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.
There has probably never been a more exciting time to be a tropical forest ecologist. The emerging global carbon market, combined with a rising interest in the principle of payments for ecosystem services (PES, Engel, Pagiola & Wunder 2008), means that tropical forest ecology and management has an unusually high profile among governments and businesses. Tropical forest nations hope that payments to protect or increase carbon stocks could generate significant revenue, help to alleviate poverty and conserve other ecosystem services (Laurance 2007). As a result, many projects aiming to reduce carbon emissions from deforestation, degradation and forest management, or enhance or conserve existing forest carbon stocks (collectively known as REDD+; Angelsen et al. 2009), are being initiated throughout the tropics. Many build on initiatives involving tree plantations and agroforestry developed under the Clean Development Mechanism of the Kyoto protocol (CDM; Hepburn 2007) and voluntary agreements to avoid degradation from logging (e.g. Brown et al. 2000). However, the potential future scale, and therefore impact, of REDD+ schemes could be far greater than the modest size of previous carbon-based PES in tropical forest countries (Eberling & Yasué 2008). This is partly because previous carbon-based initiatives have focussed on individual projects, whereas there is a strong drive to implement REDD+ as part of national mitigation strategies (UNFCCC 2008).
In this article, we focus on the role that ecological expertise should play in the interdisciplinary research that is required to ensure that carbon-based PES schemes achieve their long-term potential for reducing carbon emissions, enhancing livelihoods and protecting other ecosystem services. We use the phrase ‘carbon-based PES’ in a broad, inclusive sense (Somerville, Jones & Milner-Gulland 2009) to include all relevant types of projects defined within REDD+ (Angelsen et al. 2009) and the CDM (Hepburn 2007). In particular, we focus on the issues that are important for the large number of emerging carbon-based PES projects that are informing the development of national REDD+ strategies (Angelsen et al. 2009).
Our examples are drawn mostly from the Peruvian Amazon. This region contains 88% of the total national forested area of Peru (FAO 2005) and provides a useful context for considering the implementation of carbon-based PES because the combination of high carbon stocks (8.2 Pg C in the above-ground living biomass – c. 50 times annual UK anthropogenic carbon emissions; Saatchi et al. 2007) and large spatial variation in deforestation rates and current threats (Perz, Aramburú & Bremner 2005; Soares-Filho et al. 2006; Fig. 1) means it contains areas that are suitable for a range of different project types. As a result, there are a large number of emerging carbon-based PES initiatives. NGOs have instigated at least 17 carbon-based projects in the country and the Peruvian government is also strongly interested in implementing PES through the national protected area network (Armas et al. 2009), including schemes to fund indigenous communities to preserve standing forest (MINAM 2009).
How ecologists can contribute to developing effective carbon-based PES projects
Ecologists have much to contribute to the development of carbon-based PES in tropical forests through, for example, their knowledge of patterns of carbon stocks and biodiversity and the sensitivity of these ecosystems to changing environmental conditions and anthropogenic impacts. We consider a range of specific applications of ecological expertise that would assist the development of carbon-based PES in tropical forest countries.
Quantify the changes in carbon stocks due to forest disturbance and recovery
A key requirement for implementing carbon-based PES is a clear understanding of the spatial and temporal patterns of forest carbon stocks. Much research has therefore focussed on providing efficient methods of carbon monitoring across gradients of forest type and disturbance (Gibbs et al. 2007). However, despite advances in estimating current above-ground carbon stocks (e.g. Asner 2009) there remain challenges in understanding and quantifying the full range of processes that determine temporal variation in forest biomass and incorporating this information within project reference scenarios (e.g. as part of calculations of ‘baselines’ within projects to reduce emissions from deforestation, Parker et al. 2009). One example is the poor understanding of how disturbance influences soil carbon stocks (Lal 2004). Another important process is secondary forest growth: regrowth on land that is cleared but subsequently abandoned can make an important contribution to the landscape-scale carbon balance (Angelsen et al. 2009). For example, in the region of Madre de Dios in southern Peru, Asner et al. (2010) estimated that 18% of the carbon emissions caused by deforestation during 1999–2009 were offset by secondary forest regrowth on previously cleared land. The process of secondary forest regrowth will be a particularly important component of the landscape-scale carbon balance in regions where small-scale agriculture is the predominant alternative land-use, such as the Peruvian Amazon. More work is required to parameterise landscape-specific models of forest recovery in response to single and repeated disturbances (cf.Huang et al. 2008; Kauffman, Hughes & Heider 2009). These patterns need to be incorporated within both project reference scenarios and estimates of the impact of interventions that alter the frequency, area or intensity of disturbances.
