ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

changes in the animal comnunities. To discover the primary
causes of the changes in the population densities of the dif-
ferent species or of the successional trends of the whole
community, accurate information would have to be acquired about
the habits and responses of each component species to each
factor at the different stages of their life cycles, together
with detailed long-term microclimatic records not only in the
habitat in general, but a1 so separately in the particular
microhabitat of each species.
Direct Effects of Treatment
Considering harvesting and residue management procedures, prescribed burning is
probably the only treatment tbat directly affects forest floor macrofauna. Some
studies have concluded that the heat of the burning-over is very destructive to a1 1
grou s, and that the bulk of some populations may be destroyed (Huhta and others
1957y . Other investigators report that with the exception of mesofaunal species and
spiders, population reductions do not seem to be directly caused by heat of fire
(Ahlgren 1974)-. The direct effect of prescribed burning is not only in killing the
organisms, but in the partial or complete destruction of the 1 i t ter and humus, as
we1 1 as the above-ground portions of low-growing surface vegetation. In such cases,
only scanty material may be left on the surface of the mineral soil (Huhta and
others 19671.
Indirect Effects of Treatment
In add? tion to direct effects, harvesting and residue manipulation practices
have two general indirect effects: a change in the forest environment and micro-
climate and changes in successional development of vegetation.
Changes in the microclimate will depend on the condition of the stand prior to
treatment. The removal of all or part of a dense coniferous stand where the forest
floor is heavily shaded will have more striking effects than the manipulation of a
more open-grown stand where more light reaches the forest floor and where understory
vegetation may be more abundant,
Partial or complete removal of trees and residues alters the forest environment,
hence indirectly influencing the forest soil fauna, by changing temperature, moisture,
llght intensity, wind, and humidity regimens. Of the harvesting methods, clearcutting
no doubt has the greatest impact. However, all treatments disrupt both diurnal and
seasonal fluctuations in these physical factors.
Some animal groups, unable to tolerate the new microcl imate, are at a disadvan-
tage and disappear. Other groups not only survive the environmental change but may
even increase as a result of treatment. Some investigators have reported that the
factor deciding the succession of fauna in clearcut areas is whether the felling
residues are left on the site or removed (Huhta and others 1969). Some animals,
dependent on litter for food have been known to disappear in a burned-over area after
the unburned 1 itter had decomposed.