INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 23 
Much of the winter precipitation comes as snow. This seldom 
exceeds 4 or 5 inches in depth except in the foothills and desert moun- 
tains. Often the storms are erratic and poorly distributed. Since 
sheep depend largely on snow for water, ranges are often used unevenly. 
In severe winters or during heavy winter storms the snow often becomes 
too deep or too firmly crusted to permit effective grazing. If deep 
snow persists over large areas, the sheep become extremely poor and 
often die because they are unable to obtain sufficient forage. In the 
last 20 years such conditions have occurred several times, notably in 
the winters of 1931-32, 1936-87, 1948-49, and 1951-52. 
When strong winds accompany a snowstorm or follow immediately 
afterwards, deep snowdrifts are formed. These hamper the movement 
of sheep and limit grazing to ridges blown free of snow. 
According to rain-gage records, summer storms are also localized and 
often occur as torrential downpours of high intensity. For example, 
on May 2, 1935, 1.20 inches of precipitation fell in less than 20 minutes 
in the south end of Wah Wah Valley. Areas a short distance away 
received no rain. On July 28, 1936, Antelope Valley received 1.57 
inches of rain in 23 minutes, but there was none at the Desert Experi- 
mental Range headquarters 6 miles to the east. During such torrential 
storms much of the precipitation is lost in runoff and consequently is 
not available for plant growth. 
INFLUENCE OF PRECIPITATION ON PRODUCTION 
Forage plants on the winter range consist of a mixture of early- and 
late-growing species. Many of them, including the shrubs and such 
grasses as Indian ricegrass, squirreltail, and bearded bluebunch wheat- 
grass, begin to grow in the latter part of March or in early April, 
provided soil, moisture, and weather conditions are favorable. Some 
of these species continue to grow throughout the summer if rainfall is 
adequately distributed. In dry summers plant growth stops, the 
herbage becomes dry and brittle, and frequently the plants fail to 
produce flowers or seed. Some forage plants, primarily such annual 
forbs as Russian-thistle and such grasses as galleta, sand dropseed, and 
blue grama, begin to grow in May and June. ‘These species generally 
depend on summer precipitation to make their growth. Almost all 
plant growth on the winter range is completed by September, though 
late rains often freshen and soften the herbage. 
TOTAL HERBAGE YIELD 
The total air-dry herbage yield was estimated annually on each range 
pasture. These data were averaged and used to determine the relation 
between production and precipitation. In most years herbage produc- 
tion was estimated directly. However, yields for the first 3 years were 
calculated from plant density; and the production for 1946, when no 
data were taken, was calculated from the relation of production to 
precipitation. 
Air-dry herbage yield on all pastures for the period 1935—47 averaged 
219 pounds per acre. The maximum yield of 468 pounds per acre was 
recorded in October 1947, immediately following the 12-month period 
