ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Spiders and fire.--Several studies of the effects of fire on spiders have been
made in this country; however, the most exhaustive research on spider-fire interac-
tions has been done in Finland.
In the northern Rockies where a wildfire had been allowed to burn, Clayton
(1975) found spiders to be more numerous in areas that had been burned than in
control areas, Within the burned areas, spiders were definitely more numerous and
more species were represented in a riparian woodland than on a south slope ponderosa
pine savanna. El sewhere in these proceedings, Fell in (1 98Ob) reports the results
of a recent study of the effect of prescribed burning and harvesting practices on
spiders and other forest floor macrofauna in western Montana,
Reichert and Reeder (1972) studied the immediate and long-term effect of
burning on spiders in Wisconsin prairies, They found that species active on the
surface at the time of burning were eliminated, while those occupying subsurface
burrows, or sacs under rocks or cl umps of dense vegetation escaped thermal damage.
The greatest decrease in numbers was noticed two weeks after the burn, followed by
a slow increase. Even after 45 days, however, the numbers in the burn were not
equal to those in the controls.
Reichert and Reeder (1972) recognize that some spider species may be indirectly
affected by a burn through changes in the plant cgver and that "seasonal activity
patterns 1 argely determine the different response of spider populations to the
immediate effects of burning. " They concl uded that the abundance and species
composition of spiders are both relatively stable, and that species inhabiting the
prairie have adapted to the effects of periodic burning.
In other studies, Pearse (1943) considered sptders, along with roaches and
ants, to be well adapted for existence in a burned area; but Rice (1932), Buffington
(1967), and Heyward and Tissot (1 936) thought spiders to be one of the groups least
well adapted to burning. Algren (1974) cites several authors in reporting that
spiders, primari ly surface dwellers, are drastic81 ly reduced by fire in most areas,
with population decreases of from 9 to 31 percent. In one study, Hurst (1970)
reported an increase, primarily ground and wolf spiders, fol lowing fire.
Huhta (1965, 1971 ) has intensively studied ecology of spiders in the 1 itter and soil of Finnish forests, mostly in relation to silvicultural practices and
prescribed burning. He found that after clearcutting, the abundance of ty ical
species decreased, and species foreign to the original fauna spread into t ll e cutover
areas; though the species were varied, the total numbers of individuals were about
60 percent less than in the uncut area (Huhta and others 1967). Following burning,
which almost totally destroyed most of the origtnal populations (Huhta and others
1967), the number of individuals remained continuously low and the composition of
the fauna was unstable; most species were markedly less frequent after burning and
occurred only sporadically in the burned soil (Huhta, 19651.. Between years 7 and
13, following cutting and burning, the composition of the spider comnunity reverted
towards the original forest situation. In a more recent study, Huhta (19.76) confirmed
his earl ier observations that the density of spiders decreased considerably
after clearcutting, but in two of his clearcut areas, he was not able to show signs
of spider recovery.
El sewhere in Europe, Brabetz (1 978) studied the effects of control 1 ed burning
i.n some uncultivated grasslands. In March and April of 1975 and 1976, two parcels
of land (20 x 56 meters) were burned, and two parcels set aside as a control. In
the spring and summer after the first burning, significantly more spiders were
trapped in the burned area; however, after the second burning, spiders were more
numerous in unburned areas.