Susan Cook-Patton

A Summary of the Latest Forest Restoration Science

By Susan Cook-Patton

Updated: June 11, 2025

Forests are a tried-and-true natural climate solution. For eons, trees have pulled carbon dioxide out of the atmosphere through the oldest carbon-capture technology on Earth, photosynthesis. Trees contribute to climate action by helping to remove carbon from the atmosphere and lock it into the wood of the trees themselves.

Forests also give us clean air, clean water and habitat for wildlife. They support local and regional economies and Indigenous Peoples and local communities. Trees make us more resilient to extreme heat and flooding, and they boost our emotional and physical well-being. Yet around the world, we’ve lost forests to cities, minelands and farmlands. While protecting existing forests is more cost-, carbon- and biodiversity-effective than restoring forests, there remains ample opportunity to regrow trees, especially in places where the land is now degraded.

In the U.S., for example, we find up to 148 million acres of opportunity for reforestation. The U.S. Reforestation Hub shows these lower cost and more feasible options, where it is possible to achieve carbon removals alongside other benefits from reforestation. In Canada, we show that there are up to 19.1 million hectares available—more than enough for the 2 Billion Trees (2BT) program—but that the places best for habitat for at-risk species, carbon sequestration, land costs, freshwater provisioning, versus nature-based recreation do not overlap. This means that a mix of lands will be needed to achieve all the 2BT goals. And because many places on Earth lack detailed reforestation maps, we also created a new global map that addresses past critiques of global maps (there are many!) to help people more rapidly locate the spots that are good for climate, nature and people. This global menu of options can be explored at the Global Reforestation Hub, as well as alongside other natural climate solutions at naturebase.

We also work to quantify how the climate mitigation of restoring trees to the landscape varies depending on method and location. While we always target places where trees naturally occur, there are multiple methods for restoring forest cover—ranging from natural regrowth when growing conditions are right, to active planting when the forests need help recovering, to plantations and agroforestry where livelihoods and food production are paramount.

Natural regrowth can be a highly cost-effective method for restoring forest cover, but the carbon returns can vary 200-fold across the globe depending on location and forest age. Carbon accumulation in plantations can vary depending on the species used and management practices, and adding more species can increase the likelihood of planting success and boost carbon accumulation. Similarly, carbon returns from agroforestry can be especially wide-ranging given the sheer diversity of practices used across the globe—from dense multi-layered homegardens to individual trees within grazing lands. To help local communities and other decision makers find the right approach for their landscape, we create maps and tools that give people carbon estimates based on the best available science.

In some places, reforestation can cause global warming rather than cooling due to changes in albedo (i.e., how much sunlight is reflected from the Earth’s surface) so we developed maps to help steer projects away from these global warming zones. At the local level, trees generally provide cooling by releasing moisture into the air and providing shade. Our work shows how widespread those local cooling benefits can be across the globe and within grazing lands where livestock and rural workers are often exposed to extreme temperatures. We also show that those cooling and health benefits are not equitably distributed and that there is more work to go.

While restoring tree cover across the globe is not the sole solution to climate change, it remains one of the most cost-effective carbon removal strategies we have. And it has the potential to provide many benefits to people—helping to restore balance to the ecosystem, support economic opportunities for local communities and tackle the combined challenges of climate change and biodiversity loss.