Growth and Reproduction of Grasses Heavily Grazed Under Rest-Rotation Management

Abstract

This study evaluated the effects of heavy forage use in a rest-rotation grazing system on the basal-area growth and frequency of occurrence of native bunchgrasses from 1975 to 1984. None of these grasses increased in basal-area cover with brush competition or in basal-area cover or frequency without brush competition when subjected to periodic heavy grazing (65% utilization in June and 75% in July) during the growing season. When plants were protected from grazing, average basal-area cover increased for Idaho fescue [Festuca idahoensis Elmer] and squirreltail [Sitanion hystrix (Nutt.) J.G. Sm.] in a Wyoming big sagebrush [Artemisia tridentata wyomingensis Beetle]-Idaho fescue community type and for Thurber needlegrass [Stipa thurberiana Piper] in a Wyoming big sagebrush-bluebunch wheatgrass [Agropyron spicatum (Pursh) Scribn. & Smith] community type. Average basal-area cover was unchanged for protected Thurber needlegrass plants in a Wyoming big sagebrush-Thurber needlegrass community type. Average basal-area cover of Thurber needlegrass plants in the same community type decreased when heavily grazed during the growing season in 1 year during the first 3 years of the study and with no grazing during the growing season in the last 4 years of the study. Bluebunch wheatgrass showed no differential response to grazing or protection. Results of this study strongly implicate periodic heavy grazing during the growing season as a primary cause of restricted basal-area growth and lack of reproduction. These results support the contention that such grazing pressure can prevent range improvement in an otherwise appropriate rotation grazing system.