ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Lowest daily water use occurred at the end of the growing season (previously
defined as May 2 to October 17) when soil moisture was at its seasonal low and the
frost had already taken its toll of the herbs and shrubs. Interestingly, the under-
story-protected treatments of both clearcuts were the lowest water users at the end
of the growing season, yet were high mid-season users. I
The most predictable and least variable use patterns were displayed by the
residues-removed treatment followed by the conventional-utilization-and-burn and the
unders tory-protected treatments.
The greatest variation in daily water use occurred consistently in mid-July on
a1 1 rep1 icates and treatments. Both upper and lower clearcuts consistently demonstrated
the greatest variability in the pattern of water use. This observation is
consistent wi th the range in treatment diversity that resul ted from the imposi tion of
si lvicul tural and residue treatment combinations.
The trends shown in this study are in agreement with Tew (1967), Johnston and
others (1969), and Zeimer (1964). They found that the period of greatest water use
occurred early in the growing season and that average daily water use decreased as
availability of moisture decreased. Tew (1967) reported that 4.7 inches (12 cm) was
used from May 25 to July 13 while 1.2 inches (3 cm) was used from July 13 to September
22. Evapotranspiration data from two sagebrush watersheds in northwest and south-
central Wyoming (Sturges 1979) also fits very nicely in the lower third of the daily
use envelope that we developed in this study (fig. 15). Rich and Thompson (1974)
listed average daily evapotranspiration rates for some mixed conifer species in differ-
ent localities. All but three of the rates listed are easily encompassed within our
envelope.
Daily and annual consumptive use rates are being governed by many factors. Kovner
(1956) suggests that evapotranspiration opportunity is usually related to extent of
cover on an area rather than its character. Cline (1974) related soil moisture loss
during the growing season to not only degree of occupancy and type of vegetation
existing on a site, but also aspect and the resulting potential evapotranspiration for
a particular site. Cline and others (1977) reported that on a south slope, invading
shrub species rapidly reoccupiedothe soil mantle, and after 4 years, the shrub mono-
culture probably extracted more water from the soil during the extremely dry summer
than did the original stand. Effects of slope and aspect on solar radiation and
subsequent water consumption are also discussed by Cline and others (1977) as well as
Lee (1964, 1967) and Douglass (1967), and are believed to play a major role in regulat-
ing consumptive use. Stearns and Carlson (1960) found that soi 1 moisture correlated
best with soi 1 temperature, evaporation-pan data, and solar radiation.
S treamf 1 ow
There were no noticable departures from expected values in either peak flow or
base flow of Abbott Creek. The probable reasons for this are: (1) there were no
preharvest streamflow data for making comparisons, (2) the watershed is not a closed
system, (3) the hydrologic and geologic divides do not coincide, and (4) the equivalent
clearcut area was only 5 percent of the gauged watershed.
The chemistry of Abbott Creek (at the flume) was not significantly changed accord-
ing to Stark (1979, 1980).
Other information concerning the Abbott Creek watershed appears in appendix A and
B. It is presented primarily to document streamflow pattern in this drainage and
geographic area.