1,722,651 research outputs found
“Lógica en la calle, sobre la Experiencia e Inferencia en las estrategias de supervivencia de personas en situación de calle de la actual ciudad de Salta”.
Get PDFFil: Fernández Reyes, Luis Alfredo. Universidad de Buenos Aires.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET);Argentin
Positive biodiversity-productivity relationship predominant in global forests
No full textThe biodiversity-productivity relationship (BPR) is foundational to our understanding of the global extinction crisis and its impacts on ecosystem functioning. Understanding BPR is critical for the accurate valuation and effective conservation of biodiversity. Using ground-sourced data from 777,126 permanent plots, spanning 44 countries and most terrestrial biomes, we reveal a globally consistent positive concave-down BPR, showing that continued biodiversity loss would result in an accelerating decline in forest productivity worldwide. The value of biodiversity in maintaining commercial forest productivity alone—US$166 billion to 490 billion per year according to our estimation—is more than twice what it would cost to implement effective global conservation. This highlights the need for a worldwide reassessment of biodiversity values, forest management strategies, and conservation priorities
Scale-dependent drivers of the phylogenetic structure and similarity of tree communities in northwestern amazonia
No full textThe extent to which historical dispersal, environmental features and geographical barriers shape the phylogenetic structure and turnover of tree communities in northwestern Amazonia at multiple spatial scales remains poorly understood. We used 85 floristically standardized 0.1-ha plots (DBH ≥ 2.5 cm) distributed in three subregions of northwestern (NW) Amazonia across three main habitat types (floodplain, swamp and terra firme forests) to hypothesize that (a) historical dispersal overcome geographical barriers, which meant low local phylogenetic relatedness and low phylogenetic turnover. (b) Geographical barriers triggered dispersal limitation, causing high local and subregional phylogenetic clustering and high regional phylogenetic turnover. (c) Edaphic properties and flooding were negatively associated with stem size and determined the tree phylogenetic structure and turnover at local and regional scales in Amazon forests. We found that the extent to which environmental or evolutionary features shaped the phylogenetic structure and phylogenetic similarity of tree communities in NW Amazonia was scale dependent. Specifically, we show that the relative importance of environmental factors increases as spatial scale and species pool decreases. Furthermore, we find that these results are generally robust for both adult and juvenile trees. Synthesis. Our analysis at the regional (NW Amazon) scale lends support to the idea of Amazonian forests as a large meta-community primarily structured by historical dispersal at large spatial scales with an increasing importance of environmental factors at finer spatial scales. The convergence of ancestral lineages across habitat types may have been due to the relatively recent formation of geographical barriers that promoted local isolation and allopatric speciation
Dinámica forestal en un bosque amazónico de Yasuní
No full textEn una hectárea de bosque Amazónico en Yasuní se encuentran en promedio 670 especies de árboles y arbustos (dap ≥1 cm), de las que apenas 10% de especies tienen más de 20 individuos, mientras 25% de las especies tienen apenas un individuo por hectárea. Para estudiar la dinámica poblacional y los cambios en la funcionalidad de estos bosques es, por tanto, necesario parcelas de gran tamaño. En este estudio se investigaron los cambios poblacionales y funcionales en una parcela de 25 hectáreas en el Parque Nacional Yasuní. Estudios previos sugieren que el cambio climático está afectando la composición de especies y la estructura de los bosques amazónicos. Por ejemplo, se piensa que las especies de bosques secundarios podrían volverse más importantes con el calentamiento climático global. Igualmente se ha anticipado que los bosques experimentarán sequías más intensas y frecuentes. Si esto está ocurriendo en Yasuní, se esperaría detectar ciertos cambios consistentes con estas predicciones. Así, las especies menos tolerantes a la sequía deberían volverse más comunes en ambientes que tienden a mantenerse más húmedos, como los valles atravesados por pequeños riachuelos y menos comunes en ambientes menos húmedos como las partes altas de las colinas. En este estudio se probaron estas hipótesis la parcela de estudio que ha sido censada en cuatro ocasiones, entre 1995 y 2017, lo que permite ver los cambios del bosque en tres intervalos de tiempo de 5, 6 y 9 años (~22 años). A través del tiempo la proporción de especies con cambios poblacionales significativos creció de 26.2% a 42.1% a través del tiempo, siendo 10% mayor en las colinas que en los valles. Muy pocas especies tuvieron cambios poblacionales direccionales, ya sea aumentando o disminuyendo su población a lo largo en todos los intervalos de tiempo (4.8% en la colina y 1.7% en el valle). Cambios constantes y direccionales en los dos hábitats al mismo tiempo fue muy bajo (<1%)
Disentangling the functional trait correlates of spatial aggregation in tropical forest trees
