Distribution and determinants of Savannas

This chapter summarizes some of the points of contention related to understanding the distribution and determinants of savanna ecosystems worldwide, and describes some resolution where possible. It provides comparisons across continents and between temperate and tropical savannas, hoping to isolate some general patterns and rules that persist despite their varied histories and climates. As most savannas globally have lost much of their mammalian fauna the importance of herbivores in creating and maintaining high-rainfall savannas has never been assessed. The correlation between savanna vegetation and long dry seasons is very clear. In mesic regions there is disagreement over whether closed canopy systems are possible in savanna environments in the absence of top-down disturbances such as fire or herbivory. The drivers of arid transitions in savannas are less discussed in the literature but many of the biggest differences between the continents lie at this transition.