Spillovers of Payments for Ecosystem Services: Follow-up of a RCT in Uganda

Last registered on November 03, 2023


Trial Information

General Information

Spillovers of Payments for Ecosystem Services: Follow-up of a RCT in Uganda
Initial registration date
October 02, 2019

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
October 02, 2019, 11:13 AM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated
November 03, 2023, 5:28 AM EDT

Last updated is the most recent time when changes to the trial's registration were published.


Primary Investigator

Leibniz Centre for Agricultural Landscape Research (ZALF)

Other Primary Investigator(s)

PI Affiliation
Utrecht University
PI Affiliation
Osnabruck University

Additional Trial Information

Start date
End date
Secondary IDs
Prior work
This trial is based on or builds upon one or more prior RCTs.
Under the proposed study, we will investigate the long-term impacts of a Payments for Ecosystem Service (PES) scheme that was implemented between 2011 and 2013 in western Uganda. The PES scheme was implemented as randomized control trial in 121 villages (
RCT ID AEARCTR-0000047). A follow-up study will be conducted with both forest owners, who were eligible for PES, and additional non-forest owners. In particular, following impacts will be investigated: a) whether PES affect the propensity to engage in pro-environmental behavior in the long-term, as well as environmental attitudes and beliefs; b) whether PES changed the sharing of forest resources and access to privately owned forests at the community level; c) whether PES affect social preferences, in particular spiteful behavior, between community members, d) whether human-wildlife conflicts increased due to the intervention and how attitudes towards chimpanzee conservation were affected and e) whether the intervention changed the influence of the take-up rate at the village level on individual PES enrollment decisions (hypothetical).
External Link(s)

Registration Citation

de Laat, Joost, Stefanie Engel and Tobias Vorlaufer. 2023. "Spillovers of Payments for Ecosystem Services: Follow-up of a RCT in Uganda." AEA RCT Registry. November 03. https://doi.org/10.1257/rct.4714-1.3
Sponsors & Partners

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Experimental Details


In the treatment villages, Chimpanzee Sanctuary and Wildlife Conservation Trust (CSWCT) staff members offered an incentive contract to each household that owned forest land, under which they will receive annual payments if they meet certain terms. Landowners are required to refrain from cutting trees on their land (with some exceptions built into the contract) and also to re-forest a portion of their land. CSWCT employees monitor compliance with the contract by conducting random spot checks in the forest to look for newly cleared patches of forest or fresh tree stumps and to assess if new trees have been planted.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
1) social preferences
2) environmental preferences
3) forest sharing behavior
4) social norms related to forest sharing behavior
5) human-wildlife conflicts
6) attitude towards chimpanzee conservation
7) hypothetical enrollment in a PES program

The primary outcomes are planned to be analyzed in separate publications. Paper 1: Outcomes 1, 3, 4; Paper 2: Outcome 2; Paper 3: Outcome 5,6; Paper 4: Outcome 7
Primary Outcomes (explanation)
1) elicited through three binary decisions for resource allocation between 2 participants to identify social preferences types;
2a) decision between six seedling packages with varying compositions of eucalyptus and native tree species (eucalyptus representing the less environmentally-friendly option)
2b) self-reported tree planting within last 12 months (yes, no, type of species, reasons for planting)
3a) self-reported access restrictions of forest owners and non-forest owners
3b) framed-field experiment (2 players: 1 forest owner, 1 neighbor) concerning forest access and resource appropriation
4) incentivized elicitation of social norms regarding forest access restrictions
5) frequency of wildlife sightings, crop and livestock damage by wildlife
6) agreement with statements concerning chimpanzee conservation
7) hypothetical PES enrollment under varying payment levels and take-up rates at the village level

Secondary Outcomes

Secondary Outcomes (end points)
1) Environmental attitudes
2) Locus of control (environmental conservation)
3) Perceived forest benefits and costs
4) Motivations for tree planting

All secondary outcomes are analyzed for Paper 2.
Secondary Outcomes (explanation)
1) index of self-reported survey items
2) index of self-reported survey items
3) number of forests benefits and costs listed in open question
4) index of self-reported survey items

