ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

only when wood borers compete with man for material having economic value that they
become "harmful." Because of a drier climate, neither the borer nor the associated
deterioration problem is as acute in the northern Rockies as in the Pacific Northwest.
The second reason for promptly removing fire-weakened trees is to prevent the
buildup of bark beetle populations that often spill over to attack and kill green
trees in surrounding forests. Oftentimes, the speed at which fire-killed or fire-
weakened trees need to be removed is determined not only by the species of insect
involved, but also by the tree species involved. The problems of insects in fire-
ki 11 ed or fi re-weakened trees is of increasing importance since more prescribed
burning is being done in partial cuttings (W. C. Fischer, personal communication).
Fischer (1n press) discusses in detail the fire management implications of bark
beet1 e problems in ponderosa pine stands.
RESIDUES CREATED BY MAN
Although usually not as serious or widespread as residues created by natural
factors, man at times has created management problems for himself in the form of
residues generated by harvesting or thinning operations. With some coni fers ,
particularly ponderosa and lodgepole pines, managers need to be aware of potential
problems with engraver beetles and to pay particular attention to weather conditions
and the time of year when thinning or harvesting creates residues.
Entomological ly speaking, there is sti 11 some disagreement, and apparently
always has been, concerning the hazards of forest residues in attracting large
numbers of tree-kill ing insects-often serving as a breeding medium for some pest
species--and the use of prescribed fire in managing those residues, We have already
pointed out some of the varying philosophies of using prescribed fire to manage
residues in the late teens and early 1920's. Recently, Mitchell and Sartwell
(1974) pointed out that according to some and in some regions, the threat of outbreaks
posed by insects breeding in residues is generally overrated. They went on to say:
"Conclusions are that certain residues in Douglas-fir and ponderosa pine
often create serious pest problems that should be considered in residue
management programs. But the beneficial aspects of insects associated
with residues may have more significance to man's objectives in the long
run. "
In terms of the impact of residue management on beneficial organisms, our concerns
at the present time seem to be 1) the relative merits or drawbacks of removing
a1 1 or m~st forest residues from a site, either mechanically or by prescribed fire,
particularly in terms of impact on forest soil biology; and 2) how silvicultural
treatment, superimposed on residue treatments would affect insect and disease
relationships.
Most research has shown that fires reduce the populations of most soil and
forest floor fauna, the majority of which are generally beneficial. Complete
util ization, or removal of residue by prescribed fire, both act indiscrirninantly
and nonselectively on beneficial organisms. The disruption of beneficial arthropods
would have potential long-term consequences on all phases of residue decomposition
and nutrient cycl ing; these consequences should be considered in residue management