PESMEX20: 20 years of payments for ecosystem services in Mexico

Introduction

As some of the world’s largest, longest lasting and most researched initiatives that reward individual and communal landowners for conserving forests and associated ecosystem services, Mexico´s Payments for Ecosystem Services (PES) programmes provide a significant opportunity to examine questions of how, where, and by whom PES scholarship has been produced. The PESMEX20 database is the most up-to-date and comprehensive compendium of peer-reviewed publications for PES in a single country. It is a systematic analysis of the relevant peer-reviewed literature in English and Spanish through 2022 (N=140). Studies represent a breadth of themes, disciplinary and methodological approaches, and spatial scales.

Research questions

We address two specific research questions: 

How has the body of PES research evolved over time in terms of methodological, temporal, and geographic coverage?

What have been the main research priorities and reported results so far and how do these compare between in-country (i.e. based in Mexican institutions) and foreign scholars?

Search strategy and inclusion criteria

Our approach to article selection followed PRISMA established norms (Moher et al., 2009). We employed advanced searches for publications in several internationally recognised databases as suggested by previous PES reviews (Calvet-Mir et al., 2015; Perevochtchikova et al., 2021; Schomers & Matzdorf, 2013; Kolinjivadi et al., 2023) and other related literature reviews. Specifically, we conducted searches in three internationally recognised databases: i) Scopus (international database of peer-reviewed academic publications worldwide); ii) Scielo (international database of peer-reviewed academic publications, mainly from Latin America, Ibero-America, and South Africa); and iii) Redalyc (international database of peer-reviewed academic publications from Latin America, the Caribbean, Spain, and Portugal).

Additionally, given our specific interest in PES literature based in Mexico, we also conducted online searches of articles published in nationally-recognised scientific journals based in Mexico. Our analysis focused on peer-reviewed journals with indexation by Mexico’s Science and Technology Journal Classification System (CRMCYT) as of 2023. From a list of 109 CRMCYT indexed journals from seven thematic areas, we narrowed our search to 14 journals based on title and thematic relevance. Of these 14 journals, 11 were already included in Scopus, Scielo, or Redalyc. We therefore conducted additional searches in the 3 remaining Mexican journals: Estudios Sociológicos de El Colegio de México; Política y Gobierno; Papeles de Población.

The systematic review process first consisted of online searches of publications with keywords related to PES programmes in Mexico in English, Spanish, and Portuguese. The search elements were sought specifically in the title, abstract and keywords for Scopus and Scielo, and in the full text of the publications for Redalyc and the three individual Mexican journals. The syntax used included a wide array of combinations of the following terms: 

Mexico/Mexican AND payment/programme/scheme + ecosystem/environmental/ hydrological/biodiversity/carbon service. 

In total, 1357 records were obtained and downloaded in a single Excel spreadsheet containing records until 2022. Duplicate records (N=152) were identified and excluded, with the final publication database including a total of 1205 publications. The following step consisted of identifying the set of records related to PES programmes in Mexico from the publication database, and thus relevant for analysis. We coded each record according to two dimensions:

PES focus: publication related to actual or hypothetical PES programmes and/or providing insights related to their application. Actual PES programmes included the federal PES programmes and other public and private programmes addressed by the studies.

Mexico focus: publication provides insights and/or data collected in Mexico. This includes comparative studies based in Mexico and other geographic regions.

For each dimension, the coding process consisted of two main steps: 1) search for keywords in the title related to PES or Mexico; 2) reading the abstract to confirm PES or Mexico focus. Whenever the publication’s classification was unclear after steps 1) and 2), the body of the publication was further scanned. This codification was developed by the first author but was validated by the team of co-authors to ensure its accuracy. Once all records were coded, only those publications that combined a focus on PES and Mexico were selected for our analysis.

In total, 140 publications met this requirement and formed the empirical basis for our analysis (Included in Supplementary Materials). These 140 publications included 137 peer-reviewed journal articles and three book chapters.

Coding strategy

The publication database explores a series of variables that cover four main components: basic features, thematic coverage, methodological coverage, and reported effects. Each entry was coded twice independently in separate spreadsheets by two co-authors who have experience with PES programmes and research in Mexico. Subsequently, the spreadsheets were merged and each result was double checked for consistency and, in cases where discrepancies were found, the coders jointly deliberated to reach a final result.

The basic features component identifies the lead authors and country and institutional affiliation, publication outlet, publication year, and number of citations (citation number retrieved from Google Scholar on 8 November 2023). 

The thematic coverage component identifies the set of themes addressed by the publication. Our assessment framework situates PES research within four main stages of PES design and implementation: Assessment & planning, Implementation & evaluation, and Improvement. Each of these stages involves, in turn, a series of theme-specific categories. The framework was developed based on our existing knowledge acquired from long-term research of PES programmes and is composed of a series of well-established themes in PES literature. These themes are not mutually exclusive (publications in our database addressed on average 2.15 themes).

The methodological coverage component characterises the programme(s) studied (type, geographic location) and the study's design (if and where primary data was collected, the type of methods employed and the temporal scale of analysis).  We also captured the degree of critique towards PES based on the overall tone and language of the study’s abstract and conclusions.

The reported effects component addresses the 56 studies in our database that provided empirical evidence related to PES environmental and/or social impacts or outcomes and excluded reviews as well as conceptual, experimental and hypothetical studies. Specifically, we examined what scholars have concluded about the social and ecological effects of Mexican PES programmes in terms of key indicators used, whether the study assesses outcomes (measurable indicators of programme effects) versus impact (through counterfactual analysis), and the authors’ conclusions on the direction (positive, negative or neutral) and magnitude of effects. Classification as positive or negative was based on our interpretation of the authors' overall assessment of environmental and social outcomes (separately). If reported outcomes were predominantly positive, we classified the effects as positive, and vice versa for negative outcomes. Where findings did not allow an assessment of outcome direction, or in instances where there was a balance of positive and negative outcomes, we designated these as neutral.

Variable list

The description of variables and their corresponding values can be found in the second sheet of the Excel spreadsheet.

Acknowledgements

We thank Daniela Oropeza Calderón and Lucero Hidalgo García for excellent research assistance with the publication database in the early stages of this manuscript. We also acknowledge the helpful input from Vijay Kolinjivadi, Gert van Hecken and Pierre Merlet for the design of the coding strategy.