The native forests of Northern Patagonia have a long history of human use, being one of the most studied ecosystems of Argentina. However, there are few examples of sustainably managed native forests. We propose that this is mainly due to the lack of political will from regional authorities, forest administration agencies, technicians and researchers in assisting forest owners to implement current legislation. Historically, forest owners have been ignored by an administrative system that has not considered their needs as well as by a scientific-technologic system that not used their empirical knowledge to develop realistic management packages. We consider that, even though the sustainable management of Patagonian native forests seems to be technically feasible, its implementation will depend on the will of the public sector to generate better conditions for an intersectoral collaboration that integrates different kinds of knowledge.

Los bosques del norte de la Patagonia tienen una larga historia de uso, siendo uno de los ecosistemas forestales más estudiados de Argentina. Sin embargo, existen pocos ejemplos de bosques nativos bajo manejo sustentable. Proponemos que esto se debe principalmente a la falta de voluntad de las autoridades de aplicación, organismos de gestión, investigadores y técnicos del sector por asistir a productores forestales en la implementación de la legislación vigente. Históricamente, los productores han sido ignorados por un sistema administrativo que no ha buscado adaptarse a sus necesidades, y por un sistema científico-tecnológico que no ha utilizado sus conocimientos empíricos para generar propuestas realistas de manejo. Consideramos que, si bien el manejo sustentable de los bosques patagónicos pareciera ser técnicamente viable, su implementación dependerá de la voluntad del sector público por generar las condiciones para un diálogo intersectorial que integre distintos tipos de saberes.

SUMMARY: Tree growth models contribute to describing the structure and functioning of forests, predicting timber production, implementing appropriate silvicultural practices and assessing the economic dimension of forestry. Nothofagus alpina, Nothofagus obliqua and Nothofagus dombeyi (Nothofagaceae) form natural forests in Northwestern Patagonia of Argentina. Models of diametric increment and yield were developed for N. alpina trees from the intermediate and superior canopy strata, through Bertalanffy - Richards's functions. They were interpreted together with those for N. obliqua and N. dombeyi, formerly developed using the same methodology. In all three species, intermediate trees exhibited the lowest diametric growth, probably in response to differences in the amount and composition of light. Growth of N. alpina trees, compared to N. dombeyi, was similar for all age classes within the intermediate stratum, and lower for older classes within the superior stratum. However, the performance of this species was adequate in both strata, which would be associated with the superior shade tolerance (perceived in the intermediate stratum) and the response to increasing light (in the upper one). Nothofagus obliqua experienced the slowest growth for all social strata and age classes. Discrepancies observed among models were compatible with interspecific differences in intrinsic growth and demand of light. The simultaneous interpretation of growth models of N. alpina, N. obliqua and N. dombeyi can contribute to deeply understand ecological patterns and processes of this subantarctic forest, aimed at its conservation and sustainable management.

RESUMEN: Los modelos de crecimiento arbóreo contribuyen a describir la estructura y el funcionamiento del bosque, predecir la producción de madera, implementar alternativas silvícolas y evaluar la dimensión económica forestal. Nothofagus alpina, Nothofagus obliqua y Nothofagus dombeyi (Nothofagaceae) conforman bosques naturales en el noroeste de la Patagonia argentina. A través de la función von Bertalanffy-Richards, se desarrolló un modelo de incremento corriente y rendimiento en diámetro para N. alpina de los estratos intermedio y superior, y se los comparó con los existentes para N. obliqua y N. dombeyi. En las tres especies, los árboles intermedios exhibieron el menor crecimiento que se debería a la composición y menor cantidad de luz. El crecimiento de N. alpina, comparado con el de N. dombeyi, fue similar en todas las clases de edad para el estrato intermedio, y menor en las clases de mayor edad para el estrato superior. Sin embargo, el desempeño de esta especie fue muy adecuado en ambos estratos, que se asociaría a la mayor tolerancia a la sombra (percibida en el estrato intermedio) y la respuesta al aumento de la luz (en el superior). Nothofagus obliqua siempre presentó el crecimiento diamétrico más lento. Las discrepancias observadas en los modelos fueron compatibles con diferencias interespecíficas de crecimiento intrínseco y demanda de luz. La interpretación simultánea de los modelos de estas especies de Nothofagus contribuye a aumentar la comprensión ecológica y productiva de un valioso tipo de vegetación subantártica.

