Tiny patches of deforestation drive tropical carbon loss

The paper, published today in the journal Nature, delivers the most detailed reconstruction to date of how tropical forest carbon has changed owing to disturbances over the past three decades, and its findings are alarming.

Researchers from the Laboratory for Climate and Environmental Sciences (LSCE) in France, who are contributing to the European Space Agency’s Climate Change Initiative RECCAP-2 and Biomass projects, found that the smallest deforestation clearings, often less than two hectares in size, are responsible for more than half of total carbon losses across the Tropics.

The team used a high-resolution bookkeeping approach that combines sub-hectare satellite observations with novel biomass recovery curves, allowing them to map carbon losses and gains at a remarkably fine 30-metre scale.

The scientists identified disturbances in tropical humid forests caused nearly 16 billion tonnes of carbon loss between 1990 and 2020, while disturbances in tropical dry forests showed an overall balance between disturbance losses and gains.

But the real surprise lies in the disproportionate influence of small-scale clearings. These tiny patches of forest clearing only account for about 5% of the area disturbed, yet they drive 56% of net carbon losses.

Most of these small patches are not the result of dramatic clear-cutting or catastrophic fires, but rather the cumulative effect of modest human actions – expanding croplands, creating pasture, building roads and establishing settlements.

Unlike fire-driven carbon losses in many tropical dry forest regions, where gradual post-fire regrowth can partially restore lost carbon, humid forest landscapes altered by humans often fail to regrow, locking in long-term emissions.

The study also shows that disturbances are increasingly encroaching on denser, more carbon-rich humid forests, magnifying the climate impact of each hectare lost. This contrasts with dry forests where repeated fires are reducing per-event carbon losses as fuel loads diminish over time.

Despite these shifting pressures, undisturbed tropical forests continue to act as a net carbon sink, partially offsetting losses elsewhere – but only just enough to bring the overall tropical carbon balance close to neutral over the three-decade period.

For lead authors Yidi Xu and Philippe Ciais, from LSCE, the implications are clear, “Unlike previous global models that rely on simplified assumptions or continental averages, our approach captured how disturbance type, size, and local climate conditions shape forest recovery, thanks to new high-resolution maps of biomass from ESA.

“This allowed us to discover that small-scale human activities, not just large clear-cutting or wildfires, are quietly driving the majority of tropical carbon losses.”

The findings carry significant weight for climate policy. In regions such as Africa, where small-scale disturbances dominate, the study suggests that curbing incremental agricultural expansion could lead to greater impact than previously recognised.

It also highlights the need to safeguard regenerating forests, which lose much of their capacity to store carbon when subjected to repeated disturbances, and to strengthen monitoring along forest edges where the most carbon-dense ecosystems now face increasing threat.

Beyond identifying risks, the study offers a powerful new tool for governments and conservation planners. Its high-resolution reconstruction can improve national carbon inventories, support REDD+ initiatives, and guide targeted interventions by pinpointing where carbon losses are occurring – and where forests are successfully regrowing.

ESA’s Head of Actionable Climate Information Section, Clement Albergel, said, “As tropical forests face increasingly frequent hazards from climate change, fires and human encroachment, this study underscores a vital truth: even the smallest clearings matter.

“Long-term observation records are vital for identifying, understanding and tracking global to local environmental change. Through ESA’s maps of biomass, we’re gaining an unprecedented view of how these ecosystems lose and regain carbon – knowledge that is crucial for protecting them while there is still time.”