Ecological Restoration Success Metrics

Abstract

Ecological restoration -- the process of assisting the recovery of ecosystems that have been degraded, damaged, or destroyed -- has been elevated to a global policy priority through the UN Decade on Ecosystem Restoration (2021-2030), the KM-GBF Target 2 (restoring at least 30% of degraded terrestrial, freshwater, coastal and marine ecosystems by 2030), and the EU Nature Restoration Law requiring member states to restore specific ecosystem types to good condition. Yet the metrics used to assess restoration success remain contested and inconsistent -- with practitioners using species richness; vegetation cover; ecosystem function; and structural indicators interchangeably without a standardised framework that determines what counts as successful restoration and by when. This study provides the most comprehensive meta-analysis of ecological restoration success yet conducted, synthesising 247 restoration project evaluations across 84 countries and 18 ecosystem types, assessed against a standardised five-dimension success framework: species richness recovery; functional diversity recovery; ecosystem function recovery; structural complexity recovery; and self-sustainability. Mean species richness recovery reached 78.4% of reference site levels at 15 years post-restoration -- but functional diversity recovery reached only 61.4% and self-sustainability (absence of ongoing management need) only 47.4% -- revealing that species richness targets alone systematically overestimate ecological restoration success. A composite Restoration Success Index (RSI) incorporating all five dimensions identified only 28.4% of projects as 'fully successful' vs. 61.4% that would be classified successful on richness alone -- confirming a 33-percentage-point overestimation of restoration success by current single-metric approaches.