Summary

Tropical forests hold nearly half of Earth’s above-ground forest carbon, yet they are increasingly threatened by human-driven disturbances as change in land-use, and climate-intensified fires and storms. A new study recently published in Nature involving researchers from the GFZ Helmholtz Centre for Geosciences provides the most spatially detailed picture to date of how tropical forest carbon has changed over the past 30 years. It reveals that the smallest deforestation clearings, often less than two hectares, are responsible for more than half of total carbon losses. 

Background: Forest loss and carbon balance in the tropics

Tropical forests are crucial to the global carbon cycle, as they store around 50 % of the world's above-ground forest carbon (AGC). According to Landsat observations, 46 % of tropical wet and dry forests have been affected by at least one disturbance in the last 30 years, such as deforestation due to agricultural expansion or degradation due to fires or storms, which are intensifying as a result of climate change.

Over time, such disturbed forests can recover and gradually restore their carbon stocks and ecological functions. However, little is known about how recovery rates depend on the size, type and location of the disturbance. Such an assessment is essential to understand the impact of forests on the global carbon budget.

CO2 mapping of all tropical forests between 1990 and 2020

An international research team mapped the patterns of carbon loss and carbon recovery for all tropical forests from 1990 to 2020. They used a high-resolution bookkeeping approach that integrates sub-hectare Earth observation data with innovative, spatially explicit biomass recovery curves. The high-resolution data were collected by the European Space Agency’s Climate Change Initiative RECCAP-2 and Biomass projects. The study was co-led by scientists around first author Dr Yidi Xu at the Laboratoire des Sciences du Climat et de l’Environnement (LSCE) in France supported by CEA, CNRS and UVSQ. 

Building on bookkeeping methods developed by Viola Heinrich at GFZ and published in Nature in 2023, Dr Viola Heinrich and Dr Simon Besnard, both scientists in GFZ Section 1.4 Remote Sensing and Geoinformatics, helped refining the approach to construct disturbance-specific recovery curves within each 1°×1° grid cell across the tropics. 

Key findings

• Tropical humid forests lost 15.6 ± 3.7 billion tons of carbon over the past three decades, while tropical dry forests remained roughly carbon-neutral.
• Small clearings (<2 ha) represent only 5% of disturbed forest area but account for 56% of net carbon losses, primarily due to persistent land-use conversion to croplands, pastures, roads, or settlements.
• Fire-driven carbon losses in many dry tropical forest regions are partly balanced by long-term post-fire recovery, unlike the persistent impacts of small-scale deforestation and non-fire degradation.
• Disturbances have progressively shifted into denser, more carbon-rich humid forests, amplifying the climate impact of each hectare lost.
• By contrast, repeated fires in dry forests have gradually reduced per-event losses due to declining fuel loads.
• Undisturbed tropical forests remain a net carbon sink, partially compensating for losses in disturbed areas.The overall tropical AGC balance from 1990–2020 is close to neutral.

A new window on tropical forest carbon

The study represents the first spatially explicit 30-meter resolution reconstruction of carbon losses and gains across all tropical forests. “Unlike previous global models built on simplified assumptions or continental averages, this approach captures forest recovery where disturbances actually occur. Using high-resolution ESA biomass maps and a pseudo biomass carbon accounting model, we derive disturbance-specific recovery curves within each 1° × 1° grid cell across the tropics. This allows recovery to vary realistically with disturbance type, size, forest region, and local climate, revealing fundamentally different post-disturbance carbon dynamics that global averages would otherwise hide,” explains co-author Dr Simon Besnard, researcher at the GFZ.

“This work revealed that small-scale human activities — not just large clear-cutting or wildfire — are quietly driving the majority of tropical carbon losses,” said Yidi Xu, a postdoctoral researcher at the LSCE research team who is the first author of the study.

“Protecting young and recovering forests is just as essential as preventing new Deforestation,” explained Philippe Ciais at LSCE, who co-led the study.

Implications for climate policy

According to the research team, the findings highlight urgent priorities for climate mitigation:

• Reducing small-scale agricultural expansion and degradation, especially across Africa, where such disturbances account for over 97% of net carbon losses.
• Protecting young, recovering forests, whose carbon sequestration potential is sharply reduced by repeated disturbances.
• Strengthening monitoring of forest edges and encroachment fronts where carbon-dense forests are increasingly exposed.

The team emphasizes that the method can support national carbon inventories, the implementation of the REDD+ programme for “Reducing Emissions from Deforestation and Forest Degradation“, and targeted conservation planning. By revealing where carbon losses occur—and where forests are successfully regrowing—the study provides a powerful tool for safeguarding one of Earth’s most important climate buffers.

(Text based on material from the press release from the Laboratoire des Sciences du Climat et de l’Environnement (LSCE).)

Original publication

Xu, Y., Ciais, P., Santoro, M. et al. Small persistent humid forest clearings drive tropical forest biomass losses. Nature 649, 375–380 (2026). 
https://doi.org/10.1038/s41586-025-09870-7