We provide a comprehensive overview of the catalysts of success in CBC using a framework-informed, exploratory analytical approach that is well suited to learning from the small samples and highly dimensional, often correlated data common to CBC literature. We find that external factors and enabling conditions have a considerable influence on place-based outcomes and, to a lesser degree, certain characteristics of the communities themselves. We also find that many of the project-level interventions at the discretion of conservation practitioners do, in fact, have a positive effect on human well-being and environmental outcomes. Our findings offer key insights into what pushes the needle toward greater CBC effectiveness in delivering benefits for people and nature, provide evidentiary support for existing CBC frameworks (e.g., TNC 2017; Mahajan et al. 2021), and clarify evidence gaps requiring further study.
4.1 National contexts supportive of effective local governance affect CBC outcomes
The importance of the context in which CBC is embedded is a widely held though frequently untested assumption (Dickman et al. 2015; Miller et al. 2015). In our study, we considered several national-level variables with hypothesized relevance to CBC outcomes and found three to have significant effects, including environmental democracy, political stability, and voice and accountability. In contrast to previous reviews that aggregate several national-level variables into a single dimension and have found none or negative effects (Brooks et al. 2013; Hajjar et al. 2021), we tested the effects of each independently and found different results. We suggest that each national-level indicator represents a different aspect of the social, economic, and political context influencing the operational environment and the capacity for community governance and stewardship. Particularly important to the combined success of CBC projects were national contexts that 1) support free prior and informed consent and provide pathways for communities to seek justice in environmental matters; 2) provide communities access to information and the ability to participate and freely express their interests in political and decision-making processes (Barelli 2012; Tomlinson 2019); and 3) promote stability with respect to supra-local governance structures, regulatory environments, recognition, and enforcement of rights (Ribot et al. 2006). Consideration of these readily available national indicators provides important situational awareness for conservation practitioners with bearing on feasibility and conservation investment prioritization (e.g., Eklund et al. 2011; Garnett et al. 2011), as well as indicating which strategies might be leveraged in response. We argue that keeping these indicators disaggregated makes them more accessible and makes the interpretation of potential solutions and recommended actions more straightforward. For example, greater investment in capacity-building efforts that foster community engagement and representation in decision-making processes might be suggested where environmental democracy and voice and accountability are low. Local efforts might involve creating or strengthening community-based organizations and building the capacity for community leaders to more readily participate in decision-making fora, while supra-local efforts might involve advocacy for the enforcement of existing frameworks that call for equity and the inclusion of marginalized groups, increasing their transparency and accountability and removing barriers to access and participation (Gaventa & McGee 2013; Kennedy et al. 2022).
4.2 Social cohesion and trust affect CBC outcomes
Social cohesion and collective action are prerequisites for effective natural resource governance, which is foundational to many CBC frameworks (Olson 1965; Agrawal & Ostrom 2001; Colfer 2007; Bodin 2017; Mahajan et al. 2021). There is a substantial body of literature that discusses the importance of social cohesion to collective action and governance, which in turn is influenced by several community characteristics. Low levels of social cohesion are expected when communities lack familiarity, frequent interaction, shared identity and purpose, reciprocity and trust (Olson 1965; Ostrom 1990, 2010). It is reasonable to assume that these disabling conditions are more likely to exist in communities that are large, diverse, rapidly changing, involved in conflict, have pronounced inequality, or have experienced legacies of marginalization and dispossession (Stern & Coleman 2015; Manfredo et al. 2017). Such conditions are not uncommon in the communities where CBC occurs.
We found that social cohesion challenges had a potential negative effect on CBC outcomes, whereas acknowledgement of conflict or trust issues (an important foundational element for social cohesion) and indications that projects made attempts to address them had a significant positive effect. Collectively, these findings suggest that increased attention to the cohesiveness of the community and investments in innovative strategies that can improve it are warranted. For example, trust-building is an emerging focus of current conservation research and thinking (Pretty & Smith 2004; Metcalf et al. 2015; Stern & Baird 2015), and evidence has been provided that trust-building activities among natural resource user groups can improve communication and willingness to adopt sustainable levels of use (Meinzen-Dick et al. 2018). Examples such as these indicate that interventions that build trust and familiarity might affect real-world improvements in human well-being and the environment by creating conditions that favor the effective governance of natural resources. Others have made complimentary observations that positive forest outcomes can be achieved through the implementation of interventions focused on building shared identity and purpose (Wilkie & Painter 2021).
4.3 Existing frameworks and strategic guidance affect CBC outcomes
Consistent with earlier reviews of CBC (e.g., Brooks 2017), we found that many project-level variables influenced CBC outcomes. With regard to the specific strategies and interventions employed, it is widely assumed that sustainable, place-based economic opportunities are critically important to CBC success. However, despite the increased adoption of integrated conservation and development approaches (Roe et al. 2013; Miller 2014) and a significant investment by conservation organizations into sustainable livelihoods, evidence of their effectiveness remains mixed (e.g., Roe et al. 2015; Burivalova et al. 2019). Although positive economic outcomes are frequently reported (e.g., increased employment opportunities or income), many times they are achieved at the cost of negative social outcomes such as conflict or increased wealth inequality (Blundo-Canto et al. 2018). Furthermore, livelihood interventions have not consistently generated benefits, suggesting a need for further research on enabling conditions and unintended consequences, as well as the importance of complimentary interventions, and more thoughtful planning, design, and implementation.
