In
a landscape-scale experiment, fires were lit in replicate catchments
15-20 km2 in area, either early in the dry season (June) or late in the
dry season (September) between 1990 and 1994. For each fire,
Byram-intensity was determined in representative one ha areas of
Eucalyptus miniata – E. tetrodonta open-forest, with a ground stratum
dominated by annual grasses. Fuel weights were measured by harvest, fuel
heat content was assumed to be constant, and the rate of spread was
determined using electronic timers. Fuels consisted primarily of grass
and leaf litter, and ranged from 1.5 to 13 t ha-1; in most years,
average fuel loads were 2-4 t ha-1. Rates of spread were generally in
the range of 0.2-0.8 ms-1. The mean intensity of early dry season fires
(2100 kW m-1) was significantly less than that of the late dry season
fires (7700 kW m-1), primarily because, in the late dry season, there
was more leaf litter, fuels were drier, and fire weather was more
extreme. Crown fires, a feature of forest fires of high intensity in
southeastern Australia, were not observed in the Kapalga fires. Fire
intensity was a very good predictor of both leaf-char height and
leaf-scorch height for fires between 100 kW m-1 and 10,000 kW m-1, the
range in which the majority of experimental fires fell.