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While forest evapotranspiration (ET) dynamics in the Amazon have been studied both as point estimates using flux towers, as well as spatially coarse surfaces using satellite data, higher resolution (e.g., 30 m resolution) ET estimates are necessary to address finer spatial variability associated with forest biophysical characteristics and their changes by natural and human impacts. The objective of this study is to evaluate the potential of the Landsat-based METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model to estimate high-resolution (30 m) forest ET by comparing to flux tower ET (FT ET) data collected over seasonally dry tropical forests in Rondônia, the southwestern region of the Amazon. Analyses were conducted at daily, monthly and seasonal scales for the dry seasons (June-September for Rondônia) of 2000-2002. Overall daily ET comparison between FT ET and METRIC ET across the study site showed r² = 0.67 with RMSE = 0.81 mm. For seasonal ET comparison, METRIC-derived ET estimates showed an agreement with FT ET measurements during the dry season of r² >0.70 and %MAE <15%. We also discuss some challenges and potential applications of METRIC for Amazonian forests. [ABSTRACT FROM AUTHOR]

Fire is frequently used as tool for land management in the Amazon, but often escapes into surrounding forests, with potentially severe impacts for forest biodiversity. We investigated the effects of single wildfires on ant communities in four geographically distinct regions of the Brazilian Amazon (Roraima, Pará, Acre and Mato Grosso) where forests had burned between 8 months and 10 years before our sampling. We established 7-12 transects, 500 m each, in burned and unburned forests in each region to investigate the effects of fire on forest structure and leaf litter ant communities, which were sampled using Winkler sacks. Fire effects on forest structure were more drastic in the most recently burned forests in Acre and Mato Grosso, while the impacts of older burns in Roraima and Pará were more subtle. Ant species richness was not different between burnt and unburned areas, but community composition differed between burned and control forests in all regions except Mato Grosso. At the species level, indicator species analysis showed that a limited number of species were significant indicators of unburned control forests in all regions, except Acre. Forests structure variables and leaf litter volume were all important in shaping ant communities, but their relative importance varied between regions. Our results indicate that burned forest have different ant species communities from unburned forests, and those differences are still apparent 10 years after the disturbance, highlighting the importance of effective policies for fire management in Amazon. [ABSTRACT FROM AUTHOR]

Fire has become an increasingly important disturbance event in south-western Amazonia. We conducted the first assessment of the ecological impacts of these wildfires in 2008, sampling forest structure and biodiversity along twelve 500 m transects in the Chico Mendes Extractive Reserve, Acre, Brazil. Six transects were placed in unburned forests and six were in forests that burned during a series of forest fires that occurred from August to October 2005. Normalized Burn Ratio (NBR) calculations, based on Landsat reflectance data, indicate that all transects were similar prior to the fires. We sampled understorey and canopy vegetation, birds using both mist nets and point counts, coprophagous dung beetles and the leaflitter ant fauna. Fire had limited influence upon either faunal or floral species richness or community structure responses, and stems <10 cm DBH were the only group to show highly significant (p = 0.001) community turnover in burned forests. Mean aboveground live biomass was statistically indistinguishable in the unburned and burned plots, although there was a significant increase in the total abundance of dead stems in burned plots. Comparisons with previous studies suggest that wildfires had much less effect upon forest structure and biodiversity in these south-western Amazonian forests than in central and eastern Amazonia, where most fire research has been undertaken to date. We discuss potential reasons for the apparent greater resilience of our study plots to wildfire, examining the role of fire intensity, bamboo dominance, background rates of disturbance, landscape and soil conditions. [ABSTRACT FROM AUTHOR]

