Survival and Growth of Young Bitterbrush Browsed by Deer

Abstract

Survival and growth of young bitterbrush (Purshia tridentata) shrubs browsed by deer during several winters were compared with survival and growth of protected shrubs. One study area provided no evidence that shrub survival on a browsed portion of the range was lower than in an exclosure, during 15 years following establishment by seeding. On a second study area, survival of shrubs inside an exclosure was 20 percent greater than survival of shrubs outside the exclosure. Generally, mean surface area of protected shrubs was 1.6 to 3.4 times greater than that of browsed shrubs. Young shrubs moderately browsed each winter remain smaller than unbrowsed shrubs. Bitterbrush is a preferred browse of deer on winter ranges in southern Idaho. It has been widely used in efforts to revegetate depleted big game range in several western states (Holmgren and Basile 1959, Hubbard 1964, Cummings 1966). Holmgren and Basile (1956, 1959) and Hubbard (1964) discussed the immediate effects of deer on the success of direct seedings of bitterbrush, but nothing has been reported on survival and growth over longer periods. The question is often asked whether a bitterbrush revegetation project can be successful in the face of continued deer browsing while the plants are young. This paper compares the rates of survival and growth of young, browsed shrubs with survival and growth of unbrowsed shrubs, and should help a range manager assess the effect of wintering deer on a range revegetation project.