The Cerrado biome, spanning ~2 million km2, is one of the most extensive and biodiverse tropical savannas, yet it is paradoxically dominated by only 30 hyperdominant tree species (~2% of all species, > 50% of all stems). However, their vulnerability to climate change and the effectiveness of current conservation efforts remain uncertain. By combining (i) species distribution models calibrated with edaphic-climatic predictors and occurrence data for hyperdominant Cerrado trees with (ii) functional-trait analyses related to ecological strategies (leaf economics, bark investment, ecophysiology, drought tolerance, regeneration, and dispersal), we identified the biomass production and reproductive traits that best predict species persistence under high-emission scenarios (RCP8.5). Currently, only 427,980 km2 (~17.4%) of the modeled potential environmental suitability falls within protected areas; under future climate scenarios, this protected suitable area is projected to decline by ~45.9% to 231,377 km2 (~18.1%). This loss, resulting from land conversion with the expansion of agricultural frontiers and fire events, highlights a mismatch in current regional conservation priorities, overlooking the needs of the Cerrado and its associated biodiversity. Given ongoing land-use change and that 58% of remaining native vegetation occurs on private lands, this mismatch highlights the urgent need to align conservation and agricultural policy. Functional trait analyses revealed a clear gradient from acquisitive "fast" to conservative "slow" strategies, reflecting trade-offs in water-use efficiency and biomass allocation, with leaf structural and reproductive traits best predicting species resilience to climate change. Our results indicate that a small subset of hyperdominant species not only forms current community structure but also signals the biome's resilience/vulnerability to climate change. Conservation planning should prioritize identified climate refuges and be based on functional traits to buffer the loss of functional and structural integrity in one of the world's richest and most threatened savanna ecosystems.

Accurate characterization of the role of the dry tropics in the global carbon cycle requires precise estimation of woody biomass changes due to ecological and anthropogenic change, including deforestation, forest degradation, regrowth, mortality and enhanced tree growth due to climate change. L-band Synthetic Aperture Radar (SAR) backscatter observations offer a reliable option to consistently map these processes as they are (i) available globally since 2007 (JAXA ALOS-1, ALOS-2 and ALOS-4), and (ii) sensitive to woody structure, such as aboveground biomass density (AGBD) up to similar to 100 t ha(-1). However, we lack multi-site empirical understanding of the scattering processes that determine the relationship between L-band SAR and woody vegetation structure in the dry tropics, and how this is mediated by soil properties. This study used observations from ground plots in Africa (n = 171), Australia (n = 6), and South America (n = 44) to understand the impact of vegetation structure and soil properties on spatially and temporally coincident fully-polarimetric L-band SAR data. Fully-polarimetric L-band SAR single-look complex data were converted to scattering mechanisms/parameters using van Zyl, Cloude-Pottier, and Freeman-Durden polarimetric decompositions to elucidate the physical mechanisms involved. Multivariate SAR-vegetation-soil relationships were analysed using a theory-informed structural equation modelling approach. The strongest positive effects on volume scattering come from stem density (stems ha(-1)) and mean stem biomass of trees, and soil water and sand content (standardized regression coefficients of 0.3, 0.1, 0.2 and 0.1, respectively). The only significant effect on surface scattering is from stem density (0.1). Significant effects on double bounce scattering are from stem density (0.3) and soil sand content (-0.2). Since AGBD is the product of stem density and mean stem biomass, this modelling framework points to a stronger effect from the number of trees rather than their size/biomass. Therefore, AGBD maps relying solely on radar intensity may not reflect significant changes when AGBD is increasing due to the growth of existing stems. Additionally, such maps might overestimate changes in AGBD when driven by the recruitment of new stems or loss of existing stems. Full-polarimetric observations allow the decomposition of the radar signal into volume scattering, surface scattering, and double bounce, enabling the inversion of structural equation models to retrieve both stem density and mean stem biomass. This provides a more comprehensive description of forest structure compared to retrieving only AGBD. As this approach depends on full-polarimetric data, its effectiveness is closely tied to the availability of such observations. Our findings underscore the value of recent and upcoming missions such as ALOS-4 PALSAR-3, BIOMASS and ROSE-L, and highlight the need to prioritise the acquisition of quad-pol SAR data to support future large-scale retrieval of vegetation structure attributes.

