A powerful climate tool: Let forests regrow naturally

Trees are having a moment in the limelight as people increasingly recognize forests’ ability to soak up carbon dioxide from the atmosphere and store it for long periods of time. 

Recently, there has been a lot of attention focused on replanting trees to help combat climate change. However, when thinking about planting new trees, we should first ask whether it’s worth the extra time, money and labor to focus only on replanting when nature has been growing trees for millennia without our help. 

There are many ways to incorporate trees into the landscape. But when conditions are right, one of the cheapest and easiest options is actually to allow forests to regrow on their own. 

Natural regrowth involves simply stepping back and letting the forest recover on previously cleared lands. Multiple studies have mapped locations that are suitable for forest regrowth. However, we recognized that to make informed choices about when and where to use natural forest regrowth as a climate mitigation option, decision-makers needed a map that details how quickly new forests could pull carbon from the atmosphere.

To help in that endeavor, we and 29 collaborators worldwide scoured over 11,000 publications, compiled thousands of data points from the literature and incorporated forest inventory data from the U.S. Forest Service and beyond. We then combined the data with state-of-the art, machine-learning models to map potential carbon capture rates across the globe, based on environmental conditions. The result is a map of the potential carbon capture from letting forests grow across the globe. 

Published in the journal Nature and freely available at Global Forest Watch, this first-of-its kind map shows that natural forest regrowth can capture up to 23 percent of global carbon dioxide (CO2) emissions from the atmosphere every year. This is on top of the carbon sequestration already provided by existing forests, which absorb around 30 percent of annual CO2 emissions.

We found that the potential carbon capture in new forests varies by orders of magnitude around the world, with 26-fold variation across the United States alone. Areas with high carbon capture potential are nationwide but concentrated primarily in the Southeast and Pacific Northwest. 

This variation underscores the importance of using a map of this nature to pinpoint locations with the highest natural potential to accumulate carbon quickly. 

However, natural regrowth is not always the answer. For example, at sites that are highly degraded, far from seed sources or filled with deer that eat parts of the trees and prevent regeneration, actively planting (and protecting) trees can help to kickstart or speed recovery while helping establish the right species mix for current and future conditions. But in many places, natural forest regrowth can capture carbon and create habitat for biodiversity at a fraction of the cost required for tree planting. 

Many encouraging policies have been proposed to accelerate reforestation efforts both nationally and globally. However, it’s important to remember that regrowing trees is only one tool of many in our climate mitigation toolbox. 

Here in the United States, we also need revolutions in our energy sector and massive efforts to reduce greenhouse gas emissions across our energy, transportation and waste sectors. 

We must also prevent further loss of forests and improve how we manage them. There are many promising options in America’s farmlands, working forests and natural wetlands. Natural and working lands already reduce total U.S. emissions by 12 percent. We could nearly triple this through increased efforts to conserve, restore and improve our land management practices.

About a decade remains to make significant headway on reducing emissions to avoid the worst effects of climate change, but we are already feeling the negative consequences of rising temperatures, including increasing flood risks and more severe and frequent wildfires. 

Solving this global problem will require a collection of local actions to deploy every mitigation tool we have, and America’s natural and working lands hold a diverse and powerful set of options. 

We know forests will be part of the solution. The key to that success will be to know when to replant and when to let them regrow on their own. 

Dr. Susan Cook-Patton is a senior forest restoration scientist at The Nature Conservancy. Follow the organization on Twitter @nature_org. Dr. Nancy Harris is the forest program research director at the World Resources Institute. Follow the organization on Twitter @WorldResources.