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ECOLOGY, DISTRIBUTION, AND
VALUES OF SAGEBRUSH WITWN
THE INTERMOUNTAIN REGION
E. Durant McArthur
ABSTRACT
ECOLOGY AND DISTRffiUTION
Information for 11 sagebrush species, and their subspecies, of the Intermountain West is summarized. Big sagebrush (Artemisia tridentata) with its five subspecies is the
most common and widely distributed. Sagebrush taxa are
distributed in patterns generally controlled by moistureelevation gradients, seasonal moisture, and soil properties.
Individual sagebrush taxa result from reticulate, hybridizing, polyploid evolution facilitated by migrations of ancestral stock in response to changing climatic patterns. Sagebrush is valuable for soil stabilization, wildlife habitat,
animal feed, and ecosystem stability. Rehabilitation of
sagebrush communities degraded by fire and other disturbances may be accomplished by planting appropriate wildland stock or selected germplasms. Hybrid forms show
promise.
Sagebrushes occur from southern British Columbia to
southwestern Manitoba, south to northern Baja California
and west Texas, and from approximately the 100th meridian west longitude (the Dakotas to west Texas) to the Cascade Mountains of Oregon and Washington and the northem Sierra San Pedro Martir of Baja California (McArthur
and Plummer 1978; McArthur and others 1981). Each
taxa has an ecological niche preference as described in
table 1. Some taxa are broadly adapted and distributed;
other taxa are narrow endemics. The most broadly distributed species is big sagebrush (A. tridentata) with its
subspecies, especially basin big sagebrush (ssp. tridentata), mountain big sagebrush (ssp. vaseyana), and
Wyoming big sagebrush (ssp. wyomingensis). These three
taxa occur over most of the general sagebrush distributional range and partition out the environment on an interacting moisture-elevation gradient (fig. 1). Two less
common big sagebrush subspecies are confined to dry foothills in south-central Idaho (xeric big sagebrush, ssp.
xericensis) and high elevations in northern Utah, eastern
Idaho, northwestern Colorado, and western Wyoming
(snowbank big sagebrush, ssp. spiciformis) (Goodrich and
others 1985; McArthur 1983b; Rosentreter and Kelsey
1991; Winward 1983). In addition to moisture-elevation
gradients, seasonal moisture and soil properties are important in the distribution of sagebrush taxa (table 1).
Sagebrush ecosystems in natural condition had various
rates of catastrophic disturbance prior to settlement by
Europeans. These ecosystems were and are dominated by
various sagebrush taxa but varied and vary widely in the
diversity and density of their herbaceous components
(Blaisdell and others 1982). Big sagebrush communities
had fire cycles of greater than 50 years before European
settlement <Whisenant 1990); some depauperate communities, such as stiff sagebrush (A. rigida) and black sagebrush (A. nova), may have had very little disturbance.
Insect irruptions were no doubt occasionally devastating
prior to European settlement as they occasionally are now
(McArthur and others 1979).
Fire frequency in sagebrush communities has been
greatly increased due to invasion of alien annuals such
as cheatgrass (Bromus tectorum) in their understory. Fire
cycles on some large areas that are dominated by cheatgrass and other alien annuals are down to a 5-year return
(Whisenant 1990). Consequently, large areas of non-fire
tolerant sagebrush ecosystems, especially Wyoming big
sagebrush communities, are converted to annual grasslands lacking a shrub component (McArthur and others
INTRODUCTION
The genus Artemisia (wormwood, wormseed, sage, sagebrush, etc.) is comprised of some 250-400 species of shrubs
and forbs distributed mainly in the northern temperate
zone but extending to the southern hemisphere in some
upland situations. The true sagebrushes (subgenus Tridentatae of Artemisia) are one of four subgenera within
the genus and are confined to western North America
with a center of distribution in the Intermountain area
(Airy Shaw 1973; McArthur and others 1981). The sagebrushes are wholly woody with homogamous flowers and
are adapted to a semiarid, continental climate. Wide distribution and large populations make them a landscapecharacterizing plant of the North American West. This
report is limited to the 11 sagebrush species and their
subspecies (table 1). For information about other nonsagebrush Artemisia species of the Intermountain region, for
example, sandsage or oldman sage (A. filifolia), fringed
sage (A. frigida), longleaf sage (A. longifolia), Louisiana
sagewort (A.ludoviciana), fuzzy sage (A. papposa), birdsfoot sage (A. pedatifia), and budsage (A. spinosa), see Hall
and Clements 1923, McArthur and others 1979, McArthur
and Stevens, in preparation, and Rosentreter 1992.