RESUMO O volume de madeira das árvores em pé é uma informação essencial para as decisões de gestão. A crescente necessidade de otimizar a capacidade potencial das florestas mantendo sua conservação, requer a quantificação dos diferentes possíveis produtos de madeira possíveis. O objetivo era ajustar equações de afilamento para determinar volumes de diferentes produtos de madeira para hastes comerciais de Nothofagus alpina e N. obliqua. As árvores de ambas as espécies foram selecionadas ao acaso nas áreas de colheita do Parque Nacional Lanin (Argentina). As árvores foram derrubadas e cortadas em troncos comerciais, medindo o diâmetro com a casca em diferentes alturas até o início da coroa, e para cada árvore o diâmetro na altura do peito e altura total. Foram selecionadas cinco equações cônicas e foram empregados processos de regressão não-linear para ajustar. Obtivemos o volume através da integração da equação do perfil do caule e da rotação no seu espaço através do sólido da revolução. O modelo de Bennet e Swindel (1972) foi selecionado para as duas espécies de Nothofagus, obtendo parâmetros de equação semelhantes e observando-se diferenças no topo das hastes de árvores maiores. Portanto, o uso de um modelo integrado não é recomendado. Com as equações obtidas é possível: (i) estimar o volume em diferentes alturas e para diferentes diâmetros comerciais, e (ii) prever a altura em que ambas as espécies atingem um determinado diâmetro. O modelo apresentou algumas limitações estatísticas (por exemplo, multicolinearidade), no entanto, o ajuste da equação e a compreensão fácil das saídas o suportam como uma ferramenta útil em uma ampla gama de aplicações florestais.

ABSTRACT Timber volume of standing trees is essential information for management decisions. The increasing need to optimize the potential capacity of forests maintaining their conservation, requires the quantification of the different potential possible timber products. The aim was to adjust taper equations to determine volumes of different timber products for commercial stems of Nothofagus alpina and N. obliqua. Trees of both species were randomly selected in harvesting areas of Lanin National Park (Argentina). Trees were felled and cut into commercial logs, measuring diameter with bark at different heights up to the beginning of the crown, and for each tree the diameter at breast height and total height. Five taper equations were selected and non-linear regression processes were employed for the fittings. We obtained the volume through the integration of the stem profile equation and the rotation in the space thereof through solid of revolution. The Bennet and Swindel (1972) model was selected for both Nothofagus species, obtaining similar equation parameters and differences were observed at the top of the stems of larger trees. For this the use of an integrated model is not recommended. With the obtained equations it is possible to: (i) estimate volume at different heights and for different commercial diameters, and (ii) predict the height at which both species reach to a certain diameter. The model presented some statistical limitations (e.g. multicollinearity), however, the fitting of the equation and the easy understanding of the outputs support it as a useful tool in a broad range of forest applications.

RESUMO Primeiro passo para a construção de modelos de crescimento e produção de árvores e a avaliação da qualidade do sítio. Para estimar este atributo, várias metodologias estão disponíveis, na qual o índice de sítio (IS) é padrão. No entanto, esta abordagem, que utiliza uma altura na idade de referência, pode ser simplificada se a idade é substituída por outra variável de referência mais fácil de medir. Neste caso, o índice de índice de sítio diamétrico (ISD) representa a altura média das árvores dominantes de um diâmetro à altura do peito referência. O objetivo deste trabalho foi desenvolver ISD para florestas puras e mistas de Nothofagus alpina e N. obliqua, e comparar esses modelos com as propostas clássicas baseadas nas variáveis altura-idade, para a floresta temperada do noroeste da Patagônia da Argentina, América do Sul. Dados provenientes de parcelas temporárias e análises de tronco foram utilizados. Foram obtidos idade e diâmetro à altura do peito de cada parcela e utilizados para o estabelecimento das funções da família DSI, seguindo a metodologia da curva-guia. Classes de sítio foram proporcionalmente representados entre curvas DSI de 17,0; 21,5; 26,0; 30,5 e 35,0 m de altura da árvore dominante. O diâmetro de referência em vez da idade de referência pode ser usado com cautela para ajustar modelos de índice de sítio.

