Spatiotemporal variation in top-kill agents relative to ontogenetic resprouting strategies in African savannas.

Fire is a key control on woody plant size and abundance in semiarid tropics. Other disturbances, including cyclones, elephants, drought, frost, and tree harvesting also damage woody structures, causing top-kill or full mortality, depending on species' resprouting abilities and disturbance type. We outline expectations for resprouting adaptations in tropical African woody plant communities by integrating spatiotemporal information on disturbances with ecological impacts. Frost and fire affect smaller trees (less than 4 meters tall), cyclones and elephants affect medium to large trees, and human impacts are diverse. Historically, most of sub-Saharan African savanna trees evolved with frequent fires and high elephant densities, with implications for their resprouting patterns. Cyclone-induced toppling seldom coincides spatially with frost or drought. A considerable part of the region has lost a key top-kill agent, elephants, whereas human impacts have both spread and increased. However, in approximately 21% of the areas that lost elephants, this important ecological agent has not been replaced.