Escarpments and the Foothill Transition - Mountains and Plains: The Ecology of Wyoming Landscapes - page 161

Fig. 10.6. (above) Juniper woodland occurs on escarpments
with coarse soils, such as in this area near Bates creek in the
foothills of the Laramie Mountains, south of casper. Rocky
Mountain juniper is common in the eastern half of Wyoming;
Utah juniper is common in the western half. Both species are
found near Lander.

Fig. 10.7. (right) the small, scale-like leaves of Rocky Moun-
tain juniper are longer and narrower than the leaves of Utah
juniper. Drawing by Judy Knight.

are dominated by Wyoming big sagebrush, black sage-
brush, and broom snakeweed, but curlleaf mountain-
mahogany commonly is found in the foothills of the
Bighorn Mountains, sometimes with juniper.
Juniper expansion into adjacent grasslands or shrub-
lands, where juniper was previously absent, is one of
the most often-discussed ecological topics in the inter-
mountain West. A related phenomenon is the estab-
lishment of new junipers in formerly sparse juniper
woodlands—known as infilling.11 . 11 expansion and infill-
ing of juniper and pinyon during the twentieth cen-
tury have been documented in many areas throughout
the West. However, the process may be driven by more
than one ecological mechanism, and many woodlands
are stable communities that have persisted with little
change for hundreds or thousands of years. Woodlands

that have formed by juniper expansion into former
grasslands or shrublands during the twentieth century
tend to be found on relatively deep soils in regions hav-
ing summer-dominated precipitation patterns. in con-
trast, the older, persistent woodlands are most common
on shallow, rocky soils and in regions where precipita-
tion comes mostly in the winter . 12
What are the ecological processes that drive juni-
per expansion and infill? two mechanisms that have
received much attention are the effects of livestock
grazing and fire exclusion. Using tree-ring analysis,