. The Amazon Basin plays key roles in the carbon and water cycles, climate change, atmospheric chemistry, and biodiversity. It has already been changed significantly by human activities, and more pervasive change is expected to occur in the coming decades. It is therefore essential to establish long-term measurement sites that provide a baseline record of present-day climatic, biogeochemical, and atmospheric conditions and that will be operated over coming decades to monitor change in the Amazon region, as human perturbations increase in the future. The Amazon Tall Tower Observatory (ATTO) has been set up in a pristine rain forest region in the central Amazon Basin, about 150 km northeast of the city of Manaus. Two 80 m towers have been operated at the site since 2012, and a 325 m tower is nearing completion in mid-2015. An ecological survey including a biodiversity assessment has been conducted in the forest region surrounding the site. Measurements of micrometeorological and atmospheric chemical variables were initiated in 2012, and their range has continued to broaden over the last few years. The meteorological and micrometeorological measurements include temperature and wind profiles, precipitation, water and energy fluxes, turbulence components, soil temperature profiles and soil heat fluxes, radiation fluxes, and visibility. A tree has been instrumented to measure stem profiles of temperature, light intensity, and water content in cryptogamic covers. The trace gas measurements comprise continuous monitoring of carbon dioxide, carbon monoxide, methane, and ozone at five to eight different heights, complemented by a variety of additional species measured during intensive campaigns (e.g., VOC, NO, NO2, and OH reactivity). Aerosol optical, microphysical, and chemical measurements are being made above the canopy as well as in the canopy space. They include aerosol light scattering and absorption, fluorescence, number and volume size distributions, chemical composition, cloud condensation nuclei (CCN) concentrations, and hygroscopicity. In this paper, we discuss the scientific context of the ATTO observatory and present an overview of results from ecological, meteorological, and chemical pilot studies at the ATTO site.

/pdf/the-amazon-tall-tower-observatory-atto-overview-of-pilot-maj151xjjs.pdf

The Amazon Tall Tower Observatory (ATTO): overview of pilot measurements on ecosystem ecology, meteorology, trace gases, and aerosols

Tropical forest function is of global significance to climate change responses, and critically determined by water availability patterns. Groundwater is tightly related to soil water through the water table depth (WT), but historically neglected in ecological studies. Shallow WT forests (WT < 5 m) are underrepresented in forest research networks and absent in eddy flux measurements, although they represent c. 50% of the Amazon and are expected to respond differently to global-change-related droughts. We review WT patterns and consequences for plants, emerging results, and advance a conceptual model integrating environment and trait distributions to predict climate change effects. Shallow WT forests have a distinct species composition, with more resource-acquisitive and hydrologically vulnerable trees, shorter canopies and lower biomass than deep WT forests. During 'normal' climatic years, shallow WT forests have higher mortality and lower productivity than deep WT forests, but during moderate droughts mortality is buffered and productivity increases. However, during severe drought, shallow WT forests may be more sensitive due to shallow roots and drought-intolerant traits. Our evidence supports the hypothesis of neglected shallow WT forests being resilient to moderate drought, challenging the prevailing view of widespread negative effects of climate change on Amazonian forests that ignores WT gradients, but predicts they could collapse under very strong droughts.

The other side of tropical forest drought: do shallow water table regions of Amazonia act as large-scale hydrological refugia from drought?

We review a vast literature of Neotropical forest science and wood anatomical research that identifies 220 tree species from 46 botanical families with confirmed annual tree-ring formation. External factors that trigger annual growth rhythms include rainfall seasonality, annual long-term flooding (flood-pulse), soil water salinity (mangroves), and, with increasing latitude and altitude, photoperiod and temperature. Maximum ages for tropical angiosperms derived from tree-ring analyses generally do not exceed 400–600 years; however, at marginal sites characterized by extremely limited growth conditions individual trees might get older. Dendroecological applications provide insights into tree species’ ecology and forest dynamics. Analyses of growth trajectories and age-size relationships of trees highlight considerable variability among individual trees, species, and environments. In recent decades tree-ring studies in neotropical forests have contributed new methods to project timber harvests and to evaluate and adjust management practices to increase the sustainability of forest management. The better understanding of individual- and species-level growth patterns in the Neotropics provides necessary empirical information to conserve and manage tropical forests and the many ecosystem functions and services that they maintain.

