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

Abstract

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.