Savanna–forest hysteresis in the tropics

A simple dynamic model relating forest area in a region, its contribution to dry season precipitation and the effect on its own establishment was developed. The model equation shows hysteresis between forest and savannas as a function of imported dry season precipitation. Regions are either dominated by forests or savannas, with each ecosystem showing stability despite changes in imported dry season precipitation. Deforestation beyond a certain threshold value, however, could cause a collapse of forest ecosystems and replacement by savannas in marginal areas. The predictions of this model corroborate pollen core analysis in the Amazon basin, where historical stability of tropical forest cover has been shown despite global climate change.     

Assessing the impacts of past and ongoing deforestation on rainfall patterns in South America

Despite recent advances in modeling forest–rainfall relationships, the current understanding of changes in observed rainfall patterns resulting from historical deforestation remains limited. To address this knowledge gap, we analyzed how 40 years of deforestation has altered rainfall patterns in South America as well as how current Amazonian forest cover sustains rainfall. First, we develop a spatiotemporal neural network model to simulate rainfall as a function of vegetation and climate inputs in South America; second, we assess the rainfall effects of observed deforestation in South America during the periods 1982–2020 and 2000–2020; third, we assess the potential rainfall changes in the Amazon biome under two deforestation scenarios. We find that, on average, cumulative deforestation in South America from 1982 to 2020 has reduced rainfall over the period 2016–2020 by 18% over deforested areas, and by 9% over non-deforested areas across South America. We also find that more recent deforestation, that is, from 2000 to 2020, has reduced rainfall over the period 2016–2020 by 10% over deforested areas and by 5% over non-deforested areas. Deforestation between 1982 and 2020 has led to a doubling in the area experiencing a minimum dry season of 4 months in the Amazon biome. Similarly, in the Cerrado region, there has been a corresponding doubling in the area with a minimum dry season of 7 months. These changes are compared to a hypothetical scenario where no deforestation occurred. Complete conversion of all Amazon forest land outside protected areas would reduce average annual rainfall in the Amazon by 36% and complete deforestation of all forest cover including protected areas would reduce average annual rainfall in the Amazon by 68%. Our findings emphasize the urgent need for effective conservation measures to safeguard both forest ecosystems and sustainable agricultural practices.     

Hunting pressure modulates the composition and size structure of terrestrial and arboreal vertebrates in Amazonian forests

Overhunting is a leading contemporary driver of tropical forest wildlife loss. The absence or extremely low densities of large-bodied vertebrates disrupts plant-animal mutualisms and consequently degrades key ecosystem services. Understanding patterns of defaunation is therefore crucial given that most tropical forests worldwide are now “half-empty”. Here we investigate changes in vertebrate community composition and size structure along a gradient of marked anthropogenic hunting pressure in the Médio Juruá region of western Brazilian Amazonia. Using a novel camera trapping grid design deployed both in the understorey and the forest canopy, we estimated the aggregate biomass of several functional groups of terrestrial and arboreal species at 28 sites along the hunting gradient. Generalized linear models (GLMs) identified hunting pressure as the most important driver of aggregate biomass for game, terrestrial, and arboreal species, as well as nocturnal rodents, frugivores, and granivores. Local hunting pressure affected vertebrate community structure as shown by both GLM and ordination analyses. The size structure of vertebrate fauna changed in heavily hunted areas due to population declines in large-bodied species and apparent compensatory increases in nocturnal rodents. Our study shows markedly altered vertebrate community structure even in remote but heavily settled areas of continuous primary forest. Depletion of frugivore and granivore populations, and concomitant density-compensation by seed predators, likely affect forest regeneration in persistently overhunted tropical forests. These findings contribute to a better understanding of how cascading effects induced by historical defaunation operate, informing wildlife management policy in tropical peri-urban, rural and wilderness areas.

