ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

RESIDUES, FIRES, INSECTS, AND FOREST SUCCESSION
It is generally accepted that northern Rocky Mountain forests have evolved in
the presence of repeated fires. The pattern of forest succession following fires
in the northern Rockies has been defined as ". . .a sequential development of vegeta-
tion in which the more rapidly maturing and often shade-intolerant plants assume
initial dominance, and, in turn, are dominated by taller, slower growing, and often
more s hade-to1 erant species" (Lyon and Stickney 1976).
Natural fires have been a major influence on plant succession (Houston 1973).
However, there is evidence that suppressing fires in areas managed for "naturalness"
may be a serious disruption of natural processes (Mutch and Aldrich 1974). In
Ye1 lowstone National Park, a reduction in fire frequency through fire suppression
has resulted in a greater expression of "climatic climax" vegetation, and forest
succession has changed the relative abundance of species and increased the density
and distribution of forests. Conifers have increased, but conifer succession could
be returned to a more natural state if fire was either reintroduced (Houston 1973),
or allowed to more nearly play its natural role; fire has always been present but
its role has been seriously limited due to successful fire control (W. C. Fischer,
personal communicati on). Early photographs in the Sel way-Bi tterroot W i 1 derness
show numerous forest successional stages, attesting to the past incidence of fire,
but more recent photos indicate ". ..a loss of lifeform diversity because of a
gradual homogenous character resul ting from fire suppression activities" (Davis
1977).
There is recent, growing interest in the natural role of fire as an influence
on ecosystems, particularly in wilderness and other areas managed more for amenity
values than for timber production. There is particular interest in the effect of
periodic fires in maintaining stands of fire-de endent trees and in the diversity
of the forest in general (Habeck and Mutch 1973 7 . These interests are reflected
both in the National Forest Management Act and in the revised Forest Service fire
management pol icy, which has evolved from one of fire control to fire management
(USDA, FS 1978b). The fire management policy allows that certain wildfires can be
designated as prescribed fires if they burn under pre-selected conditions and in
pre-determined areas--call ed fire management areas.
These interests and concerns, a1 ong with current fire rnangement pol icies, have
serious imp1 ications relative to forest residues and associated insect and disease
interactions, to successional changes in our forests, and t~ our principal forest
insect and disease problems in the northern Rockies. If we accept that natural
ecosystems have evolved in the presence of fire and are at least partially dependent
on fire for continued survival, we must also accept that animals, including forest
Insects, living in these fire-adapted ecosystems may also be adapted to the presence
of fire (Clayton 1974). Hard (1974), in discussing northern coniferous forests in
southeast Alaska, points out that the folly of indiscriminate control of all wildfire
is analogous to the policy of "controlling" insect outbreaks, and says, "the lesson
here is that it may not always be wise to attempt to control a factor that is an
integral part of a natural system."
The most significant forest residue-fire-successional interactions with forest
insects in the northern Rocky Mountains involve the mountain pine beetle and the
western spruce budworm. The interaction of the role of fire, the succession of
lodgepole pine, and the m~untain pine beetle is very complex. In this region,
1 ight-medium fires and the mountain pine beetle are responsible for successionql
developments in lodgepole pine stands and for the maintenance of lodgepole pine as
a widespread forest type (D. Cole 1978). Foresters trace the current mountale