Effects of payment for environmental services (PES) on deforestation and poverty in low- and middle-income countries

Additional Info

  • Authors: Cyrus Samii, Matthew Lisiecki, Parashar Kulkarni, Laura Paler, Larry Chavis
  • Published date: 2014-12-19
  • Coordinating group(s): International Development
  • Type of document: Review, Plain language summary
  • Volume: 10
  • Issue nr: 11
  • Category Image: Category Image
  • PLS Title: Payment for Environmental Services Have Only Modest Effects on Deforestation
  • PLS Description: This Campbell systematic review examines the effects of Payment for Environmental Services (PES) programmes on deforestation and poverty, and whether environmental and poverty reduction goals conflict with one another. The review summarizes evidence from 11 studies covering six PES programmes in four countries.
  • Title: Effects of payment for environmental services (PES) on deforestation and poverty in low- and middle-income countries
  • Spanish PLS: Los pagos por servicios ambientales sólo tienen efectos modestos en la deforestación
  • Spanish PLS Description: Los bosques almacenan carbono, lo que ayuda a mitigar el efecto de las emisiones de carbono. Sin embargo, la cantidad de cubierta forestal está disminuyendo a una tasa de más de siete millones de hectáreas al año. Los pagos por servicios ambientales son contratos voluntarios para proveer un servicio ambiental a cambio de pago. En esta revisión, el servicio es el mantenimiento o rehabilitación de los bosques naturales. La revisión examina cómo los programas de PSA afectan la deforestación, los factores que afectan la eficacia del programa y si los PSA también deben apuntar a reducir la pobreza.
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About this systematic review

This Campbell systematic review examines the effects of payment for environmental services (PES) programmes on deforestation and poverty, and whether environmental and poverty reduction goals conflict with one another. The review summarizes evidence from 11 studies covering six PES programmes in four countries.

What are the main results?

The modest effectiveness of PES programmes means that they are not cost-effective. Relative to the extensive investment to measure forest conditions, efforts to assess the effects of PES programmes on deforestation and poverty are limited and methodologically weak.


Natural forest preservation in the tropics, and thus in developing countries, must be an element of any effective effort to manage climate change. Forests serve as natural carbon sinks, which help to mitigate the effect of other carbon emissions. However, forest cover is being reduced and it is estimated that deforestation is responsible for 10-17 per cent of global carbon emissions. Since 2007, governments have coordinated conservation efforts under the Reducing Emissions through Deforestation and Forest Degradation (REDD+) initiative, which has led to the implementation of various programs designed to reduce the amount of forested land converted to other purposes.

Payment for environmental services (PES) programs is one type of intervention commonly implemented under the REDD+ umbrella. PES programs allow for direct exchange between those demanding ‘environmental services’ such as protection or rehabilitation of natural forests and those in a position to provide them locally. While the primary goal of reducing deforestation is clear, the policy and academic literature debates the extent to which PES programs in developing countries should incorporate goals of poverty reduction. Some argue that the targeting of poverty goals will undermine conservation effectiveness (e.g., because behavioural change among poorer households does not have as much potential to promote conservation as that of wealthier households or commercial entities). Others argue that targeting benefits toward the poor would contribute to conservation effectiveness by either promoting sustainable livelihoods or helping to legitimize conservation programming. In this review, we assess the effects of PES programs on deforestation and welfare outcomes in low- and middle-income countries (LMICs), and whether the twin goals of improving both environmental and human welfare outcomes are at odds with each other. We also examine how inequality, institutional capacity, corruption, and democratic accountability may moderate the effects of PES programs. Conducting this review is important for moving the debate around PES beyond theoretical discussions and into a better-informed, evidence-based discussion.


The first objective of this review is to assess the evidence on the effects of PES interventions on conservation and poverty outcomes in LMICs. A second objective is to assess the extent to which effects on poverty in turn affect whether conservation benefits are realized. The third objective is to evaluate how institutional and social conditions (namely, inequality, institutional capacity, corruption, and democratic accountability) moderate the effects of PES programs.

Selection criteria

The review includes studies of PES programs that assess effects on either (i) deforestation outcomes in forest areas in developing countries or (ii) poverty conditions of populations residing in communities that are proximate to natural growth forest areas in developing countries. We included studies using a range of measures for both deforestation (on-the-ground point samples, samples created from satellite imagery) and welfare (consumption, income, or income potential). We required that PES programs have a clear start date when either payments or rewards are themselves offered to individual or corporate property holders to maintain or rehabilitate (for example, via planting endemic species) natural forests, or institutions are established to facilitate such offers.

For quantitative synthesis we included (a) randomized studies and (b) quasi-experimental studies that employ strategies for causal identification with clearly delineate treated and control areas and use some method for removing biases due to non-random assignment of the intervention. Qualitative data are used in the synthesis to provide descriptions and context for interventions that are included in the quantitative synthesis. Such data were drawn from the quantitative studies themselves as well as qualitative studies that cover the same programs or settings as the quantitative studies.

Search strategy

To find the articles included in this review, we searched a variety of databases using key words related to PES programs. The set of databases and list of keywords were assembled based on consultation with a Campbell Collaboration information retrieval specialist. We also carried out hand searches of key journals in relevant fields, using publisher search engines and references cited in papers accepted for review as well as in review papers or thematically relevant papers identified during the search.