ABSTRAT The first step for constructing models of tree growth and yield is site quality assessment. To estimate this attribute, several methodologies are available in which site index (SI) is a standard one. However, this approach, that uses height at a reference age of trees, can be simplified if age is replaced by another reference variable easier to measure. In this case, the diametric site index (DSI) represents the mean height of dominant trees at a reference mean diameter at breast height. The aim of this work was to develop DSI in pure and mixed Nothofagus alpina and N. obliqua forests, and compare these models with the classical proposals based on height-age variables, within the temperate forest of northwestern Patagonia from Argentina, South America. Data originated from temporary plots and stem analyses were used. Tree age and diameter at breast height were obtained from each plot and used for establishing DSI family functions, following the guide-curve methodology. Site classes were proportionally represented among DSI curves of 17.0, 21.5, 26.0, 30.5 and 35.0 m of dominant tree height. Reference diameter instead of reference age can be cautiously used in order to fit site index models.

The growth of the dominant height of the stand and the IS is assumed to express the effects of all relevant site factors on the growth. The objective was to develop a function which could express the dominant growth pattern in height within the range of ages and site qualities in mixed N. alpina and N. obliqua (Neuquén, Argentina). Data were obtained from stem analyses by destructive sampling, and Chapman-Richards function was used (guide curve method). A global setting for each species (specific models) and another with both species together (mixed model) were performed. Adjustments were evaluated through standard error of the estimate, the average absolute error, the coefficient of determination; besides considering the biological behavior using a graphical tree-to-tree evaluation of the goodness of fit. A graphical analysis of the dispersion of the parameters was performed by site class for each species according to the IS. Linear models were tested to detect trends in the same. Finally, we have established four classes of site quality. The growth pattern of N. obliqua and N. alpina has been significantly anamorphic among the age ranges and site quality ranges studied. Species have shown similar patterns, reinforcing the similarity found in previous studies in other dimensional variables. This has facilitated the development of a unique model, which facilitates assessment of the quality of site planning and management of mixed stands.

El crecimiento de la altura dominante y el índice de sitio (IS) de un rodal, asume que expresa los efectos de todos los factores relevantes del sitio. El objetivo fue desarrollar un modelo de altura dominante que exprese el patrón de crecimiento dentro del rango de calidades de sitio y edades en bosques mixtos de Nothofagus alpina y N. obliqua (Neuquén, Argentina). Los datos fueron obtenidos a partir de análisis fustales a través de muestreos destructivos, con los que se ajustó la función de Chapman-Richards, (método de la curva guía). Se realizó un ajuste global para cada especie (modelos específicos) y otro con ambas especies juntas (modelo mixto). Los ajustes se evaluaron a través del el error estándar de la estimación, el error absoluto medio, el coeficiente de determinación, además de considerar el comportamiento biológico mediante una evaluación gráfica árbol a árbol de la bondad del ajuste. Se realizó un análisis gráfico de la dispersión de los parámetros por clase de sitio para cada especie en función del IS, y se ensayaron modelos lineales para detectar tendencias en los mismos. Finalmente, a partir de los modelos se establecieron cuatro clases de calidad de sitio. El patrón de crecimiento de N. obliqua y N. alpina ha resultado sensiblemente anamórfico entre los rangos de edad y calidad de sitio estudiados. Las especies mostraron patrones de crecimiento similares, reforzando lo reportado en estudios anteriores para otras variables dimensionales. Esto nos permitió desarrollar un modelo único a partir de la función de crecimiento, que facilitará la evaluación de la calidad de sitio y la planificación del manejo forestal en los rodales mixtos de estas especies.

