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The Amazon forest has the highest biodiversity on Earth. However, information on Amazonian vertebrate diversity is still deficient and scattered across the published, peer‐reviewed, and gray literature and in unpublished raw data. Camera traps are an effective non‐invasive method of surveying vertebrates, applicable to different scales of time and space. In this study, we organized and standardized camera trap records from different Amazon regions to compile the most extensive data set of inventories of mammal, bird, and reptile species ever assembled for the area. The complete data set comprises 154,123 records of 317 species (185 birds, 119 mammals, and 13 reptiles) gathered from surveys from the Amazonian portion of eight countries (Brazil, Bolivia, Colombia, Ecuador, French Guiana, Peru, Suriname, and Venezuela). The most frequently recorded species per taxa were: mammals: Cuniculus paca (11,907 records); birds: Pauxi tuberosa (3713 records); and reptiles: Tupinambis teguixin (716 records). The information detailed in this data paper opens up opportunities for new ecological studies at different spatial and temporal scales, allowing for a more accurate evaluation of the effects of habitat loss, fragmentation, climate change, and other human‐mediated defaunation processes in one of the most important and threatened tropical environments in the world. The data set is not copyright restricted; please cite this data paper when using its data in publications and we also request that researchers and educators inform us of how they are using these data. [ABSTRACT FROM AUTHOR]

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 rich ecology of tropical forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-tropical and regional-scale analyses of tree vulnerability to drought. •We assembled available data on tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. •In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. •These findings indicate that repeated droughts would shift the functional composition of tropical forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some tropical forests would suffer catastrophic tree mortality. [ABSTRACT FROM AUTHOR]

This paper describes a severe outbreak of a Lepidopteran defoliator, Lusura altrix (Stoll 1782), on Brazil nut trees in Central Amazonia. The pest outbreak appeared to succeed abnormal weather conditions, and defoliation was sufficient to disrupt normal phenological patterns. [ABSTRACT FROM AUTHOR]

Amazon forests are being degraded by myriad anthropogenic disturbances, altering ecosystem and climate function. We analyzed the effects of a range of land‐use and climate‐change disturbances on fine‐scale canopy structure using a large database of profiling canopy lidar collected from disturbed and mature Amazon forest plots. At most of the disturbed sites, surveys were conducted 10–30 years after disturbance, with many exhibiting signs of recovery. Structural impacts differed in magnitude more than in character among disturbance types, producing a gradient of impacts. Structural changes were highly coordinated in a manner consistent across disturbance types, indicating commonalities in regeneration pathways. At the most severely affected site – burned igapó (seasonally flooded forest) – no signs of canopy regeneration were observed, indicating a sustained alteration of microclimates and consequently greater vulnerability to transitioning to a more open‐canopy, savanna‐like state. Notably, disturbances rarely shifted forests beyond the natural background of structural variation within mature plots, highlighting the similarities between anthropogenic and natural disturbance regimes, and indicating a degree of resilience among Amazon forests. Studying diverse disturbance types within an integrated analytical framework builds capacity to predict the risk of degradation‐driven forest transitions. [ABSTRACT FROM AUTHOR]

Extreme precipitation and drought events are predicted to become more intense and more frequent over the Amazon rainforest. Because changes in forest dynamics could prompt strong feedback loops to the global climate, it is of crucial importance to gain insight into the response of tropical forests to these recurring extreme climatic events. Here, we evaluated the Amazon forest stability (resistance and resilience) to drought in the context of past dry and wet climatic events using MODIS EVI satellite imagery and cumulative water deficit anomalies. We observed large spatial differences in the occurrence of extreme climatic events from 1980 to 2019, with an increase in drought frequency in the central and northern Amazon and drought intensity in the southern Amazon basin. An increasing trend in the occurrence of wet events was found in the western, southern, and eastern Amazon. Furthermore, we found significant legacy effects of previous climatic events on the forest drought response. An extreme drought closely preceding another drought decreased forest resilience, whereas the occurrence of a recent drier‐than‐usual event also decreased the forest resistance to later droughts. Both wetter‐than‐usual and extreme wet events preceding an extreme drought increased the resistance of the forest, and with similar effects sizes as dry events, indicating that wet and dry events have similarly sized legacy effects on the drought response of tropical forests. Our results indicate that the predicted increase in drought frequency and intensity can have negative consequences for the functioning of the Amazon forest. However, more frequent wet periods in combination with these droughts could counteract their negative impact. Finally, we also found that more stable forests according to the alternative stable states theory are also more resistant and resilient to individual droughts, showing a positive relationship between the equilibrium and non‐equilibrium stability dynamics. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Applied Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article focuses on crucial role of primary forests, such as the Amazon, in climate change mitigation that is recognized in the scientific literature. Topics include considered that Amazon fires of 2019 have heightened attention on the region and brought the question of Amazon conservation to the forefront of international debate.

