Horacio Ivancich

Modelos forzados y no forzados para el cálculo del índice de sitio en bosques de Nothofagus antarctica en Patagonia Sur

El potencial de produccion de un rodal puede definirse a traves de la calidad de sitio. Una forma de medir dicha calidad es a traves de ecuaciones de indice de sitio, existiendo distintos tipos de ecuaciones (forzadas y no forzadas). El objetivo fue comparar el ajuste de diferentes ecuaciones de indice 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 anos. 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 anos 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 autovalidacion de las ecuaciones seleccionadas fueron comparables a los encontrados por otros autores que trabajaron con curvas de indice de sitio aplicadas a bosques de Nothofagus spp. La ecuacion de Newnham fue la que mejor describio el crecimiento en altura dominante de N. antarctica, cumpliendo con las condiciones que deben tener las curvas de crecimiento. Estos resultados permiten senalar que el modelo es recomendable para ser usado como una herramienta de prediccion en la planificacion del manejo de los bosques de N. Antarctica.

Foliar anatomical and morphological variation in Nothofagus pumilio seedlings under controlled irradiance and soil moisture levels

Foliar anatomy and morphology are strongly related to physiological performance; therefore, phenotypic plasticity in leaves to variations in environmental conditions, such as irradiance and soil moisture availability, can be related to growth rate and survivorship, mainly during critical growth phases, such as establishment. The aim of this work was to analyze changes in the foliar internal anatomy (tissue proportions and cell dimensions) and external morphology (leaf length, width and area) of Nothofagus pumilio (Poepp. et Endl.) Krasser seedlings growing in a greenhouse under controlled irradiance (three levels) and soil moisture (two levels) during one growing season (measured three times), and to relate them to physiological traits. Three irradiance levels (4, 26 and 64% of the natural incident light) and two soil moisture levels (40 and 80% soil capacity) were evaluated during November, January and March. Internal foliar anatomy of seedlings was analyzed using digital photographs of histological cuttings, while leaf gross morphology was measured using digital calipers and image analysis software. Most internal anatomical variables presented significant differences under different irradiance levels during the growing season, but differences were not detected between soil moisture levels. Palisade parenchyma was the tissue most sensitive to irradiance levels, and high irradiance levels (64% natural incident light) produced greater values in most of the internal anatomical variables than lower irradiance levels (4-24% natural incident light). Complementarily, larger leaves were observed in medium and low irradiance levels, as well as under low soil moisture levels (40% soil capacity). The relationship of main results with some eco-physiological traits was discussed. Foliar internal anatomical and external morphological plasticity allows quick acclimation of seedlings to environmental changes (e.g., during harvesting). These results can be used to propose new forest practices that consider soil moisture and light availability changes to maintain high physiological performance of seedlings.

Landscape and microenvironmental conditions influence over regeneration dynamics in old-growth Nothofagus betuloides Southern Patagonian forests

Abstract Old-growth forests present a mosaic of different conditions resulting from the natural forest structure of the stands. Nothofagus betuloides forests have high spatial variability in regeneration without a clear correlation with overstory, and could be related to location of the stands in the landscape. The objective was to evaluate the influence of macro- and micro-variables over regeneration dynamics in old-growth N. betuloides forests, considering the effect of landscape (altitude and influence of the sea) and microenvironment conditions in the forest floor (closeness to trees, pits, understory cover type and bare soil). A total of four sites and 24 stands were sampled including forest structure, regeneration, understory cover and microclimate variables. Macro- (landscape) and micro- (microenvironment conditions in the forest floor) variables influenced over regeneration dynamics. Natural regeneration values (0.17 million ha−1 in the drier site vs. >4.52 million ha−1 in the other sites) not greatly depended on forest structure variables, but they were related to soil moisture (14% vs. 29–36% volumetric soil water content). Microenvironment conditions in the forest floor determined the recruitment as well as regeneration density, age and distribution of seedlings, whereas different soil moisture were related to each microenvironment type, generating positive (bare soil, ferns and mosses growing in turfs) or negative (mosses growing in mats, pits and proximity of the overstory trees) effects over regeneration, according to the soil moisture levels. These findings can be used to understand the functional integrity of the old-growth forest ecosystems and to propose silvicultural prescriptions to ensure regeneration recruitment and maximize growth potential in N. betuloides forests.

Changes in height growth patterns in the upper tree-line forests of Tierra del Fuego in relation to climate change

Resumen en: Nothofagus pumilio occupy the mountain slopes reaching to the upper altitudinal limit of the forests. This extremely stressful environment represents the...