ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

The main study site (fig. 1) occupies an east facing slope between the elevations
of 3,940 feet (1 182 m) and 5,300 feet (1 590 m) in the northern most portion of
Abbott Basin. Slopes on the cutting units range in steepness from 30 to 80 percent
(17O to 3g0) and average about 55 percent (29'). The mountain slope soils are of the
loamy-skel eta1 soi 1 famil ies (McConnell 1969; Klages and others 1976) derived mostly
from underlying Helena (Siyeh) limestone and dolomite of Precambrian Age, and a thin
mantle of glacial till of Pleistocene Age (Johns 1970).
The timber type on the study area is 1archlDouglas-fir (Cover Type 212, Society
of American Foresters 1954). This type is composed primarily of western larch and
Douglas-fir. Associated species include subalpine fir (~bies Zasiocarpa) and Engelmann
spruce (~icea enge2rnann.i.i). The study area fa1 1 s primari ly in the Abies Zasiocarpa/
Clintonia uniflora habitat type, with the following phases represented: Aralia
nudicaulis, Menziesia ferruginea, CZintonia unif lora, and Xerophy Zlwn tenax ( Pf i s ter
and others 1977; Bernard 1. Kovalchi k 1974, unpublished data1).
The Continental Divide is a primary climatic control for Coram Experimental
Forest. Two kinds of air masses give rise to the two main winter climatic events.
Pacific maritime polar air masses bring most of the 35 inches (89 cm) of mean annual
precipitation2 in Abbott Basin of Coram Experimental Forest, 50 to 65 percent of which
is in the form of snow, depending upon elevation. These air masses probably account
for 90 percent of all winter precipitation and 70 to 90 percent of summer precipitation.
Arctic continental polar air mass invasions produce light amounts of snowfall but
their main contribution to local climate is extreme cold.
Variations in summer precipitation are caused by local thunderstorms and upper
level barometric lows. Precipi tation from thunderstorm events is characterized by
both high intensity and spatial variability, whereas precipitation caused by upper
level barometric lows is typically of low intensity and long d~ration.~
Abbott Creek, in the immediate vicinity of the study area, is
only in the lower portion of the basin. It emerges at the extreme
Basin and flows for approximately 950 feet (380 m) before passing
flume. The stream is typically non-flashy and is characterized by
sustained flow.
l0n f i 1 e at Forestry Sciences Laboratory, Missoula, Mont.
a perennial stream
lower end of the
through a &foot H-
low peaks and high
From Average Annual Mountain Precipitation, Montana Map (1953-1967 period).
3Personal communication with Bernie Burnham, Meteorologist, U. S. Department of
Commerce, NOAA, National Weather Service, Missoula, Mont.