Tropical forests regain their biodiversity far faster than previously believed

Thirty years after clear-cutting, a tropical forest reclaims 90% of the biodiversity it had lost. This figure, drawn from a study conducted by more than 30 institutions, primarily German and Ecuadorian, across 62 sites in Ecuador (Chocó), and published in April 2026, overturns a certainty that has weighed on conservation policy for decades: the loss of biodiversity caused by deforestation is not permanent. It is largely reversible, on a humanly relevant timescale.

The stakes are immense. Approximately 60% of the world’s tropical forests are today destroyed or degraded. If even secondary forests — those that regrow after logging or agricultural abandonment — can reconstitute the essence of their biological wealth in a generation, then conservation strategies have at their disposal a lever they had not sufficiently taken into account. Protect what regrows, not only what resists.

The Essentials

  • A multi-institutional study published in April 2026 (Timo Metz et al.) measures that tropical secondary forests recover 90% of their biodiversity in 30 years after clear-cutting.
  • The study covers 62 sites in the Río Canandé Reserve in Ecuador (Chocó), mobilizes more than 30 institutions, and constitutes one of the most comprehensive datasets ever assembled on forest regeneration.
  • Recovery is not uniform: certain species specialized in old-growth forests remain absent or marginal after thirty years, and the speed of recovery depends heavily on local conditions (neighboring agriculture, fragmentation, human pressure).
  • This result modifies the political equation of conservation: protecting regenerating forests costs less politically than expropriating productive land, and could accelerate forest restoration commitments made by 127 countries under the Glasgow Declaration.

Secondary Forest, the Poor Relation of Conservation

For a long time, conservation biologists viewed secondary forests as substitutes. Replacement forests, useful for timber or carbon, but too young, too poor, too ordinary to rival primary forests. Conservation policies therefore focused on the last intact massifs: deep Amazon, the Congo Basin, the forests of Borneo. What had already been cut was, so to speak, accounted for as lost.

This vision was not unreasonable. Primary forests are ecosystems shaped by centuries of coevolution into structures of complexity we barely understand. Certain species of birds, insects, or orchids survive only in these precise conditions: thick humus, closed canopy for decades, hollow trees of old wood. The regeneration of a tropical forest was perceived as a process of several centuries, with the first decades producing only deceptive greenery.

What the study by Timo Metz and his co-authors corrects is precisely this chronology. The speed of recovery, on certain biodiversity indicators, is significantly higher than what models predicted. Thirty years is a generation. On the timescale of politics where budgetary decisions and climate commitments are made, it is a credible horizon.

What the study measures exactly

The study, coordinated by researcher Timo Metz and published in April 2026, relies solely on data collected in Ecuador (Chocó), with 62 sites all located in the Río Canandé Reserve managed by Jocotoco. More than 30 institutions, primarily German and Ecuadorian, contributed to a harmonized dataset, making possible analyses of a scope that earlier studies, often highly localized, could not produce.

The figure of 90% concerns biodiversity measured in terms of species present: after thirty years of natural regeneration, a tropical secondary forest hosts on average 90% of the animal and plant species one would observe in a comparable primary forest. Recovery is particularly rapid for plants, birds, and small mammals. Bats and insectivores return early, supported by shrubby vegetation that quickly provides food niches.

But the figure demands careful reading. A species present is not an established population. And 90% of species present does not mean 90% of abundance. Certain species indicative of old forest — large predators, certain wood-boring beetles specialized in dead old wood, some highly sedentary tree-dwelling primates — remain rare or absent after thirty years. The structure of the forest, with its lianas, dense understories, and stratified layers, takes longer to establish. What the secondary forest recovers quickly is its species richness; what it recovers slowly is its ecological maturity.

This nuance is important, but it does not diminish the significance of the discovery. It frames it. The secondary forest is not a reconstituted primary forest. It is a functional forest, rich, alive, capable of providing substantial ecosystem services in pertinent time. And that is where policy can act.