Data collection and analysis

For studies eligible for inclusion in the review we systematically collected data on study characteristics, findings, and moderators. Risk of bias was assessed based on the guidance of the IDCG Risk of Bias Tool (version March 2012). We extracted qualitative information from both the included quantitative studies as well as qualitative studies that covered the same types of programs and contexts as our quantitative studies. We use such qualitative data to establish that conditions recorded in quantitative data are being interpreted correctly and to provide descriptions and context for interventions that are included in the quantitative synthesis.

For effects on forest cover, whenever possible we standardized them to annual forest cover change rates. For effects on material welfare and poverty outcomes, we used percentage change over estimated average counterfactual outcome (e.g. for income effects, per cent change in income relative to the average income of the control group). For each hypothesis, we synthesised estimates using meta-analysis when the following conditions were met: (i) more than two studies meeting the quantitative inclusion criteria; (ii) effect sizes for common outcome constructs; and (iii) effects measured against similar comparators.


Our database search returned 1382 articles on PES programs. After eliminating articles that were not relevant to our hypotheses or conducted with appropriate methodological rigor, we were left with 20 articles on PES programs. Of these 11 PES articles conducted quantitative impact evaluation of these programs. The 11 PES articles cover six programs in four countries (Costa Rica, China, Mexico, and Mozambique).

The resulting evidence base is weak both in terms of the number of eligible studies and the methodological weaknesses of the included studies. None of the studies are based on randomized experiments, and so the potential for hidden selection or confounding biases is the most concerning issue. Few of the studies create comparison groups that allow them to address spill-over and leakage of effects from program areas to non-program areas. None of the studies investigated forest conservation and welfare effects jointly, which made it difficult to assess how these two goals are related.

Effects on Deforestation Outcomes The PES studies that assessed programs’ effects on forest cover included nine studies of four programs in Costa Rica and Mexico. The studies focused on two types of measures: impact on deforestation rate (where the best-case scenario is a deforestation rate of 0) and impact on forest cover (which allow for a positive outcome in the expansion of forested land). Keeping in mind the weakness of the evidence base, the studies that focus solely on reducing deforestation suggest that PES programs have, on average, tended to reduce the annual rate of deforestation by 0.21 percentage points (s.e.=0.09, 95% CI: [0.03, 0.39]). Effect sizes are a bit larger for studies that examine forest cover change, which measures not only forest loss, but also forest gain. Estimated effects on annual forest cover change rates ranged from 0.50 percentage points (s.e.=0.20, 95% CI: [0.11, 0.89]) for a study in Costa Rica to 1.6 percentage points (s.e.=0.80, 95% CI: [0.03, 3.17]) for a study in Mexico. One study suggests an outlier effect of 10 percentage points (no standard error or confidence interval provided in the original study), but this study suffers from a high risk of bias.

Effects on Human Welfare Outcomes The evidence base on the effects of PES on welfare outcomes is very limited, with only two studies in two countries (China and Mozambique) included in the review. These studies find that PES improved participating households’ incomes by 4 per cent (s.e.=1.55, 95% CI: [0.96, 7.04]) in Mozambique and by 14 per cent (s.e.=3.42, 95% CI: [7.3, 20.7]) in China. However, these average effects do not necessarily tell us how these programs affect poor households. For PES to contribute to poverty reduction, poorer household must be able to participate at high rates. But participation in PES programs is typically more difficult for poor households than wealthier households (a fact documented by in a number of the studies included in the review). The study from Mozambique includes estimates for poor households and finds that the welfare effects were substantially less in absolute terms, and not statistically significant for these households.

The Role of Institutional and Social Conditions We aimed to address a number of hypotheses regarding the influence of institutional and social conditions (inequality, institutional capacity, corruption, and democratic accountability) on the effects of PES programs. However, due to limitations of the evidence base we were unable to these hypotheses. We did however extract qualitative data from included studies and associated qualitative studies that provide some insights into the role of institutional and social conditions in the context of PES programs.

A study on the Mexican PSAH PES program found that forest conservation effects were worse in poorer areas. Qualitative information from Costa Rica was consistent with this account. Several of the studies also addressed the issue of institutional capacity, describing situations where PES programs did not have the ability to carry out their mandates. Corruption and possible misappropriation of project resources were also factors raised in a qualitative study of PES in Mexico. The study found that program resources were applied to address inadequacies in other government programs.

Authors' conclusions

Limitations in the evidence base preclude definitive hypothesis tests, however the evidence we find suggests that PES does reduce deforestation rates. The effect is modest however and seems to come with high levels of inefficiency. In terms of PES effects on poverty, we cannot say that the evidence indicates beneficial effects. Available evidence shows that PES programs are less effective in poor areas and are less likely to attract participation of poor households than wealthier ones. These are troubling findings but they are based on only a handful of cases and therefore deserve much more empirical attention. Our review aimed to assess the extent to which environmental and poverty reduction goals conflict with one another, how different conservation strategies fare in terms of such trade-offs, and the scope for ‘win-win’ strategies that generate both significant environmental and poverty reduction benefits. Based on the evidence available, we do not find that a case can be made for conservation and poverty-reduction goals being complementary in PES programming. Our final conclusion re-emphasizes the poor state of the evidence base for PES programming. Much advanced scientific effort and extensive investment has gone into measuring forest conditions around the world. Relative to that, efforts to assess the effects of PES programs on deforestation and poverty are limited and methodologically weak. Researchers should consider the recent work in development economics for guidance on executing field experiments that might provide more credible evidence (Banerjee and Duflo, 2011; Casey et al., 2012; Karlan and Appel, 2012).

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