FUEL BIOMASS AND COMBUSTION FACTORS ASSOCIATED WITH FIRES IN SAVANNA ECOSYSTEMS OF SOUTH-AFRICA AND ZAMBIA

Fires are dominant factors in shaping the structure and composition of vegetation in African savanna ecosystems. Emissions such as CO2, NOx, CH4, and other compounds originating from these fires are suspected t o contribute substantially to changes in global biogeochemical process es. Limited quantitative data exist detailing characteristics of bioma ss, burning conditions, and the postfire environment in African savann as. Fourteen test sites, differentiated by distinct burn frequency his tories and land- use patterns, were established and burned during Augu st and September 1992 in savanna parklands of South Africa and savanna woodlands of Zambia. Vegetation physiognomy, available fuel loads, th e levels of biomass consumed by fire, environmental conditions, and fi re behavior are described. In the South African sites, total abovegrou nd fuel loads ranged from 2218 to 5492 kg ha(-1) where fire return int ervals were 1-4 years and exceeded 7000 kg ha(-1) at a site subjected to 38 years of fire exclusion. However, fireline intensity was only 14 19 kW m(-1) at the fire exclusion site, while ranging from 480 to 6130 kW m(-1) among the frequent fire sites. In Zambia, total aboveground fuel loads ranged from 3164 kg ha(-1) in a hydromorphic grassland to 7 343 kg ha(-1) in a fallow shifting cultivation site. Dormant grass and litter constituted 70-98% of the total fuel load among all sites. Alt hough downed woody debris was a relatively minor fuel component at mos t sites, it constituted 43-57% of the total fuel load in the fire excl usion and shifting cultivation sites. Fire line intensity ranged betwe en 1734 and 4061 kW m(-1) among all Zambian sites. Mean grass consumpt ion generally exceeded 95%, while downed woody debris consumption rang ed from 3 to 73% at all sites. In tropical savannas and savanna woodla nds of southern Africa, differences in environmental conditions, land- use patterns, and fire regimes influence vegetation characteristics a nd thus influence fire behavior and biomass consumption.