The conditions for regeneration are not guaranteed

The recovery of 90% in thirty years is not automatic. The study identifies factors that accelerate or slow this process, and several of them depend directly on human choices.

Connectivity is the first. A secondary forest surrounded by primary forest or other regenerating forests recolonizes much faster than a plot isolated in an agricultural landscape. Birds and bats are excellent seed dispersers, but they must be able to move around. Secondary forests situated in highly fragmented landscapes, enclave between palm plantations or pastures, advance much more slowly.

Human pressure counts equally. A forest left to regenerate but subject to illegal selective logging, fuelwood collection, or extensive grazing does not reconstitute itself. The condition for regeneration is an effective moratorium on land use. In many tropical countries, enforcing this moratorium is difficult, particularly in border areas where the state has little presence.

Soil quality also matters. A forest cut and then cultivated for several years with intensive inputs leaves impoverished soil that slows germination. Forests abandoned after a brief agricultural phase recover faster than those subjected to long cultivation cycles.

These conditions do not call into question the study’s central result, but they indicate that regeneration potential must be followed by active protection policy. The forest does not reconstitute itself alone in a hostile landscape.

The shift in doctrine in conservation policy

It is on this point that the study has its most direct effect. Since the Kunming-Montreal agreement of 2022, which sets the goal of restoring 30% of degraded ecosystems by 2030, signatory states have sought concrete levers. The question this agreement posed, without fully answering it, was: how to restore at large scale without impossible budgets?

The answer suggested by the study of Metz and his co-authors is partially reassuring: allowing regeneration is already restoration. Natural regeneration, protected and facilitated, can produce results comparable to tree planting at a fraction of the cost. Active reforestation programs cost between 500 and 2,000 dollars per hectare depending on regions and species. Protecting a secondary forest in natural regeneration costs less, if surveillance conditions are met.

This modifies the political equation of conservation in a significant way. Protecting a primary forest often means confronting powerful economic interests: industrial agriculture, extensive livestock, mining or oil extraction. These conflicts are real and costly politically. Protecting secondary forests in regeneration, often situated on marginal abandoned land, meets less opposition. These are frequently unprofitable lands, already abandoned by farmers. Protecting them costs less in political capital.

The Glasgow Declaration on Forests, signed by 127 countries in 2021 (some sources cite between 110 and 145 countries depending on the timing of the count, representing 85 to 90% of global forest cover), provides for stopping deforestation by 2030 and restoring degraded forests. Until now, implementation mechanisms remained unclear. This study’s results provide additional argument for tropical countries to integrate secondary forest protection into their national contributions to the Paris Agreement and into REDD+ carbon financing mechanisms.

Countries already testing this lever

Several countries did not wait for this study to bet on regeneration. Costa Rica is the most documented example. Over forty years, by combining payments for environmental services to landowners, a strict deforestation ban, and satellite surveillance, the country reversed deforestation that had destroyed three-quarters of its forest cover in 1983. Its coverage has now risen to over 50%. Many of the forests that have regrown are secondary forests. And biodiversity has substantially returned to them.

In Latin America, the states of Minas Gerais and São Paulo in Brazil are experimenting with “passive restoration” programs in the Cerrado biome and in the Atlantic Forest, which now cover only 12% of their original area but are experiencing rapid regeneration processes where agricultural pressure is receding. Brazil has inscribed in its national forest restoration plan a goal of twelve million hectares restored by 2030, with a significant portion through natural regeneration.

In Central Africa, satellite mapping initiatives of secondary forests in the Congo Basin are enabling Congolese and Cameroonian governments to identify zones with high regeneration potential and target protections where the ecological return on investment is fastest.

These experiences are not without difficulties. Costa Rica benefited from political stability and rule of law lacking in most tropical forest countries. Brazilian programs face land disputes and variable application of forest laws across states. The question of international financing remains central: tropical countries have little reason to protect secondary forests without compensation mechanisms that make this protection economically viable for local communities.

What this result does not resolve

The Metz study brings good news, and it must be stated clearly. But it does not resolve the fundamental questions that structure the tropical biodiversity crisis.