Tropical forests are experiencing unprecedented high‐temperature conditions due to climate change that could limit their photosynthetic functions. We studied the high‐temperature sensitivity of photosynthesis in a rainforest site in southern Amazonia, where some of the highest temperatures and most rapid warming in the Tropics have been recorded. The quantum yield (Fv/Fm) of photosystem II was measured in seven dominant tree species using leaf discs exposed to varying levels of heat stress. T50 was calculated as the temperature at which Fv/Fm was half the maximum value. T5 is defined as the breakpoint temperature, at which Fv/Fm decline was initiated. Leaf thermotolerance in the rapidly warming southern Amazonia was the highest recorded for forest tree species globally. T50 and T5 varied between species, with one mid‐storey species, Amaioua guianensis, exhibiting particularly high T50 and T5 values. While the T50 values of the species sampled were several degrees above the maximum air temperatures experienced in southern Amazonia, the T5 values of several species are now exceeded under present‐day maximum air temperatures. Although high‐temperature tolerance of photosystem II (PSII) in trees from the southern Amazonian forests was the highest in the literature, maximum air temperatures during the dry periods has already reached levels that overlap with the range of PSII temperature sensitivity. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Climate change will redistribute the global biodiversity in the Anthropocene. As climates change, species might move from one place to another, due to local extinctions and colonization of new environments. However, the existence of permeable migratory routes precedes faunal migrations in fragmented landscapes. Here, we investigate how dispersal will affect the outcome of climate change on the distribution of Amazon's primate species. We modeled the distribution of 80 Amazon primate species, using ecological niche models, and projected their potential distribution on scenarios of climate change. Then, we imposed landscape restrictions to primate dispersal, derived from a natural biogeographical barrier to primates (the main tributaries of the Amazon river) and an anthropogenic constraint to the migration of many canopy‐dependent animals (deforested areas). We also highlighted potential conflict zones, i.e. regions of high migration potential but predicted to be deforested. Species response to climate change varied across dispersal limitation scenarios. If species could occupy all newly suitable climate, almost 70% of species could expand ranges. Including dispersal barriers (natural and anthropogenic), however, led to range expansion in only less than 20% of the studied species. When species were not allowed to migrate, all of them lost an average of 90% of the suitable area, suggesting that climate may become unsuitable within their present distributions. All Amazon primate species may need to move as climate changes to avoid deleterious effects of exposure to non‐analog climates. The effect of climate change on the distribution of Amazon primates will ultimately depend on whether landscape permeability will allow climate‐driven faunal migrations. The network of protected areas in the Amazon could work as 'stepping stones' but most are outside important migratory routes. Therefore, protecting important dispersal corridors is foremost to allow effective migrations of the Amazon fauna in face of climate change and deforestation. [ABSTRACT FROM AUTHOR]

Wildfires are increasingly affecting forest landscapes around the world. In the Bolivian Chiquitania, southern Amazonia, large wildfires during recent droughts have intensified public debate around more systemic solutions to address the possible root causes. While the integration of different forms of fire knowledge is gaining acceptance as an approach to dealing with increasing wildfire risk, little attention has been given to this integration in the Amazonia. In fact, mismatches between policy, science and local realities have curtailed the success of fire risk strategies in the region. To address this challenge, we conducted interviews and focus group discussions with a wide range of actors in the Chiquitania to examine different forms of knowledge and views of fire, and the extent to which these were integrated in prevalent wildfire risk strategies. We found that the risk strategies were in tension between two conflicting understandings of fire. A conceptual framework was developed to capture the configuration of knowledge underpinning this tension. Adopting a more integrated and inclusive approach to manage wildfire risk will require overcoming first this tension through a more open deliberation process within a reflexive governance framework. We proposed three "deliberation arenas" to facilitate this process, which could ultimately support more systemic, inter‐cultural fire management in the Chiquitania and other landscapes with conflicting views in the Amazonia. [ABSTRACT FROM AUTHOR]

