Determinants of inter-annual variation in the area burnt in a semiarid African savanna

Fire is a key driver of savannas. It was predicted that the area of a summer-rainfall savanna burnt per annum should depend on the amount of fuel, which depends on variable grass production resulting from variable rainfall, 'carry-over' from the preceding season and attrition of fuel by herbivores. Most fires occur during the dry season, thus the amount of green growth resulting from occasional winter rainfall could influence fuel combustibility and therefore the area burnt. These predictions were examined with a 37-year (1963-99) data set for Mkuzi Game Reserve, South Africa. Total area burnt was related to wet season rainfall separately for years with a 'wet' dry season or a 'dry' dry season. Against prediction, the amount of dry-season rainfall had no influence on the total area burnt. For years with a 'dry' dry season, rainfall of the preceding wet season had an additional influence. Herbivore density had no influence. A dry-season burn was twice as large as a wet-season burn, and the largest burns were the most intense. Monitoring of wet season rainfall is sufficient for planning burning programs. Intense, large fires can be achieved for control of bush encroachment following 2 or more successive years of high rainfall.