The Greater Yellowstone Ecosystem - Mountains and Plains: The Ecology of Wyoming Landscapes - page 263

Fig. 15.17. the grizzly bear, an omni-
vore once common across the Great
Plains and throughout the Rocky Moun-
tains, is now found only in the Greater
Yellowstone ecosystem and northward.
Photo by Mark Gocke.

of all sizes, large and small (see fig. 14.5) . 78 in some
areas, blister rust infection appears to make the larger
trees more vulnerable to mountain pine beetle attack,
probably by reducing their ability to produce sufficient
amounts of resin. 79 t hus, a warming climate not only
leads to increased burning of high-elevation forests, but
it also permits native bark beetles to move into these
previously unsuitable areas. Meanwhile, the exotic blis-
ter rust kills many of the small survivors—all leading
to a grim prognosis for whitebark pine in the northern
Rockies. 80 efforts are under way to locate and propa-
gate blister rust-resistant individuals, with the intent
of restoring whitebark pine woodlands . 81 However,
given the spatial extent and rapidity of whitebark pine
decline, many timberline forests of the GYe and other
parts of the northern Rockies may become what ecolo-
gist Jesse Logan refers to as “ghost forests. ” 82
extensive loss of whitebark pine has had a cascad-
ing impact on other ecosystem components, notably,
grizzly bears (fig. 15.17). now rare in the contiguous
United States and restricted to remote areas, the grizzly
was once common throughout the Rocky Mountains
and across the Great Plains. its current range is prob-
ably less than 1 percent of what it was in the 1800s.
With fewer than 1,000 animals in Montana, Wyoming,
idaho, and Washington combined, the grizzly was des-

ignated a threatened species in 1975. Whitebark pine
seeds had been an important late summer and autumn
food for grizzly bears, contributing to the accumulation
of fat reserves necessary for winter survival. Because
individual trees produce large amounts of seed only
every 3-5 years, it was important that the bears have
large numbers of trees over large areas, so that some
seed is available each year.
in addition to a declining number of whitebark pine
seeds, grizzly bears have also lost another food source,
the native cutthroat trout in Yellowstone Lake. the cut-
throat trout are threatened by two other non-native
species—lake trout and a microscopic myxozoan that
causes whirling disease. Lake trout were illegally intro-
duced to the lake, apparently in the mid-1980s, and
they have proven to be voracious predators of the native
cutthroat. Whirling disease, first recorded in YnP in
1998, leads to abnormal growth of a fish's bony struc-
tures, causing an inability to feed . 83 cutthroat trout
populations have plummeted, and spawning runs up
tributary streams—where the bears formerly harvested
great numbers of trout every summer—have dwindled.
Unlike the cutthroat, the lake trout do not spawn in
rivers and, in deep water, they are inaccessible to bears,
ospreys, pelicans, and other native wildlife that had fed
on the cutthroat . 84 Park managers have implemented