SHRUB DENSITIES IN RELATION TO FIRE, LIVESTOCK GRAZING, AND PRECIPITATION IN AN ARIZONA DESERT GRASSLAND

Changes in Baccharis pteronioides and Haplopappus tenuisectus densitie s in a southeastern Arizona grassland were related to patterns of live stock grazing, fire, and precipitation. Results suggested that both sp ecies increased following two periods of relatively wet winters, and d eclined during an intervening dry period. Baccharis completely recover ed through vegetative regrowth in one year after a 1987 wildfire, but Haplopappus suffered nearly total fire-caused mortality, and had not r ecovered by 1995 compared to its abundance on a nearby unburned site. In 1995, both species were most abundant in areas protected from grazi ng. Long-term (1982-1995) densities of Baccharis were stable, but Hapl opappus density increased by more than two orders of magnitude over th e same period, except in the burned area.