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By David Gibbs, Susan Cook-Patton, and Nathaniel Robinson. Cover Image by: GerolfNiessner/Alamy Stock Photo
Protecting and restoring forests are essential for curbing climate change. But while efforts often focus on conserving mature forests and planting new trees (both of which are badly needed), a critical piece of the puzzle is often overlooked: managing naturally regrowing forests to increase the carbon they remove.
Until now, scientists did not have a detailed picture of the carbon removal value of naturally regrowing forests. But new research by The Nature Conservancy, WRI, and partners shows that naturally regenerating “secondary forests” (which have regrown after being cleared by harvests, severe fires, agriculture, or other disturbances) could be especially powerful for fighting climate change. It is the first to show where, and at what ages, they can have the biggest impact.
We found that secondary forests between 20 and 40 years old can remove carbon from the atmosphere up to 8 times faster per hectare than new natural growth if they’re allowed to reach those older ages. The catch is that many secondary forests don’t regrow for this long, whether due to human activity (such as clearing or harvest) or climate-related disturbances (like fires or pests).
These findings highlight that countries may be underestimating the value of naturally regenerating secondary forests in their climate reporting and that protecting them, or encouraging their regrowth for longer periods, offers untapped opportunities for climate action.
How Quickly Can Secondary Forests Remove Carbon?
The rate at which natural forests remove carbon from the atmosphere varies with location and age. Within a forest’s first 100 years of regrowth after being cleared or destroyed, the age range covered in this research carbon removal rates generally start relatively slow, then accelerate, before slowing again. That means it may take many years before newly established forests provide their largest climate benefits.
Our new research provides the first global maps of how these carbon removal rates vary across space and time as secondary forests regenerate naturally. The maps cover any square kilometer on Earth where forests could grow. Previous estimates have not captured as much geographic or age variation, or did not provide global coverage.
We found that naturally regenerating forests typically remove carbon fastest when they’re between 20 and 40 years old. This means that older secondary forests can provide more immediate and often greater carbon removals than younger regrowing forests.
Carbon removal rates by forest age and biome in naturally regenerating forests
However, the age at which forests reach their peak carbon removal rates varies across the globe. Tropical and subtropical rainforests (such as the Amazon and the Congo Basin) and some temperate forests (such as in the United States) capture carbon fastest at younger ages. Meanwhile, boreal forests (like in Canada and Russia), Mediterranean forests, and forested areas in tropical and subtropical savanna regions (such as the Brazilian Cerrado) reach their maximum and generally lower carbon removal rates at older ages.
Age of naturally regenerating forest at maximum carbon removal rate
20-40 years is the most common age at which forests reach their maximum carbon removal rate, though this varies around the world.
Maximum carbon removal rates also vary vastly by region. On average, established secondary forests at their peak removal age absorb 10% more carbon than newly growing forests. But in some areas, the difference is as large as 820%.
Carbon removal rates change most dramatically with age in tropical and subtropical wet forests, while changes were least pronounced in Mediterranean forests and woodlands. However, there is variation within each of these ecoregions, highlighting the value of knowing how carbon removal changes through time for every square kilometer of potential forest.
Carbon removal rate at peak age vs. in newly growing forests
Older naturally regenerating secondary forests can have more than double the carbon removal rates of new forests.
GFW