ABSTRACT Aim We investigate the distribution of dispersal modes — endozoochory (via animal ingestion), synzoochory (via animal seed accumulation) and anemochory (via wind)—and seed mass of woody plants across Brazilian ecosystems, testing whether their relative abundance in local plant communities could be predicted by climate, edaphic factors and dispersal agents (e.g., the main vectors moving seeds). We expected climate to be the main predictor of dispersal strategy abundance. Location Brazilian ecosystems (Amazon, Atlantic Forest, Cerrado and Caatinga). Time Period 2004–2020. Major Taxa Studied Woody angiosperms, trees and shrubs. Methods We assigned seed mass to 1984 species and dispersal mode to 2203 species within 300 old‐growth and non‐flooded plots. We employed Random Forest regressions to assess the influence of water availability, temperature seasonality, soil fertility, wind and frugivorous primates on the community‐weighted means of seed mass and dispersal modes. We mapped predictions and estimated the area of applicability to identify regions where predictions were reliable. Results Climate was the main factor predicting tree dispersal strategies, followed by dispersal agents or soil properties. Endozoochory was prevalent in wetter regions with high water availability and greater diurnal temperature range. Anemochory was more common in drier regions with low water availability, stronger winds and greater diurnal temperature range, whereas synzoochory was more abundant in areas with low temperature seasonality. Heavier seeds were more prevalent in regions with less seasonal temperatures, smaller diurnal temperature ranges and weaker winds. Main Conclusions Climate is a key predictor of the distribution and prevalence of plants with contrasting dispersal modes and seed masses. We thus expect functional responses to environmental change associated with shifts in the relative abundance of dispersal strategies, with implications for ecosystem services. Our results also highlight the critical role of plot‐based datasets in improving our understanding of how environmental factors influence seed dispersal strategies across tropical ecosystems.

Tropical peatland wildfire incidence has risen in recent decades, driven by drainage for land use and intensified by severe droughts with global climate change. These disturbances have altered vegetation structure, disrupted ecosystem functioning, and increased carbon emissions, particularly in Southeast Asia. However, the long-term history and characteristics of wildfires in tropical peatlands remain largely unknown. Here, we compiled fifty-eight macro-charcoal records from peatlands across the tropics, ranging from lowland forested to montane peatlands, to assess millennia-scale changes and controlling factors of tropical peatland burning. We divided the datasets into four main sub-regions: Neotropical, Afrotropical, Indomalayan and Australasian ecoregions to explore regional variability. Tropical peatlands had high burning levels between 0 and 850 ce, followed by a relatively low and stable period until a marked increase during the 20th century. The general trend in tropical peatland burning follows changes in global temperature, and climate variables that control the length and severity of drought events have a notable influence on peat burning before 1900 ce. During the 20th century, regional differences were observed, with declining fire trends in the Neotropical and Afrotropical regions and increasing fire trends in the Indomalayan and Australasian regions. This difference is likely attributable to human activities, and such intervention is also evident in palm swamps and hardwood swamps under similar wet, weakly seasonal climates. With the increase in anthropogenic pressures on peatlands and greater climate variability, future wildfires in peatlands are likely to become more frequent and widespread across all tropical ecoregions. Conservation and sustainable land-use practices could be used to mitigate and control peatland burning and protect these carbon-rich sinks.

