ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

SILVICULTURE TREATMENTS
Si 1 vicul tural treatments produced the most differences in soi 1 moisture levels ,
as illustrated in figure 9. Differences were generally most apparent at the end of
the growing season. Clearcuts retained the highest percentage of moisture and the
uncu t-ma ture stands the 1 owes t percentage. Soi 1 moi s ture level s i n s he1 terwood and
group-selection treatments ranged between these two extremes. For the 3-year period,
the cl earcu t , group-sel ection , and shel terwood treatments averaged 14, 8, and 5
percent more soil moisture than in the mature forest at the end of the growing season
in the lower elevation replicate and 9, 11, and 2 percent more, respectively, in the
upper replicate. More precipitation was received in the upper replicate, which
decreased soi 1 moisture deficits .
Snowmel t recharged the soils under all treatments to about their same respective
1 eve1 s each year, wi th he exception of the spring of 1977. This year, the uncutcontrol
areas failed to reach full recharge by roughly 1.7 inches (4.3 cm) of water.
Soil moisture levels in the fa1 1 of 1976 were about normal , but a below average
snowpack that winter fa led to produce enough water to overcome the fa1 1 deficit in
the uncut controls (fig 9). . The harvested areas came into winter with less of a
deficit than the contro 1 s ; the snowpack, even though below normal , was adequate to
recharge those profiles. For example, at the end of the 1976 growing season, soi 1s
under the uncut-control stands needed 5.4 inches (13.7 cm) to reach recharge while
those in the shel terwood and clearcut needed 4.1 and 2.6 inches (10.4 and 6.6 cm) ,
respectively. Another contributing factor discussed earl ier was i ncreased snow
accumulation in the clearcuts, group selections , and shel terwoods i n re1 ation to the
mature forest--a result of redistribution.
RESIDUES TREATMENTS
No consistent trends or differences in soil water status, could be attributed
solely to the various residue treatments.
Water Use
The uncut mature larchlfir forest within the study area used about 75 percent of
the 24-i nch (61-cm) average annual on-si te precipitation. Water use wi thin the
treatments was nearly always less than that of the uncut forest but varied substan-
tially by treatment and year, A detailed summary of water use by silvicul tural and
residue treatment for 3 years of the study are presented in appendix E.