Grassland Fire Dynamics in the Serengeti Ecosystem, and a Potential Method of Retrospectively Estimating Fire Energy

(1) Grassland plots in the Serengeti National Park were burnt at the beginning of the 1986 dry season, the period of maximum fire frequency there. The available fuel was estimated by clipping. Fire temperatures were recorded continuously at three positions in the sward. Weight loss on ignition was determined for unburnt standing crops and for unburnt residue and ashes after fires. (2) Combustion in natural fires was incomplete, with combustion efficiency varying from 86% to 49%. Ignoring this residual combustible mass will give a wrong estimate of fire energy. (3) Initial standing crops were 371-1459 g m-2, and control minus residual unburnt masses 196-1444 g m-2. Fuel loads burnt were 101-1064 g m-2, and the proportion of mass burnt varied from 0.16-0.75. Mean maximum temperatures during fires were 407-830⚬C; time/temperature sums were 111-1418⚬C-minutes. Fuel load burnt was linearly correlated with both measures of fire intensity. (4) Loss of weight of ash on ignition (LOI) was correlated with fuel load burnt, mean maximum temperature and time/temperature sum, indicating that it is a useful estimator of fire energy. Rankings of ash shades were correlated with ash LOI and fire temperature, suggesting that appropriately calibrated reflectometry or a standard grey scale could be a rapid simple method of retrospectively evaluating fire energy.