Fluxes of CH4, CO2, NO, and N2O in an improved fallow agroforestry system in Eastern Amazonia

The objective of this study was to evaluate the effect of leguminous fallows on ethane (CH4), carbon dioxide (CO2), N oxides (N2O and NO) fluxes.We measured CH4, N2O, NO, and CO2 fluxes from improved fallows of Inga edulis and Acacia mangium during two successive fallow periods in an old agricultural frontier on sandy soils in eastern Amazonia. Sampling for the first fallow period was done in 1996 and 1997 while that for the second fallow was done in 1999 and 2000. We observed net CH4 uptake during majority of the sampling campaigns.We did not observe any significant difference in CH4 flux between improved fallows and unimproved fallows (control) during either of the sampling periods (P > 0.05).We observed significantly higher uptake during the dry season relative to wet season, indicating the importance of soil water content and gas transport on CH4 fluxes. For both wet and dry seasons, soil respiration rates (CO2), N2O and NO fluxes were similar for improved fallow plots and the control (P > 0.05). We did not observe any significant seasonality in soil respiration or NO fluxes, but there was a significant difference in N2O flux between seasons (P = 0.0638). Contrary to other studies, our observations suggest that improved fallows using N-fixing trees do not appear to decrease the soil CH4 sink and also do not seem to increase CO2 and N-oxide emission in these sandy Amazonian soils. The result for N oxides is particularly pertinent to greenhouse gas (GHG) accounting methods that assess N2O emissions as a fraction of N fixatio

Tree species composition and diversity gradients in white-water forests across the Amazon Basin

Aim: Attention has increasingly been focused on the floristic variation within forests of the Amazon Basin. Variations in species composition and diversity are poorly understood, especially in Amazonian floodplain forests. We investigated tree species composition, richness and alpha diversity in the Amazonian white-water (varzea) forest, looking particularly at: (1) the flood-level gradient, (2) the successional stage (stand age), and (3) the geographical location of the forests. Location: Eastern Amazonia, central Amazonia, equatorial western Amazonia and the southern part of western Amazonia. Methods: The data originate from 16 permanent varzea forest plots in the central and western Brazilian Amazon and in the northern Bolivian Amazon. In addition, revised species lists of 28 varzea forest inventories from across the Amazon Basin were used. Most important families and species were determined using importance values. Floristic similarity between plots was calculated to detect similarity variations between forest types and over geographical distances. To check for spatial diversity gradients, alpha diversity (Fisher) of the plots was correlated with stand age, longitudinal and latitudinal plot location, and flood-level gradient. Results: More than 900 flood-tolerant tree species were recorded, which indicates that Amazonian varzea forests are the most species-rich floodplain forests worldwide. The most important plant families recorded also dominate most Neotropical upland forests, and c. 31% of the tree species listed also occur in the uplands. Species distribution and diversity varied: (1) on the flood-level gradient, with a distinct separation between low-varzea forests and high-varzea forests, (2) in relation to natural forest succession, with species-poor forests in early stages of succession and species-rich forests in later stages, and (3) as a function of geographical distance between sites, indicating an increasing alpha diversity from eastern to western Amazonia, and simultaneously from the southern part of western Amazonia to equatorial western Amazonia. Main conclusions: The east-to-west gradient of increasing species diversity in varzea forests reflects the diversity patterns also described for Amazonian terra firme. Despite the fine-scale geomorphological heterogeneity of the floodplains, and despite high disturbance of the different forest types by sedimentation and erosion, varzea forests are dominated by a high proportion of generalistic, widely distributed tree species. In contrast to high-varzea forests, where floristic dissimilarity increases significantly with increasing distance between the sites, low-varzea forests can exhibit high floristic similarity over large geographical distances. The high varzea may be an important transitional zone for lateral immigration of terra firme species to the floodplains, thus contributing to comparatively high species richness. However, long-distance dispersal of many low-varzea trees contributes to comparatively low species richness in highly flooded low varzea

Diversidade de bromeliáceas epífitas na Área de Proteção Ambiental Ilha do Combu, Belém, Pará, Brasil Diversity of epiphytic bromeliads in the environmental protection area of Combu Island, Belém, Pará, Brazil

Informações sobre a diversidade no nível de espécie oferecem subsídios importantes para o desenvolvimento sustentável e a conservação biológica. Neste contexto, estudos com Bromeliaceae merecem destaque, especialmente porque o grupo é importante ecologicamente, mas ainda pouco conhecido na Região Norte. Neste trabalho, foram demarcadas duas parcelas de 100 m x 100 m em uma floresta de várzea localizada na Área de Proteção Ambiental Ilha do Combu, em Belém, Estado do Pará. Cada parcela foi subdividida em oito parcelas de 50 m x 50 m, tendo todas as espécies e espécimes de bromeliáceas epífitas registradas e quantificadas. A diversidade do grupo foi calculada utilizando o índice de Shannon-Wiener. Foram registrados 1.339 indivíduos pertencentes a oito espécies e quatro gêneros. Tillandsia e Aechmea apresentaram maior riqueza. A diversidade de espécies na área foi de H= 1,10, apresentando dominância acentuada de muitos indivíduos em poucas espécies.<br>Information about diversity at the species level offers data for sustainable development and biological conservation. In this context, studies about Bromeliaceae are noteworthy, especially because this group is ecologically important and poorly known in the North Region of Brazil. In this study, two grids (100 m x 100 m) were delineated in a floodplain forest in the environmental protection area of Combu Island, Belém, Pará, Brazil. The grids were subdivided into eight grids of 50 m x 50 m, and all species and individuals of epiphytic Bromeliaceae were recorded and quantified. The diversity was calculated using the Shannon-Wiener index. A total of 1,339 individuals, belonging to eight species and four genera were recorded. Tillandsia and Aechmea presented the greatest richness. The diversity of species was H= 1.10, presenting sharp dominance of many individuals of few species