Biophysical risks to carbon sequestration and storage in Australian drylands

Carbon abatement schemes that reduce land clearing and promote revegetation are now an important component of climate change policy globally. There is considerable potential for these schemes to operate in drylands which are spatially extensive. However, projects in these environments risk failure through unplanned release of stored carbon to the atmosphere. In this review, we identify factors that may adversely affect the success of vegetation-based carbon abatement projects in dryland ecosystems, evaluate their likelihood of occurrence, and estimate the potential consequences for carbon storage and sequestration. We also evaluate management strategies to reduce risks posed to these carbon abatement projects. Identified risks were primarily disturbances, including unplanned fire, drought, and grazing. Revegetation projects also risk recruitment failure, thereby failing to reach projected rates of sequestration. Many of these risks are dependent on rainfall, which is highly variable in drylands and susceptible to further variation under climate change. Resprouting vegetation is likely to be less vulnerable to disturbance and have faster recovery rates upon release from disturbance. We conclude that there is a strong impetus for identifying management strategies and risk reduction mechanisms for carbon abatement projects. Risk mitigation would be enhanced by effective co-ordination of mitigation strategies at scales larger than individual abatement project boundaries, and by implementing risk assessment throughout project planning and implementation stages. Reduction of risk is vital for maximising carbon sequestration of individual projects and for reducing barriers to the establishment of new projects entering the market.