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The Amazon River, its huge basin, and the changes in biological processes that are rapidly occurring in this region are unquestionably of global significance. Hence, Global Change Biology is delighted to host a special thematic issue devoted to the Large-scale Biosphere-Atmosphere Experiment in Amazônia (LBA), which is a multinational, interdisciplinary research program led by Brazil. The goal of LBA is no less modest than its subject: to understand how Amazônia functions as a regional entity in the Earth system and how these functions are changing as a result of ongoing changes in land use. This compilation of 26 papers resulting from LBA-related research covers a broad range of topics: forest stocks of carbon (C) and nitrogen (N); fluxes of greenhouse gases and volatile organic compounds from vegetation, soils and wetlands; mapping and modeling land-use change, fire risk, and soil properties; measuring changes caused by logging, pasturing and cultivating; and new research approaches in meteorology to estimate nocturnal fluxes of C from forests and pastures. Some important new synthesis can be derived from these and other studies. The aboveground biomass of intact Amazonian forests appears to be a sink for atmospheric carbon dioxide (CO2), while the wetlands and soils are a net source of atmospheric methane (CH4) and nitrous oxide (N2O), respectively. Land-use change has, so far, had only a minor effect on basin-wide emissions of CH4 and N2O, but the net effect of deforestation and reforestation appears to be a significant net release of CO2 to the atmosphere. The sum of the 100-year global warming potentials (GWP) of these annual sources and sinks of CH4, N2O, and CO2 indicate that the Amazonian forest-river system currently may be nearly balanced in terms of the net GWP of these biogenic atmospheric gases. Of course, large uncertainties remain for these estimates, but the papers published here demonstrate tremendous progress, and also large remaining hurdles, in narrowing these uncertainties in our understanding of how Amazônia functions as a regional entity in the Earth system. [ABSTRACT FROM AUTHOR]

The authors simulated the effects of Amazonian mesoscale deforestation in the boundary layer and in rainfall with the Brazilian Regional Atmospheric Modeling System (BRAMS) model. They found that both the area and shape (with respect to wind incidence) of deforestation and the soil moisture status contributed to the state of the atmosphere during the time scale of several weeks, with distinguishable patterns of temperature, humidity, and rainfall. Deforestation resulted in the development of a three-dimensional thermal cell, the so-called deforestation breeze, slightly shifted downwind to large-scale circulation. The boundary layer was warmer and drier above 1000-m height and was slightly wetter up to 2000-m height. Soil wetness affected the circulation energetics proportionally to the soil dryness (for soil wetness below ∼∼0.6). The shape of the deforestation controlled the impact on rainfall. The horizontal strips lined up with the prevailing wind showed a dominant increase in rainfall, significant up to about 60 000 km2. On the other hand, in the patches aligned in the opposite direction (north--south), there was both increase and decrease in precipitation in two distinct regions, as a result of clearly separated upward and downward branches, which caused the precipitation to increase for patches up to 15 000 km2. The authors'' estimates for the size of deforestation impacting the rainfall contributed to fill up the low spatial resolution in other previous studies. [ABSTRACT FROM AUTHOR]

Our aim with this paper is to present a novel approach for developing story lines and scenarios by combining qualitative knowledge and quantitative data from different disciplines and discussing the results with relevant decision makers. This research strategy offers a solid foundation for perspectives into the future. The "laboratory" is the Brazilian Amazon, one of the hotspots of land-use change where local and global interests both collide and converge: local livelihoods are affected by regional and global climate change and by the loss of biodiversity caused by local and global economic interests in agro-industrial land use; such use contributes, in turn, to climate change. After decades of diverse policy interventions the question arises: What can we learn from past trajectories for a more sustainable development in the future? To answer this question, we combined qualitative story lines for the region, reviewed by local experts, with quantitative land-use scenarios, to study their regional and local manifestations in space. These results were then discussed again with local and national experts. Our findings suggest that in-depth knowledge of the diverging perspectives at a very local level is a fundamental prerequisite for downscaling global scenarios and upscaling local approaches to sustainable land-use management and thus, to producing communicable and applicable results. [ABSTRACT FROM AUTHOR]

Reconstruction of Highway BR-319 (Manaus-Porto Velho) would allow for access from the 'arc of deforestation' in the southern part of Brazil's Amazon region to vast blocks of forests in central and northern Amazonia. Building roads is known to be a major driver of deforestation, allowing entry of squatters, and other actors. Rather than deforestation along the highway route, here we consider the road's potential for stimulating deforestation in a separate location, approximately 550 km north of BR-319's endpoint in Manaus. Reconstructing BR-319 has great potential impact to start a new wave of migration to this remote region. The southern portion of the state of Roraima, the focus of our study, is already connected to Manaus by Highway BR-174. We modeled deforestation in southern Roraima and simulated carbon emissions between 2007 and 2030 under four scenarios. Simulations used the AGROECO model in DINAMICA-EGO © software. Two scenarios were considered with reconstruction of BR-319 and two without this road connection. For each of the two possibilities regarding BR-319, simulations were developed for (1) a 'conservation' (CONSERV) scenario that assumes the creation of a series of protected areas, and (2) a 'business-as-usual' (BAU) scenario that assumes no additional protected areas. Results show that by 2030, with BR-319 rebuilt, deforestation carbon emissions would increase between 19 % (CONSERV) and 42 % (BAU) over and above those corresponding to no-road scenarios. [ABSTRACT FROM AUTHOR]