Old-growth tropical forests store vast amounts of carbon in their aboveground biomass (AGB), yet the relative roles of abiotic factors such as climate, soil, and topography in governing its spatial distribution remain poorly understood. In particular, the degree to which climate acts on AGB through forest structure is still poorly quantified at the pantropical scale. Using a pantropical dataset of more than 2,000 old-growth forest plots and a structure-explicit framework, we assess how climate influences AGB through its effects on four structural attributes: basal area, mean diameter, stem density, and basal area-weighted wood density. We find that climate shapes AGB primarily through its effects on forest structure. However, structural attributes respond to climate in opposite directions, so climate’s net effect on AGB largely cancels out, and no clear climate-AGB relationship emerges across tropical regions. Moreover, only wood density responds consistently, decreasing with annual precipitation and increasing with precipitation seasonality, whereas all other attributes respond to climate differently from one region to another. This geographical variation further obscures any global climatic signal on AGB and points to the role of biogeographic history in shaping forest structure. Our findings highlight the central role of the climate-structure nexus in explaining AGB variation, and call for structure-explicit models to improve carbon stock predictions and inform climate adaptation strategies.

Amazon rainforests face intensifying water stress due to increases in vapour pressure deficit and changing hydrological regimes. Embolism resistance (Ψ50) is a critical metric of tree survival under drought conditions, it is defined as a plant's capacity to resist disruption of xylem water flow due to air bubble formation from water stress. However, measurements of Ψ50 are only available for a limited number of Amazon locations and species. Conversely, data on forest taxonomic composition are abundant across Amazonia, and if Ψ50 is conserved phylogenetically, these data could provide a way to scale-up drought resistance patterns. Here we evaluate Ψ50 measurements across non-flooded Amazonian tree taxa and reveal a moderate phylogenetic signal, with phylogenetic conservatism evident at the family-level. Notably, Fabaceae is amongst the most embolism-resistant tree families in Amazonia. Leveraging the phylogenetic signal we use species composition and tree size data from 448 forest plots across Amazonia to produce a macroecological assessment of Amazonian vulnerability to embolism. The resulting estimate spatial pattern reveals that forests in the Brazilian and Guiana Shield regions, where Fabaceae abundance is high, show strong resistance to embolism. In contrast, tree communities in Western Amazonia appear more vulnerable to embolism, suggesting a reduced capacity to withstand future drought conditions.

Understanding the resilience of tropical vegetation, its ability to recover from disturbance, is fundamental to assess future responses to environmental and climatic fluctuations. The Amazon rainforest has been identified as a potential tipping element in the Earth’s climate system and there is mounting concern over its persistent degradation. Extreme climate events and continued logging, forest fire and fragmentation threaten the Amazon’s structural integrity and its role as a carbon sink, with remotely sensed data providing observational evidence of resilience loss since the early 2000s. Fragmentation and degradation of tropical forest is suggested to slow recovery from perturbations, ensuing a potential to destabilise the rainforest and cause widespread transition from forest to savanna-like ecosystem state.Remotely sensed LiDAR data provides a structural blueprint of forest canopy. The Global Ecosystem Dynamics Investigation (GEDI) spaceborne LiDAR characterises a new era of large-scale forest height quantification, with capabilities to further understand forest structure, and therefore forest response to perturbation across the entire Amazon. Although GEDI’s capabilities have been realised in boreal forest early disturbance monitoring, and to assess growth rates of tropical secondary forest, research thus far is yet to assess its ability to identify tropical forest of various degradation and recovery including logged, burned and fragmented over increasing timescales of recovery. Forest degraded by burning is characterised by different structure than selectively logged, or edge forest, and validating the ability of GEDI to represent these states is essential for identifying alternative forest states. Here, we investigate the potential of the GEDI LiDAR mission to map tropical forest along a gradient of degradation to recovery. A combination of ground data, MapBiomas secondary forest and burned area products are utilised to classify perturbed forest. We then assess the correspondence of GEDI waveform metrics including relative height and canopy cover, extracted from 2A and 2B products using the newly developed R package ‘chewie’, with airborne LiDAR across the Brazilian Amazon. This research will inform further tropical forest alternative-state study, whilst the assessment of GEDI’s structural capability to represent degraded forest types provides valuable information for forest restoration status to support post-degradation management strategies.

