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Nature-based solutions (NbS) —i.e. working with and enhancing nature to address societal challenges— feature with increasing prominence in responses to climate change, including in the adaptation plans of the most vulnerable nations. Although evidence for the effectiveness of NbS for adaptation is growing, there is less evidence on whether and how NbS reduce vulnerability to climate change in the Global South, despite this region being home to most of the world’s most climate-vulnerable people. To address this, we analysed the vulnerability-reduction outcomes of 85 nature-based interventions in rural areas across the Global South, and factors mediating their effectiveness, based on a systematic map of peer-reviewed studies encompassing a wide diversity of ecosystems, climate impacts, intervention types and institutions. We applied an analytical framework based on social-ecological systems and climate change vulnerability, coding studies with respect to six pathways of vulnerability reduction: social and ecological exposure, sensitivity, and adaptive capacity. We find widespread effectiveness of NbS in the dataset with 95% providing positive outcomes for climate change adaptation. Overall, nature-based interventions reduced vulnerability primarily by lowering ecosystem sensitivity to climate impacts (73% of interventions), followed by reducing social sensitivity (43%), reducing ecological exposure (37%), and/or increasing social adaptive capacity (34%), ecological adaptive capacity (18%) and reducing social exposure (12%). With an analysis of mediating factors, we show that vulnerability-reduction effectiveness was affected as much by social and political factors as by technical considerations. Indeed configurations of existing and introduced formal and informal institutions appear central to the efficacy and distributive effects of the studied interventions. We conclude that attention to the distinct pathways through which vulnerability is reduced can help maximise the benefits of NbS and that to be successful, careful consideration is required on their applicability to particular circumstances as well as their social dimensions.

Nature-based solutions (NbS) are increasingly recognised for their potential to address both the climate and biodiversity crises. These outcomes are interdependent, and both rely on the capacity of NbS to support and enhance the health of an ecosystem: its biodiversity, the condition of its abiotic and biotic elements, and its capacity to function normally despite environmental change. However, while understanding of ecosystem health outcomes of nature-based interventions for climate change mitigation is growing, the outcomes of those implemented for adaptation remain poorly understood with evidence scattered across multiple disciplines. To address this, we conducted a systematic review of the outcomes of 109 nature-based interventions for climate change adaptation using 33 indicators of ecosystem health across eight broad categories (e.g. diversity, biomass, ecosystem functioning and population dynamics). We showed that 88% of interventions with positive outcomes for climate change adaptation also reported measurable benefits for ecosystem health. We also showed that interventions were associated with a 67% average increase in local species richness. All eight studies that reported benefits in terms of both climate change mitigation and adaptation also supported ecosystem health, leading to a triple win. However, there were also trade-offs, mainly for forest management and creation of novel ecosystems such as monoculture plantations of non-native species. Our review highlights two major limitations of research to date. First, only a limited selection of metrics are used to assess ecosystem health and these rarely include key aspects such as functional diversity and habitat connectivity. Second, taxonomic coverage is poor: 67% of outcomes assessed only plants and 57% did not distinguish between native and non-native species. Future research addressing these issues will allow the design and adaptive management of NbS to support healthy and resilient ecosystems, and thereby enhance their effectiveness for meeting both climate and biodiversity targets.

The current focus on afforestation in climate policy runs the risk of compromising both longterm carbon storage and human adaptation. It also works against efforts to stem the tide of biodiversity loss. We outline why an emphasis on diverse, intact natural ecosystems—as opposed to tree plantations with fast-growing exotic species—will help nations deliver the goals of the Paris Agreement and much more.