Abstract: Forest edges in the Amazon are very dynamic with ongoing deforestation adding new edges as older edges are eroded. Rates of edge erosion and the composition of edge ages, together with distance from edges, are very important factors in determining the magnitude of forest degradation such as biomass collapse and carbon flux. However, we lack an understanding of how these factors change through time and over the different stages of deforestation. In this study, we quantify the spatial and temporal structures of forest edge in Rondônia, southwestern Amazon, by analyses of 22 years of annual satellite imagery, and discuss the implications for biomass dynamics and forest degradation caused by edges. Our results from three different stages of deforestation (early, intermediate and advanced) reveal that more than 50% of forest edges were eliminated in the first four years after edge creation and only 20% of edges survived more than 10 years. High edge erosion rates in the first year imply that many edges disappear before going through the process of edge-induced biomass collapse. At the early stage of deforestation, young forest edges are predominant, while at the advanced deforestation stage more than 50% of total edges are >10 years old. Rapid erosion is more prevalent in early stages, when young forest edges dominate the landscape. Edge-related biomass collapse is substantially more advanced in heavily deforested regions where forests are mostly surrounded mostly by older edges, but relatively few edges remain at this point. [Copyright &y& Elsevier]

We used two hyperspectral sensors at two different scales to test their potential to estimate biophysical properties of grazed pastures in Rondônia in the Brazilian Amazon. Using a field spectrometer, ten remotely sensed measurements (i.e., two vegetation indices, four fractions of spectral mixture analysis, and four spectral absorption features) were generated for two grass species, Brachiaria brizantha and Brachiaria decumbens. These measures were compared to above ground biomass, live and senesced biomass, and grass canopy water content. The sample size was 69 samples for field grass biophysical data and grass canopy reflectance. Water absorption measures between 1100 and 1250 nm had the highest correlations with above ground biomass, live biomass and canopy water content, while ligno-cellulose absorption measures between 2045 and 2218 nm were the best for estimating senesced biomass. These results suggest possible improvements on estimating grass measures using spectral absorption features derived from hyperspectral sensors. However, relationships were highly influenced by grass species architecture. B. decumbens, a more homogeneous, low growing species, had higher correlations between remotely sensed measures and biomass than B. brizantha, a more heterogeneous, vertically oriented species. The potential of using the Earth Observing-1 Hyperion data for pasture characterization was assessed and validated using field spectrometer and CCD camera data. Hyperion-derived NPV fraction provided better estimates of grass surface fraction compared to fractions generated from convolved ETM+/Landsat 7 data and minimized the problem of spectral ambiguity between NPV and Soil. The results suggest possible improvement of the quality of land-cover maps compared to maps made using multispectral sensors for the Amazon region. [Copyright &y& Elsevier]

Remote sensing has the potential of improving our ability to map and monitor pasture degradation. Pasture degradation is one of the most important problems in the Amazon, yet the manner in which grazing intensity, edaphic conditions and land‐use age impact pasture biophysical properties, and our ability to monitor them using remote sensing is poorly known. We evaluate the connection between field grass biophysical measures and remote sensing, and investigate the impact of grazing intensity on pasture biophysical measures in Rondônia, in the Brazilian Amazon. Above ground biomass, canopy water content and height were measured in different pasture sites during the dry season. Using Landsat Thematic Mapper (TM) data, four spectral vegetation indices and fractions derived from spectral mixture analysis, i.e., Non‐Photosynthetic Vegetation (NPV), Green Vegetation (GV), Soil, Shade, and NPV+Soil, were calculated and compared to field grass measures. For grazed pastures under dry conditions, the Normalized Difference Infrared Index (NDII5 and NDII7), had higher correlations with the biophysical measures than the Normalized Difference Vegetation Index (NDVI) and the Soil‐Adjusted Vegetation Index (SAVI). NPV had the highest correlations with all field measures, suggesting this fraction is a good indicator of pasture characteristics in Rondônia. Pasture height was correlated to the Shade fraction. A conceptual model was built for pasture biophysical change using three fractions, i.e., NPV, Shade and GV to characterize possible pasture degradation processes in Rondônia. Based upon field measures, grazing intensity had the most significant impact on pasture biophysical properties compared to soil order and land‐use age. The impact of grazing on pastures in the dry season could be potentially measured by using remotely sensed measures such as NPV. [Copyright &y& Elsevier]