Response of a semidesert grassland to 16 years of rest from grazing

Abstract

Grazing was eliminated from the Appleton-Whittell Research Ranch Sanctuary, located in south-central Arizona, in 1968. Long-term changes in canopy cover of vegetation were evaluated between 1969 and 1984, and comparisons were made between ungrazed and grazed plant communities in 1969. Long-term changes included both increases in species richness (diversity) and significant increases in canopy cover for midgrass, shortgrass, shrub, and forb species groups. Total vegetation cover was not significantly different on the grazed and ungrazed areas, but cover of midgrasses was significantly different. Increased cover of plains lovegrass (Eragrostis intermedia Hitchc.) on the ungrazed pasture was largely responsible for this difference. No differences in cover existed for the shortgrass, shrub, or forb species groups. Observations suggest that long-term (perhaps cyclical) changes in vegetation are occurring in addition to short-term influences of herbivory. Data do not support the hypothesis that continued animal impact is necessary to prevent ecosystem deterioration.