     

Neotropical seasonally dry forests and Quaternary vegetation changes

Seasonally dry tropical forests have been largely ignored in discussions of vegetation changes during the Quaternary. We distinguish dry forests, which are essentially tree‐dominated ecosystems, from open savannas that have a xeromorphic fire‐tolerant, grass layer and grow on dystrophic, acid soils. Seasonally dry tropical forests grow on fertile soils, usually have a closed canopy, have woody floras dominated by the Leguminosae and Bignoniaceae and a sparse ground flora with few grasses. They occur in disjunct areas throughout the Neotropics. The Chaco forests of central South America experience regular annual frosts, and are considered a subtropical extension of temperate vegetation formations. At least 104 plant species from a wide range of families are each found in two or more of the isolated areas of seasonally dry tropical forest scattered across the Neotropics, and these repeated patterns of distribution suggest a more widespread expanse of this vegetation, presumably in drier and cooler periods of the Pleistocene. We propose a new vegetation model for some areas of the Ice‐Age Amazon: a type of seasonally dry tropical forest, with rain forest and montane taxa largely confined to gallery forest. This model is consistent with the distributions of contemporary seasonally dry tropical forest species in Amazonia and existing palynological data. The hypothesis of vicariance of a wider historical area of seasonally dry tropical forests could be tested using a cladistic biogeographic approach focusing on plant genera that have species showing high levels of endemicity in the different areas of these forests.     

A hawkmoth crossroads? Species richness,seasonality and biogeographical affinities of Sphingidae in a Brazilian Cerrado

Aim The aim of the study was (1) to describe the biodiversity of the sphingid assemblage in a Cerrado area in the Triângulo Mineiro region, south‐east of Brazil; (2) to evaluate the seasonal variations in species composition; (3) to compare the faunistic relationships between the Cerrado biome and adjacent ecosystems; and (4) to analyse the biogeographical pattern of species distribution in the Neotropical region in a historical context. Location Panga Ecological Station (PES), 30 km south of the city of Uberlândia, and other areas of the Triângulo Mineiro region, Minas Gerais state, south‐eastern Brazil. Methods Moth richness and abundance were monitored monthly at the PES from August 2003 to July 2004, with additional collections at this locality in 2001/2002, 2005 and 2006. Complementary moth richness and abundance data were also collected in other areas of the Triângulo Mineiro region. All collections were made using light traps, and the hawkmoths were mounted and identified. Cluster analysis, rarefaction curves and estimators of total species richness were used to compare the Cerrado hawkmoth assemblage with assemblages derived from other surveys in the Neotropics. Results In total, 61 hawkmoth species were recorded for the study region and their occurrence was markedly seasonal. The hawkmoth assemblage in the study area presented the closest similarity with rain forest areas and with a tropical dry forest area in Central America. The area shared species with both rain forest and seasonally dry tropical forest (SDTF) ecosystems, including supposedly endemic species previously recorded only in the latter areas. Rarefaction curves and estimators of the total number of species showed species richness to be comparable with other highly diverse forest areas in the Neotropics, such as the Brazilian Amazon and Costa Rica. Main conclusions This short‐term study is the first systematic survey of hawkmoths in the Cerrado. It has recorded around 22% of the South American fauna and highlighted the high species richness of the region, which compares favourably with that in other rain forest ecosystems. The survey indicates high regional diversity, and has shown that the Cerrado harbours a hawkmoth fauna comprising both rain forest elements, probably distributed along humid gallery forest corridors, and SDTF elements, supporting the idea of a historical Pleistocene arc connecting the Caatinga domain and other seasonal dry forest areas across the Cerrado region.     

