60 CIRCULAR 925, U. S. DEPARTMENT OF AGRICULTURE 
Herbage production was found to increase approximately 46 pounds 
an acre with each additional inch of precipitation. This close relation 
has provided a basis for forecasting forage at the experimental range 
from precipitation records up to October of each year. Such forecasts 
would enable sheep operators to provide supplemental feed or other- 
wise make adjustments for indicated short forage before taking their 
herds to the winter range. 
In the pastures the trend of total herbage production during the 
period of study was upward under all three intensities of grazing, the 
increases being respectively 54, 46, and 34 percent for light, moderate, 
and heavy grazing. Winterfat, the most productive and palatable 
shrub in the pasture area, showed trend increases of 239, 321, and 
33 percent under light, moderate, and heavy grazing. Shadscale, 
more abundant but lower in palatability, increased slightly more under 
moderate grazing and much more under light grazing than under 
heavy grazing. Galleta and sand dropseed declined slightly under all 
intensities of grazing primarily because of infrequent favorable summer 
rainfall. Indian ricegrass, bud sagebrush, and globemallow, which 
made up small amounts of the plant cover, did not show any consistent 
response to the differential grazing treatments. 
Other plant subtypes showed changes in vegetal composition under 
two intensities of grazing on large range areas inside and outside of 
the experimental range. In a shadscale-Indian ricegrass subtype, 
yields of the palatable Indian ricegrass increased from 30 percent of 
the total in 1934 to more than 40 percent in 1947 under moderate 
grazing. Under heavy grazing production dropped to 15 percent of 
the total by 1947. 
The valuable black sagebrush increased remarkably in volume under 
moderate grazing on a depleted subtype which originally produced 
primarily winterfat, rabbitbrush, and only small amounts of grass and 
black sagebrush. This species produced only 7 percent of the herbage 
in 1934 but by 1947 made up more than 40 percent of the total, 
because of increases in vigor and establishment and growth of seedlings. 
On the adjacent part of the subtype, where heavy grazing was con- 
tinued, rabbitbrush remained the dominant species. 
Low-value annuals and undesirable shrub species were generally 
supplanted by more palatable species when grazing pressure was re- 
duced or suspended. As an example, an ungrazed enclosure was 
erected in 1937 on an area where Russian-thistle produced about 60 
percent of the vegetation. Three years later this species was almost 
completely supplanted by winterfat and Indian ricegrass within the 
enclosure. By 1947 Russian-thistle produced only 2 percent of the 
herbage in the enclosure. On the neighboring heavily grazed range, 
Russian-thistle production was 402 pounds an acre or 54 percent of 
the total herbage. 
Ewes on moderately grazed range maintained body weights of 4 to 
18 pounds more than those on heavily grazed range. They also pro- 
ducedabout a pound more wool and 11 percent more lambs. Costs 
of feeding sheep in poor condition and death losses were greatly re- 
duced. Income from herds wintered at moderate grazing levels and 
under good management practices averaged $3.46 per ewe as compared 
to $1.69 from herds on heavily grazed range. 
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