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Modelos forzados y no forzados para el cálculo del índice de sitio en bosques de Nothofagus antarctica en Patagonia Sur
Ivancich,Horacio; Martínez Pastur,Guillermo; Peri,Pablo Luis;
Bosque (Valdivia) , 2011, DOI: 10.4067/S0717-92002011000200004
Abstract: yield potential of a stand can be defined through site quality. one way to measure site quality is using site index equations, being available different equation types (constrained and non-constrained). the objective of this study was to compare the fitness of site index equations using different base ages, and validate them along site quality and age classes in nothofagus antarctica forests of south patagonia. four height growth equations were fitted using two constrained and two non-constrained models. the equations were fitted using three base ages (30, 40 and 50 years). self-validation was done using gradients of age and site quality. lower errors were obtained when a base age of 50 years was used for all the equations. besides this, the best fitting along the age and site quality gradients were obtained with weibull, richards and newnham equations. the self-validation values of the selected equation were comparable to the fitting presented by other authors, who worked with site index models in nothofagus spp. forests. newnham equation better described the height dominant growth in n. antarctica, which presented great biological significance according to the shape of the obtained curves. hence, this model can be recommended to be used as a prediction tool for forest management planning in n. antarctica forests.
Modelos forzados y no forzados para el cálculo del índice de sitio en bosques de Nothofagus antarctica en Patagonia Sur Constrained and non-constrained models for site index estimation in Nothofagus antarctica forests of South Patagonia
Horacio Ivancich,Guillermo Martínez Pastur,Pablo Luis Peri
Bosque (Valdivia) , 2011,
Abstract: El potencial de producción de un rodal puede definirse a través de la calidad de sitio. Una forma de medir dicha calidad es a través de ecuaciones de índice de sitio, existiendo distintos tipos de ecuaciones (forzadas y no forzadas). El objetivo fue comparar el ajuste de diferentes ecuaciones de índice de sitio con diferentes edades base mediante validaciones a lo largo de gradientes de edad y clase de sitio en bosques de Nothofagus antarctica de Patagonia Sur. Se ajustaron cuatro ecuaciones de crecimiento en altura, dos no forzadas y dos forzadas. Las edades base utilizadas para el ajuste fueron 30, 40 y 50 a os. Se realizaron autovalidaciones de las ecuaciones a lo largo de gradientes de edad y de calidad de sitio. Los menores errores se obtuvieron al utilizar una edad base de 50 a os para todas las ecuaciones. Los mejores ajustes en los gradientes de edad y calidad de sitio se obtuvieron con los modelos de Weibull, Richards y Newnham. Los valores provenientes de la autovalidación de las ecuaciones seleccionadas fueron comparables a los encontrados por otros autores que trabajaron con curvas de índice de sitio aplicadas a bosques de Nothofagus spp. La ecuación de Newnham fue la que mejor describió el crecimiento en altura dominante de N. antarctica, cumpliendo con las condiciones que deben tener las curvas de crecimiento. Estos resultados permiten se alar que el modelo es recomendable para ser usado como una herramienta de predicción en la planificación del manejo de los bosques de N. Antarctica. Yield potential of a stand can be defined through site quality. One way to measure site quality is using site index equations, being available different equation types (constrained and non-constrained). The objective of this study was to compare the fitness of site index equations using different base ages, and validate them along site quality and age classes in Nothofagus antarctica forests of South Patagonia. Four height growth equations were fitted using two constrained and two non-constrained models. The equations were fitted using three base ages (30, 40 and 50 years). Self-validation was done using gradients of age and site quality. Lower errors were obtained when a base age of 50 years was used for all the equations. Besides this, the best fitting along the age and site quality gradients were obtained with Weibull, Richards and Newnham equations. The self-validation values of the selected equation were comparable to the fitting presented by other authors, who worked with site index models in Nothofagus spp. forests. Newnham equation better described th
Changes in height growth patterns in the upper tree-line forests of Tierra del Fuego in relation to climate change Cambios en los patrones de crecimiento de los bosques del límite superior altitudinal de Tierra del Fuego en relación al cambio climático
Horacio S Ivancich,Guillermo J Martínez Pastur,Fidel A Roig,Marcelo D Barrera
Bosque (Valdivia) , 2012,
