How can ecologists help realise the potential of payments for carbon in tropical forest countries?

1. There is great interest among policy makers in the potential of carbon-based payments for ecosystem services (PES) to reduce carbon emissions from deforestation and protect forests in tropical countries. We discuss the contributions that ecologists can make to the interdisciplinary research required to inform the design of these initiatives. 2. First, we highlight the need to quantify the full range of processes that determine temporal variation in carbon stocks at a landscape-scale due to cycles of forest disturbance and recovery. Second, we discuss the importance of understanding how the impact of climate change on the carbon stocks of intact forests may affect the emissions reductions achieved by any given project: we show that this may reduce the effectiveness of one carbon-based PES project in southern Peru by 15%. We also discuss the need to assess project impacts on deforestation in the surrounding region and explore how different project designs influence the balance between the conservation of carbon and biodiversity. 3. The need to demonstrate emissions reductions or carbon storage to investors in carbon-based payment schemes provides an imperative for monitoring their effectiveness. Monitoring will be a significant cost in any PES project and, together with project set-up, on average accounts for more than 40% of project expenditure across six emerging Peruvian PES schemes. Ecologists will therefore have an important role in designing cost-effective monitoring strategies. The impetus for monitoring also provides opportunities to carry out research addressing many of the uncertainties highlighted above. 4. Synthesis and applications. By working closely with a range of carbon-based PES projects, ecologists can answer important fundamental questions related to the provision of ecosystem services and help improve the design of these schemes. The large number of projects currently being implemented provides an unprecedented opportunity to develop a proper evidence base for measuring and improving the practices that most successfully conserve tropical forest ecosystems.