USE OF ANNUAL PLANTS IN CALIFORNIA FOOTHILLS 25 



pastures with the lowest productivity were grazed closest and those with 

 the greatest productivity were grazed lightest. All six pastures showed 

 a consistent relation between productivity and degree of grazing. 



This consistent relation was also evident when the grazing capacity 

 of each pasture was estimated as the number of animal units that the 

 pasture would support under a moderate degree of grazing for an average 

 6-month season, from about February 1 until August 1. Stocking at 

 approximately 3.50 swale-acres per animal unit gave moderate utilization; 

 the range was from about 2.25 swale-acres for close utilization to 4.75 

 swale-acres for light utilization. Using a requirement of 3.5 swale-acres 

 per animal unit for 6 months, the 154-acre experimental pasture would 

 support 17.1 animal units under moderate grazing, and the 155-acre 

 pasture would support only 12.3 animal units. 



The grazing capacity of each site class under moderate grazing was 

 calculated from the relative yields per surface-acre shown in table 4. 

 For example, swales with a yield of 4,400 pounds per acre and a capacity 

 of 3.5 acres per animal unit for 6 months required an average of 0.58 

 acre per animal-unit month. Similarly, south exposures on open, rolling 

 slope, with a yield of 1,800 pounds per acre, required an average of 1.42 

 acres per animal-unit month. Because of variations in productivity 

 around the average for each site class, a range in grazing capacity was 

 estimated for each. The estimated range in grazing capacity for each 

 site class was: 



Acres per animal- 

 Site class: unit month 



Swale 0.50-0.70 



Gentle slope .80-1,10 



Open, rolling slope 1. 25-1 . 75 



Rocky brushy, rolling slope 2. 00-3 . 00 



Rocky brushy, steep slope 3.00-5.00 



More refinement in criteria is needed for recognition of grazing capacity 

 on steep slopes, but the range in capacity for other site classes is sufficiently 

 narrow for satisfactory use. 



The studies show that grazing capacity can be estimated by range 

 land classification. Thus range site classes are of direct use in determin- 

 ing proper ranch stocking. In addition, classification of range sites will 

 bring about more equitable evaluation of the tax base and more uniform 

 loan appraisals on foothill lands. 



Effect of Annual Precipitation on Herbage Yield 



Records of how herbage yield on the experimental range fluctuated 

 with annual precipitation show the need for flexibility in stocking. 

 Total herbage production there is typical of other parts of the California 

 foothills where average precipitation is about the same or greater. On 

 soils different from the granitic soils of the experimental range, annual- 

 plant herbage presumably would respond in a similar manner, but the 

 amount of monthly and annual precipitation required for the same plant 

 response might be different. 



The total yield at maturity of most species for each year (fig. 13) was 

 estimated as the average for all grazable soil in pastures 1, 2, and 3. 

 The estimates were based on intensive measurements made as follows: 

 1943-45, all sites in the three pastures; 1948, all sites in pastures 2 and 3; 

 1942, all slope sites in pastures 2 and 3; 1937-48, 34-acre exclosure in 

 pasture 1. 



