The interactions between hydrological and ecological processes are key issues to improve our predictions of ecosystem responses to increasing droughts. However, predicting the dynamics and the impacts of vegetation water stress remains challenging because of complex ecohydrological feedbacks. The ecohydrological optimality approach proposes that functional adjustments within plant communities may buffer the increase in vegetation water stress despite local water shortage. This study aimed to test whether vegetation water stress may be invariant across contrasting plant communities, reflecting possible optimality processes. We addressed the following question: does a lower soil water storage capacity under the same climate generate greater vegetation water stress over time? We hypothesized that vegetation water stress would be buffered around a low and constant level through the adjustment of vegetation biomass productivity net primary productivity (NPP), evapotranspiration (ET) and/or water-use efficiency (WUE) in relation with local soil water storage capacity. We monitored 12 native plant communities distributed along a gradient of soil water storage capacity (ranging from 20 mm to 120 mm) during five successive years. Net primary productivity, ET, WUE as well as soil water dynamics were assessed and modelled for each plant community throughout the 5 years of study. Vegetation water stress was determined for each plant community as the deviation of between actual ET and their maximum ETm rate achieved under non-limiting conditions. We found that NPP and ET were together proportionally related to local soil water storage capacity across the 5 years of study while WUE did not differ between plant communities. Vegetation water stress was found quite similar for all plant communities whatever the soil water storage capacity. These results suggested that vegetation water stress was strongly buffered by the community-level plant growth rates and total water use along the soil gradient, but not by WUE. Our results suggest that stressful environments rarely exist for plant communities. A dynamic scaling relationship between NPP and ET may underpin the control of vegetation water stress over seasonal and pluriannual time-scales. Such results could contribute to better understanding processes associated with ecohydrological optimality and improve the predictions of vegetation dynamics under increasing droughts. (Résumé d'auteur
SUMMARYThe objective of this work is to propose a typology of Quercus pyrenaica in the district of Bierzo, northwest Spain, applying multivariance statistics to the plots of the third national forestry inventory. Six descriptor variables were selected and nine auxiliary calculated: the composition was represented with the cover value, and the age structure with forest calibers in 4 classes. Following this method, the typology was elaborated on the base of 15 variables. The stages of the statistical analyses were: factor analyses and factor determination with maximum explained variance, clusters analyses and dendrogram confection to decide the number of types and discrimination analyses to find the variables with main discriminating power. The variables set was considered appropriate for the confection of typology because of the statistics values achieved. Thus, six types that described adequately the conditions of pastures (grazing grounds) were determined, among them: pure pole stand, degraded pole stand and mixed forests, which have been proposed as frequent for the Community of Castilla y León as well. Furthermore, this methodology allowed establishing a dichotomous key to assign new situations to the proposed types, through the use of clearly differentiable numerical parameters as well as an easily observable on field. Considering the similitude between South American Nothofagus's forests and those of European fagaceous in which typologies have developed, they make of these a promising tool of forest management for Chile and Argentina.
Análisis de crecimiento de árboles maduros de lenga (Nothofagus pumilio) en bosques de la XII Región, Chile Growing analysis of old lenga trees (Nothofagus pumilio) in forests at XII Region, Chile
SUMMARYThe National Forestry Corporation (CONAF) progresses in the implementation of the National Strategy for Climate Change and Vegetation Resources (ENCCRV). Under this context it is necessary to know the amount of carbon that can be contained by the Mediterranean Forest. The aim of this work was to development allometric functions to estimate carbon content in four species of the Chilean Mediterranean Forest: quillay, peumo, espino and litre. Nineteen sampling places, between Valparaíso and Biobío regions of the country, were selected for the cutting of 328 trees. Regarding the distribution of green weight between components, moisture content and basic density in espino and litre were similar, though different from quillay and peumo, which in turn showed similar levels to each other. According to these results, it could mean that there is influence of Mediterranean status over these variables. Carbon content in four species was around 49 % of the total dry biomass. Models found provided similar settings to most of those already published for these species biomass, with the advantage that only one allometric variable is required for what is proposed in this work. Quillay, peumo and espino had R 2 > 0.92 while espino had R 2 = 0.87.Key words: allometric functions, carbon, forest mediterranean. RESUMENLa Corporación Nacional Forestal (CONAF) progresa en la ejecución de la Estrategia Nacional de Cambio Climático y Recursos Vegetacionales (ENCCRV), bajo este contexto es necesario conocer los contenidos de carbono que pueden contener el Bosque Mediterráneo. El objetivo de este trabajo fue la elaboración de funciones alométricas para estimar contenido de carbono en cuatro especies del Bosque Mediterráneo Chileno: quillay, peumo, espino y litre. Se abarcaron 19 zonas de muestreo distribuidas entre las regiones de Valparaíso y del Biobío con un total de 328 árboles procesados. Para la distribución de peso verde entre componente, para el contenido de humedad, y para la densidad básica, litre y espino fueron similares y diferentes a quillay y peumo, que a su vez mostraron niveles similares entre sí. Ello podría significar que existe influencia de la mediterraneidad en estas variables. El contenido de carbono para las cuatro especies oscila en torno a 49 % de la biomasa seca total. Los modelos encontrados ofrecieron ajustes similares a la mayoría de los ya publicados para biomasa de las especies, con la ventaja que los propuestos en este trabajo, aportarán la componente carbono y sólo requieren una variable alométrica. Para quillay, peumo y espino el R 2 encontrado fue mayor a 0,92, mientras que para litre fue de 0,87.Palabras clave: funciones alométricas, carbono, bosque mediterráneo. INTRODUCCIÓNEn Chile existe profusa información de funciones alométricas para biomasa de las especies arbóreas de los bosques templados (Schlegel 2001, Gayoso y Guerra 2005, Picard et al. 2012. Para las especies arbóreas del bosque mediterráneo, en cambio, los trabajos son más bien escasos. CONAF (2013) destaca la abundancia de publicacio...
El objetivo de este trabajo fue proponer una metodología que permita medir cuantitativamente los efectos de actividades de restauración a escala de paisaje, comparando una condición inicial de conservación, con otra condición ideal, denominada paisaje de referencia, creada proyectando los cambios esperados por la restauración. Definido el paisaje de referencia se propuso evaluar índices de paisaje que permitieran cuantificar la ganancia en conservación lograda por la restauración. Para ello, se trabajó en una cuenca con alto grado de conservación. Los índices usados fueron: efecto borde, índice de diversidad del paisaje, índice de forma e índice de continuidad espacial, aplicándose cada uno de ellos a la condición inicial y al paisaje de referencia. Para el caso estudiado, el paisaje de referencia fue simple y sencillo de definir debido a la vasta información relativa a los bosques de la zona. En la etapa de evaluación de los índices del paisaje usado, los que presentaron el mejor desempeño para cuantificar la mejora en conservación fueron el de efecto borde y el de continuidad del paisaje. El índice de forma, en cambio, generó valores confusos entre la condición inicial y el paisaje de referencia, ya que el valor del índice aumenta o empeora solo por el aumento de la superficie. Así también el índice de diversidad obliga a un análisis complejo, principalmente porque la restauración modifica el número de clases de la condición inicial respecto al paisaje de referencia.
El presente trabajo se inserta en el ámbito de convenios de cooperación t écnica establecidos entre instituciones de fomento e investigación forestal chilenas y brasileñas, cuyo propósito es el intercambio de tecnologías en las áreas de monitoreamiento ambiental y manejo forestal
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