The demographic impacts of browsing on woody plants in savannas : from individual branches to whole populations

Abstract

Browsing ungulates can potentially have drastic impacts on vegetation patterns. This is particularly true in African savannas where many large browsers persist at high densities. Most of the theory and models outlining mechanisms of impact on plants and predicting responses are framed in terms of biomass impacts and responses. However, for trees in African savannas, fitness is more closely linked to height than above ground biomass. I evaluate the demographic impacts of browsing, making explicit contrasts with impacts on biomass. The results highlight under- explored intrinsic aspects of plants and browsers that determine the degree of browser impact on plant demography, aspects that have been under-explored due to an emphasis on biomass responses, and provide novel methods to measure and evaluate large-scale browser impacts, which have proved difficult before.