USE OF ANNUAL PLANTS IN CALIFORNIA FOOTHILLS 



23 



Table 4. — Relative herbage yields of site classes, San Joaquin Experimental 



Range 



Site class 



Yield per 

 grazable 



Grazable 

 soil 2 



Yield per 

 surface 



Swale. 



Gentle slope: 



North exposure. 

 South exposure. 



Open, rolling slope: 

 North exposure- 

 South exposure _ 



Rocky brushy, rolling slope: 



North exposure 



South exposure 



Rocky brushy, steep slope: 



North exposure 



South exposure 



Pounds 

 4,400 



3,200 

 2,800 



2,200 

 2,000 



1,400 

 1,400 



900 

 1,800 



Percent 

 100 



95 

 95 



Pounds 

 4,400 



3,040 

 2,660 



90 

 90 



70 

 70 



55 

 70 



1,980 

 1,800 



980 

 980 



495 

 1,260 



Steep, rocky bluffs. 



1 In evaluating productivity of the several site classes, the average yield of 4,400 

 pounds per acre for swales in pasture 2 during 3 years of intensive sampling (1943-45) 

 was taken as a base. Yield of each slope site class and for steep slopes in relation to 

 the base yield for swales was estimated from a limited number of sample quadrats 

 for each site class in three pastures in 1945. 



2 Percentage of grazable soil for each site class was estimated from an intensive 

 survey of the land surface actually grazable by cattle in each pasture. 



3 Yield of herbage per surface acre (Land Office acre) was computed for each site 

 class by multiplying the yield per grazable acre by the percentage of grazable soil. 



exposures on rolling topography, with thin stands of trees and shrubs, 

 yields were commonly observed to be greater than those on similar south 

 exposures. On steep north exposures, however, the stand of herbage 

 was often thinned by shading from dense tree canopies. 



That productivity of range site classes must be taken into account in 

 estimating grazing capacity is also shown by the lack of correspondence 

 between size, productivity, and degree of utilization in each of the six 

 grazing-intensity pastures on the experimental range (table 5). 



As a yardstick of productivity the acreage of each site class in each 

 pasture was reduced to its swale-equivalent in herbage production, or 

 "swale-acres." Because pasture 1, 154 acres in area, contained a rela- 

 tively great proportion of the more productive site classes (fig. 12), it 

 had a productivity equivalent to that of 60 acres of swale. But pasture 

 3, with 155 acres and a different combination of site classes, mostly of 

 lower value, was equivalent to only 43 acres of swale. Similarly, the 

 230-acre pasture 2 contained 12 more swales-acres than the 309-acre 

 pasture 4- 



Each pasture was stocked with 15 cows along with their calves and a 

 bull for part of the season. This stocking averaged approximately 19 

 animal units per pasture for a 6-month season. Consequently, the two 