Abstract: Nothofagus pumilio occupy the mountain slopes reaching to the upper altitudinal limit of the forests. This extremely stressful environment represents the optimum conditions to study changes in growth patterns due to climate variations. Our goal was to analyze recent changes in stem height growth in forests located in the upper altitudinal tree-line along Tierra del Fuego (Argentina), and establish possible linkages to changes observed in surface temperature during the last decades. Nine locations were sampled, and four plots were measured in each location. Forest structure was characterized, and stem analyses were performed to assess height growth patterns. ANOVAs and classification analyses were conducted using location and time as main variables. Tree-growth height increased with time, e.g. 1.0 cm.year-1 during 1870-1959, 2.7 cm year-1 during 1960-1979, and 5.0 cm year-1 during 1980-2010. These differences were significant between periods and locations, and can be related to its geographical situation. Increment in stem height growth seems to be related with the worldwide surface air temperature. A decline in stem height growth registered during the last two decades can also be related with the regional decrease in the mean air temperature. The analysis of stem height growth is a useful tool to evaluate the incidence of climate change over trees growing under extreme environmental conditions. Los bosques de Nothofagus pumilio ocupan las laderas de monta a hasta alcanzar el limite altitudinal del bosque. Estos ambientes extremos, donde los bosques están bajo condiciones de estrés ambiental, son óptimos para estudiar patrones de cambio debidos a variaciones climáticas. El objetivo fue analizar cambios recientes en el crecimiento en altura en bosques localizados en el tree-line altitudinal en Tierra del Fuego (Argentina) y establecer posibles vinculaciones con cambios en la temperatura observados durante las últimas décadas. Se muestrearon nueve sitios, y se midieron cuatro parcelas en cada sitio. Se determinó la estructura forestal y se realizaron análisis fustales para evaluar los patrones de crecimiento en altura. Se realizaron ANOVA y análisis de clasificación usando como factores principales al sitio y al tiempo. El crecimiento en altura aumentó a lo largo del tiempo, e.g. 1,0 cm a o-1 durante 1870-1959, 2,7 cm a o-1 durante 1960-1979 y 5,0 cm a o-1 durante 1980-2010. Esas diferencias fueron significativas entre períodos de tiempo y sitios, pudiendo estar relacionadas con la localización geográfica. El incremento en el crecimiento en altura observad
Plasticidad ecofisiológica de plántulas de Nothofagus pumilio frente a combinaciones de niveles de luz y humedad en el suelo
Martínez Pastur,Guillermo J; Lencinas,María V; Soler Esteban,Rosina; Ivancich,Horacio; Peri,Pablo L; Moretto,Alicia; Hernández,Luis; Lindstrom,Ivone;
Ecolog?-a austral , 2011,
Abstract: proposed silviculture for nothofagus pumilio forests are based on the canopy open to stimulate natural regeneration growth through the increasing of soil moisture and light availability at the understory level. seedlings growth will be related to the plasticity for these new stand conditions. for this, the objective was to analyze morphological and ecophysiological changes of seedlings growing in controlled conditions under two soil moisture levels along a light intensity gradient. two to three years-old seedlings were obtained from one old-growth forests during september 2005, and were transplanted into plastic pots in a greenhouse under two soil moisture levels (40-60% and 80-100% soil capacity) and three light intensities (4%, 26% and 64% natural incident irradiance). morphological (height, number, size and shape of the leaves, number of branches, foliar area, root density, biomass compartments and leaf histology) and ecophysiological (photosynthesis, respiration, pigment content, relative water content in leaves, stomata conductance, nutrient content and water potential of apical shoots) variables were measured during january 2006. one-way anovas was conducted to evaluate changes according to soil moisture levels for each light intensity level, as well as multivariate analyses to evaluate interactions among factors. seedlings showed best growth performances under a low soil moisture level (40-60% soil capacity). growing response to the different soil moisture levels was related to light availability, where a middle light level presented the best growth rates. high light levels produced negative results for seedling growth. in this work, evidences suggested that changes in the anatomical variables, chemical composition and water status relations, allowing to a high plasticity to survive under different conditions of soil moisture and light intensities. these results can be used to suggest better silviculture proposals to improve seedling growth after harvesting.
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