Vulnerability and resilience of the forest ecosystem carbon cycle in Australia

Background/Question/Methods

Australia is an Annex 1 developed nation and international policies related to REDD do not apply. However, it has extensive areas of primary and secondary forests, with only 15% in protected areas. The national GHG accounts in 2007 showed that 13% of total emissions were due to land use change (deforestation), not including emissions from native forest harvesting.

Vulnerability of ecosystem carbon must be considered in terms of both carbon stocks that provide long-term storage, and fluxes that create annual variability. Net loss of terrestrial carbon stocks is a major component to global GHG emissions, contributing ~30% of total anthropogenic emissions and ~ 18% of current annual emissions.

Our key question is how can human use of forest ecosystems be managed to mitigate climate change by minimising emissions of greenhouse gases?

Results/Conclusions

The main threats to forest carbon stocks are human management practices of harvesting and burning. Forests managed for timber production in Australia have an average of 15-60% of the total carbon stock in a primary forest. The main drivers of change in forest carbon fluxes are increased incidence of extreme events such as drought, wildfire and pests. For example, in a highly productive Eucalyptus forest in south-east Australia, tree mortality increased by up to 50% during a period of prolonged drought and insect attack. The net carbon exchange of this forest changed from being a sink of 6.7 tC ha^-1 yr^-1 to a source of -0.1 tC ha^-1 yr^-1. Current systems of carbon accounting fail to account for these impacts due to prevailing definitions, policies and methodologies.

Minimising emissions requires changing forest management practices to protect carbon pools and better reflect the functional role of biodiversity in ecosystem processes. The mitigation benefit of carbon sequestration by tree planting is optimised through permanent restoration of native forest cover. Biodiverse ecosystems have the greatest capacity for resilience, adaptation and self-regeneration under conditions of changing climate and disturbance regimes, thereby enhancing the security of carbon stocks.

In conclusion, mitigation of climate change cannot be achieved without protecting forest carbon stocks, reducing emissions from forest management activities, and maintaining the natural buffering of disturbances. To achieve this we need full carbon accounting in terms of gross amounts of all carbon pools, fluxes and their longevity, which includes all land use activities in all nations within a transparent system.