Paper presented at the Symposium on Ecology, Management, and Restoration of Intermountain Annual Rangelands, Boise, ID, May 18-21, 1992.
E. Durant McArthur is Project Leader and Research Geneticist, Intermountain Research Station, Forest Service, U. S. Department of Agriculture, Shrub Sciences Laboratory, Provo, UT 84606.
347
Table 1-Sagebrush (subgenus Tridentatae) taxa {species and subspecies) with their general distributions and site adaptations. After Beetle
1960, Harvey 1981, McArthur 1983b, McArthur and Plummer 1979, Winward and others 1986
Species
Low sagebrush
{A. arbuscula)
Subspecies
Distribution and site adaptation
Low sagebrush
(arbuscula)
W. Wyoming to SC. Washington and N. California on dry, sterile, rocky, shallow, alkaline,
clay soils.
cleftleaf sagebrush
{thermopo/a)
W. Wyoming, N. Utah, and E. Idaho on spring-flooded, summer-dry soils.
Lahontan sagebrush
{not formally named1)
NW. Nevada extending into adjacent California and Oregon on soils of low water holding
capacity and shallow depth usually around and above the old shoreline of Lake Lahontan.
Coaltown sagebrush
(A. argi//osa)
Jackson County, Colorado, on alkaline spoil material.
Bigelow sagebrush
(A. bige/ovii)
Four Corners area extending toNE. Utah, SE. California, and W. Texas on rocky,
sandy soils.
Silver sagebrush
(A. cana)
Bolander silver
sagebrush (bolanden)
E. Oregon, W. Nevada, and N. California on alkaline basins.
Plains silver
sagebrush (cana)
Generally E. of Continental Divide, Alberta and Manitoba to Colorado on loamy to sandy
soils of river bottoms.
Mountain silver
sagebrush (viscidula)
Generally W. of Continental Divide, Montana and Oregon to Arizona and New Mexico on
mountain areas along streams and in areas of heavy snowpack.
Alkali sagebrush
{A. longiloba)
SW. Montana, NW. Colorado, W. Wyoming, N. Utah, S.ldaho, N. Nevada, and E. Oregon
on heavy soils derived from alkaline shales or on lighter, limey soils.
Black sagebrush
(A. nova)
SE. Oregon and SC. Montana to S. California and NW. New Mexico on dry, shallow,
stony soils with some affinity for calcareous conditions.
Pygmy sagebrush
(A. pygmaea)
C. Nevada and NE. Utah to N. Arizona on desert calcareous soils.
Stiff sagebrush
(A. rigida)
E. Oregon, E. Washington, and WC. Idaho on rocky scablands.
Rothrock sagebrush
(A. rothrocki1)
California and Nevada in deep soils along the forest margins of the Sierra Nevada and
outliers.
Big sagebrush
(A. tridentata)
Threetip sagebrush
(A. tripartita)
Snowbank big sagebrush
(spiciformis)
Wyoming, Idaho, Colorado and Utah in high mountains.
Basin big sagebrush
(tridentata)
British Columbia and Montana to New Mexico and Baja California in dry, deep, welldrained soils on plains, valleys, and foothills.
Mountain big
sagebrush2 ( vaseyana)
British Columbia and Montana to S. California and N. New Mexico in deep, well-drained
soils on foothills and mountains.
Wyoming big sagebrush
(wyomingensis)
North Dakota and Washington to Arizona and New Mexico in poor shallow soils often
underlain by a caliche or silica layer.
Xeric big sagebrush
(xericensis)
WC. Idaho on basaltic and granitic soils.
Wyoming threetip
sagebrush (rupicola)
Wyoming on rocky knolls.
Tall threetip sagebrush
(tripartita)
E. Washington and W. Montana toN. Nevada and N. Utah on moderate-to-deep
well-drained soils.
This taxon is currently in the process of formal description. Winward and others (1986) informally described and characterized it.
additional treatment of subspecific taxa (forms) see Goodrich and others (1985).
