Afforestation and reforestation have varying biodiversity impacts across and within biomes

Abstract Afforestation and reforestation (AR) are effective strategies for large-scale carbon dioxide removal (CDR) and climate change mitigation, as they offer the potential to sequester vegetation and soil carbon. However, the expansion of AR raises concerns about the adverse impacts on biodiversity. While local studies have assessed these impacts, global-scale evaluations remain limited. Our study addressed the need for a comprehensive approach to mitigate the risks of AR and enhance its potential as a nature-based solution for both CDR and biodiversity conservation. Here, we introduce a novel approach for assessing AR’s strategic potential using a species distribution framework that considers both favorable and unfavorable effects on species in forest landscapes. We propose a biome-specific spatial prioritization framework to delineate where AR may negatively affect biodiversity. By adopting a habitat suitability index as a biodiversity proxy, our approach increased the compatibility between climate mitigation goals (i.e. carbon storage) and biodiversity conservation. We found that in forest biomes, and particularly in the tropical and subtropical moist broadleaf forests biome and the tropical and subtropical coniferous forests biome, many areas offer high carbon sequestration per unit area alongside high habitat suitability values. However, even within the same biome, the impact of AR on biodiversity can vary among locations. Among the non-forested biomes, the existing species in temperate grasslands, savannas, and shrublands are particularly vulnerable to AR if carbon sequestration is prioritized over biodiversity. To mitigate these risks, prioritizing ecosystem restoration can support biodiversity and restore degraded lands to produce ecosystems that are tailored to regional ecological contexts. Our approach highlights how and where AR strategies can be deployed to simultaneously achieve climate change mitigation and biodiversity conservation.