Local hydrological conditions influence tree diversity and composition across the Amazon basin

Abstract

Tree diversity and composition in Amazonia are known to be strongly determined by the water supplied by precipitation. Nevertheless, within the same climatic regime, water availability is modulated by local topography and soil characteristics (hereafter referred to as local hydrological conditions), varying from saturated and poorly drained to well-drained and potentially dry areas. While these conditions may be expected to influence species distribution, the impacts of local hydrological conditions on tree diversity and composition remain poorly understood at the whole Amazon basin scale. Using a dataset of 443 1-ha non-flooded forest plots distributed across the basin, we investigate how local hydrological conditions influence 1) tree alpha diversity, 2) the community-weighted wood density mean (CWM-wd) -a proxy for hydraulic resistance and 3) tree species composition. We find that the effect of local hydrological conditions on tree diversity depends on climate, being more evident in wetter forests, where diversity increases towards locations with well-drained soils. CWM-wd increased towards better drained soils in Southern and Western Amazonia. Tree species composition changed along local soil hydrological gradients in Central-Eastern, Western and Southern Amazonia, and those changes were correlated with changes in the mean wood density of plots. Our results suggest that local hydrological gradients filter species, influencing the diversity and composition of Amazonian forests. Overall, this study shows that the effect of local hydrological conditions is pervasive, extending over wide Amazonian regions, and reinforces the importance of accounting for local topography and hydrology to better understand the likely response and resilience of forests to increased frequency of extreme climate events and rising temperatures.

Climate influences bill shape diversification in cavity-excavating birds

“…We chose the mean, maximum and minimum annual temperature and precipitation as descriptors of the climatic niche, taking an average value of each parameter for each species. Temperature and precipitation represent the physical environment in which excavation substrates are formed (60), and are thus likely to influence the properties of this substrate and the biomechanical demands experienced by primary cavity-excavators. By measuring correlation of bill shape with climatic variables, we sought to obtain a preliminary understanding of the relationship between habitat differences (as discussed above) and differences in bill shape.…”

“…These climatic variables are proxies of the ecological niche of an organism, and are also important drivers of ecological traits (69,70), and this niche is expected to exert an influence on functional traits and morphological diversity. For example, because barbets are primary nest excavators (71), the availability of resources (suitable trees or logs) is likely to be influenced by the climatic conditions that drive habitat structure, the availability of dead or rotting trees for excavation, and the material properties of the excavation substrate (60), as with other cavity-nesting birds such as hornbills (72)(73)(74). Our results suggest that as a result of these ecological factors coupled to allometric scaling, Asian and African barbets have explored distinct regions of maxilla shape space.…”

Bill shape imposes biomechanical tradeoffs in cavity-excavating birds

“…African barbets, which occupy drier climatic regimes, exhibit deeper maxillae on average compared to the Asian barbets, which typically reside in more humid, forested regions (31, 32). Because climatic factors like temperature, precipitation and hydrological conditions affect wood decay rates and wood density, we surmise that they may also influence the availability of dead and decaying wood in the habitat (46, 47). These softer substrates are potentially easier to excavate due to their lower mechanical strength (48).…”

Forest–Fruticulture Conversion Alters Soil Traits and Soil Organic Matter Compartments

“…The Amazon Rainforest has been recognized as one of the major sources of biodiversity. The soil traits from this ecosystem were previously described in Peralta et al [ 3 ], and Marca-Zevallos et al [ 4 ], and accordingly to these authors, the BLA provides favorable conditions for many endemic plant species to inhabit. However, its soil ecosystem suffers frequent soil fertility decline as influenced by land use.…”