Tropical forests have long been portrayed as a single, vast climate machine: warm, wet and extraordinarily productive. But a new analysis suggests that this image is dangerously incomplete. The world’s major tropical forest regions do not respond to climate change in the same way, and the factors controlling how much carbon their trees store can shift dramatically from one landscape to another. Using approximately 16 million spaceborne-LiDAR-derived estimates of aboveground biomass collected across intact lowland forests in the Amazon, the Congo Basin and Southeast Asia, researchers have produced one of the broadest snapshots yet of how climate, soils, terrain and storms shape tropical-forest carbon storage.
The study, published in Nature by M. H. Nunes, H. C. Muller-Landau, E. B. Görgens and colleagues, focuses on aboveground biomass, or AGB—the mass of trunks, branches, bark and leaves held above the soil. AGB is a critical component of the global carbon cycle because carbon absorbed from the atmosphere through photosynthesis is locked into woody tissue for years or decades. When forests grow, they can remove carbon dioxide from the atmosphere; when trees die, burn or decompose, much of that carbon can return. Measuring how AGB varies across climate gradients therefore provides an important clue to how tropical forests may influence future climate–carbon feedbacks.
For years, scientists have reported apparently conflicting relationships between tropical-forest biomass and climate. Some studies have linked greater biomass primarily to rainfall or water availability, while others have emphasized temperature. Still others have found that drought, rather than average climate conditions, is the most important factor. The new research argues that these disagreements may not necessarily reflect irreconcilable scientific results. Instead, they may arise because forests in different regions operate under different environmental constraints, or because studies have used different methods, spatial scales and measurements. By analysing the three largest tropical forest regions within a unified framework, the researchers sought to separate genuine geographical variation from methodological noise.
The analysis shows that temperature becomes increasingly important in drier forests. In forests where water is already limited, a rise in temperature can intensify atmospheric demand for moisture. Warmer air can hold more water vapour, increasing evaporative demand and forcing trees to lose more water through transpiration. If rainfall does not compensate, trees may close their stomata, reducing carbon dioxide uptake and photosynthesis. Prolonged heat and dryness can also increase hydraulic stress, impair growth and raise mortality risk. According to the study, these temperature-related associations are strongest in the Congo Basin, making its forests particularly sensitive to warming compared with the Amazon and Southeast Asia under similar environmental conditions.
The findings also reveal a different vulnerability in Southeast Asia. There, the strongest declines in aboveground biomass are associated with increasing water limitation. This does not mean that Southeast Asian forests are unaffected by heat, but it suggests that drought-related stress is a particularly powerful constraint on their carbon storage. The distinction matters because climate change does not alter temperature and rainfall independently. A forest may experience a modest change in annual precipitation but a major shift in the length or intensity of dry seasons. Such changes can reduce soil moisture, restrict tree growth and increase the probability that vulnerable trees die during drought episodes.
Rather than treating temperature and drought as separate, uniform influences, the researchers found that their effects intensify with aridity and are modified by local environmental conditions. Aridity describes the balance between atmospheric water demand and available precipitation, and it can reveal stress that rainfall totals alone may conceal. Two forests receiving similar annual rainfall may experience very different levels of biological water stress if one is hotter, has a longer dry season or loses water rapidly from shallow soils. The study indicates that climatic anomalies become more consequential as forests move toward drier conditions, highlighting why regional averages can obscure the mechanisms operating on the ground.
Soils and topography further complicate the picture. Soil properties influence how much water and nutrients remain available to trees, while slopes and elevated terrain affect drainage, rooting conditions and exposure to weather. A forest growing on deep, water-holding soil may tolerate a dry period better than one on a shallow or rapidly draining substrate. Topography can also create fine-scale differences in microclimate and disturbance exposure that are invisible in broad climate maps. By incorporating these environmental factors, the study presents tropical-forest biomass as the outcome of interacting pressures rather than a simple response to one dominant variable.
One of the most striking results appears in the tallest forests. In stands exceeding 70 metres, where carbon stocks can be exceptionally high, storms emerge as a strong negative driver of biomass. Lightning strikes and windthrow can kill or damage large trees, opening gaps in the canopy and releasing stored carbon through decomposition. The effect is especially important because tall trees contain a disproportionate share of a forest’s aboveground carbon. A single storm event can therefore produce a biomass loss far larger than its footprint might suggest. This result also demonstrates why climate-based models that omit disturbance may overestimate the stability of carbon-rich tropical forests.
The study’s broad message is both a warning and a guide for the future. There is no single tropical-forest response to climate change: the Congo Basin may be especially exposed to warming, Southeast Asia to increasing water limitation, and the tallest forests to storm damage, while local soils and terrain can amplify or soften these pressures. Spaceborne LiDAR makes it possible to observe forest structure over enormous areas, offering a powerful complement to ground plots and satellite optical imagery. Yet the researchers emphasize that present-day associations should be interpreted within their environmental context rather than treated as universal laws. Reliable projections of tropical carbon storage will require models that combine temperature, drought, aridity, disturbance, soil conditions and topography. As climate extremes become more frequent, understanding these interactions may determine whether the world’s forests continue to buffer atmospheric carbon—or begin to lose that capacity in different ways across different continents.
Subject of Research: Tropical-forest aboveground biomass and its relationships with climate, drought, storms, soils and topography.
Article Title: Heterogeneous climatic controls on tropical-forest biomass
Article References: Nunes, M.H., Muller-Landau, H.C., Görgens, E.B. et al. Heterogeneous climatic controls on tropical-forest biomass. Nature (2026). https://doi.org/10.1038/s41586-026-10880-2
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41586-026-10880-2
Keywords: tropical forests, aboveground biomass, climate change, carbon cycle, drought, warming, Congo Basin, Amazon, Southeast Asia, spaceborne LiDAR, storms, aridity, forest carbon, soils, topography