1
2For
348
Elevation
High
snowbank sagebrush
elevation
mountain big sagebrush
Wyoming big sagebrush
gradient
xeric big sagebrush
basin big sagebrush
Low
Dry
moisture gradient
Mesic
Figure 1-Moisture-elevation gradient for big sagebrush and its subspecies.
Other values include being living snowfences and sources
of industrial chemicals (McArthur 1983a; Welch 1983). In
addition to providing natural soil binding, several species
are suitable for stabilizing disturbed soils, by either transplanting or seeding. When using sagebrush for revegetation purposes it is important to match precipitation, soil,
elevation, and plant germination characteristics with the
plant's original source site and to bear in mind the importance of special care in initial establishment (McArthur
1983a; Meyer and Monsen 1992).
The importance of sagebrush communities as wildlife
habitat is illustrated by the fact that at least 87 wildlife
species use them as habitat in Intermountain States; several species are obligately tied to sagebrush habitats including sage grouse (Centrocerus urophasianus) and
pygmy rabbits (Brachylagus idahoensis) (McArthur
1983a). Sagebrush provides nesting, hiding, and thermal
cover for various animal species. The feed value of sagebrush is generally good especially when it is used as
mixed winter feed. Big sagebrush in particular is very
good in digestibility, winter crude protein, and winter
phosphorus and carotene (Welch 1983; Welch and
McArthur 1990). Some forms are much more palatable
to browsing animals than others (McArthur and others
1979; Wambolt 1993; Welch 1983; Welch and others 1986,
1992). There is a concern that the essential oils of sagebrush make it undesirable forage because the oils may
interfere with animal digestion. Welch (1983) concluded
that this is a minimal problem because the plant is generally taken as a mixed feed and the oils are benignly lost
in eating and digestive processes.
Some natural populations have been shown to be superior for certain traits such as palatability to browsing
animals, nutritive quality, growth rates, and wide adaptation. Welch and his colleagues (1986, 1992) have characterized and released the germplasms 'Hobble Creek'
~ountain big sagebrush and 'Gordon Creek' Wyoming
btg sagebrush for commercial seed production and reclamation plantings. Other germplasms are currently under
evaluation.
Some of our current work is directed to make novel
hybrid combinations between sagebrush taxa. This work
might allow us to combine desirable nutritive quality
(including palatability) and growth characteristics, or
1990, these proceedings). Much of the basin big sagebrush ecosystem has been converted to urban development and agriculture. The animal components of sagebrush ecosystems are rich and varied and are also subject
to the disturbances of the system (McArthur 1983a).
SYSTEMATICS, GENETICS, AND
EVOLUTION
The sagebrushes (subgenus Tridentatae of Artemisia)
are a natural group comprising 11 species and their 13
subspecies (table 1). They differ in stature, vegetative
and floral branching patterns, leaf shape and lobation,
and leaf and bract pubescence. Bigelow sagebrush (A.
bigelovii) differs from all other taxa; its flower heads have
from 0 to 2 ray or marginal flowers in addition to the homogamous central disc flowers characteristic of the subgenus. Taxonomic keys are available; I recommend Beetle
1960, McArthur 1983b, McArthur and others 1979
'
Schultz 1986, and Winward 1980.
Sagebrushes have a base chromosome number of
x = 9 with polyploidy common in most taxa (McArthur
and others 1981; Ward 1953). Polyploidy up to 8x is
known. The diversity in the group is enhanced by outcrossing (wind pollination) although self-pollination also
occurs (McArthur and others 1979, 1988). Outcrossing is
not confined within populations of the same taxa· natural
hybridization also occurs between sympatric and'parapatric populations under certain temporal conditions
(Beetle 1960; McArthur and others 1979, 1988; Ward
1953). The evolutionary history of sagebrush is one of
dynamic reticulate connections facilitated by hybridization, ~olyploidy, and migration as contemporary taxa
came mto and out of contact as a result of past climatic
change (McArthur and others 1981, 1988; Ward 1953).
Sagebrush hybrid zones are leading to a better understanding of theoretical underpinnings of hybrid zone stability (Freeman and others 1991).
