Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Branch xylem density variations across Amazonia
S. Pati?o,J. Lloyd,R. Paiva,C. A. Quesada
Biogeosciences Discussions , 2008,
Abstract: Measurements of branch xylem density, Dx, were made for 1466 trees representing 503 species, sampled from 80 sites across the Amazon basin. Measured values ranged from 240 kg m 3 for a Brosimum parinarioides from Tapajos in West Pará, Brazil to 1130 kg m 3 for an Aiouea sp. from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average Dx across the sample plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that geographic location and plot accounted for 33% of the variation with species identity accounting for an additional 27%; the remaining "residual" 40% of the variance accounted for by tree to tree (within species) variation. Variations in plot means, were, however, hardly accountable at all by differences in species composition. Rather, it would seem that variations of xylem density at plot level must be explained by the effects of soils and/or climate. This conclusion is supported by the observation that the xylem density of the more widely distributed species varied systematically from plot to plot. Thus, as well as having a genetic component branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing and in a predictable manner. Exceptions to this general rule may be some pioneers belonging to Pourouma and Miconia and some species within the genera Brosimum, Rinorea and Trichillia which seem to be more constrained in terms of this plasticity than most species sampled as part of this study.
Environmental determinants for natural regeneration of gallery forest at the Cerrado/Amazonia boundaries in Brazil
Marimon, Beatriz Schwantes;Felfili, Jeanine Maria;Lima, Edson de Souza;Duarte, Wania M. Gon?alves;Marimon-Júnior, Ben Hur;
Acta Amazonica , 2010, DOI: 10.1590/S0044-59672010000100014
Abstract: natural regeneration and structure and their relationship to environmental variables were studied in three sections of a gallery forest, in eastern mato grosso, brazil (14o43′s and 52o21′w). the assumption was that natural regeneration is constrained by environmental determinants at all stages of development of the tree community. the objective was to analyse the forest structure and to verify the relationship between species distribution and abundance at different stages of regeneration and environmental variables. in each section, 47 contiguous (10x10m) permanent plots were established to sample trees (gbh≥15cm), following a systematic design. seedlings (0.01 to 1m height), saplings (1.01 to 2m) and poles (from 2.01m height to gbh<15cm) were sampled in sub-plots of 1x1m, 2x2m and 5x5m, respectively. in each plot, soil properties, gaps projection, bamboos, rocky cover, declivity and depth of ground watertable were determined. the relationships between the environmental variables with trees and seedling communities were assessed by canonical correspondence analysis. in spite of the sections being near to each other, they presented large differences in floristics, structure and site conditions. the forest soil presented a low cation exchange capacity and a high level of al saturation. the occurrence of bamboos and gaps and the depth of ground watertable limited the occurrence of poles and trees. the high degree of structural heterogeneity for each regeneration category was related primarily to a humidity gradient; but soil fertility (ca+mg) was also a determinant of seedling and sapling communities.
Global warming in Amazonia: impacts and Mitigation
Fearnside, Philip Martin;
Acta Amazonica , 2009, DOI: 10.1590/S0044-59672009000400030
Abstract: global warming has potentially catastrophic impacts in amazonia, while at the same time maintenance of the amazon forest offers one of the most valuable and cost-effective options for mitigating climate change. we know that the el ni?o phenomenon, caused by temperature oscillations of surface water in the pacific, has serious impacts in amazonia, causing droughts and forest fires (as in 1997-1998). temperature oscillations in the atlantic also provoke severe droughts (as in 2005). we also know that amazonian trees die both from fires and from water stress under hot, dry conditions. in addition, water recycled through the forest provides rainfall that maintains climatic conditions appropriate for tropical forest, especially in the dry season. what we need to know quickly, through intensified research, includes progress in representing el ni?o and the atlantic oscillations in climatic models, representation of biotic feedbacks in models used for decision-making about global warming, and narrowing the range of estimating climate sensitivity to reduce uncertainty about the probability of very severe impacts. items that need to be negotiated include the definition of "dangerous" climate change, with the corresponding maximum levels of greenhouse gases in the atmosphere. mitigation of global warming must include maintaining the amazon forest, which has benefits for combating global warming from two separate roles: cutting the flow the emissions of carbon each year from the rapid pace of deforestation, and avoiding emission of the stock of carbon in the remaining forest that can be released by various ways, including climate change itself. barriers to rewarding forest maintenance include the need for financial rewards for both of these roles. other needs are for continued reduction of uncertainty regarding emissions and deforestation processes, as well as agreement on the basis of carbon accounting. as one of the countries most subject to impacts of climate change, brazil
Determinants of Plant Community Assembly in a Mosaic of Landscape Units in Central Amazonia: Ecological and Phylogenetic Perspectives  [PDF]
María Natalia Uma?a, Natalia Norden, ángela Cano, Pablo R. Stevenson
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0045199
Abstract: The Amazon harbours one of the richest ecosystems on Earth. Such diversity is likely to be promoted by plant specialization, associated with the occurrence of a mosaic of landscape units. Here, we integrate ecological and phylogenetic data at different spatial scales to assess the importance of habitat specialization in driving compositional and phylogenetic variation across the Amazonian forest. To do so, we evaluated patterns of floristic dissimilarity and phylogenetic turnover, habitat association and phylogenetic structure in three different landscape units occurring in terra firme (Hilly and Terrace) and flooded forests (Igapó). We established two 1-ha tree plots in each of these landscape units at the Caparú Biological Station, SW Colombia, and measured edaphic, topographic and light variables. At large spatial scales, terra firme forests exhibited higher levels of species diversity and phylodiversity than flooded forests. These two types of forests showed conspicuous differences in species and phylogenetic composition, suggesting that environmental sorting due to flood is important, and can go beyond the species level. At a local level, landscape units showed floristic divergence, driven both by geographical distance and by edaphic specialization. In terms of phylogenetic structure, Igapó forests showed phylogenetic clustering, whereas Hilly and Terrace forests showed phylogenetic evenness. Within plots, however, local communities did not show any particular trend. Overall, our findings suggest that flooded forests, characterized by stressful environments, impose limits to species occurrence, whereas terra firme forests, more environmentally heterogeneous, are likely to provide a wider range of ecological conditions and therefore to bear higher diversity. Thus, Amazonia should be considered as a mosaic of landscape units, where the strength of habitat association depends upon their environmental properties.
