Aim and Location We assessed the effects of biophysical and anthropogenic predictors on deforestation in Brazilian Amazonia. This region has the world's highest absolute rates of forest destruction and fragmentation.Methods Using a GIS, spatial data coverages were developed for deforestation and for three types of potential predictors: (1) human-demographic factors (rural-population density, urban-population size); (2) factors that affect physical accessibility to forests (linear distances to the nearest paved highway, unpaved road and navigable river), and (3) factors that may affect land-use suitability for human occupation and agriculture (annual rainfall, dry-season severity, soil fertility, soil waterlogging, soil depth). To reduce the effects of spatial autocorrelation among variables, the basin was subdivided into >1900 quadrats of 50 · 50 km, and a random subset of 120 quadrats was selected that was stratified on deforestation intensity. A robust ordination analysis (non-metric multidimensional scaling) was then used to identify key orthogonal gradients among the ten original predictor variables.Results The ordination revealed two major environmental gradients in the study area. Axis 1 discriminated among areas with relatively dense human populations and highways, and areas with sparse populations and no highways; whereas axis 2 described a gradient between wet sites having low dry-season severity, many navigable rivers and few roads, and those with opposite values. A multiple regression analysis revealed that both factors were highly significant predictors, collectively explaining nearly 60% of the total variation in deforestation intensity (F 2,117 ¼ 85.46, P < 0.0001). Simple correlations of the original variables were highly concordant with the multiple regression model and suggested that highway density and rural-population size were the most important correlates of deforestation.Main conclusions These trends suggest that deforestation in the Brazilian Amazon is being largely determined by three proximate factors: human population density, highways and dryseason severity, all of which increase deforestation. At least at the spatial scale of this analysis, soil fertility and waterlogging had little influence on deforestation activity, and soil depth was only marginally significant. Our findings suggest that current policy initiatives designed to increase immigration and dramatically expand highway and infrastructure networks in the Brazilian Amazon are likely to have important impacts on deforestation activity. Deforestation will be greatest in relatively seasonal, south-easterly areas of the basin, which are most accessible to major population centres and where large-scale cattle ranching and slash-andburn farming are most easily implemented.

The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher's alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼ 40,000 and ∼ 53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼ 19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼ 4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

Concern about the future of Amazonian forests is growing as both the extent and rate of primary forest destruction increase. We combine spatial information on various biophysical, demographic and infrastructural factors in the Brazilian Amazon with satellite data on deforestation to evaluate the relative importance of each factor to deforestation in the region. We assess the sensitivity of results to alternative sampling methodologies, and compare our results to those of previous empirical studies of Amazonian deforestation. Our findings, in concert with those of previous studies, send a clear message to planners: both paved and unpaved roads are key drivers of the deforestation process. Proximity to previous clearings, high population densities, low annual rainfall, and long dry seasons also increase the likelihood that a site will be deforested; however, roads are consistently important and are the factors most amenable to policymaking. We argue that there is ample evidence to justify a fundamental change in current Amazonian development priorities if additional largescale losses of forests and environmental services are to be avoided. Published by Elsevier Ltd.

O MODELO da ocupação demográfica da Amazônia legalnos últimos cinqueta anos tem levado a níveis significativos de desmatamento, resultante de múltiplos fatores, tais como a abertura de estradas pioneiras, o crescimento das cidades, a ampliação de pecuária extensiva, a acelerada exploração madeireira e a crescente agricultura intensiva de monoculturas. A área cumulativa desmatada na Amazônia legal brasileira chegou a cerca de 653.000 km² em 2003, correspondendo a 16,3% da região. Este estudo visou a determinar o desmatamento dentro e fora dos atuais Unidades de Conservação (UC) e Terras Indígenas (TI) na Amazônia legal, nos estados de Mato Grosso, Rondônia e Pará, que, juntos, corresponderam por mais de 90% do desmatamento observado entre 2001 e 2003. Os resultados mostraram que o desmatamento foi cerca de dez a vinte vezes menor dentro das Unidades de Conservação e Terras Indígenas do que em áreas contíguas fora delas. Isto demonstra a importância dessas áreas protegidas para diminuir o processo do desmatamento nos três estados. Isto refuta a hipótese generalizada de que estas áreas não cumprissem a sua função principal na conservação e uso racional dos recursos na Amazônia legal.

The distribution and composition of aquatic insect communities in streams at a local scale are considered to be primarily determined by environmental factors and interactive relationships within the system. Here, we evaluated the effects of forest fragmentation and forest cover changes on habitat characteristics of streamlets (igarapés) in Amazonian forests and on the aquatic insect communities found Publication number 515 of the PDBFF Technical Series.