Unlocking the potential of OECMs for achieving conservation targets: what the global evidence shows

How can we scale up biodiversity conservation to meet the “30×30” target without relying only on formal protected areas? Other Effective Area-based Conservation Measures (OECMs) are increasingly highlighted as part of the solution: areas outside protected areas that can still deliver effective and enduring in situ biodiversity conservation under the CBD definition.

Our new open-access review in Ambio synthesises the global evidence base on potential OECMs (i.e., areas proposed in the literature as potentially meeting CBD OECM criteria) and maps how they are being identified and assessed across sectors and realms. This is directly relevant to current global and European ambitions to expand effective area-based conservation and operationalise biodiversity targets.

We conducted a global scoping review following established evidence-synthesis methods and PRISMA-ScR reporting, compiling:

• 99 documents (peer-reviewed + grey literature)

• 694 case studies

• ~237,000 sites proposed as potential OECMs

  
  

The review also consolidates the extracted information in an accompanying database (in the supplementary material) to support researchers, planners, and decision-makers developing credible OECM pathways.

Three key insights for planning and implementation

1. The evidence base is global, but engagement is uneven

Case studies are geographically widespread, covering many countries, but are concentrated in a subset of regions and countries. This matters because it suggests that global narratives about OECM “uptake” may partly reflect where assessments are published and accessible, rather than where OECM-relevant management is actually happening.

Fig. 1. Global geographic distribution (choropleth map) of the number of case studies included in the Scoping Review by country. The grey colour indicates countries with no case study

2. Potential OECMs span multiple sectors and conservation objectives

Potential OECMs span a wide diversity of sectors, ecological realms and conservation objectives. They occur across terrestrial, freshwater, and marine systems, and while many have primary conservation objectives driven by the environmental sector, others deliver biodiversity outcomes as secondary or ancillary benefits of sectoral management (e.g. fisheries, forestry, private or community-governed areas, Indigenous Peoples and Local Communities).

Fig 2. Sankey diagram representing the frequency in the combination of i) conservation objectives of the potential OECMs, ii) the OECMs sector and iii) the realm. The width of the nodes and lines is proportional to the flow quantity (i.e., the number of potential OECMs).

3. Effectiveness is often reported but uncertainty remains substantial

Across many assessed case studies, potential OECMs are reported to be effective with respect to the criteria evaluated. At the same time, a large share of studies report uncertainty/unknown effectiveness, and patterns differ across realms. Marine studies show a more heterogeneous distribution of outcomes than terrestrial and freshwater studies.

This is a key operational message: expanding OECM portfolios quickly is not sufficienτ. Ιmplementation requires more consistent assessment approaches, stronger evidence of outcomes, and clearer definitions of what “effective” means in practice.

Fig. 3. Hierarchy (packed cycles) chart representing the relationship between the realm (terrestrial, marine and freshwater) and the effectiveness (effective, ineffective, mixed, uncertain/unknown) of the potential Other Effective area-based Conservation Measures (OECMs) case studies assessed, as reported by the authors of the studies included in the Scoping review. The cycle size is proportional to the importance of the relationship (i.e., the number of case studies by realm and effectiveness).

From evidence to action

This review shows that OECMs represent an important opportunity to expand conservation impact beyond protected areas, but it also highlights recurring gaps: a heavy reliance on qualitative synthesis, limited and inconsistent use of metrics, and underrepresentation of socio-cultural values (CBD Criterion D). More consistent, transparent and science-based assessment approaches are needed if they are to credibly contribute to the 30×30 global biodiversity target under the Convention on Biological Diversity.

Reference

Petza, D., Amorim, E., Lamine, E. B., Colloca, F., Dominguez Crisóstomo, E., Fabbrizzi, E., S., Fraschetti, I., Galparsoro, S., Giakoumi, M., Kruse, V., Stelzenmüller & Katsanevakis, S. (2026). Unlocking the potential of other effective area-based conservation measures (OECMs) for achieving conservation targets: A global scoping review. Ambio, 1-23. https://doi.org/10.1007/s13280-025-02341-3 (Open access via Springer).