Using fire to manage species composition in Heteropogon contortus (black speargrass) pastures .2. Enhancing the effects of fire with grazing management

Burning in spring can increase the proportion of the desirable species Heteropogon contortus (black speargrass) when pastures remain ungrazed following burning and to a lesser extent when the pasture is grazed. Consequently, an experiment examined the effects on pasture composition of annual spring burning followed by grazing deferment for 0, 2, 4, or 6 months or for 0 months but at half the stocking rate of the other 4 treatments. Either deferring grazing for 4 or 6 months or halving the stocking rate after burning in spring resulted in an increase in the proportion of H. contortus. Burning reduced the undesirable Aristida spp. as a pasture component and this effect occurred independently of grazing treatment. The development of 2 cohorts of H. contortus seedlings was monitored for 18 months. Seedlings were selectively grazed but developed rapidly with few differences between treatments. Differences in seedling survival between years reflected differences in rainfall after establishment. Results indicate that burning in spring to increase the proportion of H. contortus will be more effective if followed by 4-6 months rest or by reduced grazing pressure.