Variation in the costs and ecological benefits of tropical natural forest regeneration.

Natural regeneration is a cost-effective alternative to tree planting for restoring degraded and converted tropical forests, contributing to climate mitigation and biodiversity recovery. However, global variation in its costs and benefits remains poorly quantified, limiting the ability of restoration programmes to strategically leverage its full potential. Here we assess this variation by integrating data on costs and ecological benefits across the tropics, spanning 7.49 million km2 of land with biophysical potential for natural forest regeneration. If completely regenerated, this additional forested area could accumulate approximately 9.57 Gt C over 30 years and reduce the overall extinction risk of forest-dependent species by about 31% relative to a baseline. We show that Indonesia, Madagascar, Philippines, México and Malaysia have the largest areas with high carbon and biodiversity benefits at low costs, which we refer to as 'holistic hotspots' for natural regeneration. We find that cost-effective areas with high carbon or high biodiversity benefits alone show different spatial patterns from holistic hotspots. These tradeoffs in achieving both benefits reduce the area of holistic hotspots to 9.67% of the entire study region. The cost-benefit maps we provide can enable decision-makers to improve their spatial planning and investment to achieve their forest restoration goals.