Escarpments and the Foothill Transition - Mountains and Plains: The Ecology of Wyoming Landscapes - page 164

tains just west of Yellowstone national Park, and in
other parts of the Greater Yellowstone ecosystem (see
chapter 15). compared to the eastern foothills, a larger
proportion of the annual precipitation occurs in the
winter, which apparently favors Douglas-fir. the soils
typically are derived from sedimentary rocks and are
more fertile . 30 L imber pine is sometimes associated with
Douglas-fir in western Wyoming, such as in Fossil Butte
national Monument.
the dynamics of Douglas-fir woodlands is much the
same as for ponderosa pine woodlands growing in simi-
lar situations, commonly with expansion into adjacent
grasslands and shrublands during long fire-free inter-
vals . 31 in parts of Montana, scars on trees have revealed
that fires occurred every few decades before 1890, con-
fining the trees to rocky sites or the lee sides of slopes,
where the fires burned less frequently. comparable
results were found for ponderosa pine woodlands in
Devils tower national Monument, where, from 1770 to
1900, the average number of years between fires was 14.
Since 1900, fires have been much less frequent, about
once every 40 years, owing to fire suppression and the
great reduction in fires ignited by humans. 32

Fig. 10.9. Limber pine occurs on rocky escarpments from low
elevations near Pine Bluffs in the southeast up to the alpine
treeline of some mountains in eastern Wyoming. in north-
western Wyoming, whitebark pine is found in the alpine
zone. this photo, taken in the Laramie Range, shows widely
scattered limper pine in a high-elevation shrubland dominated
by threetip sagebrush, fringed sagewort, junegrass, mountain
muhly, and Sandberg bluegrass. elevation 8,000 feet.

Mixed Foothill Shrublands

Sagebrush steppe extends into the foothills in many
areas, often intermingled with mountain-mahogany
shrublands and woodlands dominated by pines,
Douglas-fir, and juniper. Species composition changes
as the environment becomes cooler and relatively more
moist. Mountain big sagebrush becomes the domi-
nant variety instead of Wyoming big sagebrush, and
other shrubs are common, namely, antelope bitter-
brush, common chokecherry, serviceberry, skunkbush
sumac, snowberry, snowbrush ceanothus, wax currant,
and Woods' rose (fig. 10.11; see table 10.1). Great Basin
wildrye and antelope bitterbrush grow in ravines and
on sites where snow accumulates. common grasses
and forbs include bluebunch wheatgrass, idaho fescue,
prairie junegrass, arrowleaf balsamroot, hairy golden-
aster, and lupine.
Serviceberry is a conspicuous shrub in some mixed
foothill shrublands. two species are commonly rec-
ognized in Wyoming: Saskatoon serviceberry, which
occurs throughout the state, and Utah serviceberry,

the now-mature trees would have been protected from
excessive wind damage. once established, however,
limber pine occurs on some of the windiest sites in the
region (fig. 10.9). indeed, the unusually limber branches
that give this tree its name probably are an adaptation
to minimize wind damage. Associated species include
various shrubs, such as common chokecherry, ground
juniper, mountain big sagebrush, oregon-grape, wax
currant, and western snowberry, along with forbs and
grasses (for example, spike fescue).
Foothill woodlands in the western half of Wyoming
are dominated by Douglas-fir rather than ponderosa
pine (fig. 10.10). Many of the best examples are found
in the Sunlight Basin, the Lamar Valley of Yellowstone,
Jackson Hole, the lower slopes of the centennial Moun-