagebrush steppe,
significantly lower temperatures reduce the evaporative loss of
water from shallow soil depths, increasing the amount of
water available for plant growth. This benefits shallow rooted
grasses and forbs.
Monthly and annual precipitation patterns are
significantly different in the sagebrush steppe and sagebrush
semi-desert. Average annual precipitation in the sagebrush
steppe is about 3.25 inches more than in the sagebrush semidesert. More important is the significantly greater precipitation
almost every month, from November through June. This
period is important because low temperatures stop almost all
plant growth, virtually eliminating the removal of soil
moisture by plants. Soil moisture can re-wet the entire soil
profile, assuming precipitation is adequate. Based only on
precipitation, for a given soil type, locations in the sagebrush
steppe potentially can store significantly more water than
similar soils in the sagebrush semi-desert. Substantially more
monthly precipitation in the sagebrush steppe during the
spring growing season provides additional water for shallow
rooted grasses and forbs. Grasses and forbs in the sagebrush
semi-desert receive less water. The additional spring moisture
in the sagebrush steppe helps account for that area’s greater
production of grasses and forbs.
Topographic and Climatic Modifications to Soil Moisture
The north-south mountain ranges throughout Nevada
have many east-west trending canyons. This creates a very
undulating landscape that influences soil development and
amount of soil moisture at any specific location. Slopes with a
north or east aspect receive less direct sunlight than slopes
facing south and west. Less snow is lost to evaporation, and
less soil moisture evaporates from the shallowest depths.
Given an equal amount of precipitation and similar soils,
locations with north and east aspects usually have more soil
moisture than locations with south and west aspects. The total
amount of soil moisture available, however, is modified by
how the precipitation occurs (e.g., snow, rain) and the strength
and direction of local winds during precipitation events.
Rainfall on a given location either evaporates, infiltrates,
ponds, or runs-off down gradient. Snowfall is often
redistributed by winds, followed by melting and infiltration at
a later time (often months). Throughout both sagebrush
regions, most precipitation occurs during the winter and
spring, often as snow. Most storms have strong winds from the
southwest or west, which blow substantial amounts of snow
off south and west facing slopes (particularly steep slopes or
slopes with short vegetation), and increase snow
accumulations on adjacent north and/or east facing slopes,
and/or in nearby concave depressions. This partially explains
why north-facing slopes can have abundant native
bunchgrasses and forbs, and small amounts of sagebrush; and
nearby south-facing slopes have mostly sagebrush, few
perennial grasses and forbs, more bareground, and large
amounts of cheatgrass. On the north and east facing slopes,
more effective precipitation, less direct sunlight, and slower
snowmelt increase soil moisture at shallow depths for a longer
period. In both sagebrush regions, this process results in more
diverse plant communities on north and east facing slopes,
with proportionately greater amounts of perennial grasses and
forbs.
Species Interactions
Prior to settlement in the mid to late 1800's, the
primary disturbance in the sagebrush steppe was fire. Fire
would remove all of the sagebrush for several years. Some of
the other shrubs (e.g., rabbitbrush) can return quickly because
they grow from sprouts at the root crown, but sagebrush must
originate from seed. Healthy sagebrush produces large
amounts of seed during most years, but the seed is short-lived.
Seed banks are absent or small, and if present are largely
destroyed by the fire, because most seed is in the plant litter
directly below the mother plant. Sagebrush seed disperses only
short distances (several to tens-of-feet) from mother plants;
therefore, sagebrush can take many years to re-establish
sagebrush.
Forbs often establish in mass after a fire, for at least
three reasons. First, many produce large amounts of seed.
Second, the seed is often viable for several years or more.
Third, many seeds from forbs have a hard seed coat that
allows better survival during fires.
Perennial grasses generally produce small to
moderate amounts of seed per plant during wet years, and little
or no seed during dry years. Also, most of their seed does not
survive more than one-year; thus seedbanks are small or
absent. The initial response from grasses is largely from
existing plants that survived the fire. Existing plants provide
seed, which if the amount and timing of precipitation is
adequate, can result in many new grass plants. Perennial
grasses increase less rapidly than forbs, but quicker than
sagebrush and most other shrubs that re-establish from seed.
With time, sagebrush increases. When sagebrush
canopy cover reaches about 15%, the perennial grasses and
forbs start to decline. Initially, grasses and forbs produce less
biomass and seed per plant. The older grasses and forbs
eventually die, but the combination of fewer viable seeds and
strong competition from shrubs reduces or ends seedling
recruitment.