The historical bridge between the Amazon and the Atlantic Forest of Brazil: a study of molecular phylogeography with small mammals

Abstract Aim To examine how the genetic diversity of selected taxa of forest‐dwelling small mammals is distributed between and within the major rain forest domains of Amazonia and Atlantic Forest and the intervening interior forests of Brazil, as inferred by the relationships between gene genealogies and geography. I also addressed the historical importance of the central Brazilian forests in connecting Amazon and Atlantic Forest populations of rodents and marsupials. Methods I evaluated variation in the mitochondrial cytochrome b gene to estimate the levels of sequence divergence between those taxa occurring throughout the Amazon, Atlantic Forest, and forests in the Cerrado and Caatinga regions. I inferred the hierarchical relationships between haplotypes, populations and formal taxa using the cladistic approach of maximum parsimony. I compared areas and the clades identified by superimposing cladograms on the geographical distribution of samples. The degree of concordance both in phylogeny and the depth of the nodes in these phylogenies, in addition to patterns of geographical distribution of clades, permitted me to make inferences on how, when and where the taxa differentiated. Results Sequence similarity is often greater between samples from the Atlantic Forest and either Amazon or central Brazilian forests than it is within each of the two rain forest domains. The Atlantic Forest clades are either not reciprocally monophyletic or are the sister group to all the other clades. There is some indication of northern and southern components in the Atlantic Forest. Given the geographical distribution of clades and the relatively deep levels of divergence, the central Brazilian area does not behave as a separate region but is complementary to either Amazon or Atlantic Forest. Patterns of area relationships differ across taxa, suggesting that different processes and/or historic events affected the diversification within each lineage. Main conclusions The Amazon and the Atlantic forests are not exclusive in terms of their small mammal faunas; both overlap broadly with taxa occurring in gallery forests and dry forests in central Brazil. Central Brazilian forests are an integral part of the evolutionary scenario of lowland small mammals, playing an important role as present and past habitats for rain forest species. Therefore, representatives from this area should always be included in analyses of the evolutionary history of lowland rain forest faunas. The incongruence of branching patterns among areas is in agreement with recent results presented for Neotropical passerine birds and indicates that a single hypothesis of Neotropical area relationships is unlikely. These findings reinforce the idea that speciation in the Neotropics will not be explained by any single model of vicariance or climatic changes.     

The Amazon River as a dispersal barrier to passerine birds: effects of river width, habitat and taxonomy

Aim To evaluate the relative effectiveness of the lower and upper sections, respectively, of the Amazon River as a barrier to bird distribution, and to evaluate ecological and taxonomic factors affecting the efficacy of the river barrier. Location Amazon River of South America between its confluence with the Napo River in the west and its delta in the east. Methods Using published distribution maps for 448 species of passerine birds occurring along the Amazon River, we evaluated whether each was distributed along one bank only (river presumed to be a barrier) or both banks (no barrier) to test the predictions that the river was more effective as a dispersal barrier: (1) along the lower, wider portion of the river than the upper, narrower portion; (2) for species inhabiting forests than open country; (3) for species inhabiting forest understorey than forest canopy; (4) for species restricted to terra firme (never inundated upland forest) than those not restricted to terra firme and (5) for certain taxonomic groups. Results Our analyses demonstrated that the Amazon River was most effective as a dispersal barrier along its lower portion and for species restricted to forests and terra firme. However, the river was not significantly more of a barrier for species inhabiting forest understorey than forest canopy. The river was most significant as a barrier to dispersal for the antbirds (Thamnophilidae) and was less significant as a barrier to species belonging to several large families including woodcreepers (Dendrocolaptidae), ovenbirds (Furnariidae), flycatchers (Tyrannidae), cotingids (Cotingidae), tanagers (Thraupidae), seed‐eating finches (Emberizidae) and blackbirds (Icteridae). Main conclusions The robust widths of Amazonian rivers are widely considered to represent impediments to dispersal and gene flow for many taxa of birds and other animals, and may have represented agents of vicariance in the diversification of species. Our study reaffirms the effectiveness of the lower Amazon River as a current barrier to bird dispersal for forest birds and provides new insights into the effects of habitat and taxonomy on the efficacy of the river barrier. Although supportive of several predictions of the river hypothesis of biological diversification, our study is limited in addressing the historical impact of river barriers as agents of vicariance in the process of diversification.     

