USING A GRAZING PRESSURE INDEX TO PREDICT CATTLE DAMAGE OF REGENERATING TREE SEEDLINGS

This research investigated the potential for using rattle grazing pres sure (AU Mg-1 ha(-1)) and stocking rate (Animal Unit Days ha(-1)) for predicting basal scarring and browsing of lodgepole pine (Pinus contor ta Dougl,) seedlings on cutblocks in southern British Columbia from 19 89 to 1992, Cattle browsing on lodgepole pine seedlings occurred almos t exclusively during the first 2 years of grazing, Browsing increased (P < 0.05; r(2) = 0.71) with increasing stocking rate only during the first year of grazing, Browsing increased with increasing grazing pres sure in 1989 (P < 0.05; r(2) = 0.38) and 1990 (P < 0.05; r(2) = 0.39), Basal scarring peaked during the second year of grazing, but was corr elated (P < 0.05; r(2) = 0.79) with stocking rate only during the firs t year of grazing, Increasing grazing pressure was associated with hig her (P < 0.05) basal scarring during all 4 years of the study, and lik ely better predicts trampling damage than does stocking rate, particul arly during the first year of grazing, Basal scarring during 1989 gene rally increased to > 10% of sample trees when grazing pressure exceede d 12.0 AU Mg-1 ha(-1). This threshold grazing pressure value of 12.0 A U Mg-1 ha(-1), however, cannot Likely be extrapolated directly to othe r sites, Grazing pressure values and associated basal scarring are unq uestionably influenced by many factors (e.g., pasture size, kind of gr azing animal, forage species, tree height, water availability, topogra phy, and weather patterns during the grazing period), Nonetheless, our work provides evidence that grazing pressure-provides a useful index for predicting the potential for trampling damage of lodgepole pine se edlings by cattle.