Mitchell grass death in Queensland: extent, economic impact and potential for recovery

Summary

The project conducted the first comprehensive assessment of the health of Mitchell grass pastures during drought. The results were not encouraging. Compared with published historical information, the Mitchell grasslands are in worse condition in 2006 than in 1992 or 1978. The major decline appears to have occurred between winter 2005 and winter 2006, with condition in 2005 similar to that of 1992. However, Mitchell grass tussocks which had low vigour in 2005 did not appear to have survived into 2006 leading to a general decline in land condition. 
It is estimated that this reduced land condition across the Mitchell grasslands of central western Queensland costs industry between $5.7 and 10.4 million in lost productivity per annum. Extended periods of below average rainfall, coupled with high evaporation, are the major factors leading to dieback. It may not be as simple as more rain equating to better Mitchell grass survival, as it is likely that there is a critical duration of soil moisture remaining below wilting point which leads to plant death. There is evidence to suggest that timing of rain is also critical, with early summer rains potentially promoting survival but winter rain potentially promoting mortality, depending on the timing in relation to summer rain. Surveys of key sites of contrasting Mitchell grass survival suggest that management also has a significant influence on the occurrence of dieback, and that continuous grazing practices may exacerbate dieback even with light grazing pressure.