The impact of a run-of-the-river hydroelectric dam on a non-volant small-mammal assemblage in Brazilian Amazonia

There are few scientific studies evaluating the impact of the loss of wetlands on the banks of tropical rivers on assemblages of small non-flying mammals. To understand the possible deleterious effects of hydroelectric construction in tropical forests on this group of mammals, we used data from 2 years of monitoring carried out during the period before the filling of a hydroelectric plant reservoir in the Brazilian Amazon, and related them to vegetation, soil and topography. We captured 659 individuals of 20 small-mammal species. The species assemblage composition in the flooded areas was a subset of species that occurred in both floodable and non-floodable areas, and only one species was captured exclusively in the flooded area. Species composition was influenced by the proportion of sand, by soil nutrient concentration and distance from water bodies. We conclude that there is no evidence that the flooding of low-lying areas along the Madeira River would negatively affect the assemblage of non-flying small mammals in the short term because the remaining areas have similar assemblages of small mammals as those destined for flooding. Whether the area lost will be important for population dynamics will depend on the conservation of the remaining areas.     

Biomass of primary and secondary vegetation in Rondônia, Western Brazilian Amazon

Biomass estimates of primary and different ages of secondary vegetation are reported for a tropical forest region in Rondônia, Western Brazilian Amazon. The estimates are based on published allometric equations, and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18 years. Primary forest biomass estimates varied from 290 to 495 t ha^–1. Secondary vegetation biomass estimates accounted for 40–60% of the primary forest biomass after 18 years of abandonment. Secondary growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 t ha^–1 y^–1 between the third and the eighteenth years after abandonment. CO₂ sequestration by regrowing vegetation is discussed for two scenarios of land abandonment.     

Transitions in ancient inland freshwater resource management in Sri Lanka affect biota and human populations in and around coastal lagoons

The increasing anthropogenic pressure on natural environments results in impacts that affect tropical forest areas and their biodiversity. Adverse impacts on terrestrial and oceanic environments often compound in the intertidal area, where mangrove forest ecosystems thrive. In tropical coastal areas of many developing countries where people depend on wood and other mangrove forest products and services, forest degradation leads to socioeconomic problems. At the same time, increasing freshwater needs in these areas are expected to cause additional problems. On the basis of remote sensing and ground truthing complemented by colonial archival material from the Dutch East India Company (1602-1800), we report that changes to the historic system of inland freshwater management have increased dramatically in recent times. Hydrological changes, such as interbasin transfers, have resulted in a qualitative ecological and socioeconomic degradation in three coastal lagoons in southern Sri Lanka. Variations in river hydrology have caused changes in the areas suitable as mangrove habitat and, thus, have resulted in an altered distribution. However, increases in mangrove area can mask the degradation of the site in terms of floristic composition, significance of the species, and biodiversity (this effect is termed "cryptic ecological degradation"). It is important that such changes be carefully monitored to ensure biological and socioeconomic sustainability.     

Tropical rainforests as dynamic symbiospheres of life

The remote Tiputini-Yasuni tropical forest region of the northwest Amazon (eastern Ecuador) represents a rich biodiversity likely unsurpassed anywhere else on earth. The myriad ecosystems, habitats and organisms are embedded in layers of symbiotic expressions. This region and particularly its Tiputini Biodiversity Station operated by the Universidad San Francisco de Quito offer unique and significant opportunities for symbiosis research and needed habitat conservation support. The centrality of symbioses in tropical rainforests is discussed through a review of selected literature and based on recent first-hand field experiences.     