While our analysis was not set up to explore the reasons specific interventions succeeded or failed, we found that economic development was especially important to combined success and that diversification-based approaches (e.g., alternative methods, resources, and occupations) had a significant positive effect. A review of these has led to some key observations. Of note is that livelihood interventions are best leveraged in support of those most vulnerable to conservation-imposed costs (Wright et al. 2016); and that greater emphasis should be placed on participatory planning approaches that solicit the community’s input on livelihood opportunities in advance of their implementation, offering better alignment with local needs and priorities and a greater chance for success (Heiner et al. 2019; Sene-Harper et al. 2019). We also reiterate that we found no evidence of a positive effect for compensation-based strategies (e.g., PES), which seems consistent with the variability in evidence reported (e.g., Jayachandran et al. 2017; Burivalova et al. 2019). In short, there remains much to unpack to adequately evaluate the efficacy of different livelihood interventions, including a more thorough analysis of the importance of adequate and equitable benefits, disproportionate costs, and their durability considering alternatives and associated opportunity costs. For example, how lucrative is an acai enterprise compared to a timber lease? Although we attempted to collect some of this information, many of the studies in our sample did not adequately report on them, and evidence gaps remain. Thus, more formal tests of the relative importance of these variables to the success of livelihood interventions and CBC in general are still needed. We identify this as an important future direction.
We also found evidence that capacity-building interventions influence CBC outcomes (Moore et al. 2006), reinforcing widely held assumptions that local capacity is foundational to the success of CBC (Pretty 2003; Pretty & Smith 2004; Ostrom et al. 2009; Lockwood 2010; Agrawal & Benson 2011). Theoretical and empirical evidence suggests that community leaders and institutions can motivate collective action (Glowacki & von Rueden 2015; Warren 2016) and promote effective governance of natural resources through improved coordination, enforcement, compliance, and conflict resolution (Persha et al. 2011; Stein et al. 2011). Beyond this, community leaders and institutions can facilitate social learning and the diffusion of innovations within the community and beyond (Valente & Davis 1999; Mascia & Mills 2018). Strong leadership and institutions have been associated with positive CBC outcomes (Brooks 2017), whereas others have noted that when community leaders and institutions are ineffective, subject to corruption or elite capture, or incapable of coordination with others, CBC can fail (Knight et al. 2016; Warren & Visser 2016).
We found that interventions that strengthened human capital (training or technical assistance) had significant positive effects. Beyond this, we found that other forms of capacity-building focused on social and institutional capital (leadership or governance) or general community well-being, such as health or infrastructure interventions, had potential positive effects. Although our findings suggest only the potential for a positive effect due to health or infrastructure interventions, a range of positive estimates bounded by 0 compliments the findings of a recent study of CBC initiatives in rural Borneo, which showed that such interventions could generate improved health outcomes in addition to carbon sequestration benefits through reductions in illegal logging (Jones et al. 2020).
Although tenure security is foundational to the CBC frameworks we considered (e.g., TNC 2017), we found no evidence of a positive effect despite it being important to our overall model of combined success. Like compensation-based economic development interventions, perhaps this finding reflects the varied evidence presented by others, which highlights the nuanced effects of tenure form and security on human well-being and environmental outcomes (Liscow 2013; Robinson et al. 2014; Buntaine et al. 2015; Tseng et al. 2021). Although some have found that tenure security can promote positive outcomes for people and nature (Tseng et al. 2021), others have suggested that tenure security alone may be insufficient (Robinson et al. 2014; Vélez et al. 2020) and that the conservation benefits of actions such as titling may diminish with time (Roopsind et al. in review). These findings highlight the importance of tenure security to CBC outcomes in general but raise the possibility that the specific means of doing so and the complimentary activities undertaken might be more important (Agarwala & Ginsberg 2017). A recent global analysis of community forest management supports this interpretation (Hajjar et al. 2021), finding that clear de facto rights and the strength of community institutions for natural resource governance had a stronger association with positive social and environmental outcomes than de jure rights alone. Collectively, these findings argue for greater emphasis on tenure security interventions such as participatory mapping (Chapin et al. 2005) and the co-implementation of capacity-building interventions such as those that strengthen community-based organizations for natural resource management and provide support for community visioning and land use planning activities (e.g., Heiner et al. 2019).
Similarly, multistakeholder interventions are often a focus of CBC strategy, although we found no evidence of a positive effect. It has been observed that improper implementation of multistakeholder interventions can do more harm than good, for example, by perpetuating existing inequitable power dynamics (Edmunds & Wollenberg 2002; Warner 2007). Given that multistakeholder platforms can promote self-determination and the active participation of previously marginalized groups, an important emphasis of emerging human rights-based frameworks such as the United Nations Declaration on the Rights of Indigenous Peoples (IUCN 2012), we propose that practical insights and methodological advances on how to implement them more effectively will be important to improving the efficacy of these interventions and clarifying their contribution to CBC success (e.g., Kusters et al. 2018).
