The effects of fire on the soil in a degraded semiarid woodland .II. Susceptibility of the soil to erosion by shallow rain impacted flow

Abstract

Small (500 by 250 by 100 mm) soil monoliths collected from experimental plots subjected to various fire frequencies in a semi-arid woodland near Coolabah, N.S.W., were tested for their susceptibility to erosion by rain-impacted flows under laboratory conditions. In the tests, the erosive stress applied to the soil surfaces was controlled by using drops of uniform size (2.7 mm) falling 11.2 m onto flows whose depths were controlled between 1 and 2.7 drop diameters. Experimental data and thin-section observations showed that cryptogams provide a high degree of protection against erosion. Sediment concentration (measured in g L-1) from cryptogam-covered plots was considerably less than that from both bare-crusted surfaces and surfaces dominated by depositional material. Surfaces with cryptogamic crusts were generally free of debris, but showed only minor signs of erosion, whereas bare-crusted and depositionary surfaces suffered pronounced lowering and tended to disintegrate. Because increasing fire frequency reduces the spatial distribution of the cryptogamic cover on the soil surface in the semi-arid woodlands, increasing fire frequency must increase the erosion hazard.