Determinants of Regional Distribution of FDI Inflows across China’s Four Regions  [cached]
Kelly Liu,Kevin Daly,Maria Estela Varua
International Business Research , 2012, DOI: 10.5539/ibr.v5n12p119
Abstract: This paper performs an empirical assessment of China’s inward FDI by analysing the relative importance of the potential determinants of FDI inflows across the four regions of China for the period 2001-2009. The determinants examined are: Market size, labour cost, labour quality, physical infrastructure development, telecommunication, degree of economic openness and government incentives to attract FDI. Our paper employs a multiple regression model for each region and then compares the results across four regions. The results indicate a mixed picture, for example we find that market size holds priority for FDI inflows into coastal region and northeast regions while the degree of openness is the most important determinant for FDI inflows in central region. The labour quality has no effect in central region but has a positive impact on FDI inflows into coastal and northeast regions. These results have important implications for China’s regional policy makers as they can help them identify the kinds of industries which respond to specific drivers and identify regional social economic characteristics which are more attractive to particular FDI inflows.
Socioeconomic and Demographic Determinants of Mental Health across Canadian Communities
Jalil Safaei
The Internet Journal of Mental Health , 2012,
Abstract: Background Many factors contribute to health. This study uses community level data to estimate the impact of socioeconomic and demographic factors as well as physical health on community mental health outcomes. Method Multiple regression analysis was used to estimate the impact of determinants on community mental health outcomes for men and women using community level data from up to 113 health regions covering almost the entire population in Canada. Results Study findings indicate that communities with higher proportions of aboriginal people have greater mental illness hospitalization. Minorities have poorer perceived mental health but better objective measures of less mental illness hospitalization and self injury hospitalization. Also, communities with higher proportion of low income persons show poorer results for many objective mental health outcomes. Higher prevalence of lone parents in a community is associated with greater perceived life stress and greater mental illness hospitalizations for men. Poor physical health is also a predictor of poor mental health. Conclusion Improving the living conditions of aboriginal people and other low income people could reduce mental illness hospitalizations in a community, helping minorities the majority of whom are immigrants with their settlements in their host communities could improve perceived mental health and life stress, and helping lone parents who are men with counseling services to better cope with their situations could reduce their perceived life stress and mental illness hospitalization. Also, improving the physical health of individuals across communities could have a positive impact on mental health outcomes across communities.
Variation in aboveground biomass and necromass of two invasive species in the Atlantic rainforest, southeast Brazil
Portela, Rita Cássia Quitete;Matos, Dalva Maria Silva;Siqueira, Ludmila Pugliese de;Braz, Maria Isabel Guedes;Silva-Lima, Leonardo;Marrs, Robert Hunter;
Acta Botanica Brasilica , 2009, DOI: 10.1590/S0102-33062009000200029
Abstract: this paper describes the variation of the above-ground biomass, necromass, and net above-ground primary production (nagpp) of two weed species, panicum maximum jacquin (poaceae) and pteridium arachnoideum (kaulf.) maxon. (dennstaedtiaceae), at two sites in the po?o das antas biological reserve, southeast brazil. both species form mono-dominant stands in the matrix surrounding forest fragments. the organic matter was sampled monthly from each site, separated into biomass and necromass, and net above-ground primary production (nagpp) was calculated. there was marked intra-seasonal fluctuation for both species; pa. maximum generally had the largest values for necromass, total mass and nagpp (nagpp, pa. maximum = 3953 g.m-2.y-1, pt. arachnoideum = 2667 g.m-2.y-1). nagpp did not vary between the two growth periods for pa. maximum, but marked differences were found for pt. arachnoideum (2% compared to 44% variation around the mean). the second growth year was drier and pa. maximum produced much greater necromass in that year; pt. arachnoideum showed little variation in biomass but much greater productivity in the drier second season. pteridium arachnoideum appears to be more sensitive to climate, and especially rainfall.