Wood density is a critical control on tree biomass, so poor understanding of its spatial variation can lead to large and systematic errors in forest biomass estimates and carbon maps. The need to understand how and why wood density varies is especially critical in tropical America where forests have exceptional species diversity and spatial turnover in composition. As tree identity and forest composition are challenging to estimate remotely, ground surveys are essential to know the wood density of trees, whether measured directly or inferred from their identity. Here, we assemble an extensive dataset of variation in wood density across the most forested and tree-diverse continent, examine how it relates to spatial and environmental variables, and use these relationships to predict spatial variation in wood density over tropical and sub-tropical South America. Our analysis refines previously identified east-west Amazon gradients in wood density, improves them by revealing fine-scale variation, and extends predictions into Andean, dry, and Atlantic forests. The results halve biomass prediction errors compared to a naïve scenario with no knowledge of spatial variation in wood density. Our findings will help improve remote sensing-based estimates of aboveground biomass carbon stocks across tropical South America.

Understanding the drivers of soil organic carbon (SOC) and soil pyrogenic carbon (PyC) variation and their role in natural and managed ecosystems is increasingly important. However, PyC stocks in tropical Andean soils remain understudied. Here, we examined how edaphic and environmental factors affect PyC across elevation and disturbance gradients in 36 plots spanning natural forests and agrosilvopastoral systems in the Colombian Andes. Across the 0-100 cm soil profile, the mean SOC stock in the study region was 433.10 Mg C ha-1 (range: 67.97-1462 Mg C ha-1), while the mean PyC stock was 34.13 Mg C ha-1 (range: 2.29-305.70 Mg C ha-1), accounting for approximately ~8% of the total SOC. This PyC stock is approximately nine times greater than the Amazon-wide average. PyC (%) did not vary significantly with disturbance gradients or soil depths. However, both PyC (%) and SOC (%) varied significantly with elevation zonation (p < 0.001). The High Andes had the highest concentrations of PyC (1.3%) and SOC (14.6%), which were substantially higher than the Medium Andes (PyC = 0.17%; SOC = 6.7%) and Low Andes (PyC = 0.06%; SOC = 1.3%). Soil clay content and annual precipitation were the primary drivers of PyC, explaining 56% of the variability when combined with pH, Ca, and NDVI. PyC was positively associated with clay content (Estimate: 0.27, p < 0.001) and negatively associated with annual precipitation (Estimate: -0.18, p < 0.05). These factors may influence the physical and chemical processes that affect PyC formation and preservation in soils. This analysis provides insight into SOC and PyC variability in Andean forest soils, highlighting the substantial contribution of soil PyC to total soil carbon and its importance as persistent soil carbon under current and predicted warming conditions across the region.

The South American Cerrado, the largest savanna of the Americas and the world's most tree-biodiverse, is critically endangered, with just 8% protected and more than half deforested. However, the extent of its tree diversity and abundance remains poorly quantified. Using a unique biome-wide eco-floristic dataset with 222 one-hectare plots, we estimate the Cerrado has ~1605 tree species and has extreme hyperdominance, with fewer than 2% (30 species) accounting for half of all trees. A single family, Vochysiaceae, represents 17% of all trees, and the most abundant species, Qualea parviflora, accounts for 1 in 14 trees. In contrast, 63% of the species are rare, with fewer than 100 trees across all plots. Remote sensing and spatial modelling suggest the Cerrado has lost 24 billion trees since 1985, equivalent to three times the Earth's human population. We estimate up to 800 tree species may remain undetected in Cerrado ecosystems and could face extinction in a few decades due to deforestation. This hyperdominance parallels patterns in Amazonian forests and highlights risks both biomes face for species loss due to fragmentation, deforestation, and land-use change. Our findings highlight the Cerrado's critical but undervalued role in global biodiversity, its vulnerabilities, and the urgent need for conservation to avoid irreversible species and biome loss.

