The nature-based solution implementation gap: A review of nature-based solution governance barriers and enablers

Nature-based solutions (NbS) represent a critical umbrella concept encompassing measures that employ nature's properties to systemically address societal challenges, potentially providing benefits for biodiversity, climate and people. NbS are accordingly emerging on an ever-expanding number of policy agendas, such as the Kunming-Montreal Global Biodiversity Framework and multiple European Union strategies. However, despite this increasing political traction, NbS implementation (that is, the design, planning, construction, monitoring and maintenance of NbS) remains fragmented and is often too context-specific for their wider upscaling and mainstreaming, creating an 'NbS implementation gap' between ambitions and on-the-ground operationalization. Based on a systematic review of grey- and peer-reviewed literature and workshop results (N = 34), we identify and discuss the institutional, legal, regulatory, social and economic enablers (N = 301) and barriers (N = 307) to NbS implementation. Our results highlight the governance factors that currently facilitate or limit NbS implementation and mainstreaming, which are often homologous. These include inclusive stakeholder engagement processes and true co-design; an evidence base on NbS performance and their co-benefits, including quantitative cost-benefit analyses; the existence of or lack of knowledge products and NbS-specific expertise; and available funds earmarked for NbS. We find that polycentric governance arrangements may act as a critical enabler for NbS implementation, yet path dependencies significantly limit NbS by still favouring grey alternatives. By providing an overview of NbS implementation enablers and barriers across literature and workshop findings, this analysis represents a first step towards understanding key pitfalls and leverage points for enhancing NbS implementation and mainstreaming.