While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few ‘hyperdominant' species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region.

The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater impact per °C in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth’s climate.

Analyses of forest loss and protected areas suggest that 36 to 57% of Amazonian tree flora may qualify as “globally threatened.”

The carbon sink capacity of tropical forests is substantially affected by tree mortality. However, the main drivers of tropical tree death remain largely unknown. Here we present a pan-Amazonian assessment of how and why trees die, analysing over 120,000 trees representing > 3800 species from 189 long-term RAINFOR forest plots. While tree mortality rates vary greatly Amazon-wide, on average trees are as likely to die standing as they are broken or uprooted—modes of death with different ecological consequences. Species-level growth rate is the single most important predictor of tree death in Amazonia, with faster-growing species being at higher risk. Within species, however, the slowest-growing trees are at greatest risk while the effect of tree size varies across the basin. In the driest Amazonian region species-level bioclimatic distributional patterns also predict the risk of death, suggesting that these forests are experiencing climatic conditions beyond their adaptative limits. These results provide not only a holistic pan-Amazonian picture of tree death but large-scale evidence for the overarching importance of the growth–survival trade-off in driving tropical tree mortality.

Lineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships among species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life-history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life-history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning more than 300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal (PS) for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of pioneer and shade tolerant life-history strategies within independent lineages, the existence of significant PS allows clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change.

Comparações fl orísticas e estruturais entre duas comunidades lenhosas de cerrado típico e cerrado rupestre, Mato Grosso, Brasil RESUMO (Comparações fl orísticas e estruturais entre duas comunidades lenhosas de cerrado típico e cerrado rupestre, Mato Grosso, Brasil). Comparou-se a riqueza, a composição fl orística e a estrutura da vegetação lenhosa entre um hectare de cerrado rupestre (CR) e um de cerrado típico (CT) no leste Mato-grossense. A riqueza registrada (CT = 79 e CR = 71) e estimada pelo método de bootstrap (CT = 86,7 ± 2,3 e CR = 75,8 ± 1,8) foi maior no CT, mas o índice de diversidade foi igual entre as duas fi sionomias (3,58 no CT e 3,56 no CR; teste t de Hutcheson = t 2;0,05 = 0,43, p > 0,05). Apesar da elevada similaridade fl orística (Sørensen = 0,75 e Morisita = 0,73), a análise de ordenação (DCA) separou as parcelas do CT e do CR, indicando a seleção de espécies nas duas fi sionomias. Foram registradas altas porcentagens de indivíduos mortos no CT (28,1%) e no CR (17,3%), devido à ocorrência de uma queimada quatro meses antes da amostragem da vegetação. A área basal por parcela foi maior no CR, enquanto as densidades por parcela, as alturas e os diâmetros medianos dos indivíduos, não diferiram entre as duas fi sionomias, sugerindo que o solo raso e o afl oramento rochoso no CR não limitaram o estabelecimento e o desenvolvimento da fl ora lenhosa.Palavras-chave: diversidade, fogo, savana, substrato rochoso Letícia Gomes 1,2 , Eddie Lenza 1 , Leandro Maracahipes 1 , Beatriz Schwantes Marimon 1 e Edmar Almeida de Oliveira 1 ABSTRACT (Floristic and structural comparisons of two woody communities of typical and rocky cerrado in the state of Mato Grosso, Brazil). In this work, the vegetation richness, fl oristic composition and the structure of woody plants of 1 hectare of rocky cerrado ("cerrado rupestre") (CR) and 1 hectare of typical cerrado (CT), in eastern Mato Grosso, were compared. Th e observed (CT = 79 and CR = 71) and the estimated richness (CT = 86.7 ± 2.3 and CR = 75.8 ± 1.8), using bootstrap analysis, were higher in the CT, but the diversity index was the same for both physiognomies (3.58 in CT and 3.56 in CR; Hutcheson t test = t 2;0.05 = 0.43, p > 0.05). Despite high fl oristic similarity (Sørensen = 0.75 and Morisita = 0.73), the ordination analysis (DCA) separated the CT and CR plots, which indicated species selection in both physiognomies. A percentage of dead individuals in CT (28.1%) and CR (17.3%), due to fi res four months before sampling took place, was also found. Th e CR basal area per plot was higher, and densities per plot, heights and mean diameters of individuals did not diff er between both physiognomies, which suggests that the shallow soil and rocky outcrop of CR have not limited the establishment and development of the woody fl ora.

