Escarpments and the Foothill Transition - Mountains and Plains: The Ecology of Wyoming Landscapes - page 172

are often snow-free during late winter. Many seeds are
relocated in the spring, a time coinciding with the feed-
ing of nestlings and when food for seed-eaters is in short
supply. However, some seeds are left in the ground and
develop into new trees—commonly clumps of trees, one
from each of several seeds that were cached by the bird
in the same hole. in a similar manner, the nutcrackers
also disperse the seeds of limber pine and whitebark
pine. 51
As might be predicted, the distribution of nut-
crackers overlaps with that of pines having large, wing-
less seeds (in europe as well as north America). the
plants benefit by having their seeds dispersed more
widely and even planted. in fact, the large wingless
seeds cannot be dispersed effectively over long dis-
tances by any mechanism other than bird transport.
Seeds that simply fall to the ground are more likely
to be eaten by small mammals, and the seedlings are
less likely to become established on the litter layer of
the forest floor, a less favorable environment than that
provided by burial in mineral soil. Moreover, seedlings
that originate from fallen seed may be less likely to
survive because of competition with the nearby and
already well-developed parent tree. this coadaptation
between birds and some pines is further illustrated
by the observation that the nutcracker distinguishes
between viable and nonviable seeds. there is little to
be gained for either the bird or tree if less nutritious,
nonviable seeds are cached.
Bird dispersal appears to be one of the factors caus-
ing the patchy distribution pattern of limber and white-
bark pine. typically, these trees are found on ridges or

sunny slopes that are frequently snow-free in winter,
conditions that might reflect an instinctive preference
of the bird. Seeds cached on such sites would be more
accessible in the winter, when food is scarce. Burned for-
ests are also selected by the birds, which could increase
the probability of limber and whitebark pine becoming
part of the new forest that develops. it's well known that
grizzly bears in the Greater Yellowstone Area consume
large numbers of whitebark pine seed in the fall (see
chapter 15). From the bear's perspective, the more seeds
planted by birds, the better—especially at a time when
many of the adult trees are dying from the depredations
of mountain pine beetles and the invasive, non-native
white pine blister rust. conservation biologists are
attempting to maintain populations of whitebark pine
by planting seeds from trees that appear to be resistant
to the disease. (See chapter 14 for further discussion of
white pine blister rust.)

overall, the exposed bedrock of foothill and escarpment
landscapes creates sharp environmental boundaries and
a patchy vegetation mosaic. Such landscapes are highly
valued real estate for people, providing the amenities of
a moderate, low-elevation environment close to pictur-
esque escarpments that provide windbreaks, together
with grand vistas of the plains below and the mountains
above. Dispersed residential development has been the
fastest growing land use in the United States since 1950
and has resulted in habitat fragmentation throughout
the intermountain West—often in the foothills. As dis-
cussed further in chapter 18, debates about how best to
use these lands surely will continue.