EFFECTS OF FIRE INTENSITY ON SOIL CHEMISTRY IN A EUCALYPT FOREST

Soil samples taken in the Wombat State Forest in Victoria, at depths of 0-2, 2-5, and 5-10 cm before and after burning fuel loads of 0 (unburnt control), 15, 50, 150, and 300 t ha-1 were analysed for pH, exchangeable cations and cation exchange capacity, available and total P, organic carbon and soil moisture, over a 2-year, 2000 mm rainfall period. Short term responses (up to 6 months) occurred in levels of exchangeable NH4+, K+, and Mg2+, and long term changes (2 years or longer) over the period of the study were observed for pH, available and total P and exchangeable Ca2+ at the 0-2 cm soil depth for the burnt treatments. Following burning (and 108 mm of rain), changes in soil chemical parameters were strongly correlated with fuel load and the quantity of fuel burnt. Changes through the 0-10 cm profile for the various chemical parameters are described, together with seasonal variations. For similar yellow podzolic soils, measurement of soil pH may be a useful criterion for monitoring soil chemical changes following slash and fuel reduction burning, provided that accurate estimates of fuel loads, composition and amount burnt can be established.