Sagebrush - Mountains and Plains: The Ecology of Wyoming Landscapes - page 111

Fig. 7.3. Mixed-grass prairie inter-
mingles with Wyoming big sagebrush
steppe in the Powder River Basin. in this
area, the sagebrush cannot grow in the
ravines, probably because this habitat
is too wet for too long during the year.
Some of the shrubs on the edge of the
ravine are plains silver sagebrush, which
is more tolerant of wet soils. elevation
4,800 feet.

mie and Shirley basins where there is less snowfall, or
toward the eastern fringes of its range, big sagebrush is
found almost entirely where snow drifting occurs, such
as on the lee sides of ridges or in ravines (fig. 7.2). nota-
bly, big sagebrush is absent from very wet areas (fig. 7.3).
Big sagebrush can be observed from the western
Dakotas all the way to the cascade Mountains of oregon
and Washington, and from canada south to Arizona
and new Mexico. it grows in habitats ranging from Utah
deserts at about 3,000 feet elevation to mountain shrub-
lands at about 9,900 feet or higher. Surviving over such
a broad range of environmental conditions requires
considerable genetic variation. three varieties with dif-
ferent adaptations to water stress are commonly recog-
nized: basin big sagebrush, Wyoming big sagebrush, and
mountain big sagebrush. 4 Basin big sagebrush is found
at lower elevations (fig. 7.4) and is usually restricted to

comparatively moist ravines and valleys. it grows to a
height of 6 feet or more, much taller than the other two
varieties. in Wyoming it is most often found in the Big-
horn Basin and the southwestern quarter of the state.
Veritable woodlands of head-high basin big sagebrush
occur on stabilized dunes and other relatively moist
environments. 5 Wyoming big sagebrush, much shorter
than basin big sagebrush, is the most common shrub in
Wyoming. normally less than 1.5 feet tall, it occupies
the drier uplands. the third subspecies, mountain big
sagebrush, is most common near woodlands of aspen
and low-elevation conifers but sometimes occurs in
foothill ravines adjacent to shrublands with basin and
Wyoming big sagebrush. 6 two of the subspecies can be
found growing together where environmental condi-
tions are intermediate. All three are known to hybridize,
which can lead to identification difficulties in the field.