Langhammer, Penny F., Bull, J.W., Bicknell, J.E., et al. (2024) The positive impact of conservation action. Science, 384, 453-458. https://doi.org/10.1126/science.adj6598

Summary

The authors conducted a global meta-analysis of 186 studies dating back to 1890 which included 665 trials to assess the outcomes of conservation actions on biodiversity. They only used studies that allowed them to compare effect sizes from the rate of change under the conservation intervention to the rate of change without the intervention (i.e., that included a counterfactual). They compared effect sizes for 7 types of conservation actions including: 1) establishment and management of protected areas, 2) measures to reduce habitat loss and degradation (such as policy and restoration), sustainable use of species, 4) sustainable management of ecosystems, 5) control of pollution, 6) eradication and control of invasive alien and problematic native species (which were combined), and 7) climate change adaptation. They also compared the effect sizes of conservation interventions grouped by three different levels of ecological organization: genetic diversity, species, and ecosystems.

Results

They found that the overall impact of conservation actions are positive and significant, indicating that conservation actions often yield beneficial outcomes for biodiversity compared with the outcome in the absence of the intervention. However, more and better studies are needed for a wider range of conservation interventions and geographic regions, especially for gaps such as pollution control, climate change adaptation, the sustainable use of species, and studies on genetic diversity, as well as studies in the Global South. In two-thirds of cases, conservation actions either improved the state of biodiversity (i.e., absolute positive impacts,~45%), or at least slowed declines (relative positive impacts, ~21%). In one-fifth of the trials, biodiversity under the intervention declined more than no action (absolute relative impacts, ~21%), whereas in a smaller number of cases biodiversity improved in both the intervention and counterfactual, but the counterfactual revealed greater improvements (~12%). These cases were attributed to nontarget impacts of eradication on native species including incidental damage or mortality, or mesopredator release. Eradication and control of invasive alien species and problematic native species had a significant positive effect on biodiversity. The impacts of actions targeting different levels of ecological organization were found to be positive and significant, with the greatest effects for actions targeting species, followed by ecosystems, and then genetic diversity.

Take Home Points

• Among the 7 conservation actions tested, the eradication, control, and management of invasive alien species showed the largest positive impact on biodiversity as highlighted by the largest effect size among groupings.
• The outcomes from conservation actions on biodiversity are substantially better than no action at all in the majority of cases. However, negative impacts of conservation actions do occur, especially due to nontarget impacts.
• Although the state of biodiversity is declining across the globe (in absolute terms), conservation actions work most of the time and need to be scaled up considerably to reverse the global biodiversity crisis.