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

Abstract

This study cvahtated the effects of heavy forage use in a restrotation 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 graxing (65% utihxation in June and 75% in July) during the growing season. When plants were protected from graxing, average basal-area cover increased for Idaho fescue [Fetiucu &fuhoeusii Elmer] and squirreltail/‘Sitani hystrix (NM.) J.G. Sm.] in a Wyoming big sagebrush [Artemi& tridentata wyomingends Beetle+Idaho fescue community type and for Thurber needlegrass [St@ thur* Piper] in 8 Wyoming big sagebrush-bluebunch wheatgrass [Agmpymn spicatutn (Push) 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 yeu during the first 3 years of the study and with no grazing during the growing season in the last 4 yeus of the study. Bluebunch wheatgrass showed no differential response to grazing or protection. Results of this study strongly implicate periodic heavy graxing durhtg 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.