"It's exciting that the opportunity for low-cost reforestation appears much more plentiful than previously thought."
Neither natural regeneration nor tree planting consistently outperforms the other. Instead, the most cost-effective method varies depending on local conditions. Natural regeneration, which involves letting forests regrow on their own, is cheaper in about 46% of suitable areas. Tree planting, on the other hand, is more cost-effective in 54% of areas.
“Natural regeneration is more cost-effective in areas where tree planting is expensive, regrowing forests accumulate carbon more quickly, or timber infrastructure is distant,” said lead author Jonah Busch, who conducted the study while working for Conservation International. “On the other hand, plantations outperform in areas far from natural seed sources, or where more of the carbon from harvested wood is stored in long-lasting products.”
The research team estimates that by using the cheapest method in each location, we could remove a staggering 31.4 billion metric tons of carbon dioxide from the atmosphere over 30 years, at a cost of less than $50 per metric ton. This is about 40% more carbon removal than if only one method was used universally.
“It’s exciting that the opportunity for low-cost reforestation appears much more plentiful than previously thought; this suggests reforestation projects are worth a second look by communities that might have prejudged them to be cost prohibitive,” said Busch. “While reforestation can’t be the only solution to climate change, our findings suggest it should be a bigger piece of the puzzle than previously thought.”
To reach these conclusions, the research team gathered data from hundreds of reforestation projects and used machine-learning techniques to map costs across different areas at a 1-kilometer (0.6-mile) resolution. This detailed approach allowed them to consider crucial factors such as tree growth rates and potential species in different regions.
Ecologist Robin Chazdon, who wasn’t involved in the research, praised the comprehensive approach but highlighted important considerations beyond cost-effectiveness.
“These eye-opening findings add nuance and complexity to our understanding of the net costs of carbon storage for naturally regenerating forests and monoculture plantations,” Chazdon said. However, she emphasized that “the relative costs of carbon storage should not be the only factor to consider regarding spatial planning of reforestation.”
Chazdon pointed out some of the ecological trade-offs involved in different reforestation methods. Monoculture tree plantations, while potentially cost-effective in certain areas, often create excessive water demand and provide poor opportunities for native biodiversity conservation. In contrast, naturally regenerating forests typically offer a wider range of ecosystem services and better support local biodiversity.
“Ultimately, these environmental costs and benefits — which can be difficult to monetize — need to be incorporated in decisions regarding how and where to grow plantations or foster natural regeneration,” Chazdon said.
The study’s authors acknowledge these limitations and suggest several directions for future research. They propose extending the analysis to high-income countries and exploring other forms of reforestation, such as agroforestry or planting patches of trees and allowing the rest of an area to regrow naturally.
Additionally, the researchers emphasize the need to integrate their findings on cost-effectiveness with data on biodiversity, livelihoods and other societal needs to guide reforestation efforts in different contexts.
While the study’s findings are promising, the researchers caution that reforestation alone won’t solve the climate crisis. Even at its maximum potential, reforestation would only remove as much carbon dioxide in 30 years as eight months of current global emissions.
Reforestation is very important, but it won’t solve climate change on its own, Busch said. Ultimately, “we still need to reduce emissions from fossil fuels.”
