LAUSR

Governments recently adopted new global targets to halt and reverse the loss of biodiversity. It is therefore crucial to understand the outcomes of conservation actions. We conducted a global meta-analysis of 186 studies (including 665 trials) that measured biodiversity over time and compared outcomes under conservation action with a suitable counterfactual of no action. We find that in two-thirds of cases, conservation either improved the state of biodiversity or at least slowed declines. Specifically, we find that interventions targeted at species and ecosystems, such as invasive species control, habitat loss reduction and restoration, protected areas, and sustainable management, are highly effective and have large effect sizes. This provides the strongest evidence to date that conservation actions are successful but require transformational scaling up to meet global targets. Editor’s summary The current biodiversity crisis requires action to protect species from extinction and ecosystems from severe degradation. Billions of dollars are thus invested annually in global conservation. Assessing whether conservation initiatives result in positive outcomes for biodiversity is necessary to guide future efforts. Langhammer et al. performed a meta-analysis to determine whether conservation actions, including protected areas and management, provide better outcomes compared with no action. They found that more than half of the time, conservation actions had a net positive effect but did not necessarily stop biodiversity decline. This work shows that multiple types of conservation actions are usually beneficial and are needed to curb the loss of biodiversity. —Bianca Lopez