Abstract: Brazil is one of the major contributors to land‐use change emissions, mostly driven by agricultural expansion for food, feed, and bioenergy feedstock. Policies to avoid deforestation related to private commitments, economic incentives, and other support schemes are expected to improve the effectiveness of current command and control mechanisms increasingly. However, until recently, land tenure was unknown for much of the Brazilian territory, which has undermined the governance of native vegetation and challenged support and incentive mechanisms for avoiding deforestation. We assess the total extent of public governance mechanisms protecting aboveground carbon (AGC) stocks. We constructed a land tenure dataset for the entire nation and modeled the effects and uncertainties of major land‐use acts on protecting AGC stocks. Roughly 70% of the AGC stock in Brazil is estimated to be under legal protection, and an additional 20% is expected to be protected after areas in the Amazon with currently undesignated land undergo a tenure regularization. About 30% of the AGC stock is on private land, of which roughly two‐thirds are protected. The Cerrado, Amazon, and Caatinga biomes hold about 40%, 30%, and 20% of the unprotected AGC, respectively. Effective conservation of protected and unprotected carbon will depend on successful implementation of the Forest Act, and regularization of land tenure in the Amazon. Policy development that prioritizes unprotected AGC stocks is warranted to promote conservation of native vegetation beyond the legal requirements. However, different biomes and land tenure structures may require different policy settings considering local and regional specifics. Finally, the fate of current AGC stocks relies upon effective implementation of command and control mechanisms, considering that unprotected AGC in native vegetation on private land only accounts for 6.5% of the total AGC stock. [ABSTRACT FROM AUTHOR]

Tropical second-growth forests could help mitigate climate change, but the degree to which their carbon potential is achieved will depend on exposure to disturbance. Wind disturbance is common in tropical forests, shaping structure, composition, and function, and influencing successional trajectories. However, little is known about the impacts of extreme winds on second-growth forests in fragmented landscapes, though these ecosystems are often located in mosaics of forest, pasture, cropland, and other land cover types. Indirect evidence suggests that fragmentation increases risk of wind damage in tropical forests, but no studies have found such impacts following severe storms. In this study, we ask whether fragmentation and forest type (old vs. second growth) were associated with variation in wind damage after a severe convective storm in a fragmented production landscape in western Amazonia. We applied linear spectral unmixing to Landsat 8 imagery from before and after the storm, and combined it with field observations of damage to map wind effects on forest structure and biomass. We also used Landsat 8 imagery to map land cover with the goals of identifying old- and second-growth forest and characterizing fragmentation. We used these data to assess variation in wind disturbance across 95,596 ha of forest, distributed over 6,110 patches. We find that fragmentation is significantly associated with wind damage, with damage severity higher at forest edges and in edgier, more isolated patches. Damage was also more severe in old-growth than in second-growth forests, but this effect was weaker than that of fragmentation. These results illustrate the importance of considering landscape context in planning tropical forest restoration and natural regeneration projects. Assessments of long-term carbon sequestration potential need to consider spatial variation in disturbance exposure. Where risk of extreme winds is high, minimizing fragmentation and isolation could increase carbon sequestration potential. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The number of species is known to decrease from the humid tropics towards drier and colder climates, but how species richness varies along environmental and spatial gradients within the tropical rain forests is not clear. We inventoried 214 transects of 0.25 ha to document species diversity patterns in an example plant group (ferns and lycophytes) across non-inundated rain forests of western and central Amazonia, and assessed how well these conformed with proposed hypotheses about species richness. The observed number of species varied between 6 and 71 per transect. The effective number of species (emphasising the degree of unevenness in species abundances) varied between 1.02 and 8.60, and diversity profiles revealed considerable differences among transects in community structure. Although the density of individuals varied over almost two orders of magnitude, species diversity was better explained by other variables. In particular, within-transect species diversity increased substantially with increasing soil cation concentration. It also increased with soil aluminium concentration, heterogeneity in soil chemistry, annual rainfall and dry season rainfall, and was higher in western than in central Amazonia. Multiple regression models explained up to 70% of the variance in species diversity, but the relationships between species diversity and the environmental gradients became progressively weaker as species abundances were given more weight in the calculation of diversity. Our results conformed to the proposal that site productivity promotes species diversity. This seemed to arise from larger species pools on more fertile soils and in wetter climates, even when it could be expected that the older and more widespread infertile soils would have provided more opportunities for speciation. [ABSTRACT FROM AUTHOR]

