Impact of mulga thinning on forage and livestock productivity

Abstract

Savannas, woodland and forests are utilised for grazing domestic stock around the world. In most systems a higher density of woody plants leads to reduced herbaceous forage productivity. Graziers often reduce woody biomass through clearing or thinning, which has implications for carbon stocks, biodiversity and ecosystem function. In Australia’s semi-arid regions, Acacia aneura (mulga) woodlands are widespread, with mulga often either cut/felled to provide a maintenance livestock diet and drought fodder reserve or cleared to improve forage productivity. Three replicated experiments were established in mulga woodland with initial density of 1900 to 5600 trees/ha in the 1960s to study the impact of thinning to 40, 160 and 640 trees/ha. Individual trees were tagged at two sites. These experiments were reassessed 50-60 years later to investigate long-term woodland recovery, differences in individual tree growth and health, and woodland basal area and carbon stocks. This paper reports on individual tree growth and survival,and models the impact of thinning on forage productivity.
All thinning treatments demonstrated substantial regrowth post-thinning, with all treatments having similar woodland basal area after 50-60 years, but with forage productivity having been much higher for the first ~25 years after thinning. Detailed economic assessment and property design considerations are recommended to determine the best combination of management strategies across a property, with any contemplated changes in vegetation management considered in the context of regulatory guidelines. Insights gathered from these experiments demonstrate the value of long-term trials and datasets to provide clear evidence of multidecadal responses to management impacts such as woodland recovery after thinning on environmental and economic goals.