THE FATE OF NUTRIENTS DURING FIRES IN A TROPICAL SAVANNA

The nutrient loads contained in the grassy fuel before fires, and of a sh subsequently, were compared to determine the fluxes of macronutrien ts, copper and zinc during fires at Kapalga in Kakadu National Park. T he fluxes were estimated in three vegetation types: forest, woodland a nd open woodland. The magnitudes of the fluxes were greatest in the fo rest community where grassy fuel loads were highest at about 6.3 t ha( -1). In these sites, 54-94% of all measured nutrients in the fuel were transferred to the atmosphere during the fires. For each nutrient, th e proportion transferred to the atmosphere as entrained ash was calcul ated-by assuming that calcium was not volatilized during the fires. If the transfer of entrained ash represents local redistribution only, t hen rainfall accession and the deposition of these particulates should replace most of the losses of all nutrients except nitrogen (N). Esti mated rates of biological fixation of N appear to be insufficient to r eplace the annual losses of N. It is therefore concluded that a regime of annual fires that completely burn the available grassy fuel would deplete N reserves in these savannas, unless there are other sources o f biologically fixed N, which are unknown at present.