There is evidence that climate change induced tree mortalities in boreal and temperate forests and increased forest turnover rates (both mortality and recruitment rates) in Amazon forests. However, no study has examined China's tropical and subtropical evergreen broadleaved forests ( TEBF) that cover >26% of China's terrestrial land. The sustainability of this biome is vital to the maintenance of local ecosystem services (e.g., carbon sequestration, biodiversity conservation, climatic regulation), many of which may influence patterns of atmospheric circulation and composition at regional to global scales. Here, we analyze time-series data collected from thirteen permanent plots within China's unmanaged TEBF to study whether and how this biome has changed over recent decades. We find that the numbers of individuals and species for shrub and small tree have increased since 1978, whereas the numbers of individuals and species for tree have decreased over this same time period. The shift in species composition is accompanied by a decrease in the mean diameter at breast height ( DBH) for all individuals combined. China's TEBF may thereby be transitioning from cohorts of fewer and larger individuals to ones of more and smaller individuals, which shows a unique change pattern differing from the documented. Regional-scale drying is likely responsible for the biome's reorganization. This biome-wide reconstitution would deeply impact the regimes of carbon sequestration and biodiversity conservation and have implications for the sustainability of economic development in the area. [ABSTRACT FROM AUTHOR]

The dense, intact rainforests of the Guianas (northern Amazonia) are important for the regulation of the local and regional climate, but preclude easy access so a large data gap exists. The rainforest-savannah boundary may also be particularly susceptible to increasing pressures from ecosystem exploitation and climate change. It is important therefore to establish a baseline climate regime so that the impacts of any future change can be determined. Currently this area is not covered by the publicly available climate data sets, so interpolated data sets are not an accurate representation of the climate of this area, emphasizing the need for a more detailed analysis in this region. Here, we collate the available data sets and use these to derive maps of observed precipitation and temperature across the region. To overcome the limitations in the inadequate observational data sets, we also test and use the ECMWF ERA-40 reanalysis data set for the period 1958-2001 at a ∼125 km2 (1.125°) resolution. Mean differences (biases) and annual average spatial correlations are examined between modelled and observed time series comparing the seasonal cycles and the yearly, monthly and monthly anomaly time series. The results show that with the exception of sub-grid resolution mountain environments, reanalysis data for the Guianas provide a consistent and relatively accurate spatial distribution of temperature. Precipitation is modelled less accurately, with best results for the average timings, length and severity of the dry periods. This study provides consistent and quantitative details on the spatial variations in seasonality, particularly in areas lacking observations, thereby advancing beyond previous studies. Precipitation is highly variable in the region so care must be taken when averaging modelled data over large geographical areas for comparisons with gridded data sets based on few observations. This is the first comprehensive study of the recent historical climate and its variability in this area. Copyright © 2011 The Authors. Journal compilation © 2011 The Royal Meteorological Society [ABSTRACT FROM AUTHOR]

There is great interest among policy makers in the potential of carbon-based payments for ecosystem services (PES) to reduce carbon emissions from deforestation and protect forests in tropical countries. We discuss the contributions that ecologists can make to the interdisciplinary research required to inform the design of these initiatives. First, we highlight the need to quantify the full range of processes that determine temporal variation in carbon stocks at a landscape-scale due to cycles of forest disturbance and recovery. Second, we discuss the importance of understanding how the impact of climate change on the carbon stocks of intact forests may affect the emissions reductions achieved by any given project: we show that this may reduce the effectiveness of one carbon-based PES project in southern Peru by 15%. We also discuss the need to assess project impacts on deforestation in the surrounding region and explore how different project designs influence the balance between the conservation of carbon and biodiversity . The need to demonstrate emissions reductions or carbon storage to investors in carbon-based payment schemes provides an imperative for monitoring their effectiveness. Monitoring will be a significant cost in any PES project and, together with project set-up, on average accounts for more than 40% of project expenditure across six emerging Peruvian PES schemes. Ecologists will therefore have an important role in designing cost-effective monitoring strategies. The impetus for monitoring also provides opportunities to carry out research addressing many of the uncertainties highlighted above. Synthesis and applications. By working closely with a range of carbon-based PES projects, ecologists can answer important fundamental questions related to the provision of ecosystem services and help improve the design of these schemes. The large number of projects currently being implemented provides an unprecedented opportunity to develop a proper evidence base for measuring and improving the practices that most successfully conserve tropical forest ecosystems. [ABSTRACT FROM AUTHOR]

