G. Martínez Pastur

Successive media to improve the in vitro rhizogenesis of Nothofagus nervosa (Phil.) Dim. et Mil.

In vitro rooting constitutes a difficult step during the micropropagation process of forest species. The successive media culture technique represents one way to overcome this barrier and includes modifying physical (e.g. photoperiod) and chemical (e.g. flavonoids) factors during the rooting phases. The aim of this study was to obtain a successive media protocol based on the incorporation of flavonoids during the in vitro rooting of Nothofagus nervosa. The factors evaluated were the type, concentration, and combination of flavonoids in relation to the rooting phases, the presence of IBA in the culture medium, the photoperiod, and the effect of flavonoids on total tissue peroxidase activity. The photoperiod used included a darkness period during the rooting induction stage and the presence of 0.61 µMIBA in the culture medium. The results showed that flavonoid incorporation at a concentration of 20 µM accelerated the appearance of roots and improved the quality of the already formed ones. Each type and concentration of flavonoid produced different responses, with (±)naringenin giving the best results. The latter caused a peak in the peroxidase activity that was absent in the control treatments. This work allowed identifying an optimized rooting protocol through a successive media culture technique that improved the speed of appearance, as well as the quantity and quality of roots for a single N. nervosa clone.

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.

Crecimiento diamétrico de Nothofagus pumilio para dos condiciones de copa en un sitio de calidad media en Santa Cruz, Argentina

Nothofagus pumilio es la especie de mayor distribucion geografica e importancia economica de los bosques patagonicos. Son pocos los modelos biometricos relacionados con la planificacion del manejo forestal en la Patagonia, por lo que se decidio construir un modelo de crecimiento individual en diametro para N. pumilio bajo dos condiciones de competencia de copa en un bosque de calidad media (IS60 = 9,8 m) de la provincia de Santa Cruz (Argentina). El modelo de Chapman-Richards presento muy buenos estadisticos y una excelente significacion biologica. Al analizar los ritmos de crecimeinto de acuerdo a su clase de copa, estos se comportaron de manera diferencial. La culminacion del crecimiento fue a los 62 y 52 anos para el estrato superior e inferior, siendo los crecimientos maximos promedios de 0,303 cm/ano para arboles dominantes y de 0,192 cm/ano para arboles intermedios. Al realizar una validacion indirecta a partir del crecimiento volumetrico por hectarea aplicando el modelo construido, se detectaron diferencias que variaron entre el 2,5 p. 100 y el 20 p. 100 respecto del crecimiento real estimado a partir del analisis de tarugos.

Análisis de la ciclofisis y la topofisis en Populus deltoides Bartr desde la formación del estaquero hasta una plantación comercial

La propagacion comercial de especies de la familia Salicaceae, muy influenciada por las relaciones ortet-ramet, se realiza por medio de estacas. Las relaciones que se citan con mayor frecuencia dentro de la literatura son la topofisis y la ciclofisis. El objetivo de este trabajo fue estudiar si los fenomenos de ciclofisis y topofisis afectan la capacidad de enraizamiento y la modalidad de crecimiento de los brotes en estacas de P. deltoides en los primeros anos de crecimiento en estaquero y el comportamiento posterior de las estacas obtenidas de este en una plantacion comercial al primer ano. Los resultados obtenidos muestran que la ciclofisis afecto tanto la arquitectura de la nueva planta como su ritmo de crecimiento. Las estacas provenientes de guias diagravitropicas, generan plantas con ramas mas horizontales, producen mas metros de ramas, mayor numero de hojas y mayor biomasa, respecto de las ortogravitropicas. Estas diferencias en los parametros medidos indican que existe un efecto residual del habito de crecimiento de la estaca en la guia, que se pone de manifiesto al formar una nueva planta y que ademas la eficiencia del explanto esta condicionada a su ubicacion en la planta madre. La topofisis modifica el enraizamiento, siendo este mayor en las estacas apicales y basales respecto de las del tercio medio. La baja obtencion de plantas a partir de estacas del tercio medio de las guias (5 p. 100), puede tener causas fisiologicas o causass geneticsa del clon en estudio, que no hemos podido aclarar en este experimento. El fecto de la topofisis y de la ciclofisis sobre el enraizamiento de la estaca y el crecimiento de la planta en su primer ano en estaquero, determiann la obtencion de una poblacion altamente heterogenea. De acuerdo con estos resultados se debera tener en cuenta el origen del material a plantar, tanto por su topofisis como por su ciclofisis, con el fin de mejorar las plantaciones en sus primeras etapas de crecimiento.

Modelos de perfil de tronco en "Nothofagus pumilio" (Poepp. et Endl.) Krasser y su utilización en el cálculo del volumen total

Se trabajo con 60 arboles de Nothofagus pumilio seleccionados a lo largo de un gradiente de sitios entre calidades 1 a 3 en Tierra del Fuego (Argentina). Con estos datos se desarrollaron ecuaciones de prediccion de perfil del tronco del arbol para bosques secundarios (originados a partir de la regeneracion de un bosque intervenido), comparando cuatro modelos tradicionales con otro no tradicional que utiliza la calidad de sitio como variable predictora. Por otra parte, a partir de los resultados obtenidos con los modelos, se incorporo la forma a ecuaciones de volumen comunmente utilizadas para N. pumilio, evaluando su ajuste mediante un analisis de comportamiento de residuos. El modelo de perfil de Muhairwe de exponente variable, que utiliza como variables el diametro a 1,3 m de altura, la altura total y la altura del tronco a la que se encuentra un diametro determinado, tiene el mejor comportamiento general, adecuandose a diferentes calidades de sitio, diametro y alturas relativas. El modelo propuesto en este trabajo, que incluye la calidad de sitio como variable predictora, tiene un peor ajuste, pero es mas economico y posee una mayor practicidad, ya que no necesita de la medicion de la altura total. Por otra parte, se ha demostrado que la inclusion de la forma en la construccion de los modelos de volumen a traves de una metodologia sencilla, mejora el ajuste sin aumentar la complejidad de los modelos tradicionales.