Primary deforestation continues. In 2023, the area of tropical primary forests lost worldwide reached nearly 3.7 million hectares, according to the World Resources Institute. Secondary forest regeneration can offset part of these losses, but it cannot compensate for the irreversible destruction of primary forests, which harbor species that no secondary forest will be able to shelter for centuries.

Financing for forest restoration remains structurally insufficient. Approximately 5.2 to 5.6 billion dollars have been committed to multilateral REDD+ funds since 2008 — an amount well below the 10 billion sometimes mentioned, the latter figure likely mixing several financing sources with different scopes. The needs to achieve the Kunming-Montreal objectives are of a wholly different order of magnitude: the agreement itself, based notably on the Financing Nature report (Paulson Institute et al., 2020), estimates the biodiversity financing gap at approximately 700 billion dollars per year by 2030 — an order of magnitude gap with the funds currently mobilized. The Metz study does not bridge this gap, but it can contribute to reducing it by making restoration less costly where natural regeneration is possible.

Finally, the communities that live in and around tropical forests are not neutral actors in their regeneration. They are often the first dependent on them. Protection policies that exclude local populations from using these forests regularly fail. Programs that involve communities in monitoring, that guarantee them land rights and alternative revenues, succeed better in the long term. This social condition of forest regeneration is as real as the biological condition.

Secondary forest has a poor reputation. It suffers from an image deficit compared to old-growth forest, just as artificial wetlands or reconquered grasslands do. Yet at the scale of decisions that will be made in the coming years on land use in tropical countries, this ordinary forest regrowing after cutting may be the most accessible lever.

The real question posed by the Metz study is not scientific. It is political: will international financing mechanisms for climate and biodiversity adapt quickly enough to value natural regeneration equally with tree planting or primary forest protection? And will forest states seize this tool, which demands less political confrontation, but still requires state capacity that many struggle to deploy in their most remote forest territories?

Sources

  1. Agence Science-Presse, “Les forêts tropicales récupèrent plus vite que prévu”, April 2026 — https://www.sciencepresse.qc.ca/actualites-scientifiques/2026/04/20/forets-tropicales-recuperent-plus-vite-prevu
  2. Global Forest Watch / World Resources Institute — data on tropical primary deforestation 2023 (no URL, data available on globalforestwatch.org)
  3. Kunming-Montreal Agreement, COP15 Biodiversity, December 2022 — Convention on Biological Diversity (CBD)
  4. Glasgow Declaration on Forests and Land Use, COP26, November 2021
  5. World Bank — report on REDD+ financing 2009-2023 (Forest Carbon Partnership Facility)
  6. IPBES — Global Framework for Biodiversity, estimates of financing needs for restoration
  7. Metz et al. 2026 study – Nature (primary source) — https://www.nature.com/articles/s41586-026-10365-2
  8. University of Würzburg – official press release on the study — https://www.uni-wuerzburg.de/en/news-and-events/news/detail/news/resilience-rainforest/
  9. WRI – Global Forest Review 2023 (primary forest loss) — https://gfr.wri.org/global-tree-cover-loss-data-2023
  10. CBD – Final text Kunming-Montreal 2022 — https://www.cbd.int/article/cop15-final-text-kunming-montreal-gbf-221222
  11. Mongabay / ButlerNature – analysis of Glasgow Declaration signatories — https://www.butlernature.com/2021/11/05/what-countries-are-leaders-in-reducing-deforestation-which-are-not/
  12. Carbon Balance and Management (2023) – REDD+ financing — https://cbmjournal.biomedcentral.com/articles/10.1186/s13021-023-00228-y
  13. European Parliament – analysis of GBF Kunming-Montreal (2024) — https://www.europarl.europa.eu/RegData/etudes/IDAN/2024/754196/IPOL_IDA(2024)754196_EN.pdf
  14. Nature Climate Change – Busch et al. 2024 (natural regeneration vs. planting) — https://www.nature.com/articles/s41558-024-02068-1