A century-old forest in Panama offers a solution to a climate challenge: how to restore rainforests without direct tree-planting. Daisy Dent, a senior scientist at ETH Zurich, has spent decades observing natural regrowth at Barro Colorado Nature Monument, where abandoned agricultural and logging sites demonstrate how ecosystems rebuild themselves. Her findings contradict the prevailing assumption that reforestation demands extensive human efforts—such as planting uniform rows of trees or using drones to disperse seeds.
Tropical forests like those in Panama hold nearly 40% of the carbon stored in terrestrial ecosystems, making their recovery essential for climate mitigation. Dent’s research demonstrates that undisturbed forests can regain near-old-growth conditions in as little as 30 years, absorbing carbon more efficiently than monoculture plantations. The process relies on animal and fungal networks that disperse seeds and support young trees.
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At Barro Colorado, Dent examines plots where clear-cutting left barren land. Some areas now host diverse species after animals, including spider monkeys, bats, and parrots, replanted them through seed dispersal. Others, dominated by a single long-lived species like Gustavia superba, show how rodents such as agoutis can influence forest structure but fail to restore biodiversity. Her data indicates that recovery depends on which animals persist after deforestation and how quickly ecological connections re-form.
These insights challenge the €203bn global initiative to plant a trillion trees, an approach popularized in 2015 by ecologist Thomas Crowther, who proposed reforestation could offset a decade of global emissions. Dent’s work in Panama and Brazil reveals that 215 million hectares, an area larger than Mexico, could regenerate naturally under the right conditions. The focus should shift from planting trees to identifying which ecosystems can heal independently and where human intervention is necessary.
How secondary forests became Earth’s dominant jungles
Dent’s career began in Borneo, where she witnessed old-growth forests cleared for palm oil plantations. By 2005, she joined Prorena, a Smithsonian-Yale initiative studying secondary forests, the jungles that regrow after logging or agriculture. Early research dismissed these forests as secondary, but as deforestation accelerated, they became the dominant tropical canopy, covering 70% of all forest areas. A 2009 study by Dent showed that animal populations recover quickly in naturally regenerating sites, reducing the need for expensive planting programs.
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In 2010, she expanded her research to Barro Colorado, where American ecologist Julie Denslow had established long-term regrowth plots. The site’s decades-long records allowed Dent to compare how different clearings recovered, some thriving, others hindered by invasive grasses or the absence of seed dispersers. A 2016 Nature study co-authored by her team found that a hectare of secondary forest absorbs 11 times more carbon annually than old-growth forest, due to young trees competing for sunlight. Later research in 2022 confirmed that even plots with just 35% tree cover could develop into functional forests.
When human help speeds up nature’s recovery
However, not all sites can rely solely on natural processes. In southern Panama, Dent collaborates with carbon-crediting firms like Ponterra to design interventions for degraded lands. Some areas require “assisted natural regeneration,” such as planting key species to accelerate recovery, while others benefit from reconnecting forest fragments or reintroducing wildlife. The aim is to avoid the vulnerabilities of monocrop plantations, which often fail under drought or disease stress.
Researchers have tracked plots at Barro Colorado that began regrowing in the late 1800s, offering a century-long timeline of forest recovery. Early stages show pioneer species dominating, creating light-filled understories that later give way to taller, slower-growing trees. Data from 20- to 100-year-old plots reveal shifts in species composition as seed-dispersing mammals and birds return. Where animal movement corridors remain intact, a wider range of seedlings establishes, speeding up the transition to a mature canopy.
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Grasses, fungi, and the hidden forces blocking regrowth
In contrast, some clearings remain dominated by a single shade-tolerant tree, a pattern linked to persistent grasses introduced during cattle ranching. These grasses can suppress new saplings for up to 150 years, delaying the growth of larger, carbon-rich trees. Soil fungi also play a vital role, with mycorrhizal networks enhancing nutrient uptake for young trees and connecting them to established individuals. This underground system supports faster growth in naturally regenerating stands.
International efforts now use Barro Colorado’s data to inform restoration projects. The 2ndFor network coordinates studies across continents, testing how minimal interventions can enhance natural recovery. In degraded areas dominated by invasive grasses, practitioners apply assisted natural regeneration by planting native seed-bearing species that attract dispersers. This method boosts diversity without creating monocultures.