Further ecological research is also required to understand the complexity of the changes in carbon stocks that occur during project implementation. For example, neither the temporal and spatial variation of carbon stocks in agroforestry systems (Schroth et al. 2002), nor the carbon benefits of reduced impact logging (Putz et al. 2009), are well understood. Quantifying the impact of reduced impact logging could be particularly valuable in the Peruvian Amazon: such projects could be well-suited to the region of Loreto, where deforestation rates have been low (Fig. 1; Perz, Aramburú & Bremner 2005), but timber concessions are an important land-use (13% of area or 4·7 million ha, Fig. 1; Salo & Toivenen 2009). Although results from the Brazilian Amazon suggest that reduced impact logging reduces the decrease in forest carbon stocks compared with conventional logging by 7 Mg C ha−1 (Putz et al. 2009), it is difficult to extrapolate to other regions where forest composition, conventional logging practices and the potential effectiveness of reduced impact logging will differ. Overall, more research is required to understand the complex transitions that occur during forest degradation as a result of disturbance and recovery cycles and incorporate these changes in carbon stocks in project reference scenarios (Putz & Redford 2010).
Assess the permanence of project outcomes
Quantifying the long-term stability of increased carbon storage or emissions reductions is vital for maximising the effectiveness of PES interventions and demonstrating their potential to satisfy the criterion of ‘permanence’ required for some carbon-based PES schemes. In particular, climate change could have important effects on permanence, but is currently not considered under UNFCCC reporting, since national inventories of greenhouse gas emission relate exclusively to direct, human-induced changes in carbon stocks (IPCC 2003). Ecologists could play an important role in quantifying the potential impact of climate change on the carbon stocks of intact forests and developing methods to include these predictions in project reference scenarios. The uncertainty of these estimates should also be incorporated in assessments of the level of risk associated with individual projects. To explore the importance of these effects, we compared the emissions reductions that a Peruvian REDD+ project in the Tambopata National Reserve aspires to achieve, with the potential carbon losses due to predicted increases in drought frequency from the above-ground biomass of trees ≥10 cm diameter in intact forest within the project area. In this region, predictions of an increased probability of drought (Cox et al. 2008) suggest that intact forest may lose biomass through drought-induced mortality over the coming decades (Phillips et al. 2009). Our analysis indicates that over the 20-year lifetime of the project, the intact forest acts as a carbon sink at first, but as droughts become more frequent, the cumulative emissions are positive (Fig. 2a). The carbon losses due to drought could reduce the predicted emissions reductions achieved over the full project by 15% (Fig. 2b). For any given project, the importance of this effect will depend on the trajectory of climate change, reference scenarios of deforestation and degradation and the proportion of intact forest in the project area. Other ecological processes that reduce carbon stocks, such as fire frequency or intensity, could also be influenced by climate change (Cochrane & Laurance 2008) and should also be included in these assessments. Overall, ecological research is required to understand how climate change may influence the carbon stocks of intact and regenerating forests and develop methods to incorporate this knowledge within project reference scenarios.
Accurately assess leakage
Ecologists also have a role in helping to measure and understand patterns of leakage: negative impacts of a project outside its area due to the transfer of activities that cause degradation and deforestation (Angelsen 2008). Although national-level approaches to REDD+ aim to prevent leakage from individual projects undermining the integrity of emissions reductions achieved by any given country (Eberling & Yasué 2008), it will still be important to understand leakage at sub-national scales to identify the specific interventions that are most effective. This is particularly important within a region such as the Peruvian Amazon that is adopting a ‘nested’ approach to REDD+ implementation (Angelsen 2008), where a large number of different projects run by different institutions are likely to contribute to an overall national strategy to reduce emissions from deforestation. Ecologists are well-placed to inform analyses of the impact of underlying environmental variation on patterns of leakage, based on their knowledge of the relationships between edaphic and climatic factors, and forest structure, dynamics and composition. Such analyses also need to account for socioeconomic factors that may also influence patterns of deforestation and degradation. An interdisciplinary perspective is therefore required to accurately assess patterns of leakage from existing projects in order to understand how far leakage extends in different contexts and to identify the types of interventions that are most effective in reducing net carbon emissions (cf.Jagger et al. 2009). For example, in the Peruvian Amazon, substantial leakage of forest degradation was considered to have occurred following the implementation of new forest concessions based on an analysis of degradation patterns within and outside concession areas (Oliveira et al. 2007). However, this analysis excluded the potential effect of environmental or socioeconomic factors and may therefore have overstated the role of this policy on patterns of forest degradation (cf.Andam et al. 2008).
Understand the implications for biodiversity conservation
There is concern that carbon-based PES may increase the rate of loss of tropical biodiversity by focusing payments to reduce deforestation on areas with the highest carbon stocks and displacing deforestation and degradation to landscapes that are highly biodiverse but low in carbon (Putz & Redford 2009). Careful monitoring of patterns of deforestation and the investment of carbon-based PES funds is required to detect the emergence of any such trend, as well as research to explore the impact of current carbon-based projects on biodiversity within the area of individual projects. To maximise the benefits of carbon-based projects for biodiversity conservation, a first step is to explore the trade-offs between biodiversity and carbon storage (Miles & Kapos 2008; for the UK, see Anderson et al. 2009). In tropical forests, this should provide renewed impetus for testing methods of estimating species richness at appropriate large spatial scales (e.g. Harte, Smith & Storch 2009). More specifically, research is needed at the scale of individual projects and nationally to explore how different project designs influence the balance between the conservation of carbon or biodiversity for a given financial investment. At a pan-tropical scale, such studies suggest that changing the allocation of REDD+ funding can increase biodiversity protection without causing large declines in carbon emissions reductions (Venter et al. 2009). However, there is a strong need for similar studies at scales that are useful for planning the design of individual projects to maximise the protection of both carbon and biodiversity.