Management practices are important disturbance agents at local level and their incorrect implementation may affect the sustainability of natural forests. Usually, silviculture based on the shelterwood system was carried out in the mixed stands composed of Nothofagus dombeyi, N. alpina and N. obliqua, located at Lanín Natural Reserve (Neuquén Province, Argentina). However, the effect of this scheme on the composition and structure of natural regeneration is still rather unknown. In this study, composition, age, abundance and spatial pattern of adults and saplings of Nothofagus species were evaluated in a 3-ha plot logged in 1993. At pre-harvest period, adult density was 26 % for N. dombeyi, 38 % for N. alpina and 35 % for N. obliqua. Regeneration consisted mainly of N. nervosa. After logging, composition of adult trees was 20 %, 43 % and 37 % for N. dombeyi, N. alpina, N. obliqua, respectively; whereas regeneration was 45 % for N. obliqua and 42 % for N. dombeyi. Within species, no relationship was found between basal area of adult trees and density of saplings. For all tree species, age regeneration was larger in areas where tree canopy cover exhibited higher values. N. alpina was the last installed species. Preservation of the relative species composition after logging did not maintain the original abundance within regeneration. Consequently, it is necessary to adjust silvicultural practices, and particularly the level of canopy openings, in order to maintain species composition unaffected as a key indicator of sustainability at management unit scale.

Las prácticas silviculturales constituyen un importante agente de disturbio y su inadecuada implementación afecta la sostenibilidad de los bosques naturales. En la Reserva Nacional Lanín, el manejo silvicultural del bosque de Nothofagus dombeyi, N. alpina y N. obliqua se realiza tradicionalmente mediante aclareos sucesivos; y se desconoce su efecto sobre la composición y estructura de la regeneración natural. La cobertura del dosel, composición y área basal de los individuos adultos, y la composición, edad y distribución espacial de los renovales fue evaluada en una parcela de 3 ha intervenida en 1993 mediante una corta diseminatoria. La densidad de adultos antes de la corta fue 26 % para N. dombeyi, 38 % para N. alpina y 35 % para N. obliqua, y la remanente fue 20, 44 y 36 %, respectivamente. Previamente al aprovechamiento, el 92 % de la regeneración estaba constituida por N. alpina, y luego principalmente por N. obliqua (45 %) y N. dombeyi (42 %). Estos valores no se correlacionaron con el área basal de adultos. La edad de los renovales fue mayor en sitios con alta cobertura de dosel y N. alpina fue la especie que se instaló última. El aprovechamiento del bosque de Nothofagus no promovió el mantenimiento de la composición relativa original de la regeneración. El tiempo de colonización de las especies de Nothofagus disminuiría y una mayor cantidad de renovales de N. alpina, especie más tolerante a la sombra, se establecería si la cobertura remanente fuera superior a la recomendada en los planes de manejo.

Invasive alien species management in Patagonia, Argentina: Prioritization, achievements and science-policy integration challenges identified by the National Parks Administration: Invasive alien species are a threat to biodiversity. Management options encompass prevention, early detection, eradication, control, exclusion and even"no action." More technical information is needed to achieve complex management actions successfully. In addition, managers and researchers address the problem with different approaches. Managers seek to prioritize management actions, and for researchers, these species are an opportunity to study basic and/or theoretical aspects, but not always applied to management. However, the management strategies offer a unique opportunity for both groups to work together seeking mutual benefits. Currently, management decisions are often based on experiences or information from other countries, which is not always useful for local problems. We present several management experiences in the Argentine National Parks Administration to show achievements, difficulties and challenges usually faced by managers. We found that: a) it is important, when resources are scarce, to generate effective prioritization tools and networks; b) it is also vital to involve the community in the management actions; c) on the other hand, research directly applied to pilot eradication is required; and d) also, a careful planning, and continuity and monitoring of management actions and environmental results based on different types of first class technical information, are key aspects for successful management. Finally, managers and researchers must ensure that the results of applied research are known and understood by decision makers and the general public, to secure management support.

