ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

pine beetle problem in the northern Rockies to catastrophic (stand replacement)
fires of nearly a century ago. They (the fires) triggered the growth of large
stands of lodgepole which are now about the same age over vast areas of western
Montana, northern Idaho and in Yellowstone National Park (Kugl in 1980). At this
time, an appreciable percentage of logdepole pine stands, near and east of the
Continental Divide in Montana, contain from two to several age classes, mainly
because of the mountain pine beet1 e/fi re history and severe conditions that excl uded
other species (D. Cole 1978) (fig. 15).
In many areas where natural fires have been suppressed, forest residues resulting
from mountain pine beetle epidemics accumulate until hot fires occur. According to
D. Cole (1978), "such fires are normally more destructive than ones that would have
otherwise occurred if fires had not been suppressed, and they tend to perpetuate
future extremes in the mountain pine beetle/lodgepol e pine/fir interactions."
Several opinions have been expressed that the bark beetle epidemics now rampant in
the Rockies and Intermountain West may be a product of fire exclusion (Schwennesen
1979). In Glacier National Park, the mountain pine beetle epidemic took such a
strong hold because fire suppression programs were so successful and trees that
ordinarily might have burned are now mature and ripe for the beetles (Kugl i n 1980).
Figure 15.--Along the ContinentaZ Divide in Montana, an appre&abZe
percentage of pure ZodgepoZe pine stands contaGa f~om too to severaZ
age ctasses, mainZy because of the rnoun-tain pine beetZe-fire hiskory
and severe site conditions ID. Cole 1978).
Western spruce budworm infestations in the northern Rockies are influenced not
only by the interaction of forest residues, fire and succession, but also by the
interaction of the budworm and the mountain pine beetle. One recommendation for
ameliorating the impact of the western spruce budworm is to return the more xeric
Douglas-fir sites to pine (.Williams and others 1971 ). However, in many young
ponderosa pine stands, the mountain pine beetle not only kills many desirable crop
trees and creates understocking in the stand, but also appears to be converting the
stands from ponderosa pine to Douglas-fir (McGregor 1973). This succession could
predispose such stands to be more susceptible to the western spruce budworm. The
same successional situation can be created by silvicultura1 practices that harvest
pine and favor Douglas-fir or the true firs.