The Hydrological Effects of a Wildfire in a Eucalypt Afforested Catchment

SYNOPSIS

A high-intensity wildfire through a humid, upland catchment which was partially afforested to Eucalyptus fastigata, markedly increased stormflows and caused high soil losses off the afforested slopes. Total streamflow yield was unchanged but baseflow was reduced after the fire. The change in stormflow generation was caused by increased overland flow which resulted in shorter times of concentration and higher peak discharges during storms. Increased overland flows are linked to the widespread presence of water repellency in the plantation soils. The fire also increased the erodibility of the surface soils which were readily entrained by the overland flow, hence the accelerated soil erosion. Measured soil losses on the afforested slopes (55 t/ha) were roughly five times higher than those estimated from sediment in the stream (10 t/ha). The difference is attributed in large part to a healthy riparian buffer zone which was observed to have trapped large amounts of eroded soil and ash. The potential loss of site fertility and the threat of downstream flooding and sedimentation after such wildfires, lead us to advise forest managers to adopt a more positive approach to forest fuel management.

Keywords:

• fire effects
• water repellent soil
• streamflow generation
• catchment response
• soil erosion