Why Naturally Regenerating Forests Matter for Climate Mitigation

Large-scale removals of atmospheric carbon dioxide are crucial for combating climate change.

While significant research focuses on protecting and restoring forests, these efforts primarily concentrate on conserving mature forests or engaging in reforestation by planting new trees.

However, an often-overlooked approach to forest conservation is the protection and preservation of naturally regrowing forests, which can enhance their carbon removal capacity.

A study by the Nature Conservancy, the World Resources Institute (WRI), and partners, “Protect young secondary forests for optimum carbon removal,” demonstrates that naturally regenerating “secondary forests” are effective in combating climate change. The study is the first of its kind to show where and at what ages these forests can have the most significant impact regarding the amounts of atmospheric carbon dioxide they capture.

To better understand how natural forest regrowth removes atmospheric carbon dioxide, the authors created high-resolution 1-kilometre aboveground carbon (AGC) curves. Combining the curves with maps of forest age and areas suitable for regrowth enables the authors to estimate the amount of carbon that can be removed from the atmosphere over different periods.

The amount of field data used in this study is eight times more than in previous studies – 109,000 forest plots compared to approximately 13,000 before. Data is grouped into 5-year age ranges, combining each one with 66 environmental factors, including climate, soil, radiation, landscape features, and biome type, to train machine learning and predict carbon storage for forests of different ages. With the aboveground carbon (AGC) curves, the study can do the following:

1. Measure how carbon storage and removal rates vary across locations and over time,

2. Pinpoint where and when forests remove the most carbon and,

3. Estimate how much natural forest regrowth could help slow climate change.

The study shows that secondary forests, when allowed to grow, can capture carbon 8 times faster than new natural growth when they are aged between 20 and 40 years. The problem is that they do not often allow secondary natural forests to grow long enough to reach their full potential due to factors such as clearing, harvesting, fires, or pest infestations.

This finding offers an essential insight into the secondary forests’ untapped potential to combat climate change, provided they are protected and managed effectively.

These peak carbon removal rates of forests also vary according to their location, the study shows. In tropical and subtropical forests, such as those in the Amazon and the Congo Basin, as well as some temperate forests in the United States, the carbon capture ability of secondary forests is highest at a younger age.

In boreal forests, such as those in Russia and Canada, and tropical and subtropical savanna regions like the Brazilian Cerrado, the opposite is true: secondary forests are most impactful when they are older.

However, on average, regardless of their global location, established secondary forests are 10 times more effective in absorbing carbon than new forests. In some areas, the difference can be as high as 820%.

The sad reality is that secondary never reached its peak carbon removal age. In tropical regions, the average time to forest regeneration is just 7.5 years before the forest is cut down, with only 6% reaching 20 years of regrowth. In the Brazilian Amazon, 50% of secondary forests are harvested within 8 years; in Costa Rica, the average regeneration age is the longest at 20 years.

This new data indicates that older secondary forests are among the most effective at removing carbon within this critical window. The study presents new, crucial data on the potential of secondary forests to remove carbon dioxide, provided they are allowed to grow for at least 20 years or more.

Before this age, these secondary forests were prevented from reaching their peak carbon removal capabilities, which significantly undermined the many benefits they offer, in addition to faster carbon removal. These co-benefits include restoring biodiversity and cost-effectively protecting water bodies.