Evaluating the evaluators: what are the trends and patterns in studies on mangrove conservation policy effectiveness?

INTRODUCTION: Mangrove forests provide critical ecosystem services but have been extensively converted or modified. With more than half of global systems at risk of collapse, global efforts are being undertaken to reforest, protect, and restore mangrove forests, but a comparison of the diverse interventions to conserve mangrove systems and their documented effectiveness remains lacking. Evidence regarding the effectiveness of mangrove interventions is important to support tailored programs that maximise impact, but program impact evaluations are rarely done rigorously and publicly available. METHODS: Here, we conduct a Systematic Quantitative Literature Review (SQLR) to synthesize the current state of knowledge regarding the effectiveness of mangrove program and policy interventions and address this knowledge gap. RESULTS: There were 42 papers that matched our inclusion criteria. The literature does not evenly cover global mangrove distribution; studies were disproportionately conducted across Asia (62%), with many regions containing large extents of mangroves not represented, such as Oceania. Protected areas (representing 13 / 45 studies) and community-based forest management were the most common interventions to be evaluated (representing 10 / 42 studies), though these intervention components frequently co-occurred with each other or other policy interventions. A ‘before’ and ‘after’ comparison of satellite-derived mangrove extent was the most frequently used method to measure changes in the outcome attributed to the intervention. We found four studies that used credible counterfactuals (e.g. with quasi-experimental methods). Significant geographic, methods, and outcome gaps remain in impact evaluation published literature despite significant efforts by mangrove conservation practitioners worldwide; researchers should work to strengthen meaningful collaborations with conservation groups in underrepresented areas to fill evaluation gaps. CONCLUSION: Conserving mangroves and protecting the communities that rely on them as climate change impacts intensify requires shifting focus to underrepresented but threatened systems that need protection with effective interventions.