THE ROLE OF HABITAT DISTURBANCE, SEED PREDATION AND ANT DISPERSAL ON ESTABLISHMENT OF THE EXOTIC SHRUB CYTISUS-SCOPARIUS IN CALIFORNIA

Effects of experimental habitat disturbance on seedling establishment of Scotch broom Cytisus scoparius, an alien shrub species now naturalized in California, were examined at two locations (the Sierra Nevada foothills and the northern coastal region). Variation in the species and foraging behaviors of ant dispersers of Scotch broom at the two sites resulted in differences in local seed dispersion at these sites. At the foothill location, soil disturbance significantly promoted seedling establishment. At the coastal site quail and grouse preferentially foraged in disturbed areas. The interaction of seed predators and dispersers modified the abiotic effects of habitat disturbance on seedling establishment, resulting in no significant differences being found among habitat disturbance treatments at the coastal site. Results of this study indicate effects of disturbance on seedling establishment of a given species are not generalizable from one population or habitat to another.