Using fire to manage species composition in Heteropogon contortus (black speargrass) pastures. 1. Burning regimes

A reduction in the proportion of the desirable grass Heteropogon contortus (black speargrass) and an increase in the undesirable Aristida spp . (wiregrasses) are evident in commercially grazed pastures. This paper evaluates the effectiveness of spring burning regimes over a period of 4 years (1989-92) in reversing this form of pasture degradation. Burning increased the proportion of H. contortus when pastures remained ungrazed but not when pastures were grazed, because cattle selectively grazed H. contortus after burning. Burning reduced the proportion of Aristida spp and other undesirable grasses such as Bothriochloa decipiens and Chloris divaricata . A strong ‘year of burning’ effect was evident. Burning increased recruitment of H. contortus which, in turn, increased plant density and later basal area. Burning reduced the basal area of Aristida spp initially by reducing tussock size and later by reducing tussock numbers. Results indicate that spring burning can restore pasture composition and that burning in at least 2 successive years appears to be necessary. Light stocking rates should be adopted so that the proportion of H. contortus can be maintained and so that pastures can be burnt when and if required.