VALUES
Sagebrushes' principal values are for soil stabilization
wildlife habitat, animal feed, and ecosystem stability. '
349
drought and fire tolerance (McArthur and others 1988,
1992). The latter potential combination is particularly
appropriate in the context of these symposium proceedings. Large areas of the sagebrush ecosystem have been
lost to the cheatgrass fire cycle, dramatically reducing
wildlife habitat, carrying capacity, ecosystem integrity,
and structural diversity on these lands. Our putative artificial hybrids between Wyoming big sagebrush (drought
tolerant but not fire tolerant) and silver sagebrush (Artemisia cana) and three tip sagebrush (A. tripartita) (fire
tolerant but not drought tolerant) hold some promise of
rebuilding a badly damaged and perhaps partially lost
ecosystem (McArthur and others 1992).
of symposia; 1981 September 15-17; Twin Falls, ID and
1982 June 22-24; Elko, NV. Gen. Tech. Rep. INT-157.
Ogden, UT: U.S. Department of Agriculture, Forest
Service, Intermountain Forest and Range Experiment
Station: 150-157.
McArthur, E. D. 1983b. Taxonomy, origin, and distribution of big sagebrush (Artemisia tridentata) and allies
(subgenus Tridentatae). In: Johnson, K. L., ed. Proceedings of the first Utah shrub ecology workshop; 1981
September 9-10; Ephraim, UT. Logan, UT: Utah State
University, College ofNatural Resources: 3-13.
McArthur, E. D.; Blauer, A. C.; Plummer, A. P.; Stevens,
R. 1979. Characteristics and hybridization of important
Intermountain shrubs. III. Sunflower family. Res. Pap.
INT-220. Ogden, UT: U.S. Department of Agriculture,
Forest Service, Intermountain Forest and Range Experiment Station. 82 p.
McArthur, E. D.; Pope, C. L.; Freeman, D. C. 1981. Chromosomal studies of subgenus Tridentatae of Artemisia:
evidence for autopolyploidy. American Journal of
Botany. 68:589-605.
McArthur, E. D.; Plummer, A. P. 1978. Biogeography and
management of western native shrubs: a case study,
section Tridentatae of Artemisia. Great Basin Naturalist Memoirs. 2: 229-243.
McArthur, E. D.; Romney, E. M.; Smith, S. D.; Tueller,
P. T., comps. 1990. Proceedings-symposium on
cheatgrass invasion, shrub die-off, and other aspects
of shrub biology and management. 1989 April 5-7;
Las Vegas, NV. Gen. Tech. Rep. INT-276. Ogden, UT:
U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 351 p.
McArthur, E. D.; Sanderson, S. C.; Andersen, W. R. 1992.
Assay of controlled hybridization between populations
of sagebrush (Artemisia subgenus Tridentatae) using
morphological, chemical, seed set, and DNA data.
American Journal of Botany. 79(6s): Abstr. 282.
McArthur, E. D.; Stevens, R. [In preparation]. Composite
shrubs. In: Monsen, S. B.; Stevens, R., eds. Rehabilitation of western ranges and wildlands.
McArthur, E. D.; Welch, B. L.; Sanderson, S. C. 1988.
Natural and artificial hybridization between big sagebrush (Artemisia tridentata) subspecies. Journal of
Heredity. 79:268-276.
Meyer, S. E.; Monsen, S. B. 1992. Big sagebrush germination patterns: subspecies and population differences.
Journal of Range Management. 45:87-93.
Rosentreter, R. 1992. Camas Prairie and possible evolutionary links with oldworld Artemisia species: a presymposium tour. In: Clary, W. P.; McArthur, E. D.;
Bedunah, D.; Wambolt, C. L., comps. Proceedingssymposium on ecology and management of riparian
shrub communities; 1991 May 29-31; Sun Valley, ID.
Gen. Tech. Rep. INT-289. Ogden, UT: U.S. Department
of Agriculture, Forest Service, Intermountain Research
Station: 223-227.
·
Rosentreter, R.; Kelsey, R. G. 1991. Xeric big sagebrush,
a new subspecies in the Artemisia tridentata complex.
Journal of Range Management. 44: 330-335.
ACKNOWLEDGMENTS
This work was facilitated by the Pittman-Robertson
Cooperative Wildlife Habitat Restoration Project W-82-R
and by the U.S. Department of Agriculture C. S. R. S.
Competitive Grant 91-38300-6157. I appreciate assistance from and meaningful discussions with Gary L.
Jorgensen, Stanley G. Kitchen, Stephen B. Monsen,
Richard Stevens, Scott C. Walker, Bruce L. Welch,
Stanford A. Young, and especially Stewart C. Sanderson
in the work that led to this report.
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