ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Si 1 v
Former
culture and Residue Treatments Affect
Water Used By A LarchlFir Forest
Howard C. Newman
Consul ti ng Hydrologist;
y Research Associate, School of Forestry
University of Montana, Missoula
and
Wyman C. Schmidt
Project Leader and Research Silvicul turist
USDA-Fores t Service
Intermountain Forest and Range Experiment Station
ABSTRACT
Three silvicultural systems--clearcut, shelterwood, and group
sel ecti on--were coup1 ed with four residues treatments, ranging
from intensive to conventional uti 1 i zation and broadcast
burning, to evaluate the environmental effects of harvesting
1 arch/Douglas-fir forests in Montana. Effects of the 12
treatment combinations on accumulated precipitation, water used
during the growing season, and soil water status during the year,
were evaluated for the first 4 years after harvesting. The
study was conducted on a steep east aspect at about 4,500 feet
(1 370 m) elevation.
Si 1 vicul tural treatments increased the amount of precipitation
that reached the forest floor, most in clearcuts and group
selections and 1 ess in shel terwoods . Snow accumulation
which accounted for about 50 percent of the annual precipi-
tation, increased about 80 percent in clearcuts, 50 percent
in group selections, and 40 percent in shelterwoods when
compared to uncut mature forest. During the growing season,
the uncut mature forest used about 75 percent of the total
annual precipitation. Differences in water use following
harvesting were less than expected. Shelterwoods used about
4 percent, group selections 10 percent, and clearcuts 11
percent less than the uncut control. Rapid revegetation on
a1 1 harvested areas, the residual stand in the shel terwoods ,
and soil water deficits in the uncut forest apparently
ameliorated some differences between uncut forest and treated
areas. As a function of differences in accumulated precipitation,