Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/1998
Publication Date: N/A
Interpretive Summary: Bitterbrush is a palatable and important shrub for deer, elk, and cattle on western rangelands. It is frequently added to seed mixtures in revegetation projects, but there is little information on whether or not cattle grazing affects newly established bitterbrush. We conducted a study to determine how either early-season or late-season cattle grazing affected newly established bitterbrush. When forage grasses were green an growing, cattle grazed about 6% of the shrubs each day. After grasses begin to produce seed stalks, cattle looked for bitterbrush and used nearly all the shrubs in a pasture in 6 to 8 days. After 3 years, bitterbrush in pastures grazed by cattle early in the growing season was twice as big as bitterbrush in ungrazed pastures. Shrubs grazed after grasses stopped growing were only half the size of bitterbrush in ungrazed pastures. Early-growing season use of grasses by cattle appears to stimulate the growth of young bitterbrush. Late-season grazing reduces shrub stature an growth. Thus, early-season cattle grazing can be used as a tool to stimulate bitterbrush growth.
Technical Abstract: Due to its palatability and sustained levels of forage quality, bitterbrush is one of the most desired shrubs on western U.S. rangelands. Because little information is available on the grazing management of newly established bitterbrush, this study was conducted to: 1) determine the effects of early and late-season cattle grazing on bitterbrush, 2) determine when cattle were most likely to forage on these shrubs, and 3) relate use on shrubs to the quantity, quality, and phenology of accompanying herbaceous forages. When grasses were green and growing, cattle grazed about 6% of the shrubs per day. When grasses and forbs were dormant, about 13% of the shrubs were grazed each day. Rates of use on shrubs were not correlated with amounts of herbage available, levels of forage utilization, stocking pressure, or digestibility or crude protein content of forages. In stepwise regressions, Julian date and IVOMD accounted for 98% of the variation in rates of use on the shrubs, suggesting that bitterbrush was grazed more heavily as the growing season advanced and forage quality of the grasses declined. When trials ended, shrubs in early-grazed paddocks significantly exceeded their counterparts in the dormant-grazed paddocks in height, diameter, and volume. Shrubs in early-treatments also exceeded ungrazed controls in diameter and volume.