Dendroecological Studies in the Neotropics: History, Status and Future Challenges

There is a consensus about negative impacts of droughts in Amazonia. Yet, extreme wet episodes, which are becoming as severe and frequent as droughts, are overlooked and their impacts remain poorly understood. Moreover, drought reports are mostly based on forests over a deep water table (DWT), which may be particularly sensitive to dry conditions. Based on demographic responses of 30 abundant tree species over the past two decades, in this study we analyzed the impacts of severe droughts but also of concurrent extreme wet periods, and how topographic affiliation (to shallow - SWTs - or deep - DWTs - water tables), together with species functional traits, mediated climate effects on trees. Dry and wet extremes decreased growth and increased tree mortality, but interactions of these climatic anomalies had the highest and most positive impact, mitigating the simple negative effects. Despite being more drought-tolerant, species in DWT forests were more negatively affected than hydraulically vulnerable species in SWT forests. Interaction of wet-dry extremes and SWT depth modulated tree responses to climate, providing buffers to droughts in Amazonia. As extreme wet periods are projected to increase and at least 36% of the Amazon comprises SWT forests, our results highlight the importance of considering these factors in order to improve our knowledge about forest resilience to climate change.

The other side of droughts: wet extremes and topography as buffers of negative drought effects in an Amazonian forest.

Rising habitat loss is one of the main drivers of the global amphibian decline. Nevertheless, knowledge of amphibian diversity needed for effective habitat protection is still highly inadequate in remote tropical regions, the greater part of the Amazonia. In this study we integrated molecular, morphological and bioacoustic evidence to evaluate the species richness of the treefrogs genus Scinax over a 1000 km transect across rainforest of the Purus-Madeira interfluve, and along the east bank of the upper Madeira river, Brazilian Amazonia. Analysis revealed that 82% of the regional species richness of Scinax is still undescribed; two nominal species, seven confirmed candidate species, two unconfirmed candidate species, and one deep conspecific lineage were detected in the study area. DNA barcoding based analysis of the 16s rRNA gene indicates possible existence of three discrete species groups within the genus Scinax, in addition to the already-known S. rostratus species Group. Quantifying and characterizing the number of undescribed Scinax taxa on a regional scale, we provide a framework for future taxonomic study in Amazonia. These findings indicate that the level to which Amazonian anura species richness has been underestimated is far greater than expected. Consequently, special attention should be paid both to taxonomic studies and protection of the still-neglected Amazonian Scinax treefrogs.

/pdf/high-species-richness-of-scinax-treefrogs-hylidae-in-a-j5navyb808.pdf

High Species Richness of Scinax Treefrogs (Hylidae) in a Threatened Amazonian Landscape Revealed by an Integrative Approach.

/pdf/productivity-of-aboveground-coarse-wood-biomass-and-stand-4sasccmk7a.pdf

Productivity of aboveground coarse wood biomass and stand age related to soil hydrology of Amazonian forests in the Purus-Madeira interfluvial area

In Amazonia, wetlands constitute about 30% of its entire basin, of which ancient fluvial terraces located in vast interfluvial regions cover a large portion. Although the increased number of permanent plots in the recent years has contributed to improved understanding of regional variation in forest dynamics across the Amazon Basin, the functioning of large lowland interfluvial wetlands remain poorly understood. Here we present the first field-based estimate for tree ages, wood biomass productivity and biomass turnover rates for eight 1 ha plots in wetland and non-flooded forests distributed along the BR-319 Highway along a distance of about 600 km crossing the Purus–Madeira rivers interfluvial region in central-southwestern Amazon Basin. We estimate stand age, wood biomass productivity and biomass turnover rates combining tree-ring data and an allometric equation based on diameter, tree height and wood density and relate these structural parameters to physical soil and hydrological restrictions. Wood biomass and productivity varied twofold among the plots, with wood biomass stocks ranging between 138–294 Mg ha −1 and productivity varying between 3.4–6.6 Mg ha −1 yr −1 . Soil effective depth, topography, structure and mainly soil water saturation significantly affected stand age (64–103 yr) and forest dynamics in terms of annual biomass turnover rates (2.0–3.2%). On harsher soils characterized by a poor structure, low effective depth and high water saturation, biomass turnover rates were increased and forests stands were younger compared to well-drained sites. We suggest that soil constraints, especially soil water saturation, limit the development of the stand structure, resulting in forests with younger stand ages and higher biomass turnover rates compared to forests growing on well-drained soils. We do not find, however, any relation between physical soil restrictions or hydrology and wood biomass productivity, but there is a trend of increasing wood biomass productivity and phosphorus concentrations at the soil surface. Based on our results we establish hypotheses for different dynamical processes between forests growing on waterlogged and well-drained soils and discuss how these results can be applied in the background of conservation as well as the potential development of forest management plans in this region, which will experience increased deforestation due to the construction of the BR-319 Highway crossing the interfluvial region of the Purus–Madeira rivers.

/pdf/soil-physical-restrictions-and-hydrology-regulate-stand-age-4lyxf4bduc.pdf

Soil physical restrictions and hydrology regulate stand age and wood biomass turnover rates of Purus–Madeira interfluvial wetlands in Amazonia

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Productivity of aboveground coarse wood biomass and stand age related to soil hydrology of Amazonian forests in the Purus-Madeira interfluvial area

Soil physical restrictions and hydrology regulate stand age and wood biomass turnover rates of Purus–Madeira interfluvial wetlands in Amazonia