Can spring cattle grazing among young bitterbrush stimulate shrub growth?
Due to its palatability and forage quality, antelope bitterbrush (Purshia tridentata Pursh DC) is a desirable shrub across western US rangelands. Because little information is available regarding grazing management of young bitterbrush, a study was undertaken to explore stocking pressure thresholds and quantify effects of light and heavy spring cattle grazing on shrub growth. Rates of browsing and trampling and forage availability were monitored over 3 years in southeast Oregon. Across years, 29% of bitterbrush endured trampling in light-grazing treatments, and 55% experienced trampling under heavy grazing. Linear models relating time and cattle density successfully explained (r2 = 0.84-0.86) probabilities of bitterbrush being trampled. Forage utilization averaged 32% and 59% in lightly and heavily grazed units, and 14 and 62% of bitterbrush were browsed in lightly and heavily-grazed pastures, respectively. Cattle began browsing when herbaceous standing crop declined to 100-150 kg ha-1
