Photosynthetic response to different light intensities and water status of two main Nothofagus species of southern Patagonian forest, Argentina

Net photosynthetic rate (A) and stomatal conductance (gs) of seedlings of Nothofagus. pumilio and N. antarctica leaves were measured at different light intensity (20, 150, 250, 500, 750, 1000, 1500 and 2200 µmol m-2 s-1 photosynthetic photon flux density, PPFD) and after 60 minutes of severe shade to determine the lag in the rise of photosynthesis rate from low to high irradiance levels (induction state). Also, A and gs were measured to evaluate the responses to water stress and the tolerance to waterlogging in the two species. N. pumilio had higher A values than N. antarctica for all light intensities measured with a maximum value of 16.8 µmol CO2 m-2 s-1 saturated at 1000 µmol m-2 s-1 PPFD. Values of gs for both Nothofagus species also declined as light intensity decreased at a rate of 0.0002 mol H2O m-2 s-1/µmol m-2 s-1 PPFD. The times required for full induction of A were 18 and 27 minutes after the increase of PPFD (full sun) for N. pumilio and N. antarctica, respectively. There was a negative relationship between A and water stress expressed as pre-dawn leaf water potential (ψlp) where the reduction in gs was the main factor that reduced A in both species. A reached a negative value from -17.0 bar for N. pumilio and from -27.0 bar for N. antarctica. Tolerance to waterlogging was related with changes in A and gs being N. antarctica was more tolerant. After 10 days of waterlogging the average decrease in A was 83% for N. pumilio and 65% for N. antarctica. These defined photosynthetic results of Nothofagus leaves to fluctuating light regimes, water stress and waterlogging could be used to estimate the responses of regeneration to environmental conditions under the dynamic of natural stands, after silviculture practices, and degraded sites for restoration plans.Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin

Understory plant diversity assessment of Szemao pine (Pinus kesiya var. langbianensis) plantations in Yunnan, China

Evaluación de la diversidad de plantas de sotobosque en plantaciones de pino Szemao (Pinus kesiya var. langbianensis) en Yunnan, China.— La sostenibilidad es un objetivo clave para la gestión tanto de bosques naturales como de plantaciones, mientras que los estudios sobre biodiversidad constituyen herramientas muy útiles para mejorar la conservación de especies amenazadas. El pino Szemao (Pinus kesiya var. langbianensis) es un árbol nativo de China que se usa en plantaciones. Este estudio evalúa la diversidad del sotobosque en plantaciones de pino Szemao (SP) y otros tipos de vegetación local, como bosques secundarios perennifolios (SE) y tierras de cultivo abandonadas (AF), en la provincia de Yunnan, China. El muestreo se realizó en tres rangos altitudinales, y se evaluó riqueza y cobertura de hierbas y arbustos además de factores ambientales. En general, la riqueza promedio y la diversidad de Shannon-Wiener fueron mayores en SE que en SP, y a su vez que en AF, mientras que la equitatividad tendió a ser mayor en SP. Asimismo, dichos índices tendieron a aumentar con la altitud en SP y AF, aunque en SE fueron mayores a altitudes bajas y medias. La inclusión de factores ambientales resaltó las diferencias entre rangos altitudinales, siendo el contenido de agua (en el estrato herbáceo) y el tipo de suelo (en el estrato arbustivo) las variables más significativas. Las plantaciones de pino Szemao en Yunnan afectan al sotobosque, encontrándose pocas especies raras o amenazadas en su interior. Las reservas naturales y los trasplantes podrían ser una alternativa para proteger a las especies amenazadas si se llevan a cabo anticipadamente a las plantaciones.Sustainability is a key objective for managers of both natural forests and plantations, and biodiversity assessments are important tools to improve conservation of endangered species. Szemao pine (Pinus kesiya var. langbianensis) is a native Chinese tree species used in plantations. This study evaluated differences in understory diversity among Szemao pine plantations (SP) and other local current vegetation types: secondary evergreen forests (SE) and abandoned farmlands (AF) in Yunnan Province. Sampling was performed at three elevation ranges, where species richness, species cover, and environmental variables in the herb and shrub layers were measured. We found that indexes for average richness and Shannon?Wiener diversity were higher in SE than in SP, which were in turn higher than in AF, while the index for evenness was higher in SP. These indexes increased with elevation in SP and AF, but were higher at low and medium elevations in SE. Inclusion of environmental factors highlighted elevation differences, with water content (at herb layer) and soil type (at shrub layer) being the most significant variables. In conclusion, plantations of Szemao pine negatively affect understory diversity in Yunnan, and furthermore, only a few rare or threatened species could be found in the plantations. Nature reserves and transplanting could protect threatened species if established before plantations.Fil: Wang, H.F.. Research Center for Eco-Environmental Sciences; ChinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Ross Friedman, Cynthia. Thompson Rivers University.; CanadáFil: Zhu, Z.X.. Institute of Botany. Chinese Academy of Sciences; ChinaFil: Qiu, J. Research Center for Eco-Environmental Sciences; Chin

Diameter growth: Can live trees decrease?

