Tropical dry forests (TDFs) have been defined as a single biome occurring mostly in the lowlands where there is a marked period of drought during the year. In the Neotropics, dry forests occur across ...contrasting biogeographical regions that contain high beta diversity and endemism, but also strong anthropogenic pressures that threaten their biodiversity and ecological integrity. In Colombia, TDFs occur across six regions with contrasting soils, climate, and anthropogenic pressures, therefore being ideal for studying how these variables relate to dry forest species composition, successional stage and conservation status. Here, we explore the variation in climate and soil conditions, floristic composition, forest fragment size and shape, successional stage and anthropogenic pressures in 571 dry forest fragments across Colombia. We found that TDFs should not be classified solely on rainfall seasonality, as high variation in precipitation and temperature were correlated with soil characteristics. In fact, based on environmental factors and floristic composition, the dry forests of Colombia are clustered in three distinctive groups, with high species turnover across and within regions, as reported for other TDF regions of the Neotropics. Widely distributed TDF species were found to be generalists favored by forest disturbance and the early successional stages of dry forests. On the other hand, TDF fragments were not only small in size, but highly irregular in shape in all regions, and comprising mostly early and intermediate successional stages, with very little mature forest left at the national level. At all sites, we detected at least seven anthropogenic disturbances with agriculture, cattle ranching and human infrastructure being the most pressing disturbances throughout the country. Thus, although environmental factors and floristic composition of dry forests vary across regions at the national level, dry forests are equally threatened by deforestation, degradation and anthropogenic pressures all over the country, making TDFs a top priority for conservation in Colombia.
Extreme drought events have negative effects on forest diversity and functioning. At the species level, however, these effects are still unclear, as species vary in their response to drought through ...specific functional trait combinations. We used long‐term demographic records of 21,821 trees and extensive databases of traits to understand the responses of 338 tropical dry forests tree species to ENSO2015, the driest event in decades in Northern South America. Functional differences between species were related to the hydraulic safety‐efficiency trade‐off, but unexpectedly, dominant species were characterised by high investment in leaf and wood tissues regardless of their leaf phenological habit. Despite broad functional trait combinations, tree mortality was more widespread in the functional space than tree growth, where less adapted species showed more negative net biomass balances. Our results suggest that if dry conditions increase in this ecosystem, ecological functionality and biomass gain would be reduced.
Extreme drought events have negative effects on forest diversity and functioning. We used long‐term demographic records of 21,821 trees and extensive databases of traits to understand the responses of 338 tropical dry forests tree species to an extreme. Our results indicate that irrespective of the drought adaptations, most trees will be negatively affected under drier scenarios predicted for tropical dry forests.
Abstract
We tested the idea that functional trade‐offs that underlie species tolerance to drought drive shifts in community composition via their effects on demographic processes and subsequently on ...shifts in species' abundance. Using data from 298 tree species from tropical dry forests during the extreme ENSO‐2015, we scaled‐up the effects of trait trade‐offs from individuals to communities. Conservative wood and leaf traits favoured slow tree growth, increased tree survival and positively impacted species abundance and dominance at the community‐level. Safe hydraulic traits, on the other hand, were related to demography but did not affect species abundance and communities. The persistent effects of the conservative–acquisitive trade‐off across organizational levels is promising for generalization and predictability of tree communities. However, the safety–efficient trade‐off showed more intricate effects on performance. Our results demonstrated the complex pathways in which traits scale up to communities, highlighting the importance of considering a wide range of traits and performance processes.
