Great Basin Naturalist


The objectives of this study were to compare vegetative and reproductive growth characters of bitterbrush (Purshia tridentata Pursh) stands as they relate to browsing levels. Growth characters were measured on 10 ecologically diverse stands in southwestern Montana on which browsing ranged from 0% to 60% of all current annual long shoot (LS) growth. Bitterbrush plants exhibited both twig-level and plant-level responses to browsing. Total bud density per plant was similar for browsed and unbrowsed sites, but differed (P < 0.01) between browsed and unbrowsed twigs. Browsed twigs produced one-half the leaf cluster density produced by unbrowsed twigs. No significant (P < 0.05) relationship between browsing levels on browsed plants and bud densities was found. Length of old-growth twigs per plant was shorter (P < 0.001) on browsed sites than on unbrowsed sites. Burning at 2 environmentally paired sites reduced flower bud density (P < 0.001) 9 and 10 growing seasons later although LS length was not affected. Growth of LS showed a site-by-year interaction (P < 0.05). Our data suggest that long-term unbrowsed plants should not be used as a standard for comparison with normally browsed plants.