Las especies exóticas invasoras amenazan la biodiversidad. Existen diferentes opciones para su manejo: prevención, detección temprana, erradicación, control, exclusión e incluso la"no acción". A mayor complejidad de manejo, más información se requiere para ejecutarlo exitosamente. Además, gestores e investigadores abordan la problemática con enfoques e intereses diferentes. Mientras los primeros priorizan acciones de manejo, los segundos encuentran una oportunidad para estudiar aspectos básicos y/o teóricos, no siempre aplicados al manejo. La gestión de estas especies ofrece una ocasión única para que ambos grupos trabajen juntos en busca de beneficios mutuos. Actualmente, las decisiones de manejo suelen basarse en experiencias o información de otros países, no siempre adaptables a la problemática local. En este trabajo presentamos varias experiencias de manejo en la Administración de Parques Nacionales para exponer logros, dificultades y desafíos a los que usualmente se enfrenta la gestión institucional. Encontramos que: a) ante recursos escasos es importante generar herramientas de priorización efectivas y redes de trabajo; b) es imprescindible involucrar a la comunidad en las acciones de manejo; c) se requieren investigaciones aplicadas al manejo específico; y d) es necesario una detallada planificación previa y un monitoreo de las acciones ejecutadas y de sus resultados, basados en información técnica de primer nivel, ya que son aspectos claves para un manejo exitoso. Finalmente, gestores e investigadores deben cerciorarse que los resultados de estas investigaciones aplicadas sean conocidos y comprendidos por los tomadores de decisiones y la opinión pública, para asegurar el apoyo a la gestión.

Non-linear, Bertalanffy-Richards-type models of diameter growth were developed for Nothofagus obliqua and fitted for different social tree strata using the diameter annual increment (id) and diameter at breast height (dap). The biological and statistical analyses were conducted from two different sources; an independent data set taken mainly from permanent sample plots and a real growth series obtained from tree cores and stem analyses. Models for different purposes were obtained through both data sets. For the prediction of short-term diameter increments, a model was obtained that related independent data of trees belonging to the same social stratum. Models of higher biological meaning were obtained by relating the growth series and their significance and are discussed here. By means of these biological models, the growth dynamics of N. obliqua were analyzed under different competitive status.

Se han desarrollado varios modelos de crecimiento diamétrico para la especie Nothofagus obliqua. Este trabajo continúa a otros similares realizados con N. nervosa (Chauchard 1991) y N. dombeyi (Chauchard et al. 2001). El modelo seleccionado para realizar el estudio es uno no lineal usualmente denominado Bertalanffy-Richards. El mismo se ajustó a partir de tres fuentes de datos: parcelas permanentes (con sólo dos mediciones cada una), análisis fustales y tarugos de incremento. Estos datos fueron segregados por estrato social y luego para cada uno se ajustó el citado modelo con las variables incremento diamétrico (id)-diámetro a la altura del pecho (dap). Los ajustes y análisis se realizaron a partir de dos agrupamientos de los datos. Por un lado se utilizaron datos independientes que provenían principalmente de las parcelas de muestreo, mientras que por otro se emplearon series reales de crecimiento obtenidas de los tarugos y los análisis fustales. Con ambos grupos se obtienen modelos con aplicaciones diferentes. Con los datos independientes se obtienen modelos de interés para la predicción del incremento diamétrico en el corto plazo, mientras que con las series de crecimiento se obtienen modelos de una alta significancia biológica. A través de estos modelos biológicos se interpretó la dinámica de crecimiento de N. obliqua bajo diferentes estados de competencia.