Grassland fire dynamics in the Serengeti ecosystem, and a potential method of retrospectively estimating fire energy.
Grassland plots in the Serengeti National Park were burnt at the beginning of the 1986 dry season during the period of max. fire frequency. The available fuel was estimated by clipping. Fire temp. were recorded continuously at 3 positions in the sward. Wt loss on ignition was determined for unburnt standing crops and unburnt residue and ashes after fires. Combustion in natural fires was incomplete, with combustion efficiency varying from 86% to 49%. Ignoring this residual combustible mass could give a wrong estimate of fire energy. Initial standing crops were 371-1459 g/m2 and control minus residual unburnt masses were 196-1444 g/m2. Fuel loads burnt were 101-1064 g/m2 and the proportion of mass burnt varied from 0.16-0.75. Mean max. temp. during fires were 407-830°C; time/temp. sums were 111-1418°-min. Fuel load burnt was linearly correlated with both measures of fire intensity. Wt loss of ash on ignition (LOI) was correlated with fuel load burnt, mean max. temp. and time/temp. sum, indicating that it was a useful estimator of fire energy. Rankings of ash shades were correlated with ash LOI and fire temp., suggesting that appropriately calibrated reflectometry or a standard grey scale could be a rapid simple method of retrospectively evaluating fire energy.