Carbon recovery potential of Afrotropical secondary forests
Based on extensive field data from 12 African countries, this study reveals that while Afrotropical secondary forests accumulate substantial carbon within two decades, full recovery to old-growth levels takes 36 to 92 years, indicating that secondary regrowth alone cannot meet 2050 climate targets and underscoring the critical need to conserve remaining old-growth forests.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Tropical forests are the planet's great carbon vaults, holding vast amounts of the greenhouse gas that warms our atmosphere within their trees and soil. When these forests are cut down for farming or other uses, that stored carbon is released, contributing to climate change. However, nature has a remarkable ability to heal itself. When fields are abandoned, new trees grow back, creating what scientists call secondary forests. These regrowing woodlands act as sponges, pulling carbon back out of the air as they mature. For decades, researchers have looked to these recovering forests as a potential solution to offset the damage caused by deforestation, hoping they might grow back fast enough to help meet global climate goals. But a critical question has remained unanswered: just how fast can they grow, and how long does it take for them to become as rich in carbon as the ancient, untouched forests they replaced?
A massive new study has finally begun to answer this question for the forests of sub-Saharan Africa, a region that is home to the world's second-largest tropical forest but has been surprisingly understudied compared to its counterparts in the Americas. An international team of researchers traveled to twelve different African countries, from Angola to Tanzania, to measure the carbon stored in nearly one thousand forest plots. These plots represented a timeline of recovery, ranging from fields that had been cleared just one year ago to woodlands that had been regrowing for sixty years. By measuring the diameter and height of trees in these plots, the team calculated exactly how much carbon was accumulating over time. They compared these regrowing forests to nearby old-growth forests, which serve as the ultimate benchmark for a fully recovered ecosystem.
The results reveal a story of both hope and caution. In the first twenty years after a field is abandoned, these secondary forests do indeed regain a substantial amount of carbon, with some sites accumulating between 11 and 109 metric tons of carbon per hectare. This early growth is driven by the rapid return of fast-growing trees and the carbon that remains in the stumps and roots of trees left behind after clearing. However, the study found that if researchers do not carefully distinguish between the new growth and the leftover carbon from the old trees, they can significantly overestimate how much new carbon the forest is actually capturing. This distinction is vital for accurate accounting, as it separates the forest's true productivity from the legacy of what was there before.
When the researchers looked at the long-term picture, the timeline for full recovery proved to be much longer than many had hoped. To reach 90 percent of the carbon stock found in a nearby old-growth forest, the regrowing sites needed anywhere from 36 to 92 years, with a median time of 59 years. In some locations, the uncertainty was so high that the recovery window could stretch beyond a century. This means that while secondary forests are valuable carbon sinks, they cannot reliably replace the carbon lost when ancient forests are destroyed within the few decades needed to meet global climate targets for 2050. The study suggests that relying on regrowth alone to fix the climate is a gamble; the process is simply too slow and too variable to be a guaranteed solution.
The speed of this recovery is not the same everywhere. The researchers found that forests in wetter regions tended to accumulate carbon faster, while areas with severe seasonal droughts saw slower recovery rates. Yet, even with these environmental clues, predicting exactly how long a specific forest would take to fully recover remained difficult. The models used to forecast these trajectories were much better at predicting short-term gains than long-term recovery times. This uncertainty stems from complex factors that are hard to measure from a distance, such as the history of the land, the specific mix of seeds available to start the new forest, and how different species compete with one another as they grow.
Ultimately, this work provides the most comprehensive ground-level look at African forest recovery to date, offering a realistic baseline for policymakers and conservationists. It confirms that while natural regeneration is a powerful force that can restore significant carbon stocks, it operates on a timescale of generations rather than years. The study concludes that protecting the remaining old-growth forests is not just an option but an absolute necessity. Because these ancient forests hold carbon that regrowing woodlands cannot match for a very long time, their preservation is the only way to ensure that the carbon stored in Africa's trees remains secure while the world works toward a stable climate.
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