VEGETATION TRENDS IN A YOUNG CONIFER PLANTATION AFTER GRAZING, GRUBBING, AND CHEMICAL-RELEASE

A 3-year-old Jeffrey pine (Pinus jeffreyi Grev. & Balf.) plantation in northern California was released by grazing with sheep for 5 years, m anual grubbing for 3 years, and applying a herbicide 1 year. These tre atments plus an untreated control provided an opportunity to evaluate density and developmental trends for the pine, shrub, and grass compon ents of the plant community during 1986-1994. Creating a near free-to- grow condition by applying Velpar herbicide modified the plant communi ty by controlling the shrubs, reduced cheatgrass in the second and thi rd years, and caused mean pine diameter, foliar cover, and height to b e significantly greater than counterparts in all other treatments. Gra zing caused two significant, but opposing changes in the plant communi ty. Nipping of twigs by sheep stimulated foliar cover of snowbrush to more than three times that of similar plants in the control. Grazing s ignificantly reduced greenleaf manzanita cover. Grubbing a 4-foot radi us around pine seedlings, and grazing with sheep did not increase Jeff rey pine development relative to the control. Because of this ineffect iveness, the efficacy of grazing as a silvicultural tool is questioned and suggestions for its betterment are presented.