Predicting semidesert range perennial grass production from recent precipitation and grazing levels

Abstract

Perennial grass production on the Santa Rita Experimental Range about 4o miles south of Tucson is studied for responses to recent precipitation, use, key species, and range condition. Responses were evaluated by multiple linear regression analysis, cOrrelation coefficient analyses, and path coefficient analyses. Data were made available by the U. S. Dept. Agr. Forest Service. Observations were recorded annually from 1957 to 1966 for use, precipitation, and perennial grass production on 20 transects in each of four pastures. Perennial grass and shrub intercepts were read from the same transects for the period 1956-1966, excluding 1960. Range condition ratings were made on each of the transects in 1966. Perennial grass production was shown to be dependent on the product of current August X previous June-September precipitation. Use levels generally had weak negative effects on production. Range condition was found to be correlated with 10-year mean use. Range condition was not closely correlated with perennial grass production. Forage cover and percent invaders, decreasers, and increasers were the major determinants of range condition rating. These factors were not strongly correlated with perennial grass production.