Escarpments and the Foothill Transition - Mountains and Plains: The Ecology of Wyoming Landscapes - page 166

in species composition may also occur following fire.
Most of the shrub species have the ability to resprout
from surviving roots and other belowground structures
(big sagebrush and juniper are notable exceptions).
Fires commonly expose mineral soil, facilitating the
re-establishment or addition of some species through
seedling recruitment. Antelope bitterbrush, snow-
brush ceanothus, skunkbush sumac, and mountain-
mahogany are capable of nitrogen fixation because
of the actinorhizae formed by bacteria in the genus
Frankia. this adaptation enables the establishment of
these species on relatively infertile soils. Snowbrush
ceanothus is capable of layering, but in addition, seed
dormancy in this shrub is broken by the heat of a fire;
seedlings commonly are abundant in burns where the
species existed previously.
Greasewood occurs in a few places in the foothills,
an interesting anomaly, as it is usually found where
groundwater is near the surface on saline soils in des-
ert shrublands. the presence of greasewood on escarp-
ments has been attributed to porous lignite seams that
cause groundwater to move to the surface on hillsides . 34
Seeps or perched water tables, with concomitant salt
accumulation as some of the water evaporates, typically
develop on such sites.

with succession or if grazing is confined to the period
when the plant is dormant. 37
Some foothill grasslands occur on extraordinarily
windswept plateaus or slopes with shallow soils. the
grasses are scattered and small forbs are common.
Many of the forbs have the cushion plant growth form
(see fig. 8.9), which keeps the stems and leaves densely
aggregated at the soil surface, where the air is warmer.
cushion plants are typical of windswept areas in alpine
tundra as well as in the lowlands, though the species
are different. 38

Deciduous Woodlands

Four other vegetation types in the foothill-escarpment
mosaic are woodlands characterized by different com-
binations of aspen, chokecherry, Gambel oak, and bur

Fig. 10.12. Ravines in the foothills of the Bear Lodge Moun-
tains and Black Hills near Sundance typically have choke-
cherry, skunkbush sumac, Woods' rose, and other shrubs.
Shrublands such as this are sometimes referred to as woody
draws. Mixed-grass prairie occurs on the upland, with pon-
derosa pine on some ridgetops. elevation 3,900 feet.

Foothill Grasslands

Foothill grasslands can be found on windy slopes or pla-
teaus, where snow does not accumulate in large quanti-
ties, soils are too shallow for most shrubs, or summer
rainfall is higher. Bluebunch wheatgrass is the charac-
teristic plant, occurring most often on relatively warm,
dry sites. idaho fescue is typical of the higher, more
mesic montane grasslands (above 6,900 feet) . 35 t hreetip
sagebrush, a dwarf shrub, occurs with idaho fescue on
windswept, shallow soils (see fig. 10.9). Little bluestem
is sometimes found on the slopes of escarpments at low
elevations. 36
Bluebunch wheatgrass is a highly preferred forage
species for livestock and big game. At lower, warmer
elevations, it is usually found on north slopes or near
snowbanks, if it occurs at all. Various investigators have
observed that bluebunch wheatgrass becomes less com-
mon after hot fires or heavy grazing in spring or sum-
mer. cheatgrass is a common invader following such
disturbances, but bluebunch wheatgrass increases again