Amazonia’s exceptional biodiversity, cultural significance, and ecosystem services make it pivotal to global and regional sustainability. However, the region is increasingly threatened by climate extremes, which exacerbate the effects of land use change (Barlow et al., 2018) and bring about abrupt changes in social and ecological condition (Bennett et al., 2023; Berenguer et al., 2021; Campanharo et al., 2022; Lapola et al., 2023; Libonati et al., 2022; Lima et al., 2024; Machado-Silva et al., 2020; Tadano et al., 2024). Yet, while climate extremes are increasing in many parts of the world (Huntingford et al., 2024), we lack a high-resolution Amazon-wide assessment that compares if they differ from climate averages or identifies spatial hotspots where rates of change are highest. Here we address this by assessing Amazonia’s changing climate at high spatial resolution within seasons and across the year, considering both central trends (50th percentile) and trends of extremes (5th and 95th percentiles). Our analysis includes a new measure of water deficit that accounts for the effects of temperature on evapotranspiration. High temperature extremes and temperature-linked measures of water deficit are both changing at a much faster rate than central trends, and their rates of change are greatest in the driest period. While the central trend of mean temperature change across Amazonia (0.21°C per decade, dec-1) is comparable to the global average, the upper extreme of maximum temperatures in the driest period increased by 0.50°C dec-1. These Amazon-wide trends also mask considerable spatial variation. Crucially, we identify a new region of high climate risk in central-north Amazonia, where over 700,000 square kilometres have experienced increases in extreme dry season temperatures of at least 0.77 °C dec-1 (i.e., ≥3.31 ºC over 43 years). Adaptation measures are urgently required to address the impacts of these rapid changes in climate extremes, including preventing the key stressors of deforestation, forest fires and other disturbances that amplify climate risks.

AbstractSecondary forests in the Amazon are important carbon sinks, biodiversity reservoirs, and connections between forest fragments. However, their regrowth is highly threatened by fire. Using airborne laser scanning (ALS), surveyed between 2016 and 2018, we analyzed canopy metrics in burned (fires occurred between 2001 and 2018) and unburned secondary forests across different successional stages and their ability to recover after fire. We assessed maximum and mean canopy height, openness at 5 and 10 m, canopy roughness, leaf area index (LAI) and leaf area height volume (LAHV) for 20 sites across South‐East Amazonia (ranging from 375 to 1200 ha). Compared to unburned forests, burned forests had reductions in canopy height, LAI, and LAHV, and increases in openness and roughness. These effects were more pronounced in early successional (ES) than later successional (LS) stages, for example, mean canopy height decreased 33% in ES and 14% in LS and LAI decreased 36% in ES and 18% in LS. Forests in ES stages were less resistant to fire, but more resilient (capable of recovering from a disturbance) in their post‐fire regrowth than LS stage forests. Data extrapolation from our models suggests that canopy structure partially recovers with time since fire for six out of seven canopy metrics; however, LAI and LAHV in LS forests may never fully recover. Our results indicate that successional stage‐specific management and policies that mitigate against fire in early secondary forests should be implemented to increase the success of forest regeneration. Mitigation of fires is critical if secondary forests are to continue to provide their wide array of ecological services.

Understanding how the traits of lineages are related to diversification is key for elucidating the origin of variation in species richness. Here, we test whether traits are related to species richness among lineages of trees from all major biogeographical settings of the lowland wet tropics. We explore whether variation in mortality rate, breeding system and maximum diameter are related to species richness, either directly or via associations with range size, among 463 genera that contain wet tropical forest trees. For Amazonian genera, we also explore whether traits are related to species richness via variation among genera in mean species-level range size. Lineages with higher mortality rates—faster life-history strategies—have larger ranges in all biogeographic settings and have higher mean species-level range sizes in Amazonia. These lineages also have smaller maximum diameters and, in the Americas, contain dioecious species. In turn, lineages with greater overall range size have higher species richness. Our results show that fast life-history strategies influence species richness in all biogeographic settings because lineages with these ecological strategies have greater range sizes. These links suggest that dispersal has been a key process in the evolution of the tropical forest flora.