At sagebrush canopy cover levels of 30% to 40%,
virtually all of the herbaceous species are lost from the
community. If this state persists for many years the seedbank
for most species is lost, sharply reducing their potential for
rapid recovery after a fire. The near absence of perennial
grasses and very low seed production per plant prevents their
ability to rapidly recover. Decadent sagebrush sites are prone
to invasion of introduced annual weeds with or without the
presence of fire, or other intense disturbances. Once a few
weeds are established, and desired perennial grasses and forbs
are absent, large and/or intense disturbances accelerate the
complete takeover of the site by the undesired annual weeds.
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Livestock grazing can have substantial impacts on
interactions between shrubs and herbaceous species. The
population of any species that is grazed heavily and repeatedly
during either its growth, and/or reproductive phases generally
declines. Populations of species grazed during dormancy
generally increase or remain static. Studies in both sagebrush
regions have shown that grazing sagebrush communities in the
fall when sagebrush is producing seeds, and the grasses and
forbs are dormant, has decreased the amount of sagebrush and
increased the amount of perennial grasses and forbs. For
sagebrush, both plant density and average plant size (biomass
production) can decline with fall grazing. The decrease in
shrubs and associated increase in herbaceous species with fall
grazing can occur faster than on adjacent ungrazed sites.
Species and Landscape Interactions
The ratio of woody to herbaceous vegetation at any
point in time is a function of site potential (i.e., precipitation
and soil quality); how precipitation may be redistributed;
disturbance history (e.g., fire, drought, insects, wildlife use,
flooding, erosion, and deposition); and the type, intensity,
timing, and duration of land uses (e.g., livestock grazing,
farming, mineral exploration, and recreation). These factors
and processes interact to determine the current species
composition at any location, and the suite of alternative
vegetative states (i.e., species compositions) that could occur
under different management actions. Within each sagebrush
region, landscape locations with soils that store more water for
longer periods will have more production of perennial
herbaceous species. These sites may be more resilient to
vegetation change induced by herbivores, in part because
better soil moisture during and after the grazing period allows
the grazed plants to restore both their leaf area and
carbohydrates in their roots. Landscape locations with higher
soil moisture levels are more likely to endure fire and other
types of disturbances better.
Bibliography
Christensen, E. M. 1959. A comparative study of the climates
of mountain brush, pinyon-juniper, and sagebrush
communities in Utah. Proceedings Utah Academy of
Science 36:174-175.
Laycock, W. A. 1967. How heavy grazing and protection
affect sagebrush-grass ranges. Journal of Range
Management 20:206-213. Perryman, B. L., A. M.
Maier, A. L. Hild, and R. Olson. 2001. Demographic
characteristics of 3 Artemisia tridentata Nutt
subspecies. Journal of Range Management 54:160-170.
Ludwig, J., D. Tongway, D. Freudenberger, J. Noble, and K.
Hodgkinson (editors)ndscape Ecology. Function and
Management. Principles from Australia’s Rangelands.
Lyneham Canberra, Australia. 158 pages.
Perryman, B. L., A. M. Maier, A. L. Hild, and R. Olson. 2001.
Demographic characteristics of 3 Artemisia tridentata
Nutt subspecies. Journal of Range Management 54:160170.
Robertson, J. H. 1947. Responses of range grasses to different
intensities of competition with sagebrush (Artemisia
tridentata Nutt). Ecology 28:1-16.
West, N.E. 1983. Great Basin-Colorado Plateau Sagebrush
Semi-Desert. Pages 331-349. In: N. E. West (ed).
Ecosystems of the World 5. Temperate Deserts and
Semi-Deserts. Elsevier Scientific Publishing Company.
New York, New York. 522 pp.
West, N. E. 1983. Western Intermountain Sagebrush Steppe.
Pages 351-374. In: N. E. West (ed). Ecosystems of the
World 5. Temperate Deserts and Semi-Deserts. Elsevier
Scientific Publishing Company. New York, New York.
522 pp
West, N. E., K. H. Rea, and R. O. Harniss. 1979. Plant
demographic studies in sagebrush-grass communities of
southeastern Idaho. Ecology 60:376-388.
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Figure 1. Area of sagebrush semi-desert. From West 1983a.
Figure 2. Area of sagebrush steppe. From West 1983b.
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MEAN MONTHLY AND ANNUAL HIGH TEMPERATURE
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TEMPERATURE (F°)
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Sagebrush Steppe
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Figure 3. Comparison of mean monthly and mean annual high temperatures at nine locations in both the
sagebrush steppe and sagebrush semi-desert
MEAN MONTHLY AND ANNUAL PRECIPITATION
PRECIPITATION (in)
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Figure 4. Mean monthly and annual precipitation at nine locations in both the sagebrush steppe and
sagebrush semi-desert.