Net effects of large mammals on Acacia seedling survival in an African savanna

Trees of the genus Acacia are widespread and important components of savanna ecosystems. Factors or organisms that influence the survival of Acacia seedlings are likely to affect tree recruitment and therefore community and ecosystem dynamics. In African savannas, large mammals, especially elephants, have been considered the most important agents of mortality for adult trees, but their impacts on tree seedlings are not well known. We investigated the effects of large mammals on Acacia seedling survival by excluding large mammals from replicated 4-ha plots. Approximately twice as many seedlings were killed in plots with large mammals absent as on plots with large mammals present. Rodents and some invertebrates were more abundant on plots without large mam-mals and were responsible for these higher predation rates. Seedlings in areas with large mammals were more likely to die of desiccation; however, net seedling survival was approximately twice as high in the presence of large mammals. Our results indicate that large mammals may indirectly increase Acacia seedling survival and thus accelerate, rather than inhibit, tree recruitment.