Impact of tree-based interventions in addressing health and wellbeing outcomes in rural low-income and middle-income settings: a systematic review and meta-analysis.

The impact of nature-based solutions on human health is increasingly recognised; however, our understanding of the strength of evidence and the extent to which it supports policy and practice is insufficient. We aimed to assess the health and wellbeing impacts of solutions in low-income and middle-income settings in which trees are a central feature in the protection, restoration, and sustainable management of landscapes. For this systematic review and meta-analysis, we searched Web of Science, Embase, APA PsycInfo, MEDLINE ALL, Global Health, Global Index Medicus, GreenFILE, SciELO, EconLit, and Africa-Wide Information for studies that evaluated the impacts of relevant interventions on health and wellbeing. Searches were limited to records published from Jan 1, 2000, to the search date; an initial search was conducted on Nov 23, 2021, and was updated on Feb 27-28, 2023. We extracted data from studies comparing interventions with matched controls, calculated standardised mean differences, and pooled the effects using random-effects meta-analysis with adjustments for potential effect dependence. Studies were assessed for quality using seven risk-of-bias domains. Our search identified 23 402 studies, of which 54 were included in the meta-analysis. We found significant positive pooled effects for agricultural yields (standardised mean difference 0·41 [95% CI 0·11 to 0·70]), dietary diversity (0·10 [0·02 to 0·18]), total household income (0·21 [0·09 to 0·33]), poverty reduction (0·17 [0·07 to 0·27]), child growth (0·11 [0·00 to 0·22]), and self-reported wellbeing (0·21 [0·00 to 0·43]). Loss of income from timber production could be a negative outcome (-0·13 [-0·29 to 0·02]); however, these effects might be partially offset by increased income from non-timber forest products (0·32 [0·04 to 0·61]). Effects varied substantially by intervention type, with more positive effects associated with interventions in which the primary target was livelihood improvement than with interventions that targeted biodiversity or carbon mitigation. However, cautious interpretation is urged owing to the low certainty of the evidence. In conclusion, evidence suggests that tree-based solutions can support the health and wellbeing of the implementing communities. Such evidence strengthens the case for aligning health objectives with the goals of nature-based solutions by making community wellbeing an integral component of conservation programmes. Future studies should examine a wider range of outcomes that have direct relevance for health.