Assessing the past and future impact of a long‐term island restoration program

Given the pressing biodiversity crisis and the limited resources made available to support conservation, impact evaluation is crucial in understanding the effectiveness of conservation strategies. The use of experimental and quasi‐experimental methods of impact evaluation in conservation continues to grow, but they are not always compatible with conservation projects. The IUCN Green Status of Species (GSS) provides a qualitative, inferential approach to evaluate the past and potential future impacts of conservation. Using the GSS, we present the impact of conservation on 10 species endemic to Mauritius (six reptiles, three birds and one tree). Like many island ecosystems, Mauritius has experienced extensive habitat destruction and biodiversity loss in recent centuries, and has therefore been the site of decades of conservation conducted in collaboration between governmental and non‐governmental organizations, both local and international. Using inferential, qualitative approaches to generate counterfactual scenarios, we explored the impact to date of conservation in Mauritius on species extinctions and species' ongoing dependence on conservation. We found that conservation efforts have prevented extinction in all but one species assessed, with the counterfactual scenarios taking into account the effects of conservation actions including biosecurity measures, invasive species control, habitat restoration, and species reintroduction. The results quantifying the assessed species' dependence on continued conservation action were more varied, with the reptiles assessed in this study being more reliant on continued conservation than the other taxa assessed. The findings of this study demonstrate using a real‐world case study how the IUCN Green Status of Species and the associated counterfactual analysis can be used to understand and communicate conservation impact. We show the high impact of past conservation actions and the importance of their continuation. We attribute the successful outcomes we observed to long‐term investment in conservation programs and highlight this as an important consideration to deliver positive outcomes.