Examinando por Autor "Gallo, Leonardo Ariel"

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    Artículo
    Crack willow changing riverine landscapes in Patagonia
    (Wiley, 2017) Datri, Leonardo; Faggi, Ana; Gallo, Leonardo Ariel
    In Patagonia (Argentina) in recent decades, the exotic species and hybrids of Salix alba - Salix fragilis complex has spread over wide areas along watercourses, taking advantage of it is sexually and vegetatively propagation. It out-competes with native vegetation, facilitated by stochastic events related to large floods of long-lasting duration higher than the average maximum of 186 m3/sec for more than a day. We analysed the exotic willow’s increase along the braiding Azul River, and the hydrological regime between 1966 and 2012. We evaluated the links between regime and tree density over time using dendrochronological data. Results showed an increase of the forest’s cover from 2.1% to 70.8% over the last 46 years. The densities of exotic willows grew exponentially between 1966 and 1973, during a period which was free of higher floods. The initial native populations declined as willow’s population increased. Up to 1973 there was an increase in the native populations too. Then from 1974 on, the willow showed a gradual growth coupled with a decline in the native trees. Up 1977 the willow expansion could be linked to an extreme flood that reached 392 m3/sec (210.75%) greater than the average of the maximum flows). We concluded that plant succession in the Azul River follows a “Red Queen” effect whereby the exotic willow and native trees repeatedly reorganized the system after pulses and periods of extreme flooding events.
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    Artículo
    A drendrogeomorpholigical study of the local effect of climate change
    ([2017?]) Datri, Leonardo; Maddio, Rafael; Faggi, Ana; Gallo, Leonardo Ariel
    The climatic and environmental conditions of Patagonia changed substantially after 1850 and after the mid-1970s decade. The impact of these changes is being observed in the new configuration of rivers and their riverine vegetation. The objective of this work is to integrate dendrogeomorphological techniques to the mapping and modeling of the recent distribution of vegetation of the riverine landscape, as an indicator of the local effect of climate change. The hydrological regime and the evolution of riparian vegetation at the confluence of the Cuyín Manzano and Traful Rivers were synchronized using the data obtained from 34 samples of plots of 6x6 meters. The plots were adjusted to the pixel resolution of two SPOT 7 satellite images (flood and dryness), concentric to an area of 18x18 meters, in order to validate a supervised classification of vegetation, belonging to different fluvial geoforms. In the plots with woody vegetation two trees corresponding to one or two age classes characteristic of the stands were drilled. The results indicate that, in agreement with global and Patagonia climate change estimates, there is a slight tendency of change in the flood and drought regime, with decreases in mean annual minimum flows and a period of drought in the last six years. The most outstanding result of our study indicates that the change of the hydrological regime implies a slight reduction of the average minimum flows, without this entailing a modification of the regime of flood pulses that in some cases are very extreme. This situation has a marked incidence in the fact that the woody vegetation colonizes new substrates and emerged landforms, while it is affected by frequent and intense flood events, with a change of the compositions and distribution of the vegetation.
  • Miniatura
    Artículo
    Entre el orden y el caos: invasiones con dinámicas no lineales de sauces y álamos en el norte de la Patagonia
    (Asociación Argentina de Ecología de Paisajes, 2016) Datri, Leonardo; Faggi, Ana; Gallo, Leonardo Ariel
    ¿Cómo es la dinámica de un paisaje ribereño, cuyos componentes no comparten una historia evolutiva común? Proponemos el estudio de las invasiones de salicáceas exóticas en los valles de los ríos Limay y Azul sobre la base de modelos matemáticos. La hipótesis de partida plantea que el proceso de sucesión vegetal interactúa con pulsos hidrológicos estocásticos que introducen disturbios. Se realizó un muestreo dendrogeomorfológico de árboles con el fin estimar las tasas de reemplazo de árboles y su posición topográfica. Se modelaron dos sistemas multiespecíficos de árboles ribereños, suponiendo que las probabilidades de transición de especies están afectadas por el disturbio (parámetro β). Los parámetros teóricos de los modelos se ajustaron a un conjunto de dominios de comportamientos dinámicos de la ecuación, que determinaron la respuesta no-lineal. De acuerdo al modelo del río Azul, los sauces muestran un crecimiento del tipo logístico con un ajuste asintótico hacia el año 1995, con frecuencias de disturbios relativamente altas. El modelo predice un bosque diverso de Salix fragilis colonizando superficies inestables, que facilita a Nothofagus dombeyi, Austrocedrus chilensis y Myrceugenia exsucca. Las trayectorias sucesionales obtenidas por el modelo del río Limay explican que S. alba y Populus nigra para un rango de disturbios bajos y densidades iniciales equitativas, experimentan crecimientos logísticos. El modelo sauce – álamo, aquí propuesto no plantea diferencias iniciales entre ambas especies, razón por la cual los álamos dominan rápidamente el sistema. Pero con un rango de disturbios elevados ambas densidades se reducen al punto que los bosques declinan prácticamente hasta su extinción en 75 años. Las capacidades de sauces y álamos como especies ingenieras configuraron neoecosistemas ribereños. El futuro de las especies nativas del paisaje ribereño queda abierto al devenir histórico entre orden y cambio.