Soil erosion following wildfire in Royal National Park, NSW.

Abstract

Soil losses from a sandstone catchment in the Royal National Park, south of Sydney Australia, were recorded regularly for 12 months following a wildfire on 9th January 1983, then irregularly for 6 years. High intensity, drought-breaking rains in mid March 1983 resulted in significant overland flow that eroded both ash and sand from the hillslopes as well as from fire trails and walking tracks. Large volumes of sand and debris were carried from the slopes into the streams and deposited in Port Hacking. Serious downstream flooding damaged houses and bridges. Soil losses by the end of March (day72) ranged from 28.4 to 45.9 t ha-1 and by the end of the first year they ranged from 39.6 to 64.2 t ha-1. This compares with 2.5 to 8 t ha-1 reported from similar terrain north of Sydney during a relatively dry year. Soil flux rates remained at 9.7 kg m-1y-1 by the end of the first year. Litter cover did not change markedly in the first year after the initial leaf drop and most cover recovery was in the 0-0.5 m stratum. Similar high rainfall events 3.5 years after the fire produced minimal erosion of 0.25 to 2.19 t ha-1. Monitoring continued until another fire in 1994. The results of this study highlight the importance of the more extreme rainfall events as erosive agents. The high rates of soil erosion have implications for management of sandstone catchments around Sydney.