1. Climate change predictions in the Amazon have largely focused on carbon-water relations, while the impacts of increased air temperature and reduced precipitation on host-pathogen relationships have not been extensively explored. These relationships are known to affect recruitment of many Amazonian plant species. 2. Host-pathogen relationships are well suited to a dynamical analysis of the effects of climate change due to the direct linkages between pathogen behaviour and abiotic factors such as temperature and rainfall. 3. Seedlings of the palm Iriartea deltoidea experience significant mortality due to infection by the fungus Diplodia mutila. This host-pathogen interaction was examined by combining a semi-analytical model with field data illustrating the temperature sensitivity of D. mutila reproductive rates and I. deltoidea seedling mortality in response to infection. 4. The data-model combination shows that projected climatic shifts in rainfall and temperature for the Amazon region will tend to reduce recruitment by altering pathogen activity and reducing palm fecundity. The magnitude of the reduction is sensitive to the details of the epidemiology of the D. mutila-I. deltoidea host-pathogen system, and ranges from 10% to 56% under plausible scenarios. 5. Although considerable uncertainty remains, the proposed model provides a blueprint for research on one aspect of ecosystem change in future climate models. 6. Synthesis. The study illustrates the potential for ecosystem responses to climate change, which can be investigated through tractable models simple enough to assimilate into climate modelling frameworks. Particular environmental sensitivities in fungal dynamics are identified. The implications of combined plant physiological stress and enhanced pathogenic activity under future climate scenarios are highlighted as critical issues for projecting forest response. [ABSTRACT FROM AUTHOR]

We report on the population response of a species of rodent, Necromys lasiurus, to southern oscillation index (SOI) and extent of regional fire in an Amazonian savanna. Information on temporal variation in local abundance of N. lasiurus in a 4.0 ha savanna plot was obtained from 1985 to 1989, from 1997 to 1998 and 2000–2006, giving data on 14 of the 22 years. Throughout this period, rodent density declined by 90%. Densities were positively associated with SOI and the extent of fire in the region. Rainfall was related to SOI and negatively influenced the extent of fire. However, the amount of rain had no measurable direct effect on rat densities. Thus, small changes in temperature, and consequently fire probability and intensity, may have drastic consequences on the biota of Amazonian savannas, especially in El Niño periods. [ABSTRACT FROM AUTHOR]

•The large-scale loss of Amazonian rainforest under some future climate scenarios has generally been considered to be driven by increased drying over Amazonia predicted by some general circulation models (GCMs). However, the importance of rainfall relative to other drivers has never been formally examined. •Here, we conducted factorial simulations to ascertain the contributions of four environmental drivers (precipitation, temperature, humidity and CO2) to simulated changes in Amazonian vegetation carbon ( Cveg), in three dynamic global vegetation models (DGVMs) forced with climate data based on HadCM3 for four SRES scenarios. •Increased temperature was found to be more important than precipitation reduction in causing losses of Amazonian Cveg in two DGVMs (Hyland and TRIFFID), and as important as precipitation reduction in a third DGVM (LPJ). Increases in plant respiration, direct declines in photosynthesis and increases in vapour pressure deficit (VPD) all contributed to reduce Cveg under high temperature, but the contribution of each mechanism varied greatly across models. Rising CO2 mitigated much of the climate-driven biomass losses in the models. •Additional work is required to constrain model behaviour with experimental data under conditions of high temperature and drought. Current models may be overly sensitive to long-term elevated temperatures as they do not account for physiological acclimation. [ABSTRACT FROM AUTHOR]