Experimental Design

Experimental Design
One hundred and thirty-six villages in the Hoima and Kibaale districts of Uganda were randomly assigned to either the treatment or the comparison group. Households in both treatment and control groups received a baseline questionnaire prior to the PES program being implemented. Additionally, pre-intervention high-resolution QuickBird satellite images were taken of the study area. Boundaries of land parcels were demarcated with handheld GPS units and netbook computers and linked to the remote-sensing images to create images of and measures of the forest cover on each household’s land. Endline data collection, including both a household survey and Quickbird satellite images, will be conducted after the intervention has been implemented for two years.
The follow-up survey collects additional outcome measures that have not been collected in the household surveys before (neither baseline nor endline). The follow-up study therefore applies a cross-sectional experimental design, harnessing the random allocation of the treatment as an instrument.
Experimental Design Details
Randomization Method
In each subcounty, public lotteries were conducted to select which of two stratified groups of villages received the PES program.
Randomization Unit
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
original RCT: 136 villages, follow-up: 121 villages
Sample size: planned number of observations
1210 land owners in total: 726 forest owners (at the start of the intervention), 484 neighbors of forest owners
Sample size (or number of clusters) by treatment arms
121 villages: 60 treatment, 61 control
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials

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Institutional Review Boards (IRBs)

IRB Name
Innovations for Poverty Action IRB
IRB Approval Date
IRB Approval Number
IRB Name
Mild May Uganda Research & Ethics Committee (MUREC)
IRB Approval Date
IRB Approval Number
Analysis Plan

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Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
August 01, 2013, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
November 05, 2019, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
753 households
Final Sample Size (or Number of Clusters) by Treatment Arms
58 treatment villages, 61 control village
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Payments for ecosystem services (PES) are increasingly being implemented worldwide as conservation instruments that provide conditional economic incentives to landowners for a prespecified duration. However, in the psychological and economic literature, critics have raised concerns that PES can undermine the recipient’s intrinsic motivation to engage in pro-environmental behavior. Such “crowding out” may reduce the effectiveness of PES and may even worsen conservation outcomes once programs are terminated. In this study, we harnessed a randomized controlled trial that provided PES to land users in Western Uganda and evaluated whether these incentives had a persistent effect on pro-environmental behavior and its underlying behavioral drivers 6 y after the last payments were made. We elicited pro-environmental behavior with an incentivized, experimental measure that consisted of a choice for respondents between more and less environmentally friendly tree seedlings. In addition to this main outcome, survey-based measures for underlying behavioral drivers captured self-efficacy beliefs, intrinsic motivation, and perceived forest benefits. Overall, we found no indications that PES led to the crowding out of pro-environmental behavior. That is, respondents from the treatment villages were as likely as respondents from the control villages to choose environmentally friendly tree seedlings. We also found no systematic differences between these two groups in their underlying behavioral drivers, and nor did we find evidence for crowding effects when focusing on self-reported tree planting behavior as an alternative outcome measure.
Vorlaufer, Tobias, Stefanie Engel, Joost de Laat, and Björn Vollan. 2023. ‘Payments for Ecosystem Services Did Not Crowd out Pro-Environmental Behavior: Long-Term Experimental Evidence from Uganda’. Proceedings of the National Academy of Sciences 120 (18): e2215465120. https://doi.org/10.1073/pnas.2215465120.
Conservation policies and programs may trigger unintended, potentially irreversible, changes that were initially not anticipated. Concerns have been raised that the introduction of payments for environmental services (PES) fosters the privatization of natural ecosystems to the detriment of marginalized groups. We assess the long-term impacts of PES on sharing of access to natural resources, associated norms, and social preferences. The studied PES program was implemented as a randomized control trial in western Uganda. Using survey and experimental data collected six years after the last payments were made, we find that the PES program did not lead to a lasting shift in resource sharing practices but did induce stronger social norms for resource sharing. Moreover, landowners in former PES villages exhibit more egalitarian social preferences than landowners in control villages. These results highlight that despite introducing unequal conservation benefits to communities, long-lasting negative spillovers of PES could be avoided.
Vorlaufer, Tobias, Joost de Laat, and Stefanie Engel. 2023. ‘Do Payments for Environmental Services Affect Forest Access and Social Preferences in the Long Run? Experimental Evidence from Uganda’. Journal of the Association of Environmental and Resource Economists 10 (2): 389–412. https://doi.org/10.1086/721440.

Reports & Other Materials