30 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE _ 
that the initial production was 15 pounds per acre lower. Under light 
grazing, yields increased enough to overcome the original deficit of 54 
pounds per acre and remained above those on the heavily grazed range 
except for a slight deficit in 1944. 
It is especially noteworthy that, during the 5 years from 1939 to 
1943 which included 4 years with below-average precipitation, yields 
under moderate grazing exceeded those under heavy. In 1943 after 
2 years of drought, total production dropped to its lowest point under 
all grazing intensities, being 84, 83, and 58 pounds per acre for light, 
moderate, and heavy grazing. Herbage yields under light and mod- 
erate grazing thus were 45 and 43 percent greater than the yield under 
heavy grazing. 
Calculated yield trends for the period of study are shown as straight 
lines in figure 13. They were upward for all three intensities of grazing, 
but more so for hght and moderate grazing than for heavy grazing— 
54 and 46 percent as against 34 percent for the 13-year period. 
Increases in total herbage production under light and moderate 
erazing as compared with heavy grazing are not easily detected on 
winter ranges. The results at the Desert Experimental Range, how- 
ever, are comparable with those obtained on other classes of rangeland 
where production is generally higher, such as the spring-fall sagebrush- 
wheatgrass ranges in Idaho (4, 13), yearlong shortgrass range in 
Montana (23), and black grama range in New Mexico (10). 
INDIVIDUAL SPECIES 
Yield of the major forage plants during the period of study under 
each intensity of grazing is givenintable7. For effective interpretation 
of yield trends under the three intensities of grazing, it is important to 
consider the average utilization that each species received (table 5). 
Winterfat showed the greatest changes in relation to grazing intensity 
during the 13-year period of study (fig. 14). Under moderate grazing 
this species made the greatest increase, and because of its relative 
abundance it was largely responsible for the increase obtained in total 
herbage. 
Initial yields of winterfat, as calculated from density estimates, 
were 19, 53, and 96 pounds an acre in the range pastures assigned to 
light, moderate, and heavy grazing. Despite these great initial dif- 
ferences, production under moderate grazing increased enough to 
surpass that under heavy grazing in 1939. During the next 3 years, 
yields were about equal for both intensities, that for moderate grazing 
being slightly below heavy. After. the second successive drought year 
in 1943, yields under moderate grazing again exceeded those under 
heavy grazing and remained above in the last 4 years of study. 
Yields of winterfat under light grazing were generally upward, with 
declines during the dry years. The rate of recovery was slow, which 
is not surprising in view of the low initial production. 
Calculated yield trends of winterfat for all treatments, also shown 
in figure 14, were upward—239, 321, and 33 percent, respectively— 
for light, moderate, and heavy grazing. Average utilization of winter- 
fat herbage for the 13-year period was 49, 55, and 66 percent. The 
heaviest use occurred in the low production years from 1939 to 1943. 
