Trees are allies in the fight against climate change, and reforestation to sequester carbon could be cheaper than we thought. According to a new study published in
Nature Climate ChangeA strategic mix of natural regrowth and tree planting could be the most cost-effective way to sequester carbon.

Researchers analyzed reforestation projects in 138 low- and middle-income countries to compare the costs of different reforestation approaches. They found that it is possible to remove ten times more carbon for $20 per tonne, and almost three times more for $50, than the Intergovernmental Panel on Climate Change (IPCC) had previously estimated.

“It is exciting that the opportunities for cost-effective reforestation are apparently much greater than previously thought.”

Neither natural regeneration nor tree planting is consistently better than the other. Rather, the most cost-effective method depends on local conditions. Natural regeneration, which involves allowing forests to grow back 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 far away,” said lead author Jonah Busch, who conducted the study while working for Conservation International. “On the other hand, plantations perform better in areas that are far from natural seed sources or where more carbon from harvested wood is stored in long-lasting products.”

The research team estimates that by applying the cheapest method at each location, we could remove an incredible 31.4 billion tons of carbon dioxide from the atmosphere over 30 years at a cost of less than $50 per ton. That’s about 40 percent more carbon dioxide removal than if only one method were used everywhere.

“It’s exciting that the opportunities for low-cost reforestation appear to be much greater than previously thought. This suggests that reforestation projects are worth a second look for communities that may have considered them too expensive,” Busch said. “While reforestation cannot be the only solution to climate change, our findings suggest that it should be a bigger piece of the puzzle than previously thought.”

To reach these conclusions, the research team collected data from hundreds of reforestation projects and used machine learning techniques to map costs for different areas at a resolution of one kilometer (0.6 miles). This detailed approach allowed them to take into account crucial factors such as tree growth rates and potential species in different regions.

Ecologist Robin Chazdon, who was not involved in the research, praised the comprehensive approach but stressed that important considerations needed to be made beyond cost-effectiveness.

“These insightful findings nuance and refine our understanding of the net cost of carbon storage for naturally regenerating forests and monoculture plantations,” Chazdon said. However, she stressed that “the relative cost of carbon storage should not be the only factor to consider in spatial planning for reforestation.”

Chazdon pointed out some of the environmental trade-offs associated with different reforestation methods. While potentially cost-effective in certain areas, monoculture tree plantations often create excessive water demands and offer little opportunity to protect native biodiversity. In contrast, naturally regrowing forests typically provide a wider range of ecosystem services and better support local biodiversity.

“Ultimately, these environmental costs and benefits – which are difficult to quantify in monetary terms – must be factored into decisions about how and where to establish plantations or encourage natural regeneration,” Chazdon said.

The study’s authors acknowledge these limitations and suggest several directions for future research. They suggest extending the analysis to high-income countries and examining other forms of reforestation, such as agroforestry or planting stands of trees and allowing the rest of an area to grow back naturally.

In addition, 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 results are promising, researchers warn that reforestation alone will not solve the climate crisis. Even at its maximum potential, reforestation would only remove as much carbon dioxide in 30 years as current global emissions do in eight months.

While reforestation is very important, it will not solve climate change on its own, Busch said. Ultimately, “we still have to reduce emissions from fossil fuels.”