4.4 Project period and implementation stage affect CBC outcomes
Though both were treated as controls, we found that the period in which a project occurred, and its age had notable effects on CBC outcomes. First, we found that later projects had a significant positive effect on combined success. Many have argued that attention to human wellbeing can generate benefits for people and nature (Bennett et al. 2017; Ellis & Mahrabi 2019), and we posit that shifts in the framing of conservation to be more inclusive and equitable could be one potential explanation for this trend (Chapin 2004; Chan et al. 2007; Kareiva & Marvier 2012). Second, while we did not detect a significant positive effect of project age as observed by others (Brooks 2017), we did observe a potential negative effect for early-stage, very young projects and a potential positive effect for late-stage projects. We interpret this to suggest that CBC projects require a certain minimum maturation before positive human wellbeing and environmental outcomes might be expected. Given that the breakpoints of our variable align with a typical 3-year funding cycle, this would suggest that at least a second round of investment would be required to expect positive outcomes, though sustainable financing and plans to transition to community management and ownership would be important additional considerations.
4.5 Limitations and caveats
We apply a novel analytical approach to our review of the efficacy of CBC and what catalyzes its success. To our knowledge, we are among the first to use machine learning methods to analyze CBC projects and identify the variable most associated with their ability to deliver positive human well-being and environmental outcomes from many promoted by existing practitioner-oriented frameworks. As is well documented, there are general limitations associated with the comprehensiveness and quality of the CBC literature and its potential reporting bias (Pullin & Stewart 2006). In addition, we acknowledge limitations specific to our process of curating a sample, its resulting size and representativeness, our coding decisions, variable processing and selection criteria, and analytic process.
First, we do not capture the universe of CBC projects but have curated an adequate and reasonable sample of projects from across the globe employing many of the interventions commonly promoted by existing practitioner frameworks. Encouragingly, RFC is amendable to small samples, and our model performed reasonably well on training and test data. Nevertheless, certain geographies (e.g., North America, Australia) and biomes (e.g., freshwater, marine) remain underrepresented in our sample. As a result, it is unclear how much our findings would change with the expansion of our sample, although we offer a transparent and repeatable process for doing so. We identify an expansion of search terms to better capture the diverse literature on this topic and the various perspectives by which it is approached to be an important future direction.
Second, the way in which we constructed and coded our variables has an acknowledged bearing on our results. We accept this as a necessary caveat for conducting such analyses, and as others have done, we provide detailed documentation of the response and explanatory variables we extracted from the literature and how they were defined (see Table S2). Unfortunately, we found that many variables of theoretical significance and hypothesized importance to CBC outcomes were unavailable for our modeling effort (see the evidence gaps identified in Table S4, with definitions in Table S2). For example, “meaningful engagement and participation” is a common recommendation for effective CBC (Vermeulen & Sheil 2006; Persha et al. 2011; Andrade & Rhodes 2012). Yet we found it to be ill-defined and inadequately reported in our sample. We attempted to characterize meaningful engagement and participation as a function of community consultation in project design, community integration in project management, and community involvement in project activities. However, each of these variables had missing data proportions that precluded their further consideration. Observations such as these reiterate the need for better monitoring and reporting of key components and assumptions, as well as further analysis of their importance to CBC outcomes. We identify this as an important future direction.
Third, analytical methods such as RFC have certain advantages over conventional analytical approaches, which we reiterate is a novel contribution of this work; nevertheless, certain limitations and caveats exist. Foremost is that RFC is challenged by overly small and unbalanced samples. We address this by imputation of missing values to avoid further reductions in sample size, synthetic matching to balance training data, and bootstrapping to improve model performance and provide a means of calculating confidence intervals appropriate to the data. To address the implications of these analytic decisions, we provide additional analyses in the supplement that explore the sensitivity of our results to the 1) assignment of test and training data, 2) balancing of the training data, 3) missingness and imputation among our explanatory variables, and 4) response variable definition (see Figures S5-S7 and Table S5). In general, these analyses are supportive of the approach taken.
Further, we use RFC to identify variables most important to combined success, but because this method only identifies which variables are important to prediction but not how, we pair it with an estimation of accumulated local effects. We qualify our results by emphasizing that the variables we considered were only a set of possibilities motivated by existing theoretical and applied CBC frameworks, which were further reduced by processing and selection processes (see Table S4). The relative importance and effects reported are contingent on this as well as our overall analytic process (see Table S1). As a result, we do not claim to have captured all the variables that could be important to CBC outcomes in and beyond our sample, nor do we claim causality for the 17 variables ultimately included. Like any method, RFC is sensitive to the analytic dataset, but the variables that emerged from our modeling effort are important predictors of combined success for the 128 CBC projects in our sample. Taken together and situated with other evidence on CBC efficacy, we believe our results provide important advances relevant to the design and implementation of CBC projects more broadly.