Amazonian peatlands are carbon-rich ecosystems that act as long-term carbon sinks but have faced increasing fire risks in recent decades. As a legacy of past fires, the contribution of pyrogenic carbon (PyC) to carbon cycling in these peatlands remains poorly understood. Here, we assess PyC accumulation variability using six cores spanning peatlands in northwestern Amazonia using hydrogen pyrolysis. We also estimate the PyC stock for the entire Amazonian peatlands by combining our field dataset with published sources. The PyC to total organic carbon ratio averaged 1.2% across our sites and increased with peat age. We estimate a total peatland PyC stock of 0.73 ± 0.61 Pg for the Amazon Basin, representing 1.6% of their TOC stock. Due to the slower turnover of PyC in peatland ecosystems, our findings indicate the importance of PyC generated by past fires and highlight the potential long-term carbon sequestration role of PyC in the future carbon cycle.

Aim: This study investigated how human activities and local environmental variables shape tree assemblages (species composition in a defined location), comparing their effects on edible and inedible tree species. Three hypotheses were tested: (1) Environmental filtering impacts spatial beta-diversity more than dispersal limitation; (2) human activities significantly influence regional tree beta-diversity; and (3) predictors of beta-diversity differ between edible and inedible species. Location: Tropical forest in Nigeria and Cameroon in West and Central Africa. Methods: Tree data were collected between 2002 and 2019 from 66 forest plots. Species were categorised as edible and inedible by humans using interviews and online databases. Pairwise beta-diversity (partitioned into total beta-diversity and turnover) between plots was analysed using Generalised Dissimilarity Models (GDMs) with geographical distance, plot-specific variables (forest composition, climate, elevation, stem density, human influence indicators), and human influence indicators (distance to closest human presence [DCHP], and nearest anthropogenic edges [DNAE]) as predictors. Results: The dataset included 236 edible species (11,097 stems) and 472 inedible species (17,202 stems), with high species turnover (> 90%) dominating beta-diversity patterns. Due to local plot-level factors, environmental filtering (deviance explained for all species: 37.4%, edible: 18.9% and inedible: 31.4%) exerted greater influence on species assemblages than geographical distance alone. Beta-diversity drivers differed between edible and inedible species: elevation strongly influenced turnover in inedible species, whereas forest composition significantly shaped the assemblage of edible species, reflecting patterns of human-mediated species selection and species dominance. Human presence impacted the overall beta-diversity of inedible species but only influenced the turnover component of edible species. Main Conclusions: Tree assemblages in the Nigeria-Cameroon forest region were primarily structured by local environmental conditions and human activities rather than by dispersal limitation. Effective conservation should incorporate sustainable human activities and traditional ecological knowledge, with further research needed to explore the long-term anthropogenic impacts on these forests.

Plants cope with the environment by displaying large phenotypic variation. Two spectra of global plant form and function have been identified: a size spectrum from small to tall species with increasing stem tissue density, leaf size, and seed mass; a leaf economics spectrum reflecting slow to fast returns on investments in leaf nutrients and carbon. When species assemble to communities it is assumed that these spectra are filtered by the environment to produce community level functional composition. It is unknown what are the main drivers for community functional composition in a large area such as Amazonia. We use 13 functional traits, including wood density, seed mass, leaf characteristics, breeding system, nectar production, fruit type, and root characteristics of 812 tree genera (5211 species), and find that they describe two main axes found at the global scale. At community level, the first axis captures not only the 'fast-slow spectrum', but also most size-related traits. Climate and disturbance explain a minor part of this variance compared to soil fertility. Forests on poor soils differ largely in terms of trait values from those on rich soils. Trait composition and soil fertility exert a strong influence on forest functioning: biomass and relative biomass production.