Dynamics, Patterns and Causes of Fires in Northwestern Amazonia  [PDF]
Dolors Armenteras, Javier Retana
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0035288
Abstract: According to recent studies, two widespread droughts occurred in the Amazon basin, one during 2005 and one during 2010. The drought increased the prevalence of climate-driven fires over most of the basin. Given the importance of human-atmosphere-vegetation interactions in tropical rainforests, these events have generated concerns over the vulnerability of this area to climate change. This paper focuses on one of the wettest areas of the basin, Northwestern Amazonia, where the interactions between the climate and fires are much weaker and where little is known about the anthropogenic drivers of fires. We have assessed the response of fires to climate over a ten-year period, and analysed the socio-economic and demographic determinants of fire occurrence. The patterns of fires and climate and their linkages in Northwestern Amazonia differ from the enhanced fire response to climate variation observed in the rest of Amazonia. The highest number of recorded fires in Northwestern Amazonia occurred in 2004 and 2007, and this did not coincide with the periods of extreme drought experienced in Amazonia in 2005 and 2010. Rather, during those years, Northwestern Amazonia experienced a relatively small numbers of fire hotspots. We have shown that fire occurrence correlated well with deforestation and was determined by anthropogenic drivers, mainly small-scale agriculture, cattle ranching (i.e., pastures) and active agricultural frontiers (including illegal crops). Thus, the particular climatic conditions for air convergence and rainfall created by proximity to the Andes, coupled with the presence of one of the most active colonisation fronts in the region, make this region differently affected by the general drought-induced fire patterns experienced by the rest of the Amazon. Moreover, the results suggest that, even in this wet region, humans are able to modify the frequency of fires and impact these historically well preserved forests.
Environmental and Demographic Determinants of Avian Influenza Viruses in Waterfowl across the Contiguous United States  [PDF]
Matthew L. Farnsworth, Ryan S. Miller, Kerri Pedersen, Mark W. Lutman, Seth R. Swafford, Philip D. Riggs, Colleen T. Webb
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032729
Abstract: Outbreaks of avian influenza in North American poultry have been linked to wild waterfowl. A first step towards understanding where and when avian influenza viruses might emerge from North American waterfowl is to identify environmental and demographic determinants of infection in their populations. Laboratory studies indicate water temperature as one determinant of environmental viral persistence and we explored this hypothesis at the landscape scale. We also hypothesized that the interval apparent prevalence in ducks within a local watershed during the overwintering season would influence infection probabilities during the following breeding season within the same local watershed. Using avian influenza virus surveillance data collected from 19,965 wild waterfowl across the contiguous United States between October 2006 and September 2009 We fit Logistic regression models relating the infection status of individual birds sampled on their breeding grounds to demographic characteristics, temperature, and interval apparent prevalence during the preceding overwintering season at the local watershed scale. We found strong support for sex, age, and species differences in the probability an individual duck tested positive for avian influenza virus. In addition, we found that for every seven days the local minimum temperature fell below zero, the chance an individual would test positive for avian influenza virus increased by 5.9 percent. We also found a twelve percent increase in the chance an individual would test positive during the breeding season for every ten percent increase in the interval apparent prevalence during the prior overwintering season. These results suggest that viral deposition in water and sub-freezing temperatures during the overwintering season may act as determinants of individual level infection risk during the subsequent breeding season. Our findings have implications for future surveillance activities in waterfowl and domestic poultry populations. Further study is needed to identify how these drivers might interact with other host-specific infection determinants, such as species phylogeny, immunological status, and behavioral characteristics.
The social determinants of child health: variations across health outcomes – a population-based cross-sectional analysis
Charlemaigne C Victorino, Anne H Gauthier
BMC Pediatrics , 2009, DOI: 10.1186/1471-2431-9-53
Abstract: This population-based cross-sectional study used data from the 2003 US National Survey of Children's Health involving 102,353 children aged 0 to 17 years. Using multivariate logistic regression models, the association between household income, education, employment status, parental mental health, number of children, family structure and the following child health outcomes were examined: presence or absence of asthma, headaches/migraine, ear infections, respiratory allergy, food/digestive allergy, or skin allergy.While the associations of some determinants were found to be consistent across different health outcomes, the association of other determinants such as household income depended on the specific outcome. Controlling for other factors, a gradient association persisted between household income and a child having asthma, migraine/severe headaches, or ear infections with children more likely to have the illness if their family is closer to the federal poverty level. Potentially mediating variables, namely parental mental health, number of children, and family structure had consistent associations across health outcomes.There appears to be evidence of an income gradient for certain child health outcomes, even after controlling for other traditional measures of socioeconomic status. Our study also found evidence of an association between certain child health outcomes and potential mediating factors.There is almost universal agreement about the importance of children, who are often referred to as the "future of a nation" and a "nation's greatest resource" [1]. Indeed, October 1, 2007 was proclaimed "Child Health Day" in the United States. Despite this strong commitment to the health of children, advances in medical technology and increased global wealth, there are still concerns about poor health outcomes amongst children. Furthermore, the disparity in children's health and their determinants is greater in the United States than elsewhere [2]. The number of American
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.