INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 27 
Mortality of shadscale was relatively high during the drought period 
1942-43, when it was estimated that 20 to 30 percent of the shadscale 
plants died. During this same period very little loss occurred in other 
forage species. Although production of shadscale and winterfat each 
declined to 18 pounds per acre in 1943 following 2 years of drought 
accompanied by heavy mortality of shadscale, they responded quickly 
to favorable precipitation the following years. In 1944 with just below 
average precipitation, 2.62 inches of which came in the October— 
December period and 2.45 inches in the April—June period, the dormant 
winterfat plants quickly revived and many shadscale seedlings appeared. 
In that year shadscale and winterfat produced 93 and 69 pounds per 
acre, respectively. By October of 1947, following 4 years of average 
or above-average precipitation, yields of these two shrubs reached a 
maximum. Winterfat produced about 90 pounds per acre and shad- 
scale 195 pounds, more than twice their average yield. This demon- 
strates the remarkable ability of the winter range vegetation to recover 
from the effects of drought. 
The three major grasses—Indian ricegrass, galleta, and sand drop- 
seed—showed differing responses to variations in precipitation, but in 
general their yields were closely correlated with previous 15-month 
precipitation (fig. 12) rather than with the previous 12-month pre- 
cipitation. Analysis of data for the period 1938-45 and for 1947 
showed that sand dropseed followed variations in 15-month precipitation 
most closely. In 1936, yield of this species as calculated from plant 
density was unusually high (59 pounds per acre). Most of the increase 
was due to the numerous seedlings produced in 1935 and 1936 as a 
result of favorable late spring and summer rains. Many of these 
seedlings failed to survive through 1937. . 
Yields of galleta followed variations in 15-month precipitation closely 
but somewhat less so than those of sand dropseed. Relatively high 
yields of both these grasses occurred in 1938, 1939, 1941, and 1947, all 
years with high spring and summer rainfall. 
Production of Indian ricegrass showed the lowest correlation with 
15-month precipitation. In 1938, with prior 15-month rainfall of 11.10 
inches, yield of Indian ricegrass was 17 pounds per acre; in 1939, with 
2 inches less rainfall, yield was the same; and in 1945, with 8.79 inches, 
yield was only 9 pounds. 
Yields of all three grasses fluctuated with precipitation but showed 
a general decline from 1935 to 1942-43, during a period generally char- 
acterized by below-average rainfall. The lowest yields of all grass 
species occurred in 1943 following the 2 years of drought. After the 
drought period production increased rather rapidly until 1947 when 
yields were highest. Although grass yields improved following the 
drought, the recovery was not nearly as great as that of winterfat and 
shadsceale. 
INFLUENCE OF GRAZING INTENSITY 
ON VEGETATION 
The great fluctuations in plant growth due to differences in precipita- 
tion from year to year tend to overshadow the effects of grazing, 
particularly during short periods of time. To segregate one effect from 
the other, it is necessary to compare results obtained under different 