The Arc of Deforestation, a Cerrado-Amazon transition region, faces large-scale agricultural expansion and land degradation, fostering fire spread and recurrence, particularly during extreme droughts driven by climate change. While previous research has focused on aboveground changes, the impacts of fires on soil functions, such as carbon (C) storage and nutrient cycling, remain understudied. This study investigated how forest-to-agriculture conversion and fire frequency in standing forests affect soil C and nitrogen (N) in the Arc of Deforestation. We also examined the effects of these disturbances on stable isotopes (delta C-13 and delta N-15) and how the changes in Soil Organic Matter (SOM) influence other soil health indicators. Four treatments were considered: (i) annual forest burns; (ii) forest burning every 3 years; (iii) undisturbed forest; and (iv) long-term agriculture. Annual burns depleted soil C stocks (0-30 cm) by 16 %, triennial burns by 19 %, and long-term agriculture by 38 %, compared to the undisturbed forest. Annual and triennial burns reduced aboveground C stocks by 40 % and 60 %, respectively, showing that fire impacts on soil and vegetation differed. In burned forests, delta C-13 indicated no grass invasion, remaining below -27 parts per thousand and rising slightly (similar to 2 parts per thousand) with depth. In agricultural areas, the delta C-13 was uniform (-24 parts per thousand) due to C-4 plants' influence and soil mixing from tillage. The relationships between soil C and health indicators suggested that SOM depletion from fire and agriculture disrupted soil structure and negatively affected nutrient cycling. Our findings revealed long-lasting fire legacies in tropical forest soils, with SOM loss and harmful effects on soil health persisting nearly a decade after the fire, but no evident effect of fire frequency was found. Soil degradation was less severe when the forest was repeatedly burned than when converted to agriculture. Conservation and management practices prioritizing forest protection, wildfire prevention, and halting agricultural expansion are needed to preserve soil health in the Amazon.

Trees can differ enormously in their crown architectural traits, such as the scaling relationships between tree height, crown width and stem diameter. Yet despite the importance of crown architecture in shaping the structure and function of terrestrial ecosystems, we lack a complete picture of what drives this incredible diversity in crown shapes. Using data from 374,888 globally distributed trees, we explore how climate, disturbance, competition, functional traits, and evolutionary history constrain the height and crown width scaling relationships of 1914 tree species. We find that variation in height-diameter scaling relationships is primarily controlled by water availability and light competition. Conversely, crown width is predominantly shaped by exposure to wind and fire, while also covarying with functional traits related to mechanical stability and photosynthesis. Additionally, we identify several plant lineages with highly distinctive stem and crown forms, such as the exceedingly slender dipterocarps of Southeast Asia, or the extremely wide crowns of legume trees in African savannas. Our study charts the global spectrum of tree crown architecture and pinpoints the processes that shape the 3D structure of woody ecosystems.

Climate change and increasing availability of resources such as carbon dioxide are modifying forest functioning worldwide, but the effects of these changes on forest structure are unclear. As additional resources become available, for example, through CO2 fertilization or nitrogen deposition, large trees, with greater access to light, may be expected to gain further advantages. Conversely, smaller light-suppressed trees might benefit more if their light compensation point changes, while bigger trees may be the most negatively impacted by increasing heat and drought. We assessed recent changes in the structure of Earth's largest tropical forest by analysing 30 years of Amazonian tree records across 188 mature forest plots. We find that, at a stand level, trees have become larger over time, with mean tree basal area increasing by 3.3% per decade (95% CI 2.4; 4.1). Larger trees have increased in both number and size, yet we observed similar rates of relative size gain in large and small trees. This evidence is consistent with a resource-driven boost for larger trees but also a reduction in suppression among smaller trees. These results, especially the persistence and consistency of tree size increases across Amazonian forest plots, communities and regions, indicate that any negative impacts of climate change on forests and large trees here have so far been mitigated by the positive effects of increased resources.