Interrelationships between net primary production, ground-storey condition and grazing capacity of the Acacia aneura rangelands of semi-arid Australia

Abstract

A simulation model which estimates the net primary production of the ground-storey component of the extensively grazed Acacia aneaura rangelands of semi-arid Queensland, Australia, was applied to the assessment of grazing capacity. The method described represents an alternative approach to the traditional method used by land administrators. Historic climatic records for a continuous period of 25 years were analyzed for one centre. Annual live herbage biomass production fluctuated widely in relation to both climate and grund-storey condition class. Herbage biomass carryover from year to year decreased significantly as the level of herbage utilization through animal consumption increased. At a conservative level of use, herbage biomass carryover provided an important reserve to supplement the smaller amount of live biomass produced in low rainfall years. Consequently, grazing capacity was related to the total herbage biomass available to the grazing animal at the end of each summer growing period. There were only small changes in the mean value of end-of-summer peak herbage biomass crop and sheep carrying capacity over the excellent to good ground-storey condition classes. However, there was a pronounced decline in these values as condition class decreased from moderate to poor. The implications of this method assessing grazing capacity for semi-arid rangeland management and administration are discussed.