•Remote sensing data are a key tool to assess large forested areas, where limitations such as accessibility and lack of field measurements are prevalent. Here, we have analysed datasets from moderate resolution imaging spectroradiometer (MODIS) satellite measurements and field data to assess the impacts of the 2005 drought in Amazonia. •We combined vegetation indices (VI) and climatological variables to evaluate the spatiotemporal patterns associated with the 2005 drought, and explore the relationships between remotely-sensed indices and forest inventory data on tree mortality. •There were differences in results based on c4 and c5 MODIS products. C5 VI showed no spatial relationship with rainfall or aerosol optical depth; however, distinct regions responded significantly to the increased radiation in 2005. The increase in the Enhanced VI (EVI) during 2005 showed a significant positive relationship ( P < 0.07) with the increase of tree mortality. By contrast, the normalized difference water index (NDWI) exhibited a significant negative relationship ( P < 0.09) with tree mortality. •Previous studies have suggested that the increase in EVI during the 2005 drought was associated with a positive response of forest photosynthesis to changes in the radiation income. We discuss the evidence that this increase could be related to structural changes in the canopy. [ABSTRACT FROM AUTHOR]

Ecology Letters (2010) 13: 793-802 Abstract We test for two critical phenomena in Amazonian ecosystems: self-organized criticality (SOC) and critical transitions. SOC is often presented in the complex systems literature as a general explanation for scale invariance in nature. In particular, this mechanism is claimed to underlie the macroscopic structure and dynamics of terrestrial ecosystems. These would be inextricably linked to the action of fire, which is conceived as an endogenous ecological process. We show that Amazonian savanna fires display the scale-invariant features characteristic of SOC but do not display SOC. The same is true in Amazonian rainforests subject to moderate drought. These findings prove that there are other causes of scale invariance in ecosystems. In contrast, we do find evidence of a critical transition to a megafire regime under extreme drought in rainforests; this phenomenon is likely to determine the time scale of a possible loss of Amazonian rainforest caused by climate change. [ABSTRACT FROM AUTHOR]

Positive aboveground biomass trends have been reported from old-growth forests across the Amazon basin and hypothesized to reflect a large-scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old-growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data-based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near-identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential–power law distribution to account for potential large-scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change. [ABSTRACT FROM AUTHOR]

There is increasing consensus that the global climate will continue to warm over the next century. The biodiversity-rich Amazon forest is a region of growing concern because many global climate model (GCM) scenarios of climate change forecast reduced precipitation and, in some cases, coupled vegetation models predict dieback of the forest. To date, fires have generally been spatially co-located with road networks and associated human land use because almost all fires in this region are anthropogenic in origin. Climate change, if severe enough, could alter this situation, potentially changing the fire regime to one of increased fire frequency and severity for vast portions of the Amazon forest. High moisture contents and dense canopies have historically made Amazonian forests extremely resistant to fire spread. Climate will affect the fire situation in the Amazon directly, through changes in temperature and precipitation, and indirectly, through climate-forced changes in vegetation composition and structure. The frequency of drought will be a prime determinant of both how often forest fires occur and how extensive they become. Fire risk management needs to take into account landscape configuration, land cover types and forest disturbance history as well as climate and weather. Maintaining large blocks of unsettled forest is critical for managing landscape level fire in the Amazon. The Amazon has resisted previous climate changes and should adapt to future climates as well if landscapes can be managed to maintain natural fire regimes in the majority of forest remnants. [ABSTRACT FROM AUTHOR]

We analyzed the most extensive data set of tree inventory plots spread over the complete Amazon basin and Guiana shield. We aimed to separate the regional and local tree alpha-diversity to investigate the drivers of diversity at the relevant scale. Our results are consistent with the partitioning of total tree alpha-diversity into regional and local components, which are controlled by evolutionary- and ecological processes, respectively. Regional diversity is correlated with palaeo-climatic stability (31%), and long-term large-scale ecosystem dynamics (14%), as represented by the age of the geological formation. Both mechanisms contribute to high diversity in the central to western Amazon. Actual rainfall seasonality is correlated with regional tree diversity to a certain extent (19%), but we argue that this is of little consequence for the evolutionary drivers of the regional species pool. Frequency of disturbance is the main process driving local diversity, although its explanatory power is relatively small (17%). [ABSTRACT FROM AUTHOR]

