INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 25 
HERBAGE PRODUCTION (POUNDS PER ACRE) 
STANDARD 
ERROR OF Se 
4 
PRECIPITATION (INCHES) 
Fiaure 10.—Relation of October herbage production to precipitation during the pre- 
- ceding 12 months at the Desert Experimental Range. This chart can be used to 
estimate herbage production from the precipitation in other years. | 
To use the chart a vertical line is projected upward from the amount 
of precipitation until it intersects the estimating line. A horizontal 
line is then projected across to the left-hand margin where an estimate 
of herbage production can be read. Asan example, the average herbage 
production expected for a year with rainfall of 8 inches would be ap- 
proximately 275 pounds per acre, as read from the chart. The actual 
production obtained may be higher or lower than the estimated amount, 
depending on seasonal distribution and character of the precipitation 
and whether or not precipitation was above or below average the pre- 
ceding year. However, in about two-thirds of the years, the actual 
herbage yields obtained would not be expected to vary more than 41 to 
50 pounds above or below the estimated amounts. ‘These limits are 
indicated by the dashed lines in figure 10. 
This method of prediction has been useful in providing an estimate 
of herbage production, without the time-consuming necessity of sam- 
pling the vegetation, before sheep reach the winter ranges. Herd owners 
have thus been enabled to purchase supplemental feeds or otherwise 
provide for anticipated short forage. Although the data apply par- 
ticularly to the range area at the Desert Experimental Range, they can 
also be applied to other winter range areas where the vegetation, con- 
dition of the range, and amounts of rainfall are similar. Where these 
conditions are not similar, relationships could be developed for specific 
areas from herbage weight determinations made over a period of years. 