Se describe e ilustra a Sanguisuga caesarea, un género nuevo y una especie nueva deCytinaceae de Colombia y el primer registro de esta familia en Sudamérica. El géneronuevo es afín a Bdallophytum ...pero se diferencia por presentar andromonoecia, conlas flores masculinas en la base de la inflorescencia, flores zigomorfas comprimidasdorsiventralmente, semicerradas, con los tépalos arqueados e incurvos; tépalo inferiormediosigmoide-lingüiforme y nectarífero y las semillas más alargadas, obpiriformescon una relación largo/ancho de 1,5-1,8
Se describe e ilustra a Sanguisuga caesarea, un género nuevo y una especie nueva de Cytinaceae de Colombia y el primer registro de esta familia en Sudamérica. El género nuevo es afín a Bdallophytum ...pero se diferencia por presentar andromonoecia, con las flores masculinas en la base de la inflorescencia, flores zigomorfas comprimidas dorsiventralmente, semicerradas, con los tépalos arqueados e incurvos; tépalo inferiormedio sigmoide-lingüiforme y nectarífero y las semillas más alargadas, obpiriformes con una relación largo/ancho de 1,5-1,8. Sanguisuga caesarea, a new genus and species of Cytinaceae from Colombia and the first record of this family in South America, is described and illustrated. Sanguisuga is close to Bdallophytum but differs from it by exhibiting andromonoecia, with male flowers only at the base of the inflorescence, flowers zygomorphic, semiclosed, and dorsoventrally compressed. The tongue-shaped tepals are arched, curved inwards and include a ventral, sigmoid, nectar-secreting tepal. The elongated seeds are obpyriform with a length/width ratio of 1,5-1,8.
La formación de etringita retardada (DEF) es un fenómeno expansivo que se origina en estructuras de hormigón sometidas a altos niveles de temperatura (>70°C) durante su etapa inicial de curado, esto ...puede ocurrir en las estructuras de hormigón masivo que desarrollan altas temperaturas producto del calor generado por la reacciones de hidratación del cemento. Es por esta razón, que en estructuras de este tipo se toman costosas medidas con el objetivo de no sobrepasar ciertos niveles de temperatura y así evitar el potencial desarrollo del fenómeno DEF.;
Este trabajo tiene por objetivo comprobar la hipótesis respecto del efecto inhibidor sobre el fenómeno de formación de etringita retardada (DEF) de las adiciones puzolánicas que se incorporan para la fabricación de la mayoría de los cementos chilenos y de esta forma determinar la posibilidad de flexibilizar las restricciones de temperatura máxima establecidas para los hormigones masivos.;
El procedimiento experimental desarrollado se basa la metodología implementada por Ross Duggan, denominada Ensayo Duggan, el cual consistió en la fabricación de probetas de mortero confeccionadas con cementos con distintas proporciones de adición, las cuales luego ser sometidas a un curado térmico a una temperatura máxima de 85°C ± 2°C se les aplicó una series de ciclos de humedecimiento y secado, con el objetivo de acelerar el fenómeno expansivo. Luego se tomaron mediciones de longitud periódicas con el fin de determinar el comportamiento expansivo de cada cemento estudiado frente a las condiciones de curado impuestas que favorecen el fenómeno. Paralelamente, se realizaron ensayo de resistencia para determinar la influencia de las altas temperatura de curado sobre la resistencia a la compresión de probetas cubicas de hormigón.;
Se verificó que el contenido de trióxido de azufre (SO3) es el componente del cemento con mayor influencia en el desarrollo del fenómeno DEF. Se determinó que el cemento con mayor efecto expansivo corresponde al cemento clasificado como Portland Puzolánico el cual coincide con el de mayor proporción de trióxido de azufre (SO3) mientras que el cemento clasificado como Portland puro desarrolla una expansión moderada luego de finalizadas las mediciones. El cemento clasificado como Puzolánico no desarrolla presenta un comportamiento expansivo durante la etapa de estudio, este cemento corresponde al de menor proporción de trióxido de azufre (SO3) al mismo tiempo que corresponde al con mayor contenido de puzolana (≈39%).;
Respecto a los ensayos de resistencia, se determinó que los cementos con adiciones puzolánicas presentan un aumento moderado de la resistencia a los 28 días producto del curado a alta temperatura, mientras que el cemento Portland sin adición presenta una leve disminución de su resistencia a los 28 días. Estos comportamientos indicarían una disminución de la tasa de desarrollo de la resistencia a más largo plazo.
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