Productivity and Management of Mulga in South-Western Queensland in Relation to Tree Structure and Density

Abstract

Regression analysis was used to characterize the important fodder tree mulga (Acacia aneura F. Muell.) growing in south-western Queensland.

Significant relationships were found between the tree bole circumference, measured 30 cm above ground level, and the canopy area and leaf and wood weight. There was an asymptotic relationship between tree bole circumference and tree height. Leaf area index increased linearly with tree circumference. Leaflwood ratios decreased from 0.69 for trees less than 20 cm in circumference to 0.15 for those greater than 60 cm. The mean tree asymmetry and standard error for mulga was 1.21 ± 0.02. It is concluded that mulga trees 40-50 cm in circumference are the most suitable for maintenance as drought fodder reserves.

Continuous coring showed that the majority of tree roots were located in the top 30 cm of soil, though roots were still present to a depth of 120 cm. Root density decreased with increasing distance from the tree.

Incoming radiation at ground level was less at high tree densities than at low densities, but the radiation reaching the ground under very dense mulga should be adequate for photosynthetic activity of the lower tree leaves and the ground storey flora.

Density and tree size characteristics of mulga forests, together with tree structure data and existing climatic-plant-animal data, show that 7,000 ha of a 12,000-ha property in the Charleville area could be cleared for ground storey production without seriously depleting drought fodder resources. This assumes that the property supports 5000 head of sheep and a mulga resource of 710 trees ha^-1.