ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

At least two studies have been made of mesofaunal populations in California
forest soils. Price (lW3), in a study of the fauna in the organic and upper soil
layers under a ponderosa pine stand near Grass Valley, Calif. showed a population
density of about 200,000 arthropods per square meter of forest floor. About 150 spe-
cies were encountered, mostly mites (primarily oribatids), followed by springtail s
(Col lembola). Wenz (1 976) investigated the effects of wildfire on forest soil
microarthropod populations in California. He found that of two wildfires studied
both reduced virtually all arthropod groups, and the effects were still evident 2
and 3 years after the fires.
RESEARCH IN EASTERN UNITED STATES
Some of the most comprehensive research in this country on the effect of
si 1 vicul tural practices and prescribed fire on soi 1 mesofauna has been conducted by
Metz and his co-researchers (fig. 14). Metz and Farrier (1971, 1973) presented the
first information concerning the effects prescribed burning of forest residues has
on forest soil mesofauna under defined conditions and frequency. Metz and Farrier
define the forest floor as all organic debris overlying the mineral soil, and
divide it into three layers: the L, or litter layer, made up of freshly fallen
undecomposed material; the F, or fermentation layer, consisting of partially decom-
posed L still recognizable as to origin; and the H, or humus layer, consisting of
we1 1 -decomposed organic rnqtter unrecognizable as to origin.
In their first study (1971 ), they found that mite populations were reduced
more in the surface 3 inches (75 mm) of mineral soil than in the forest floor,
while numbers of collembolans decreased in the forest floor with 1 ittle change in
the mineral sail. In 1973, Metz and Farrier studied mesofaunal populations in
unburned areas and in periodically and annually burned areas. They found annual
burns had the most serious impacts on animals, whlle the number of animals on the
periodically burned plots was significantly greater. The number of animals in the
control s was not significantly different from those in the periodically burned
areas. They conclude that there are more mesofauna 1) in a coniferous forest floor
than in the soil beneath it, 2) in the surface of the mineral soil than in the
underlying layers, 3) in the lower layers of the forest floor than in the surface,
and 4) when sampled immediately before and after burning on annwlly burned plots,
the number of animals was reduced drastically. Metz and Farrier (1973) point out
that there are no data in the literature to indicate that their results are applicable
to other forest types or burning regimes,
Hill, Metz, and Farrier (1975) reviewed the effects of four silvicul tural
practices--ferti 1 izers, insecticides, fire, and cutting--on forest flo~r mesofauna.
With respect to fire, they note that when fire destroys much of the forest floor,
the mesofauna are considerably reduced, either as a result of death from heat and
suffocation or by the removal of much of their food supply and living space. They
indicate that light prescribed burns where only the L and part of the F layers are
consumed, and where there is no erosion problem, have no lasting effects on mesofauna,
but that the effects of wildfire are more drastic and longer lasting. Metz and
Dindqhl (1 975) report that species diversity of collembolans wqs increased by both
annual and periodic fires. Concerning cutting (mostly clearcutting), Hi1 1, Metz
and Farrier (1 975) after citing somewhat contradictory results of several studies,
indicate that mesofauna usually are decreased after cutting, and slowly return to
normal after a number of years.