Deforestation in Amazonia seems likely to continue in the 21st century, and fire risk could increase as a result of global climate change. With deforestation activities providing a source of ignition, the combination of this with increased fire risk could lead to widespread impacts on Amazonian ecosystems. This would also contribute further to climate change through feedbacks on the global carbon cycle. This study uses the McArthur Forest Fire Danger Index and an ensemble of variants of the HadCM3 climate model to simulate potential changes to fire risk in Amazonia over the 21st century. Significant increases in central and eastem Amazonia are simulated by 2020, and high fire danger for over 50% of the forest is simulated in all model runs by 2080. By 2080, as much as 25% of Amazonia shows high levels of agreement in projections of combined fire risk and deforestation. The areas simulated with high fire danger are also those projected to be impacted most significantly by deforestation. If the regional climate changes simulated for Amazonia by HadCM3 are realistic, the risk of significant forest damage could become high, and deforestation activities could, therefore, have a greater potential for impacting on wider areas of forest. [ABSTRACT FROM AUTHOR]

Warmer and drier climates over Eastern Amazonia have been predicted as a component of climate change during the next 50–100 years. It remains unclear what effect such changes will have on forest–atmosphere exchange of carbon dioxide (CO2) and water, but the cumulative effect is anticipated to produce climatic feedback at both regional and global scales. To allow more detailed study of forest responses to soil drying, a simulated soil drought or ‘throughfall exclusion’ (TFE) experiment was established at a rain forest site in Eastern Amazonia, Brazil, for which time-series sap flow and soil moisture data were obtained. The experiment excluded 50% of the throughfall from the soil. Sap flow data from the forest plot experiencing normal rainfall showed no limitation of transpiration throughout the two monitored dry seasons. Conversely, data from the TFE showed large dry season declines in transpiration, with tree water use restricted to 20% of that in the control plot at the peak of both dry seasons. The results were examined to evaluate the paradigm that the restriction on transpiration in the dry season was caused by limitation of soil-to-root water transport, driven by low soil water potential and high soil-to-root hydraulic resistance. This paradigm, embedded in the soil–plant–atmosphere (SPA) model and driven using on-site measurements, provided a good explanation ( R2 > 0.69) of the magnitude and timing of changes in sap flow and soil moisture. This model-data correspondence represents a substantial improvement compared with other ecosystem models of drought stress tested in Amazonia. Inclusion of deeper rooting should lead to lower sensitivity to drought than the majority of existing models. Modelled annual GPP declined by 13–14% in response to the treatment, compared with estimated declines in transpiration of 30–40%. [ABSTRACT FROM AUTHOR]

Aim Using a Dynamic Global Vegetation Model (DGVM), we assessed the independent and co-varying effects of temperature, precipitation and atmospheric CO2 on nonlinear (threshold) responses in carbon-based processes, and evaluated whether these underlying process thresholds translate to the ecosystem-scale. Location Amazon Basin, South America. Methods The Lund-Potsdam-Jena model (LPJ) was employed to determine responses in net primary production (NPP), heterotrophic respiration (RH), vegetation carbon (CV), soil carbon (CS), and plant functional type (PFT) composition to variations in temperature (± 9 °C relative to the control), precipitation (up to 80% reduction in rainfall relative to the control) and atmospheric CO2 (± 100 p.p.m.v. relative to the control). Results Our modelling experiments show that increases in temperature result in lower and steeper NPP and RH curves, indicating a thermal threshold at current temperature conditions. Under a combination of temperature and precipitation change, CV responds more to precipitation, while CS closely follows temperature gradients. Ecosystem thresholds, measured in terms of PFT composition stability, are surprisingly few. Simulations indicate an ecosystem threshold occurring at 80% reduction in rainfall; however, due to modelling limitations, this threshold is likely to occur at earlier drought stress conditions. Further empirical research on abiotic stress tolerance levels in tropical ecosystems must be performed in order to refine PFT descriptions used in DGVMs. Main conclusion In evaluating simulation scenarios that promote major changes in PFT assemblage, we conclude that the ‘natural’ Amazonian rain forest is resilient to environmental change, particularly to decreases in temperature and precipitation. Determining to what extent anthropogenic pressures have altered this resiliency is of utmost importance in predicting the future fate of the Amazon Basin. [ABSTRACT FROM AUTHOR]

