The article evaluates the cost-effectiveness of natural forest regeneration and plantations for climate mitigation. It finds that natural regeneration (46%) and plantations (54%) are each more cost-effective for mitigating climate change across about half the area suitable for reforestation in 138 low- and middle-income countries. Using the more cost-effective method at each location, the 30-year, time-discounted abatement potential of reforestation below US$50 per tCO₂ is 31.4 GtCO₂, which is 44% more than natural regeneration alone or 39% more than plantations alone. Reforestation offers 10.3 times more abatement below US$20 per tCO₂ than the most recent IPCC estimate. Reforestation, the restoration of tree cover to areas where forests naturally occur but have been removed, contributes to climate change mitigation by removing carbon dioxide from the atmosphere and storing it in biomass and soil. The cost-per-ton of reforestation varies by method and location, with plantations generally having higher implementation costs than natural regeneration but potentially higher carbon accumulation rates. Plantations can also generate revenue from wood products, while naturally regenerated forests provide greater biodiversity, water provisioning, and erosion control. The study maps the cost-effectiveness of natural regeneration and plantations across 138 low- and middle-income countries, considering implementation and opportunity costs, likely plantation genus, and carbon accumulation. It finds that natural regeneration is more cost-effective in regions such as Western Mexico, the Andean region, Southern Cone of South America, West and Central Africa, India, Southern China, Malaysia, and Indonesia, while plantations are more cost-effective in the Caribbean, Central America, Brazil, North, East, and Southern Africa, northern China, mainland Southeast Asia, and the Philippines. The study also produces marginal abatement cost curves, showing that natural regeneration could remove up to 21.8 GtCO₂ below a cost of US$50 per tCO₂, while plantations could remove up to 22.6 GtCO₂. Using the more cost-effective method at each location, reforestation could remove 31.4 GtCO₂ below US$50 per tCO₂. Latin America holds 56% of potential abatement from reforestation using the more cost-effective option below US$50 per tCO₂, followed by Asia (33%) and Africa (11%). The top ten countries for potential cost-effective abatement are Brazil, China, Mexico, India, Myanmar, Colombia, Indonesia, Thailand, Democratic Republic of the Congo, and Venezuela. The study highlights the importance of considering spatial variations in abatement costs and the potential for reforestation to contribute significantly to climate mitigation. It also notes the limitations of the study, including the exclusion of offsite costs, transaction costs, andThe article evaluates the cost-effectiveness of natural forest regeneration and plantations for climate mitigation. It finds that natural regeneration (46%) and plantations (54%) are each more cost-effective for mitigating climate change across about half the area suitable for reforestation in 138 low- and middle-income countries. Using the more cost-effective method at each location, the 30-year, time-discounted abatement potential of reforestation below US$50 per tCO₂ is 31.4 GtCO₂, which is 44% more than natural regeneration alone or 39% more than plantations alone. Reforestation offers 10.3 times more abatement below US$20 per tCO₂ than the most recent IPCC estimate. Reforestation, the restoration of tree cover to areas where forests naturally occur but have been removed, contributes to climate change mitigation by removing carbon dioxide from the atmosphere and storing it in biomass and soil. The cost-per-ton of reforestation varies by method and location, with plantations generally having higher implementation costs than natural regeneration but potentially higher carbon accumulation rates. Plantations can also generate revenue from wood products, while naturally regenerated forests provide greater biodiversity, water provisioning, and erosion control. The study maps the cost-effectiveness of natural regeneration and plantations across 138 low- and middle-income countries, considering implementation and opportunity costs, likely plantation genus, and carbon accumulation. It finds that natural regeneration is more cost-effective in regions such as Western Mexico, the Andean region, Southern Cone of South America, West and Central Africa, India, Southern China, Malaysia, and Indonesia, while plantations are more cost-effective in the Caribbean, Central America, Brazil, North, East, and Southern Africa, northern China, mainland Southeast Asia, and the Philippines. The study also produces marginal abatement cost curves, showing that natural regeneration could remove up to 21.8 GtCO₂ below a cost of US$50 per tCO₂, while plantations could remove up to 22.6 GtCO₂. Using the more cost-effective method at each location, reforestation could remove 31.4 GtCO₂ below US$50 per tCO₂. Latin America holds 56% of potential abatement from reforestation using the more cost-effective option below US$50 per tCO₂, followed by Asia (33%) and Africa (11%). The top ten countries for potential cost-effective abatement are Brazil, China, Mexico, India, Myanmar, Colombia, Indonesia, Thailand, Democratic Republic of the Congo, and Venezuela. The study highlights the importance of considering spatial variations in abatement costs and the potential for reforestation to contribute significantly to climate mitigation. It also notes the limitations of the study, including the exclusion of offsite costs, transaction costs, and