植被气候关系与我国的植被分区

气候制约着植被的地理分布,植被是区域气候特征的反映和指示,两者之间存在密不可分的联系.揭示植被与气候之间的关系是正确认识植被分布的前提,是进行植被区划的理论基础.植被区划是植被研究的归纳和总结,是其他自然地理区划和农林业区划的基础.本文在简要回顾中国植被气候关系及植被分区的研究历史的基础上,对我国以往的主要植被分区原则、依据和方案进行了评述,对有争议的主要植被界线进行了讨论.我们认为,在当今我国大部分地区的原生植被已遭到破坏的现实情况下,根据原生植被及其衍生植被类型的分布,确定其分布与限制性气候因子的关系,以此来进行植被带(区)的划分,不仅反映植被气候间密不可分的关系,在实践上也便于操作.尽管在一些植被带的命名、具体界线的划定上有分歧,但最近的中国植被分区方案大都认为我国基本的植被区有8至9个,即针叶林、针阔叶混交林、落叶阔叶林、常绿落叶阔叶混交林、常绿阔叶林以及雨林季雨林、草原、荒漠以及高寒植被.通过分析主要植被带附近的植被、气候等特征,本文认为,1)秦岭淮河线是一条重要的水分气候带,而不是温度带,不是亚热带植被的北界;2)我国亚热带植被的北界基本上沿长江北岸,从杭州湾经太湖、安徽宣城、铜陵经大别山南坡到武汉往西,与WI值130-140 ℃·月一致;3)我国热带区域的面积极小,仅分布在海南岛的东南部和台湾南端及其以南地区; 4) 我国东部地区暖温带的水热条件南北差异甚大,建议以秦岭淮河为界,将暖温带划分为两个植被带,即落叶阔叶疏林带和落叶常绿阔叶混交林带;华北地区的地带性植被为落叶阔叶疏林.最后,本文还强调了对应于气候变化进行动态植被分区的重要性.     

Fire history data as reference information in ecological restoration

Fire plays a fundamental role in the ecology of Araucaria-Nothofagus forests. This paper highlights the utility of dendrochronological techniques in providing the historical reference conditions to guide ecological restoration. In the Araucarian region human activity has dramatically changed the fire frequency in the Araucaria-Nothofagus forest ecosystems. Although further critical evaluation is required, our preliminary data show that, compared with the Native American period (pre-1883), there was widespread burning of forests associated with the subsequent Euro-Chilean settlement phase. Vast areas of subalpine forest were deliberately burned to increase pasture for cattle ranching. This process is documented by a major increase in the frequency of fires in the forested Araucaria-Nothofagus landscape during the 20th century. Prior to the 1880s the fire regime was characterized by infrequent catastrophic fires with long intervening periods of stability. The immediate reduction of human-induced fire is necessary to move these altered forest ecosystems towards the range of natural structural conditions and reestablish the historical variability of this ecological process. A better understanding of the fire ecology seems crucial in developing strategies for the restoration and management of these fire-dependent forest ecosystems.     

Regional application of an ecosystem production model for studies of biogeochemistry in Brazilian Amazonia

The degree to which primary production, soil carbon, and trace gas fluxes in tropical forests of the Amazon are limited by moisture availability and other environmental factors was examined using an ecosystem modelling application for the country of Brazil. A regional geographical information system (GIS) serves as the data source of climate drivers, satellite images, land cover, and soil properties for input to the NASA Ames-CASA (Carnegie-Ames-Stanford Approach) model over a 8-km grid resolution. Simulation results lead us to hypothesize that net primary production (NPP) is limited by cloud interception of solar radiation over the humid north-western portion of the region. Peak annual rates for NPP of nearly 1.4 kg C m^–2 year^–1 are localized in the seasonally dry eastern Amazon in areas that we assume are primarily deep-rooted evergreen forest cover. Regional effects of forest conversion on NPP and soil carbon content are indicated in the model results, especially in seasonally dry areas. Comparison of model flux predictions along selected eco-climatic transects reveal moisture, soil, and land use controls on gradients of ecosystem production and soil trace gas emissions (CO₂, N₂O, and NO). These results are used to formulate a series of research hypotheses for testing in the next phase of regional modelling, which includes recalibration of the light-use efficiency term in NASA-CASA using field measurements of NPP, and refinements of vegetation index and soil property (texture and potential rooting depth) maps for the region.     