The nature of Amazonian ecosystem responses to the large-scale environmental changes characterizing glacial–interglacial cycles is poorly understood. We investigated this issue with a series of transient, continuous 21 000-year simulations using a dynamic process-based ecosystem model. Our results indicate that the Amazon Basin has been dominated by evergreen rain forests since the last glacial maximum (LGM), demonstrating the resilience of this ecosystem to glacial–interglacial environmental change. We find that biome shifts in ecotonal areas since the LGM were driven predominantly by climate change, while coincident, increased ecosystem carbon storage throughout the Amazon Basin was driven largely by CO2. Our findings imply that recent observed biomass increases in contemporary rain forest plots might be part of a long-term trend driven by the anthropogenic rise in CO2 over recent centuries. [ABSTRACT FROM AUTHOR]

Climate modelling studies predict that the rain forests of the Eastern Amazon basin are likely to experience reductions in rainfall of up to 50% over the next 50–100 years. Efforts to predict the effects of changing climate, especially drought stress, on forest gas exchange are currently limited by uncertainty about the mechanism that controls stomatal closure in response to low soil moisture. At a through-fall exclusion experiment in Eastern Amazonia where water was experimentally excluded from the soil, we tested the hypothesis that plants are isohydric, that is, when water is scarce, the stomata act to prevent leaf water potential from dropping below a critical threshold level. We made diurnal measurements of leaf water potential ( Ψl), stomatal conductance ( gs), sap flow and stem water potential ( Ψstem) in the wet and dry seasons. We compared the data with the predictions of the soil–plant–atmosphere (SPA) model, which embeds the isohydric hypothesis within its stomatal conductance algorithm. The model inputs for meteorology, leaf area index (LAI), soil water potential and soil-to-leaf hydraulic resistance ( R) were altered between seasons in accordance with measured values. No optimization parameters were used to adjust the model. This ‘mechanistic’ model of stomatal function was able to explain the individual tree-level seasonal changes in water relations ( r2 = 0.85, 0.90 and 0.58 for Ψl, sap flow and gs, respectively). The model indicated that the measured increase in R was the dominant cause of restricted water use during the dry season, resulting in a modelled restriction of sap flow four times greater than that caused by reduced soil water potential. Higher resistance during the dry season resulted from an increase in below-ground resistance (including root and soil-to-root resistance) to water flow. [ABSTRACT FROM AUTHOR]

To model long-term trends in plant species distributions in response to predicted changes in global climate.Amazonia.The impacts of expected global climate change on the potential and realized distributions of a representative sample of 69 individual Angiosperm species in Amazonia were simulated from 1990 to 2095. The climate trend followed the HADCM2GSa1 scenario, which assumes an annual 1% increase of atmospheric CO2 content with effects mitigated by sulphate forcing. Potential distributions of species in one-degree grid cells were modelled using a suitability index and rectilinear envelope based on bioclimate variables. Realized distributions were additionally limited by spatial contiguity with, and proximity to, known record sites. A size-structured population model was simulated for each cell in the realized distributions to allow for lags in response to climate change, but dispersal was not included.In the resulting simulations, 43% of all species became non-viable by 2095 because their potential distributions had changed drastically, but there was little change in the realized distributions of most species, owing to delays in population responses. Widely distributed species with high tolerance to environmental variation exhibited the least response to climate change, and species with narrow ranges and short generation times the greatest. Climate changed most in north-east Amazonia while the best remaining conditions for lowland moist forest species were in western Amazonia.To maintain the greatest resilience of Amazonian biodiversity to climate change as modelled by HADCM2GSa1, highest priority should be given to strengthening and extending protected areas in western Amazonia that encompass lowland and montane forests. [ABSTRACT FROM AUTHOR]

Comments on the article "Natural Forest Disturbance and Change in the Brazilian Amazon," by B. W. Nelson. Alterations in undisturbed tree communities in central Amazonia; Peak wet-season rainfall, first 5 months of each year, at Manaus, Brazil from 1968 to 2000; Tree mortality rates.