No full textEnvironmental filtering and dispersal limitation can both maintain diversity in plant communities by aggregating conspecifics, but parsing the contribution of each process has proven difficult empirically. Here, we assess the contribution of filtering and dispersal limitation to the spatial aggregation patterns of 456 tree species in a hyperdiverse Amazonian forest and find distinct functional trait correlates of interspecific variation in these processes. Spatial point process model analysis revealed that both mechanisms are important drivers of intraspecific aggregation for the majority of species. Leaf drought tolerance was correlated with species topographic distributions in this aseasonal rainforest, showing that future increases in drought severity could significantly impact community structure. In addition, seed mass was associated with the spatial scale and density of dispersal-related aggregation. Taken together, these results suggest environmental filtering and dispersal limitation act in concert to influence the spatial and functional structure of diverse forest communities
Temporal coexistence mechanisms contribute to the latitudinal gradient in forest diversity
No full textThe tropical forests of Borneo and Amazonia may each contain more tree species diversity in half a square kilometre than do all the temperate forests of Europe, North America, and Asia combined. Biologists have long been fascinated by this disparity, using it to investigate potential drivers of biodiversity. Latitudinal variation in many of these drivers is expected to create geographic differences in ecological and evolutionary processes, and evidence increasingly shows that tropical ecosystems have higher rates of diversification, clade origination, and clade dispersal. However, there is currently no evidence to link gradients in ecological processes within communities at a local scale directly to the geographic gradient in biodiversity. Here, we show geographic variation in the storage effect, an ecological mechanism that reduces the potential for competitive exclusion more strongly in the tropics than it does in temperate and boreal zones, decreasing the ratio of interspecific-to-intraspecific competition by 0.25% for each degree of latitude that an ecosystem is located closer to the Equator. Additionally, we find evidence that latitudinal variation in climate underpins these differences; longer growing seasons in the tropics reduce constraints on the seasonal timing of reproduction, permitting lower recruitment synchrony between species and thereby enhancing niche partitioning through the storage effect. Our results demonstrate that the strength of the storage effect, and therefore its impact on diversity within communities, varies latitudinally in association with climate. This finding highlights the importance of biotic interactions in shaping geographic diversity patterns, and emphasizes the need to understand the mechanisms underpinning ecological processes in greater detail than has previously been appreciated
Patterns of nitrogen-fixing tree abundance in forests across Asia and America
No full textSymbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of ~4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought
Temporal population variability in local forest communities has mixed effects on tree species richness across a latitudinal gradient
No full textAmong the local processes that determine species diversity in ecological communities, fluctuation-dependent mechanisms that are mediated by temporal variability in the abundances of species populations have received significant attention. Higher temporal variability in the abundances of species populations can increase the strength of temporal niche partitioning but can also increase the risk of species extinctions, such that the net effect on species coexistence is not clear. We quantified this temporal population variability for tree species in 21 large forest plots and found much greater variability for higher latitude plots with fewer tree species. A fitted mechanistic model showed that among the forest plots, the net effect of temporal population variability on tree species coexistence was usually negative, but sometimes positive or negligible. Therefore, our results suggest that temporal variability in the abundances of species populations has no clear negative or positive contribution to the latitudinal gradient in tree species richness
Neither species geographic range size, climatic envelope, nor intraspecific leaf trait variability capture habitat specialization in a hyperdiverse Amazonian forest
No full textMany plant species exhibit strong association with topographic habitats at local scales. However, the historical biogeographic and physiological drivers of habitat specialization are still poorly understood, and there is a need for relatively easy-to-measure predictors of species habitat niche breadth. Here, we explore whether species geographic range, climatic envelope, or intraspecific variability in leaf traits is related to the degree of habitat specialization in a hyperdiverse tropical tree community in Amazonian Ecuador. Contrary to our expectations, we find no effect of the size of species geographic ranges, the diversity of climate a species experiences across its range, or intraspecific variability in leaf traits in predicting topographic habitat association in the ~300 most common tropical tree species in a 25-ha tropical forest plot. In addition, there was no phylogenetic signal to habitat specialization. We conclude that species geographic range size, climatic niche breadth, and intraspecific variability in leaf traits fail to capture the habitat specialization patterns observed in this highly diverse tropical forest
Pan-tropical prediction of forest structure from the largest trees
No full textLarge tropical trees form the interface between ground and airborne observations, offering a unique opportunity to capture forest properties remotely and to investigate their variations on broad scales. However, despite rapid development of metrics to characterize the forest canopy from remotely sensed data, a gap remains between aerial and field inventories. To close this gap, we propose a new pan-tropical model to predict plot-level forest structure properties and biomass from only the largest trees
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