Rivers,refuges and population divergence of fire‐eye antbirds (Pyriglena) in the Amazon Basin

The identification of ecological and evolutionary mechanisms that might account for the elevated biotic diversity in tropical forests is a central theme in evolutionary biology. This issue is especially relevant in the Neotropical region, where biological diversity is the highest in the world, but where few studies have been conducted to test factors causing population differentiation and speciation. We used mtDNA sequence data to examine the genetic structure within white‐backed fire‐eye (Pyriglena leuconota) populations along the Tocantins River valley in the south‐eastern Amazon Basin, and we confront the predictions of the river and the Pleistocene refuge hypotheses with patterns of genetic variation observed in these populations. We also investigated whether these patterns reflect the recently detected shift in the course of the Tocantins River. We sampled a total of 32 individuals east of, and 52 individuals west of, the Tocantins River. Coalescent simulations and phylogeographical and population genetics analytical approaches revealed that mtDNA variation observed for fire‐eye populations provides little support for the hypothesis that populations were isolated in glacial forest refuges. Instead, our data strongly support a key prediction of the river hypothesis. Our study shows that the Tocantins River has probably been the historical barrier promoting population divergence in fire‐eye antbirds. Our results have important implications for a better understanding of the importance of large Amazonian rivers in vertebrate diversification in the Neotropics.     

Fire as a Recurrent Event in Tropical Forests of the Eastern Amazon: Effects on Forest Structure,Biomass, and Species Composition1

The effects of fire on forest structure and composition were studied in a severely fire-impacted landscape in the eastern Amazon. Extensive sampling of area forests was used to compare structure and compositional differences between burned and unburned forest stands. Burned forests were extremely heterogeneous, with substantial variation in forest structure and fire damage recorded over distances of <50 m. Unburned forest patches occurred within burned areas, but accounted for only six percent of the sample area. Canopy cover, living biomass, and living adult stem densities decreased with increasing fire inrensiry / frequency, and were as low as 10–30 percent of unburned forest values. Even light burns removed >70 percent of the sapling and vine populations. Pioneer abundance increased dramatically with burn intensity, with pioneers dominating the understory in severely damaged areas. Species richness was inversely related to burn severity, but no clear pattern of species selection was observed. Fire appears to be a cyclical event in the study region: <30 percent of the burned forest sample had been subjected to only one burn. Based on estimated solar radiation intensities, burning substantially increases fire susceptibility of forests. At least 50 percent of the total area of all burned forests is predicted to become flammable within 16 rainless days, as opposed to only 4 percent of the unburned forest. In heavily burned forest subjected to recurrent fires, 95 percent of the area is predicted to become flammable in <9 rain-free days. As a recurrent disturbance phenomenon, fire shows unparalleled potential to impoverish and alter the forests of the eastern Amazon.     

中国热带森林植被类型研究历史和划分探讨

热带森林是我国森林植被的重要组成部分,明确其森林植被类型分类对于生物多样性维持机制研究和保护管理等都具有重要意义。该文以中国热带森林植被分类研究中存在的问题为出发点,通过阐述我国各省区植被类型分类的研究历史,在综合考虑多种生物和非生物影响因素的基础上,提出一个新的热带森林植被类型分类框架以供探讨。结果表明:(1)尽管针对我国热带森林的分布范围和群落特征等都已开展了诸多研究,但对我国热带森林植被类型的划分依据和分类体系仍存在争议。(2)尽管我国的热带森林都处于季风气候区带内,但许多热带地区的森林植被类型并不只是受季风影响,而是气候带、关键气候因子、地形、土壤反馈和物种适应等多种因素共同作用的结果。(3)我国的热带森林植被包括5个植被型,即非典型性热带雨林、热带季雨林、热带山地雨林、热带山顶苔藓矮林(热带云雾林)和热带针叶林,其中热带季雨林植被型包含4种植被亚型[热带落叶季雨林、热带半落叶(半常绿)季雨林、热带常绿季雨林和热带石灰岩(石山)季雨林]。(4)阐明了上述热带森林植被型和植被亚型在我国各省区的分布情况,并提出未来有必要对人工恢复后的热带森林进行评估和植被类型划分。综上所述,该文提出一个新的热带森林植被类型分类框架,以期为今后基于不同地区开展热带森林比较研究提供参考。     

