In the western Amazon Basin, recent intensification of river-level cycles has increased flooding during the wet seasons and decreased precipitation during the dry season. Greater than normal floods occurred in 2009 and in all years from 2011 to 2015 during high-water seasons, and a drought occurred

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Se planean actividades de dragado por el proyecto hidrovía amazónica y existe limitada evidencia científica de cómo el dragado propuesto podría afectar tanto a la biodiversidad como a la población local. Una matriz modelo fue utilizada para evaluar las posibles consecuencias del dragado sobre la fauna silvestre. De acuerdo con la matriz, las especies acuáticas muestran poblaciones decrecientes cuando el nivel de agua está bajo y las especies terrestres se ven afectadas negativamente cuando las inundaciones son intensivas. La población indígena Cocama viene adaptándose a los cambios poblacionales de la fauna silvestre, dedicándose más a la pesca cuando las poblaciones de animales de caza disminuyen. Las áreas poco profundas, localmente denominados como “malos pasos” constituyen tipos de hábitat importantes para peces y delfines. De acuerdo a la matriz que se presenta en este estudio, el mejor escenario sería que, las actividades del dragado no afecten los niveles de agua normales; mientras que, el peor escenario sería cuando se presenten sequías e inundaciones intensivas.

The continued functioning of tropical forests under climate change depends on their resilience to drought and heat. However, there is little understanding of how tropical forests will respond to combinations of these stresses, and no field studies to date have explicitly evaluated whether sustained drought alters sensitivity to temperature. We measured the temperature response of net photosynthesis, foliar respiration and the maximum quantum efficiency of photosystem II (Fv/Fm) of eight hyper‐dominant Amazonian tree species at the world's longest‐running tropical forest drought experiment, to investigate the effect of drought on forest thermal sensitivity. Despite a 0.6°C–2°C increase in canopy air temperatures following long‐term drought, no change in overall thermal sensitivity of net photosynthesis or respiration was observed. However, photosystem II tolerance to extreme‐heat damage (T50) was reduced from 50.0 ± 0.3°C to 48.5 ± 0.3°C under drought. Our results suggest that long‐term reductions in precipitation, as projected across much of Amazonia by climate models, are unlikely to greatly alter the response of tropical forests to rising mean temperatures but may increase the risk of leaf thermal damage during heatwaves.

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Background Many significant ecosystems, including important non-forest woody ecosystems such as the Cerrado (Brazilian savannah), are under threat from climate change, yet our understanding of how increasing temperatures will impact native vegetation remains limited. Temperature manipulation experiments are important tools for investigating such impacts, but are often constrained by access to power supply and limited to low-stature species, juvenile individuals, or heating of target organs, perhaps not fully revealing how entire or mature individuals and ecosystems will react to higher temperatures. Results We present a novel, modified open top chamber design for in situ passive heating of whole individuals up to 2.5 m tall (but easily expandable) in remote field environments with strong solar irradiance. We built multiple whole-tree heating structures (WTHSs) in an area of Cerrado around native woody species Davilla elliptica and Erythroxylum suberosum to test the design and its effects on air temperature and humidity, while also studying the physiological responses of E. suberosum to short-term heating. The WTHSs raised internal air temperature by approximately 2.5 °C above ambient during the daytime. This increased to 3.4 °C between 09:00 and 17:00 local time when thermal impact was greatest, and during which time mean internal temperatures corresponded closely with maximum ambient temperatures. Heating was consistent over time and across WTHSs of variable size and shape, and they had minimal effect on humidity. E. suberosum showed no detectable response of photosynthesis or respiration to short-term experimental heating, but some indication of acclimation to natural temperature changes. Conclusions Our WTHSs produced a consistent and reproducible level of daytime heating in line with mid-range climate predictions for the Cerrado biome by the end of the century. The whole-tree in situ passive heating design is flexible, low-cost, simple to build using commonly available materials, and minimises negative impacts associated with passive chambers. It could be employed to investigate the high temperature responses of many understudied species in a range of complex non-forest environments with sufficient solar irradiance, providing new and important insights into the possible impacts of our changing climate.

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<p>Ongoing global warming threatens to exceed the physiological limits of forests, especially in the tropics, where species operate close to their thermal limits of photosystems. Understanding the relationship between leaf temperature, climatic variables and functional traits is therefore essential to predict the impacts of warming on forest ecology. The climatic safety margins  can be defined as the range of climatic values within which a species in a given environment maintains its physiological functions without risk of severe damage that can ultimately lead to death and are typically computed as the difference between an operational variable of physiological tolerance (e.g. temperature that corresponds to a 50% drop in the quantum photosynthetic efficiency of photosystem II) and a variable of exposure to physiological stress (e.g. maximum leaf temperature). Here, we aim to understand how thermal safety margins vary in response to increased air temperature and water stress at multiple spatial and temporal scales and relate these to species-level functional traits. We present an unprecedented set of surface temperature data measured with Unmanned Aerial Vehicle (UAV) thermal imaging in long-term forest plots in regions subjected to strong seasonal drought and rising temperatures in the southern edge of the Amazon and also for a 20-year drought experiment in northern Amazonia. The data collected includes diurnal patterns of crown temperature collected with UAVs in the dry and wet seasons, climatic variables and functional traits related to thermal and hydraulic tolerance. We examine seasonal variations in canopy temperatures and thermal safety margins and evaluate the extent to which these vary according to canopy structure, leaf size, soil properties and soil moisture availability. Our data provides insights into leaf resilience to warming and factors controlling leaf temperatures in tropical forests. Our results will ultimately help indicate which forest types and species will be better able to cope with future temperature increases.</p>