Reforestation is an increasingly popular way to fight climate change, as evidenced by recent initiatives such as the UN Decade on Ecosystem Restoration, the Trillion Trees Campaign, the EU Nature Restoration Law. Reforestation programs have diverse goals, from restoring ecosystems to generating revenue from wood products. One challenge such programs face is determining which method of restoring tree cover offers the biggest “bang for the buck” for the climate in different places (that is, the lowest cost per ton of carbon dioxide sequestered).

In our newly published  paper in Nature Climate Change, we determined where it is more cost-effective to establish tree plantations (which can generate income from harvested wood products), and where it is more cost-effective to let forests regrow naturally (and in doing so provide natural habitat for plants and animals). We did so by integrating hundreds of observations on the costs of reforestation projects with other biophysical and economic data.

After crunching the numbers across 138 low- and middle-income countries, we found that natural regeneration and plantations are each more cost-effective over roughly half the land suitable for reforestation. A combination of the two reforestation methods can outperform either on its own. By applying each of the methods where it is more cost-effective, reforestation could achieve up to ten times more low-cost mitigation than previously estimated by the IPCC.

Natural regeneration and plantations each have their place

We found that both natural regeneration and plantations have an important role to play in climate mitigation. That is, each method is more cost-effective over roughly half the land considered suitable for reforestation in low- and middle-income countries (Fig. 1).

Natural regeneration is more cost-effective than plantations across 46% of suitable land. Often, these are areas where tree planting is expensive, regrowing forests accumulate carbon more quickly, or timber infrastructure is distant. Conversely, plantations outperform natural regeneration in 54% of suitable land. These are often areas far from natural seed sources, or where more of the carbon from harvested wood is stored long-lasting products.  

Because natural regeneration and plantations offer roughly equal shares of low-cost reforestation potential, forest restoration initiatives that have often favored tree planting (such as national climate pledges) should give greater consideration to natural regeneration.

Fig. 1. The more cost-effective reforestation method within areas suitable for reforestation across 138 low- and middle-income countries.

A mix out-performs either method alone

Only reforesting with a single method exclusively would be missing out on reforestation’s full potential. Below a cost of $50/tCO₂, natural regeneration on its own has the potential to remove up to 21.8 GtCO₂. Meanwhile plantations on their own could remove up to 22.6 GtCO₂. But by combining the two methods, and applying each where it is more cost-effective, reforestation could remove up to 31.4 GtCO₂— nearly half as much again as either method on its own (Fig. 2).

Plantations could remove more than 12 GtCO₂ at negative cost, that is, while turning a profit. But for “unprofitable” mitigation, another income stream is needed. For example, a carbon price that pays land users to reforest based on how the amount of carbon their forests remove from the atmosphere. The higher a hypothetical price of carbon, the more mitigation reforestation would provide, and the greater share of reforestation would come from natural regeneration.

Fig. 2. Marginal abatement cost curves for alternative reforestation methods

More low-cost potential than previously estimated

By combining natural regeneration and plantations and applying each method where it is more cost effective, reforestation can achieve considerably more mitigation at a given cost than previously estimated by the IPCC. Reforestation could remove more than ten times as much carbon dioxide below a cost of $20/tCO₂ than previously estimated, or nearly three times as much below a cost of $50/tCO₂ (Fig. 3). The potential for more low-cost mitigation from reforestation implies that reforestation can play a larger role in climate mitigation efforts than previously considered.

Even so, reforestation can only comprise a small portion of global efforts to reduce and remove greenhouse gases; reforestation is no substitute for rapidly cutting fossil fuels and deforestation. Even if reforestation were hypothetically applied to its maximum potential across low- and middle-income countries, it less carbon dioxide over 30 years than eight months of current global greenhouse gas emissions. However, while reforestation can’t stop climate change on its own, it can help meet global temperature targets while also contributing to biodiversity and livelihood goals. And as our research shows, its potential to do so cheaply is larger than previously thought.

 Fig. 3. Comparison of our results to IPCC (2022). Note that the numbers shown here are greater than in the analysis described above due to different assumptions regarding time-discounting of future costs (0% in this figure vs. 5% in analysis).

How we crunched the numbers

To map the abatement cost ($/tCO₂) of natural regeneration and plantation, we generated and mapped a variety of data sets: the implementation cost of each method, based on hundreds of observations from reforestation projects; the opportunity cost of using land for reforestation rather than crops or livestock; the amount of carbon accumulated from forest regrowth over 30 years; and the likely plantation genus, as well as information on the decay rate of carbon stored in harvested wood products and the price of harvested wood products.  We combined these data, and screened locations based on their suitability for reforestation and the feasibility of natural regeneration and plantations, to produce marginal abatement curves.

In future research we hope to estimate abatement cost for reforestation in high-income countries, and for other reforestation methods such as agroforestry and assisted natural regeneration. Our maps of abatement cost can be combined with data on biodiversity, livelihoods, and other societal needs and preferences to explore whether, where and how to reforest in different contexts.

For a more thorough explanation of methods, see our paper.