Environmental drivers of plant community assembly in Isla de los Estados at Southern Atlantic Ocean

The comprehensive assessment of environmental gradients influencing species assemblages is important for implementing new conservation strategies under climate change. This study aims to determine the multi-scale effect of altitudinal and longitudinal gradients as drivers of richness and plant community assembly in mountain landscapes of Isla de los Estados (Argentina) to identify areas with greater conservation value in Southern Patagonia. We chose three fjords across the island that extends from West to East and we categorized landscapes into four ecosystem types according to their vegetation type (forests and open-lands) and elevation (lower lands, 0–100 m.a.s.l. and upper lands, 300–400 m.a.s.l.). Forest structure, soil cover (woody debris, rocky outcrop and bare soil) and vegetation cover (vascular and non-vascular), including richness and growthforms (trees, shrubs, prostrate and erect herbs, tussock and rhizomatous grasses, ferns and inferior plants) were measured in 60 sampling areas (3 fjords × 2 vegetation types × 2 elevations × 5 replicates). ANOVAs and multivariate methods were used to analyse heterogeneity in forest structure, plant richness, and life-form. In addition, species richness and the Simpson’s diversity index were calculated to understand plant assembly at multiple-scales (α, β and γ). Our results showed that environmental gradients (altitudinal and longitudinal) are more important drivers of change of ecosystem type than forest spatial structure. Furthermore, forest structure significantly varied with altitudinal and longitudinal gradients affecting most of the studied variables. A greater similarity (in richness and cover) between open-lands of lower and higher elevations was detected, as well as between forests. Fjords showed a West-East gradient, where the western and center fjords were more closely related to each other than to the eastern fjord. A multi-scale diversity approach may play central role in improving our understanding the main environmental drivers of richness and plant community assembly in these forests, both theoretical and empirical, and may be used to identify the spatial scale at which ecosystem types have greater conservation value. This study indicates that for southern forest conservation at regional level, efforts must cover all environmental gradients, including the different vegetation types to assure ful conservation of all the species assemblages.

Incidence of browsing by guanaco (Lama guanicoe Müller) on early regeneration of lenga [Nothofagus pumilio (Poepp et Endl) Krasser] forests in Tierra de Fuego, Argentina.

In this work we analyze the early regeneration of Nothofagus pumilio forests, as well as the impact of browsing by guanacos (Lama guanicoe), in Tierra del Fuego, Argentina. First, we describe the structure of three N. pumilio stands with differing management schedules: a native virgin forest stand (BV), a stand that was logged in 1991-93 leaving a certain homogeneous density of parent trees («shelterwood cut», CP), and a third stand that was selectively and intensively logged (FL) in 1995. In these three stands we quantify the use by guanacos (estimated from the density of fecal remains) and the frequency of browsed seedlings ( 0.5 cm in stem diameter). Results show a high incidence of browsing, which was higher for the native forests stand (100 % and 95.7 %), than for CP (69.9 % and 72.1 %) and FL (67.3 % and 61.5 %, for basal and apical damage of browsed plants, respectively). These differences are mainly due to the fact that patches where big trunks accumulate in managed stands, provide shelter from damage by guanacos. Comparison of observed and expected (according to calculated growth models) sapling heigth show that recurrent damage by guanacos prevent successful growth, the corresponding height loss being 83.1 % for BV, 45.7 % for CP, and 50.3 % for FL. We conclude that guanacos effectively limits early regeneration in both native and managed stands, though a wider time scale is needed for a conclusive assessment of the incidence of browsing in forest dynamics and production.

CRECIMIENTO EN CORTINAS CORTAVIENTO DE POPULUS NIGRA CV "ITALICA" EN PATAGONIA SUR (ARGENTINA)

La implantacion de cortinas contribuyo al desarrollo agricola en Patagonia sur. Predecir el crecimiento y la dinamica de estas plantaciones permite cuantificar el area protegida de los cultivos y la rentabilidad maderera. Este trabajo presenta modelos biometricos para Populus nigra cv ‘Italica’ en diferentes sitios, condiciones de copa y distanciamientos en cortinas cortavientos de Santa Cruz (Argentina). Para el ajuste del crecimiento diametral y en altura se utilizo una modificacion de la funcion de Chapman-Richards. Para la ecuacion de volumen se empleo la funcion de Schumacher-Hall, mientras que usando tecnicas de regresion multiple se definieron los modelos de dinamica de clases de copa. Los modelos ajustados presentaron muy buenos estadisticos, ya que los multiples factores que inciden en el crecimiento de cortinas cortaviento pudieron ser explicados a traves de variables de facil medicion (DAP, altura total, clases de copa, sitio).