ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

As indicated in figure 11 and appendix E, the relative amounts of water used by
the different treatments remained about the same during the second, third, and
fourth year after the harvesting was completed. However, the magnitude of the
differences decl i ned during that period. In the second year (1976) after harvesting,
the clearcuts used 18 percent less water than the controls, the group selections 14
percent less, and the shelterwoods 8 percent less. By the fourth year (1978), these
differences had declined to 9, 11, and 1 percent, respectively. of course, during
that same period, understory vegetation had begun its rapid recovery and was demand
substantial amounts of water (Schmidt 1980).
Accumulative water use curves for the different si 1 vicul tural treatments para1
leled each other early in the rowing season, but became increasingly divergent as
the season progressed (fig. 12 7 . Very little difference in accumulative use was
apparent between the three silvicul tural treatments until late July, but the uncut
mature forest areas diverged early in the growing season. Concurrent with water use
divergence was the beginning of significant water use from the lower end of the soil
profiles. Heavy frequent rains are common in June, but July and August are normally
hot and dry in this area.
WATER USE BY S ILV ICULTURAL TREATMENT - 1976
Figure 12.--AccmZative water use during the growing season on areas
differing silvicuZtura2 treatments, 2 years after hmesting was compZeted.
The differences shown between the treatments and the controls (uncut mature
forest) are conservative, Actual differences under regular management would probably
be greater for several reasons. A limited amount of preharvest water use data indi-
cated that preharvest water use differences existed on some of the sites. For example,
the uncut mature forest on the area later harvested for a shelterwood, was using more
water than its corresponding control. The soils on the control of one of the repli-
cates were shallower and consequently a smaller total water reservoir was available