Integrated above‐ and below‐ground ecological monitoring for nature‐based solutions

Abstract As the development of nature‐based solutions (NbS) increases globally, it is important to ensure that projects meet the objective of delivering benefits for biodiversity, alongside tackling societal challenges. However, this is challenging because most NbS projects do not directly monitor ecological outcomes, and those that do often focus on a limited set of metrics. We identify the most informative and feasible above‐ and below‐ground ecological metrics for monitoring the ecological outcomes of NbS. We identify possible biodiversity and soil health metrics using a structured non‐systematic literature review, and rank these using a scoring system to assess their informativeness and feasibility for monitoring. Metrics are categorised into compositional, structural, and functional aspects of biodiversity, and biological, physical and chemical aspects of soil health. We group biodiversity and soil health metrics into Tier 1 (the most informative and feasible metrics), Tier 2 (informative metrics with some limitations in scope or feasibility) and Future metrics (highly informative metrics which are currently less feasible to monitor). Tier 1 metrics collectively address multiple aspects of biodiversity and soil health and are the highest priority for NbS project assessments. For biodiversity, 9 Tier 1, 6 Tier 2 and 15 Future metrics were identified, and for soil health there are 11 Tier 1, 6 Tier 2 and 5 Future metrics. We identify existing standardised methodologies, threshold and reference values for monitoring these metrics, although in many cases, these are not available. Solution . Our study provides practitioners with a framework for selecting optimum metrics for assessing above‐ and below‐ground ecological outcomes of NbS relevant to the location in which they are being implemented. We summarise the relevance of each metric to biodiversity or soil health and provide standardised methodologies for collecting data to support ecological monitoring protocols for NbS projects. The information on each metric is freely available as a searchable online database designed for UK practitioners, but with wider applicability.