海南岛热带森林植被的类群及其特征

对海南岛热带森林植被的历史变迁进行了回顾。讨论了海南岛热带森林植被类型的分类单位与等级 ,提出了海南岛热带森林的植被分类系统 ,海南岛热带森林植被可分为 2个植被型组 ,7个植被型 ,4个植被亚型 ,35个群系 ,2 1个亚群系 ,1 0 9个群丛组或群丛 ;并对代表类群进行了描述     

Fire history data as reference information in ecological restoration

Fire plays a fundamental role in the ecology of Araucaria-Nothofagus forests. This paper highlights the utility of dendrochronological techniques in providing the historical reference conditions to guide ecological restoration. In the Araucarian region human activity has dramatically changed the fire frequency in the Araucaria-Nothofagus forest ecosystems. Although further critical evaluation is required, our preliminary data show that, compared with the Native American period (pre-1883), there was widespread burning of forests associated with the subsequent Euro-Chilean settlement phase. Vast areas of subalpine forest were deliberately burned to increase pasture for cattle ranching. This process is documented by a major increase in the frequency of fires in the forested Araucaria-Nothofagus landscape during the 20th century. Prior to the 1880s the fire regime was characterized by infrequent catastrophic fires with long intervening periods of stability. The immediate reduction of human-induced fire is necessary to move these altered forest ecosystems towards the range of natural structural conditions and reestablish the historical variability of this ecological process. A better understanding of the fire ecology seems crucial in developing strategies for the restoration and management of these fire-dependent forest ecosystems.     

Distribution of aboveground live biomass in the Amazon basin

The amount and spatial distribution of forest biomass in the Amazon basin is a major source of uncertainty in estimating the flux of carbon released from land‐cover and land‐use change. Direct measurements of aboveground live biomass (AGLB) are limited to small areas of forest inventory plots and site‐specific allometric equations that cannot be readily generalized for the entire basin. Furthermore, there is no spaceborne remote sensing instrument that can measure tropical forest biomass directly. To determine the spatial distribution of forest biomass of the Amazon basin, we report a method based on remote sensing metrics representing various forest structural parameters and environmental variables, and more than 500 plot measurements of forest biomass distributed over the basin. A decision tree approach was used to develop the spatial distribution of AGLB for seven distinct biomass classes of lowland old‐growth forests with more than 80% accuracy. AGLB for other vegetation types, such as the woody and herbaceous savanna and secondary forests, was directly estimated with a regression based on satellite data. Results show that AGLB is highest in Central Amazonia and in regions to the east and north, including the Guyanas. Biomass is generally above 300 Mg ha⁻¹ here except in areas of intense logging or open floodplains. In Western Amazonia, from the lowlands of Peru, Ecuador, and Colombia to the Andean mountains, biomass ranges from 150 to 300 Mg ha⁻¹. Most transitional and seasonal forests at the southern and northwestern edges of the basin have biomass ranging from 100 to 200 Mg ha⁻¹. The AGLB distribution has a significant correlation with the length of the dry season. We estimate that the total carbon in forest biomass of the Amazon basin, including the dead and belowground biomass, is 86 Pg C with ±20% uncertainty.