Research Branch Report No. 256
The effects of fire in eucalypt forests on soils, nutrient cycling, tree growth and catchment hydrology: A review with particular reference to fuel-reduction burning. D. W. Flinn, P. W. Farrell, H. T. L. Stewart, C. J. Leitch and P. Hopmans. August 1984. 44 pp. (unpubl.)
This paper reviews published data from Australian and overseas studies on the effects of fire on soils, nutrient cycling, tree growth and catchment hydrology. Where possible, comparisons are drawn between the effects of wildfire and fire prescribed for hazard reduction (fuel-reduction burning in eucalypt forests on these factors.
It is shown that fire has the potential to markedly influence the chemical and biological properties of surface soils, with the degree of change in such properties being strongly linked with fire intensity and hence, soil heating. The loss, redistribution and transformation of nutrients contained in both the soil and biomass during and following fire are emphasised in this review, as the continued availability of nutrients governs the productivity of a site to a large extent. This is especially important in eucalypt forests where soils commonly have a relatively low nutrient capital and plants rely heavily on recycling of nutrients for their growth and stability. Thus, although the effects of a single prescribed fire can be forecast with a certain degree of confidence, insufficient data are available to accurately predict the cumulative effects of repeated prescribed fires on soils, nutrient cycling and site productivity in eucalypt forests compared with the known adverse effects of a single, intense wildfire.
In contrast, the effects of fire on catchment hydrology are shown to be relatively well-understood. Fire is known to affect hydrologic processes such as interception, overland flow, evapotranspiration and soil infiltration capacity. The magnitude of these effects depends largely on fire intensity and frequency, the proportion of catchment burnt, soil properties, rate of revegetation and post-fire climate, and can be manifested through changes to streamflow behaviour and streamwater quality. Several Australian studies have reported substantial changes in streamflow behaviour (e.g. annual water yield, peak flow, runoff response) and streamflow quality (e.g. physical properties) following wildfire, though few data exist for low-intensity prescribed fire. However, given the known effects of high-intensity fire on hydrologic processes, there is convincing evidence that the single effects of an intense wildfire on catchment hydrology are likely to significantly outweigh any cumulative effects caused by frequent fuel-reduction burning.
Flinn, D. W., Farrell, P. W., Stewart, H. T. L., Leitch, C. J. and Hopmans, P. (1984) The effects of fire in eucalypt forests on soils, nutrient cycling, tree growth and catchment hydrology: A review with particular reference to fuel-reduction burning. Proc. Symp. Fuel-reduction Burning, Mon. Univ., Clayton, Victoria, Sept. 1983, pp. 146-185.