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.

INTR ODUCT IONOne of the key goals of ecological studies is to describe and understand large-scale patterns of diversity. In a recent review, Hawkins et al. (2003) showed that current climate is a strong descriptor of broad-scale species-richness patterns in terrestrial systems. They also noted that there is often a latitudinal shift in the relative importance of different climatic variables. Rainfall is often the best predictor of species richness in the tropics and warm temperate zones, whereas at high latitudes species diversity correlates best with water-energy variables (for plants) or with energy variables (for animals) (Hawkins et al., 2003). ABSTRACTAim To determine the effect and relative importance of geographic and local environmental factors on species richness and turnover of ant assemblages in floodplain forests across the Amazon basin.Location Twenty-six mature forest sites scattered along the entire extension of the Amazon River in Brazil. The study area encompassed nearly 18°of longitude and 3.5°of latitude.Methods Systematic collections of ants were performed at each site during the low-water season (i.e. when forests are not inundated) using three complementary sampling methods. We used variance partitioning techniques to assess the relative effects of the spatial (latitude and longitude) and environmental (rainfall, length of the dry season and flood height) variables on ant species richness and composition. ResultsThere was a twofold variation in the number of species per site, which was largely explained by inter-site variations in rainfall seasonality and flooding intensity. In general, there were more species at sites located in the western part of the basin, where the dry season is less severe, or near the river estuary, where precipitation is also high and flooding is less intense. Ant community composition was also affected by environmental heterogeneity. For instance, some species only occurred at those sites less affected by the river's seasonal flooding, whereas others were mostly associated with the drier or wetter regions of the basin. In addition, the turnover of species increased significantly as geographic distances increased. Nevertheless, the rate of change was small given that many species had a broad distribution across the study area.Main conclusions Ant distribution patterns along the floodplain forests of the Amazon appear to be controlled to a relatively large extent by the current gradient in flooding intensity and -most importantly -in precipitation. Altered rainfall regimes resulting from global warming and land-use change thus have the potential to influence these patterns.

SummaryRecent studies suggest that deforestation rates in the Brazilian Amazon could increase sharply in the future as a result of over US$ 40 billion in planned investments in highway paving and major new infrastructure projects in the region. These studies have been challenged by several Brazilian ministries, which assert that recent improvements in environmental laws, enforcement and public attitudes have fundamentally reduced the threat posed to forests by such projects. The notion that hazards to Amazonian forests have declined over the last decade was assessed using available data on deforestation rates from 1978 to 2000. Although the alarmingly high rate of forest loss during 1978-1989 (1.98 million ha yr Ϫ1 ) declined somewhat in 1990-1994 (1.38 million ha yr Ϫ1 ), it rebounded to a high level in the period 1995-2000 (1.90 million ha yr Ϫ1 ). Moreover, correlation and regression analyses reveal that both absolute and per caput rates of forest loss accelerated significantly over the last decade. These trends fail to support the assertion that deforestation pressure in Amazonian forests has been brought under control. Poor enforcement of existing environmental laws, rapidly expanding logging and mining industries, increasing population pressure and other challenges are greatly hindering efforts to limit the environmental impacts of development activities in Brazilian Amazonia.

Aim To analyse the effects of forest fragmentation on ant communities in an Amazonian landscape that has been fragmented for over a century.Location The region surrounding the village of Alter do Chão in the Brazilian Amazonian state of Pará (2°30¢ S, 54°57¢ W).Methods Collection of ants and measurements of tree density were performed along transects established in eight sites in continuous forest and in 24 forest fragments surrounded by savanna vegetation. Data on size, perimeter, and degree of isolation (distance to continuous forest and distance to nearest area of forest > 5 ha) of each fragment were obtained from a georeferenced Landsat image of the study area.Results There were significant differences in species richness and composition between fragments and continuous forest, and these differences were not related to intersite variation in vegetation structure (tree density). Fragments supported fewer ant species per plot, and these species tended to represent a nested subset of those found in continuous forests. Fragments had significantly fewer rare species and fewer ant genera. However, fragments and continuous forest had similar numbers of species that also occur in the savanna matrix (i.e. that are not forest specialists). Multiple linear regression analyses indicated that species richness and composition in the fragments are significantly affected by fragment area, but not by fragment shape and degree of isolation. More species were found in larger fragments.Main conclusions Forest fragmentation influences the organization of ant communities in Amazonian savanna/forest landscapes. Forest fragments harboured, on average, 85% of the species found in continuous forest. That these fragments, despite their long history of isolation, support a relatively large complement of the species found in continuous forest is surprising, especially given that in some recently fragmented landscapes the proportion of species surviving in the fragments is lower. Differences in inter-fragment distance and type of matrix between Alter do Chão and these other landscapes may be involved. The fact that fragments at Alter do Chão are surrounded by a natural (rather than an anthropogenic) habitat, and that most of them are less than 300 m from another forest area, may have helped to ameliorate the adverse effects of forest fragmentation.

No abstract