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 occurrence of cerrado (as tree and shrub savanna is called in Brazil) and forest formations side by side is common at the southern margin of the Brazilian Amazonian Forest, and previous studies have demonstrated the advance of forests over cerrado areas. The aim of the present study is to provide an accurate documentation of the transition process between the two major biomes. Tree data (≥ 5 cm diameter at 0.3 m above soil level) from three plots of cerrado sensu stricto lying near three of cerradão (the taller, denser form of cerrado) were inventoried starting in 2002 in an area of 1.5 ha made up of 150 subplots of 10 × 10 m (50 in each area). This showed that the most important species of the cerradão were invading areas previously occupied by smaller, lower forms of cerrado (although it is sometimes difficult to define which are ‘forest’ and which ‘cerrado’ species as many are flexible in size – for instance Emmotum nitens can often be intermediate, establishing in cerrado that develops into cerradão and on to forest). Some typical species such as Eriotheca gracilipes and Emmotum nitens, established since the first inventories, have increased their populations (between 27 and 210%). Tachigali vulgaris, a typical, weedy, adventive species of the Cerrado–Amazonian Forest transition, showed the largest increase in abundance in areas of cerrado sensu stricto (between 100 and 1200%), and is probably the most important pioneer species in the initial advance of the forest into cerrado at the Southern Amazonian border.

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AIMS: Investigated how the loss of environmental integrity affects damselfly species composition in nine sites with different levels of environmental integrity in a Cerrado-Amazon transition region known as "arc of deforestation" in Mato Grosso State, Brazil. We also tested the influence of environmental variables on species composition. METHODS: We collected in transects of 100 m and used ordination (PCoA) and simple linear regression. RESULTS: Species composition was strongly influenced by the environmental quality of sites, and the best model to explain species composition included variables related to channel morphology. CONCLUSIONS: These results are connected to the environmental homogenization and loss of environmental integrity as a result of extensive agricultural practices which alter stream communities of dragonflies in this region.

Our goal was to investigate whether the loss of riparian forests alters the structure of assemblages and populations of dragonflies and damselflies. We tested the hypothesis that the composition of the odonate assemblages found upstream from dams are significantly different from those found downstream of these barriers. To test the hypothesis, we investigated stream sectors upstream and downstream of three dams located at the extreme of the southern Amazon basin, in the Brazilian state of Mato Grosso. We collected 111 adult odonates, 45 upstream and 69 downstream, representing 18 species, 12 upstream and 10 downstream. The most abundant species was Epipleoneura williamsoni Santos, 1957 (n = 41, 36.9%), followed by Epipleoneura metallica Rácenis, 1955 (n = 20, 18%) and Hetaerina curvicauda Garrison, 1990 (n = 17, 15.3%). Statistical ordination separated the different sectors, with the greatest dissimilarity being found between the upstream and downstream I (DS I), and our hypothesis was further supported by the fact that six of the 18 species recorded in the study did not occur in the upstream sector. As this process may lead to the local extinction of part of the biodiversity of the Amazon-Cerrado transition, even before it is fully understood, we would recommend that the observed pattern be verified through the analysis of other taxonomic groups and on a more ample spatial scale.

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The tropical vegetation growing in dystrophic soils is capable of recycling nutrients through litterfall and thus maintaining soil fertility. However, climate changes can alter this production and, consequently, the litter layer over the soil, affecting the carbon cycle and the integrity of the ecosystem. In this study, we investigated whether a reduction in rainfall increased the litterfall and the litter layer (stock) and, if so, whether the effects are more evident in degraded environments. We compared the litterfall and the litter layer in years with higher (1575.3 mm) and lower (1360.8 mm) rainfall rates in three environments: ''cerradão'' (CD; savanna woodland), typical ''cerrado'' (savanna-like vegetation) and successional area (SA). We recorded increasing litterfall in the SA and in the litter layer in the three environments during the year with lower rainfall rates. We also detected alterations to the seasonal variation in the litter layer and the production of reproductive parts. The reduction in rainfall increased the return of carbon to the soil, especially in open areas. Our results indicate that climatic extremes (e.g., reduced rainfall) can modify the availability of nutrients and their absorption by plants and therefore compromising important ecosystem functions, such as carbon cycle.

Os efeitos de queimadas induzidas sobre a comunidade de abelhas Euglossini (Hymenoptera: Apidae) foram avaliados em floresta de transição entre o Cerrado e a Floresta Amazônica, no leste do Estado de Mato Grosso, Brasil. A riqueza, abundância e a composição de Euglossini foram determinadas em uma área controle não queimada (preservada), uma área queimada anualmente desde 2004 (degradação intermediária) e uma área queimada trienalmente desde 2004 (degradação elevada). Testamos a hipótese de que áreas com diferentes frequências de queimadas apresentam menor abundância de machos, menor riqueza e diferente composição de espécies de Euglossini em relação à área controle. As técnicas de coleta ativa e passiva de abelhas foram aplicadas usando seis substâncias puras para atração dos machos: β-ionona, benzoato de benzila, geraniol, fenil-etil-acetato, salicilato de metila e vanilina. Sete espécies foram catalogadas e não houve diferença nas abundâncias entre as três áreas amostradas (F (2, 12) = 0,150; p= 0,8). A riqueza estimada de espécies na área controle foi superior à área com fogo trienal (12 ± 3,8; 4 ± 2, respectivamente), enquanto a área com fogo anual apresentou riqueza intermediária (8 ± 4,35) e superior àquela da área com fogo trienal. A análise de UPGMA revelou diferença significativa quanto a composição de espécies da área de fogo trienal para as outras duas áreas. As queimadas anual e trienal reduziram a riqueza de espécies e alteraram a composição de espécies, com efeitos mais evidentes na área com fogo trienal, causando efeitos deletérios sobre a comunidade das abelhas das orquídeas. The effect of Fire on the Community of Euglossini (Hymenoptera: Apidae) in a Cerrado-Amazon Transitional Forest (Mato Grosso, Brazil) Abstract. We evaluated the effects of induced burned on Euglossini bee assemblages (Hymenoptera: Apidae) in a transitional area between Cerrado and Amazonia, eastern Mato Grosso, Brazil. We determinate abundances, richness and composition of Euglossini in three plots: control plot (unburned), plot burned each year since 2004 (intermediate degradation), plot burned each three years since 2004 (high degradation). We tested the hypothesis that two burned plots present lower male abundances, less species richness and different species composition in comparison with the control plot. We collected male bees actively and passively by using six pure fragrances: β-ionona, benzoato de benzila, geraniol, fenil-etil-acetato, salicilato de metila e vanilina. We collected seven species with no differences in male abundances among three plots (F (2, 12)= 0.150; p= 0.8). Estimated richness species in control the plot was higher than the plot burned each three years (12 ± 3.8; 4± 2, respectively), while plot burned each year showed intermediate richness (8 ± 4.35) and higher than plot burned each three years. Cluster Analysis (UPGMA) revealed significant differences in species composition of the triennial fire area to the other two areas. Our results suggest that fire occurring with different frequencies in transitional forest promote decreases in richness of species and modifications in species composition. These modifications were clearer in plot more degraded (burned each three years) and induce deleterious effects on orchid bee assemblage.