Yellowstone's Northern Range - Greater Yellowstone Science ...

Figure 6.1.
Yellowstone's
northern range,
outlined in blue,
trends northwest-bysoutheast
along the
drainages of the
Lamar and
Yellowstone rivers.
Opinions vwyon the
historic and
prehistoric northward
extent of ungulate
migrations during
winter; as shown
here, the range
encompasses the
sOllth end of Paradise
Valley, downstream of
Yankee Jim Canyon.
Map by Yellowstone
Spatial Anaiysis
Centel:
THE NORTHERN RANGE
68
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fN;
Northern Range Boundary
Major Park Roads
The high mountains and plateaus of
Yellowstone provide summer range for an estimated
38,000 ungulates of seven native species
found in dozens of discrete herd units (Mack et al.
1990; Mack and Singer 1992a, I 992b). Yet, due
to snowfalls that accumulate to more than 10 feet
in depth on interior plateaus, only one-half to twothirds
of those ungulates winter within the park's
boundaries. On the average about 20 percent (the
variation is about 10-50 percent) of the northern
elk herd and most of the northern mule deer herd
winter north of the park boundary, where little
snow accumulates (Figure 6.1).
The Mrthern elk herd provides an important
example of the human benefits that this elk herd
generates in the form of sport-hunting outside
park boundaries. In addition to sport-hunting
being a popular pastime in Montana it is also an
important economic generator. Since the implementation
of Yellowstone's natural regulation
policy the northern herd has become Montana's
single most valuable elk herd (Duffield 1988). Of
the total number of herd units analyzed statewide,
the northern Yellowstone herd had the highest site
or herd value and the second highest net economic
value per hunting trip (Duffield 1988).
CARRYING CAPACITY
OF THE NORTHERN RANGE
For more than half a century, biologists have
attempted to define the carrying capacity of the
northern range. Ecologists have recognized that
there are at least two general types of carrying
capacity (Caughley 1979, Coughenour and Singer
1991). One is the traditional type employed by
livestock managers, now known as economic
carrying capacity. That is the number of animals
that is believed to provide the highest economic
return on a sustainable basis. Economic carrying
capacity is not concerned with native plant species
composition or diversity, except to the extent that
the available plants best serve the purpose of
adding weight to livestock. The other is ecological
carrying capacity. That is the varying number of
animals that nature, left alone, would sustain on the
range. The population numbers derived from the
two concepts are often quite different, but numbers
of ecological carrying capacity are always greater.
Most important, ecological carrying capacity will
vary greatly, even from year to year, depending
upon the environmental factors that dictate food
availability. For most of the history of the northern