Vegetation trends in young conifer plantation after 10 years of grazing by sheep

Abstract

An 11-year-old ponderosa pine (Pinus ponderosa Dougl. ex Laws. var. ponderosa) plantation in northern California was grazed annually in summer by 600-1150 dry (nonlactating) ewes in an attempt to reduce competing vegetation and increase growth of pine seedlings. The sheep also provided an opportunity to evaluate density and developmental trends in the pine, shrub, grass, thistle, and forb components of the plant community. A manual release and a deer-only treatment provided contrast to the effects of grazing by sheep. In general, stem diameter and foliar cover of ponderosa pines, rarely damaged by sheep or deer, were significantly greater in manually grubbed areas, but only after 8 years. Pines in grazed areas never differed significantly in height, stem diameter, or foliar cover from control areas. Density, cover, and height of deerbrush (Ceanorhus integerrimus H. & A,) were generally fewer and lower if grubbed and grazed, but grass and bull thistle (Cirsium vulgare [Savi] Ten.) were larger and more numerous in these treatments. Forb cover was highest in the rubbed treatment. In general, average density, cover, and height of deerbrush, bull thistle, grasses, and forbs did not differ significantly among treatments grazed by deer or sheep suggesting that sheep did not have a deleterious effect on deer in terms of forage availability.

Citation

McDonald, Philip M.; Fiddler, Gary O. 1993. Vegetation trends in young conifer plantation after 10 years of grazing by sheep. Res. Paper. PSW-RP-215. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. 9 p