ABSTRACT(Floristics of fl oodplain 'murundus' of the Pantanal of Araguaia, Mato Grosso, Brazil). Th is study aimed to compare angiosperm species richness and composition between fl oodplain 'murundus' (FM) of Araguaia State Park (ASP) in one of Brazil´s largest fl oodplains. ASP is located in Novo Santo Antônio, Mato Grosso state, and is bordered on the east by the Araguaia River, and on the west by Das Mortes River. Intensive fl oristic inventories were made on 11 hectares, and adjacent areas, of FM distributed over ASP. Environmental studies were performed by in situ descriptions. Th e soils are deep, mineral hydromorphic plinthosols, imperfectly to poorly drained, with low permeability. A total of 318 species, 193 genera and 66 families were collected, and FM values ranged from 51 to 135 species, 42 to 107 genera and 27 to 52 families. Erythroxylum suberosum is a typical species of Brazilian FM, Curatella americana typical of Mato Grosso FM and Byrsonima cydoniifolia typical of the ASP. Th e physical and spatial distribution pattern of the "murundus" (earthmounds) may refl ect the seasonal fl ood pulse, since the fl oristic composition of the FM varied between the areas under the infl uence of the rivers that border the park. Th is was the largest fl oristic inventory ever undertaken in FM, with a signifi cant increase in our knowledge and recording of typical species of the Cerrado Biome which occur in this phytophysiognomy.

The occurrence of a monodominant tropical forest dominated by the tree species Brosimum rubescens Taub. (Moraceae) in the transition zone between the cerrado region and the Amazonian rain forests along the Araguaia valley in the state of Mato Grosso in Brazil is reported. A 6000m2 (40×150m) area located in the central portion of a forest (14°50∞47◊S, 52°08∞37◊W ) on the Eldorado Farm in Nova Xavantina was sampled to determine the structure, phytosociology and soil properties. A total of 44 tree species was found in the forest, with a Shannon diversity index (H∞) of 2.37 and the Pielou evenness index (J∞) of 0.63. These values were similar to those reported by other workers in an Amazonian monodominant forest dominated by Peltogyne gracilipes. Average tree density equal or greater than (Á) 5cm dbh was 1066ha−1 and basal area 37.46m2 ha−1. Dead standing individuals represented 7.03% of the total density and lianas 8.12%. The main families were Moraceae, Rubiaceae, Burseraceae, Hippocrateaceae and Leguminosae-Caesalpinioideae. The species with the highest importance value indices were B. rubescens (124.55), Amaioua intermedia var. brasiliana (32.97), Cheiloclinium cognatum (22.41), Tetragastris balsamifera (19.58) and Protium pilosissimum (16.64). Brosimum rubescens alone accounted for 85.5% of the individuals Á30cm dbh, 80.35% of those Á20cm dbh, 57.33% of those Á10cm dbh, and 35.85% of those Á5cm dbh.The forest was composed of upper, middle and lower storeys. Diameter distribution was unbalanced for the community and for the main species, suggesting that establishment has been episodic. The surface soil was acid, with high exchangeable Al levels and low fertility, as is the case for most cerrados and Amazonian forests. The availability of K was in the range of adequacy, as compared with most native soils. However, concentrations of available Mg in the soil was higher than that of available Ca, with Mg/Ca ratios above three, unlike most cerrados and Amazonian forests, but similar to the soils of many monodominant tropical forests reported in the literature. Soils were characterized by high concentrations of available Fe. Besides the high Mg/Ca ratios, a high proportion of K as compared with the bivalent cations Ca and Mg, and toxicities of Fe and Mn due to strong acidity could be factors influencing the occurrence of species in this forest.