“I was totally surprised how quickly it went,” said Lourens Poorter, an ecologist at Wageningen University in the Netherlands and lead author on the paper. “These forests can recover very fast and they can do it by themselves.”
Burgeoning secondary forests are good for the climate as well. They are able to sequester more carbon dioxide from the atmosphere than established forests; like the voracious food intake of a sprouting teen compared to that of an older adult.
“It does provide a glimmer of hope for this process of tropical reforestation,” said Meg Lowman, a conservation biologist and author of “The Arbornaut: A Life Discovering the Eighth Continent in the Trees Above.” “My only caution is that I don’t think it’s ever a substitute for the importance of saving big trees and old growth forests.”
Older forests ultimately store more carbon dioxide than young forests, and deforestation rereleases those stockpiles, which helps drive climate change. The study found that it took more than a century for the overall biomass of tropical forests — and thus their carbon storage ability — to return fully. The recovery of a forest’s species makeup lasted a similar period.
The longer time frame for the revival of these key benefits is among the reasons that Poorter says maintaining current forest cover is crucial. “First, stop deforestation and conserve old growth forests,” he emphasized. The fact that deforested land can recover “is not a license to kill.”
A 2019 study estimated that some 5.5 million hectares of tropical forest — an area more than twice the size of Belize — is lost each year to expanding commercial cropland, pastures and tree plantations. But cleared land is often abandoned as cultivation shifts, said Poorter, and researchers wanted to know, “Can it recover?”
The answer is yes, and relatively quickly — a phenomenon that Poorter says is due to a number of factors. The subsurface soil, for example, often remains relatively vibrant after deforestation, which enables a faster recovery. The warmth and humidity of the tropics also allow trees to grow extremely fast, with some species climbing more than a dozen feet per year.
And this all happens largely without human intervention, Poorter said. Seeds, roots and stumps embedded in the soil, or the spread of plants from adjacent forests, kick-start the recovery process.
“The influence of humans is relatively minor compared to what nature itself is doing,” he said. “The conditions are that there has to be nearby forests, and the soil can’t be too degraded.”
Although these trends had been previously observed on the local level or in a small number of locations, this paper drew on 77 sites in three continents, comprising 2,275 plots and 226,343 stems. Poorter, who was among the study’s almost 100 authors said, “For the first time, we brought together all these plots from all these different scientists.”
That is perhaps the paper’s greatest strength, said Daniel Nepstad, a tropical ecologist and president of the San Francisco-based Earth Innovation Institute. “The results are not surprising, but it’s brought a good level of rigor and replication across many sites,” said Nepstad, who was not involved in the study. “That’s definitely a major contribution.”
And, he argues, the research bolsters the policy argument for a nature-based approach to forest restoration. “The cheapest way to get forest back on the land is to let nature do the work,” he said. And he would encourage governments to incentivize farmers and landowners to protect secondary forests and promote regrowth. “I think a small incentive is all you’d need.”
Organizations such as the Natural Capital Project advocate for similar approaches to ecosystem services restoration. Costa Rica recently won Prince William’s Earthshot Prize for a program that helps reverse deforestation by paying farmers to protect and reforest their land.
At the U.N. climate conference in Glasgow, Scotland, in November, dozens of nations pledged to end deforestation by 2030 while simultaneously conserving and restoring forests. “Waiting to do it naturally is okay, but it’ll happen a lot faster if we help it along,” David Pearson, a conservation ecologist at Arizona State University, said of forest recovery.
Poorter said that this study also can inform forest recovery monitoring and evaluation. Large-diameter trees, variety in tree size and a large number of species, he said, were all indicators of a robust recovery.
But there is more work that he and other researchers would like to do. The plots in this study, for instance, were in areas with fairly high tree cover. “It would be nice to expand our universe and study not only where it works relatively well but also study the hard and difficult conditions,” he said. That could include large soy or sugar cane plantations, where forests may not be as near.
For Pearson, though, the value of this paper is clear and resides as much in the detail as in the overarching optimism it offers.
“We’ve had this gloom and doom for so long,” he said. “It’s about time we started seeing that there’s got to be ways that we can actually recover these forests.”