Other areas where ecologists should be involved
There are a range of important research questions associated with ensuring that the benefits of carbon-based PES are equitably distributed and other benefits such as poverty alleviation are achieved, where the interdependence of social and ecological issues means that a strongly interdisciplinary approach is required (Nicholson et al. 2009). For example, the benefits of carbon-based PES can only be equitably distributed if there is a sufficiently strong evidence base for decisions on which communities, or individuals within communities, should be recipients. Working with other disciplines, ecologists therefore need to help to develop local-scale, community-based project monitoring systems (Angelsen et al. 2009).
How should these questions be addressed?
The central requirement of PES, that service provision is monitored to ensure conditionality (Somerville, Jones & Milner-Gulland 2009), means that there is a strong impetus to design effective monitoring systems for emerging REDD+ projects (Jagger et al. 2009). There is also an important need to ensure that monitoring is efficient: current data from REDD+ projects in the Peruvian Amazon show that set up and monitoring costs are on average 41% of the total current and projected project expenditure, similar to other projects in Brazil and Bolivia (Fig. 3). This pattern indicates that there are substantial benefits to be gained by reducing the cost of these project components. The need to develop low-cost monitoring systems provides an important context for determining how ecologists should approach their research, whether associated with improving our understanding of variation in carbon stocks, permanence, leakage or the impacts of carbon-based projects on biodiversity.
In practice, what should this mean? First, ecologists should take advantage of the major opportunity that exists to work closely with institutions implementing carbon-based projects due to the need to improve our knowledge of the effectiveness of these initiatives. Secondly, they should use their results to assist the development of cost-effective monitoring systems: for example, they may be able to suggest context-specific indicators of ecosystem services that could be used by local communities and project staff (Stickler et al. 2009) or indicate how existing data could be used within monitoring strategies. Ecologists could compare simple indicators with more direct assessments of ecosystem services (e.g. Reed, Dougill & Baker 2008) to inform decisions about those aspects that should be monitored, based on their importance and the accuracy and cost of monitoring.
We provide two specific examples from the Peruvian Amazon of how these principles might apply in relation to monitoring the poorly understood and complex process of forest degradation (Putz & Redford 2010). First, a cost-efficient monitoring system of the impact of reduced impact logging on carbon stocks in certified forest concessions in southern Peru could include the use of existing mapped data on timber stocks and harvesting patterns combined with analysis of remote sensing data (e.g. Asner 2009) to obtain large-scale estimates of forest degradation. Secondly, significant degradation of the extensive palm swamps of the northern Peruvian Amazon occurs through destructively harvesting female trees of the dioecious palm Mauritia flexuosa for their fruit (Manzi & Coomes 2008). Annual monitoring of the ratio of male and female individuals, easily distinguished during flowering and fruiting, might provide a broadly based indicator of the level of degradation of these habitats, related to their carbon stocks, ability to support bird and mammal populations and value as a source of food and income for local communities.
Finally, in order to inform wider debates concerning the implementation of REDD +, an important direction for ecological research is to compare projects that are being implemented in different social, institutional and environmental contexts. For example, predictions of decreased rainfall in future decades vary strongly between different regions of Amazonia (Malhi et al. 2008), implying that the risk posed by climate change to the long-term permanence of individual projects (Fig. 2) varies markedly. Comparing projects in different settings would allow modifications to these initiatives to take account of knowledge concerning, for example, spatial variation in the trajectory of climate change or the organisational structures that are proving particularly successful. Understanding the full context of any given site requires ecologists to work as part of interdisciplinary teams (Nicholson et al. 2009), supported by statistical analyses that tease apart the effect of different factors on project outcomes among sites (Ferraro & Pattanayak 2006; Jagger et al. 2009).
Overall, we suggest that the effectiveness of ecological research for informing the development of PES will be enhanced by working closely with institutions implementing carbon-based PES projects and by taking a comparative approach across many individual projects. Such an approach would take advantage of the sheer number of new carbon-based PES schemes being implemented, and the resulting unprecedented opportunity to develop a proper evidence base for measuring and improving the practices that most successfully conserve tropical forest ecosystems.
We thank all contributors to the project ‘Capacity building for carbon- and biodiversity-based payments for ecosystem services in the Peruvian Amazon’ (NE/G00840X/1, http://www.geog.leeds.ac.uk/projects/espa/index.html) and particularly those who provided project cost data: Madreacre SAC (Nelson Kroll), CIMA-Cordillera Azul (Tatiana Pequeño), ACCA (Cesar Moran-Cahusac, Augusto Mulanovitch) and AMPA. We acknowledge funding for this project from NERC, ESRC and DfiD, UK, through the Ecosystems Services for Poverty Alleviation (ESPA) research programme. T.R.B. also acknowledges support from an RCUK Academic Fellowship. J.P.G.J. acknowledges the Leverhulme Trust. Finally, we thank three anonymous reviewers who provided valuable comments on earlier versions of this manuscript.