Effects of Spring Wildfires on Astrebla (Mitchell grass) Grasslands in North-West Queensland Under Varying Levels of Growing Season Rainfall.

Abstract

The response of Asr~ebla (Mitchell grass) grasslands to burning was determined in relation to the amount of rainfall re- ceived in the following growing season. Nine A. lappacea and three A. pecrinata locations in north-west Queensland were studied [:or both species, fire tended to increase the number and total dry weight of new tillers, although the individual tillers were smaller. Very low and very high rainfall resulted in sub-optimal new tiller formation in unburnt areas of A. lappacea. 1,lowering and seed set was also stimulated by wildfires. The nitrogen content of new tillers in burnt treatments was higher than for those in unburnt treatments under low growing season rainfall and lower under high growing season rainfall. Dry matter production from burnt A, lappacea, relative to unburnt areas, decreased under low rainfall and increased under high rainfall. Burning at a time of high soil moisture resulted in higher dry matter production and higher nitrogen content than burning during the spring period when soil moisture was low. The ecological and management implications of these responses are discussed