Escarpments and the Foothill Transition - Mountains and Plains: The Ecology of Wyoming Landscapes - page 170

(a natural rest rotation). elk populations still fluctuate,
but probably to a lesser extent because of winter feed-
ing programs. notably, the number of elk has declined
during the past 12 years or so, almost certainly because
of the reintroduction of gray wolves in 1995 combined
with droughts. Furthermore, some evidence suggests
that the wolves harass elk herds from time to time, caus-
ing them to move rather than stay in one aspen grove
for a long period. Aspen could be one of the beneficia-
ries of restoring the region's top carnivore (but see chap-
ters 12 and 15 for further discussion of this topic and
sudden aspen decline).
Wildlife managers are sometimes sensitive about elk
receiving so much of the blame for aspen groves that
appear to be in bad condition. they argue, correctly in
some cases, that livestock frequently congregate under
the trees because of the abundant forage that develops
in the relatively moist environment where aspen is
typically found. cattle and sheep can cause consider-
able damage to aspen through browsing, trampling, and
bedding.
Fire is another factor that cannot be ignored in ex-
plaining the apparent decline in some aspen groves.
University of colorado ecologists thomas Veblen and
Diane Lorenz, working in colorado, suggested that
widespread burning in the late 1800s and early 1900s,
whether caused by lightning or humans, might have
triggered the initiation of new stands of aspen over
large areas . 47 those stands are now aging, which could
explain why the groves are failing over large areas. How-
ever, aging stands could also be the result of fire sup-
pression during the past 60 or 70 years. Possibly more
important, with fire suppression conifers have become
dominant in some groves, so that the fewer remain-
ing aspen are subjected to more browsing than before.
Large-scale fires could stimulate the development of
new aspen forests, providing a larger food base and
removing some of the browsing pressure on any partic-
ular grove. notably, many new aspen seedlings became
established in the Greater Yellowstone Area after the
1988 fires (see chapter 15).
there is still much debate on the relative significance
of elk browsing, fire suppression, and wolf predation on
the condition of aspen woodlands in the foothills. cli-
mate change could be another contributing factor, pos-
sibly reducing aspen vigor if summers become longer

and drier, as discussed in chapter 11. the magnitude
of the problem is not well known. What proportion of
the aspen groves in different mountain ranges is in a
degraded condition? could some aspen groves have
been in “poor condition” long before the arrival of
euroAmericans in the 1800s?

Winter Rangelands for Deer and Elk

the winter survival of pronghorn, deer, elk, and moose
depends largely on adequate food during the summer
and fall for the development of fat reserves sufficient to
sustain the animals during long, harsh winters. Deep
snow or unusually cold winters cause a more rapid
depletion of fat reserves, but fortunately, the snow com-
monly melts rather quickly on south slopes in the foot-
hills. Also, the rugged topography makes it relatively
easy for the animals to find windbreaks. the bark and
twigs of trees and shrubs, though generally not pre-
ferred, often are consumed during this time, partly
because they are visible above the snow. Browse lines
develop on junipers, willows, and other tall shrubs but
are not necessarily an indication of excess numbers of
wintering animals at the present time (fig. 10.16).
By the time spring arrives, winter ranges may seem
to be heavily grazed and browsed, yet the plants typi-
cally recover quickly, because the herbivory occurs
largely when they are dormant. Depending on manage-
ment practices and the extent of overlap between the
summer plant preferences of livestock and the winter
preferences of big game, winter range plants may have
a full summer of rest and become senescent before they
are again subjected to large ungulates. the seasonal
movements of the animals create a natural rotation sys-
tem. 48 More than one year of rest may result if the herd
selects a different part of the foothills for wintering or if
high mortality during a particularly severe winter leads
to fewer animals during the following winter.
A primary concern of wildlife managers during the
past 10 years has been the decline in mule deer. Long
periods of drought—possibly climate-change-induced
drought—probably have been a contributing factor,
because inadequate moisture limits the summer forage
available to build up fat reserves. Another factor has
been winter habitat fragmentation by exurban devel-
opments. All such factors reduce the amount of forage