Present-Day Environments and Climate Change - Mountains and Plains: The Ecology of Wyoming Landscapes - page 30

Fig. 3.3. on this sandstone escarpment, limber pine and
Rocky Mountain juniper grow only in cracks along fracture
planes where soil, water, and nutrients are available. this es-
carpment is part of the Frontier Formation and is located near

Muddy Gap, north of Rawlins and west of the Ferris Moun-
tains. Wyoming big sagebrush and greasewood shrublands
are found on the adjacent fine-textured soils. Photo by Ken
Driese.

or meandering stream channels. the ecological sig-
nificance of such features is a recurring theme in this
book.
constituting another third of Wyoming, the moun-
tains are characterized by lakes, streams, coniferous
forest, aspen groves, subalpine meadows, and alpine
tundra. environmental factors vary greatly, with freez-
ing temperatures possible every month of the year at
high elevations. Geographers have classified the Lara-
mie, Medicine Bow, and Sierra Madre mountains in the
southeast as part of the Southern Rocky Mountains and
most of the other mountain ranges as part of the Middle
Rocky Mountains (see fig. 1.2). only the Beartooth,
Madison, and Gallatin ranges of the Greater Yellow-
stone Area are in the northern Rockies.

sure of water availability. 4 Where precipitation is higher,
such as in mountain forests, other factors may be more
limiting (for example, temperature or the length of
the growing season). in all cases, water availability to
plants is affected as much by the infiltration and water-
holding characteristics of the soil as by the amount and
timing of precipitation.
throughout Wyoming and much of the region, the
mean annual precipitation varies by a factor of 10, from
6 to 60 inches (about 15-150 cm; fig. 3.4). the two dri-
est areas are the Great Divide Basin, near Wamsutter
on interstate 80, and the northern part of the Bighorn
Basin, between Lovell and Powell. in general, the inter-
mountain basins in the western two-thirds of the state
are drier than the Great Plains to the east, with averages
of 6-12 and 12-16 inches per year, respectively. the
foothills and mountains receive 16-60 inches, with the
highest annual precipitation in the southwestern corner
of Yellowstone national Park.
With prevailing westerly winds, the western slopes
of the mountains receive relatively more precipita-
tion, the result of condensation as air moves upward,
cooling as it crosses the mountains. the leeward

Precipitation

As in other semi-arid environments, precipitation has
a significant effect on plants and animals, as well as
on human activities. in a given temperature zone, the
amount of plant growth in grasslands and shrublands
is typically correlated with rainfall or some other mea-