Long-term estimates of live above-ground tree carbon stocks and net change in managed uneven-aged mixed species forests of sub-tropical Queensland, Australia

Summary

Estimates of carbon stocks and their annual change for extensive Australian sub-tropical forests are based on indirect estimates or on data derived from temperate forests. We estimated live above-ground tree carbon (LAC) stocks at landscape level from 355 000 measurements of 94 127 tree stems from 604 permanently monitored plots representing 2.6 million ha of managed uneven-aged mixed-species native forests in sub-tropical Queensland. These plots were established between 1936 and 1998 and re-measured every 2 to 10 years up to 2011. Landscapes were represented by 16 broad vegetation groups growing across a mean annual rainfall range of 500 to 2000 mm. Landscape-mean LAC stocks varied from 20.8 ± 4.3 t C ha⁻¹ in inland eucalypt woodlands to 146.4 ± 11.1 t C ha⁻¹ in coastal wet tall open forests. Landscape maximum LAC stock, defined as the mean of maximum LAC stocks over the entire measurement history for a specified landscape under prevailing environmental conditions and disturbance regimes, including sustainable forest management, ranged from 34.0 ± 7.2 t C ha⁻¹ in inland eucalypt woodlands to 154.9 ± 19.4 t C ha⁻¹ in coastal wet tall open forests. Annual live above-ground net carbon flux (C-flux) across all forests types ranged from 0.46 to 2.92 t C ha⁻¹ y⁻¹ with an overall mean of 0.95 t C ha⁻¹ y⁻¹ (n = 2067). Comparison of our results with Intergovernmental Panel on Climate Change (IPCC) estimates shows that in all cases, except for the sub-tropical steppe, the IPCC over-estimated stocks by between 13% and 34%. Conversely, the IPCC estimated C-fluxes were between 14% and 40% less than the Queensland estimates. These results extend statistically valid estimates of landscape LAC stocks and fluxes to the sub-tropical regions of Australia.

Keywords:

• carbon
• stocks
• climate change
• forests
• Queensland

Acknowledgements

The data set used is co-jointly held by the Queensland Herbarium, the Department of Science, Information Technology, Innovation and the Arts (DSITIA) and the Department of Agriculture, Fisheries and Forestry (DAFF). The legacy and contribution of past Queensland Government Forestry Departments and staff in data collection, collation and maintenance for over seven decades is greatly acknowledged. Assistance provided by Queensland Parks and Wildlife Service field staff, and Jiaorong Li in GIS, Rosemary Niehus, Jian Wang, David Moore and Sue Philips for 2011 field measurements is gratefully acknowledged. Rod Fensham is acknowledged for providing access to R scripts of the selected allometric equations. Helpful review and suggestions provided by Arnon Accad Don, Butler and Russell Fairfax are acknowledged.