INCREASING FORAGE YIELDS ON INTERMOUNTAIN WINTER RANGES 29 
Yield trends, for total herbage and for individual species under light, 
moderate, and heavy intensities of grazing, were computed by the 
least-squares method described by Snedecor (18). 
TOTAL PRODUCTION 
Total annual herbage production of all plants within shadscale and 
winterfat subtypes as represented in the experimental range pastures 
for the three intensities of grazing is shown in figure 13. Total pro- 
duction is the sum of the increases and decreases of individual species 
and therefore shows the over-all average difference between grazing 
treatments. 
~ When the studies were begun in 1935, average herbage production 
in the range pastures assigned at random to light and moderate grazing 
was somewhat lower than in those assigned to heavy grazing. Initial 
yields, calculated from density estimates, were 232, 271, and 286 
pounds per acre, respectively, for light, moderate, and heavy grazing. 
Herbage production dropped during the next 2 years under heavy 
grazing. Production also showed a decline under light and moderate 
grazing in 1937 following a year with below-average precipitation. 
Yields under all three intensities rose in 1938 after favorable precipita- 
tion. In every year following 1938 more herbage was produced on the 
moderately grazed range than on that heavily grazed, despite the fact 
300 
200 
HERBAGE PRODUCTION (POUNDS PER ACRE ) 
O 
1935 1937 1939 194] 1943 1945 1947 
Figure 13.—Average annual herbage production of all plants and calculated trend 
of production in 6 lightly, 7 moderately, and 7 heavily grazed range pastures 
within shadscale and winterfat subtypes, 1935-47. 