Growth refers to an increase in dimensions with time and is implicit in the expected continual increase in tree dimensions. Tree diameters, however, could decrease during the growing season due to water depletion. Annual negative growth measurements are usually attributed to human error and not to other physiological or physical processes. Although seasonal and diurnal fluctuations of diameter have been well documented, perennial decrement of diameter has not been the focus of physiological research. The aim of this work was to analyse the potential causes of decrease in annual diameter growth related to tree mortality due to self-thinning in Nothofagus pumilio forests and to quantify the variations in water depletion of the tree trunks. Some trees did present negative annual diameter increments associated with a water content decrease in the trunks (77 per cent in live trees compared with 56 per cent in recently dead individuals), which produced a contraction (more than 8 per cent of the initial diameter) in the wood and the bark. Trees could survive during 2-5 growth seasons with continual decreases in their diameters (14 per cent, standard error 5 per cent of the trees in the studied stand) until the water content reached a limit where mortality resulted. Therefore, the occurrence of data showing a diameter decrease in successive forest inventories may be due to physiological and physical processes in the natural dynamics of the stand, and not exclusively be explained away as the results of human measurement errors.Facultad de Ciencias Agrarias y ForestalesConsejo Nacional de Investigaciones Científicas y Técnica

Diameter growth: Can live trees decrease?

Growth refers to an increase in dimensions with time and is implicit in the expected continual increase in tree dimensions. Tree diameters, however, could decrease during the growing season due to water depletion. Annual negative growth measurements are usually attributed to human error and not to other physiological or physical processes. Although seasonal and diurnal fluctuations of diameter have been well documented, perennial decrement of diameter has not been the focus of physiological research. The aim of this work was to analyse the potential causes of decrease in annual diameter growth related to tree mortality due to self-thinning in Nothofagus pumilio forests and to quantify the variations in water depletion of the tree trunks. Some trees did present negative annual diameter increments associated with a water content decrease in the trunks (77 per cent in live trees compared with 56 per cent in recently dead individuals), which produced a contraction (more than 8 per cent of the initial diameter) in the wood and the bark. Trees could survive during 2-5 growth seasons with continual decreases in their diameters (14 per cent, standard error 5 per cent of the trees in the studied stand) until the water content reached a limit where mortality resulted. Therefore, the occurrence of data showing a diameter decrease in successive forest inventories may be due to physiological and physical processes in the natural dynamics of the stand, and not exclusively be explained away as the results of human measurement errors.Facultad de Ciencias Agrarias y ForestalesConsejo Nacional de Investigaciones Científicas y Técnica

Efecto de las características del hábitat y el paisaje sobre el ensamble de aves de bosques con ganadería integrada en Tierra del Fuego

Los cambios en la estructura del bosque y en el paisaje modifican los ensambles de aves. El objetivo del estudio fue determinar qué variables del paisaje y de la estructura forestal influyen en la densidad del ensamble de aves de bosques de ñire (Nothofagus antarctica) con ganadería integrada en Tierra del Fuego (Argentina). Utilizamos datos provenientes de puntos de conteo de aves (3 censos/mes en enero y febrero de dos años consecutivos en 32 sitios distribuidos en dos estancias) donde se caracterizaron la estructura forestal y el paisaje. Los datos se evaluaron mediante un análisis de correspondencia canónico, utilizando una matriz de densidad de 18 especies por 120 muestras, que se contrastó contra 13 variables del paisaje y 2 de estructura forestal. Los resultados indican que tanto la reducción del área basal como las modificaciones en el perímetro y la conectividad de los parches afectarían la conformación de los ensambles de aves.Changes in forest structure and landscape modify bird assemblages. The objective of the study was to determine what landscape and forest structure variables influence density of birds in ñire ( Nothofagus antarctica) forest with livestock use in Tierra del Fuego (Argentina). We use data from bird point counts (3 censuses/month in January and February of two consecutive years in 32 sites distributed in two livestock ranches), where forest structure and landscape were characterized. The data were evaluated by a canonical correspondence analysis, using a density matrix of 18 species x 120 samples, which was contrasted against 13 landscape and 2 forest structure variables. The results indicate that the reduction of the basal area and the changes in the perimeter and the connectivity of the patches would affect the conformation of the bird assemblages.Fil: Benitez, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Rosas, Yamina Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin

Efecto de variables ambientales a diferentes escalas espaciales sobre las aves en bosques de ñire con ganadería integrada de Tierra del Fuego

Las características del ambiente local y los atributos del paisaje influyen en la abundancia y diversidad local de las aves. A su vez, diferentes especies responden a diferentes escalas espaciales. El objetivo fue analizar estructura de las comunidades de aves en diferentes estados del bosque de Nothofagus antarctica (ñire) en Tierra del Fuego, evaluando el efecto de variables ambientales a escala local y del paisaje. Se estudiaron 4 tipos de bosque: uno con raleos (Abiertos) y tres sin raleos (Muy Cerrados, Cerrados y Muy Abiertos) en 4 establecimientos ganaderos (N= 48, 12 réplicas). La densidad de aves se estudió en puntos de observación fijos, mediante conteos durante enero y febrero de 2 años consecutivos. El efecto de variables ambientales a escala local (estructura forestal, cobertura del suelo y oferta alimenticia vegetal y de la artropofauna), y a escala de paisaje (área, perímetro y forma del parche; área, número de parches, índice del parche más grande y conectividad de bosques y áreas abiertas; y total de bordes y densidad de bordes), se evaluó mediante CCA. Al analizar variables de diferentes escalas espaciales (local y paisaje), se pudo observar que las mismas influyeron sobre diferentes grupos de especies. Por ejemplo, la estructura forestal (área basal, cobertura de copas) y el área del parche de bosque tuvieron mayor efecto sobre especialistas de bosque (ej. Pygarrhichas albogularis). Mientras que otras variables de configuración del paisaje (ej. parches de áreas abiertas más grandes) influyeron sobre la densidad de especies generalistas de hábitat (ej. Cinclodes fuscus). Se concluye que ciertas características a nivel local (ej. mayor área basal, cobertura de copas y de renovales, y proporción de himenópteros), así como a nivel de paisaje (ej. parches de bosque grandes e irregulares, conectividad entre áreas abiertas), favorecen a una mayor diversidad de aves en los bosques de N. antarctica de Tierra del Fuego.Fil: Benitez, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Lencinas María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Barrera Marcelo Daniel. Universidad Nacional de La Plata; ArgentinaVI Jornadas Forestales Patagonicas: El rol de los bosques en un mundo diferenteSan Carlos de BarilocheArgentinaInstituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de BarilocheConsejo Nacional de Investigaciones Científicas y TécnicasMinisterio de Agricultura de la Nació

Seasonal diet of Lama guanicoe (Camelidae: Artiodactyla) in a heterogeneous landscape of South Patagonia.

Large diversity of habitat types, plant species assemblages, and silvopastoral activities in Nothofagus spp. forests condition the food availability for native herbivores. This work evaluates the seasonal diet of Lama guanicoe linked to plant life forms and habitat types in sub-Antarctic forests. The study evaluated the vegetation availability and habitat types by floristic surveys (n = 206) in Tierra del Fuego, and seasonal diet of L. guanicoe by micro-histological analysis of feces (n = 4 in four areas, during four season). Open lands showed the highest plant richness, while lowest values corresponded to primary Nothofagus pumilio forests. Nothofagus pumilio (21.6%), Carex spp. (17.2%), Misodendrum spp. (10.6%), and Deschampsia spp. (8.6%) were the most frequent items found in feces. Significant differences were seasonally found in diet composition and trophic niche breadth: grasses were all consumed along the year, while tree browsing decreases in winter and the proportion of shrubs increased. This study highlights the widespread use of different habitats by guanaco, including harvested forests. In summer and spring Nothofagus spp. forests was the main source of food for guanacos, depending more on open lands during winter. The knowledge of plant-native herbivores interactions in productive landscapes could improve the management plans towards an ecologically sustainable strategy.La heterogeneidad de hábitat, distintos ensambles de especies vegetales y las actividades productivas en bosques del género Nothofagus condicionan la disponibilidad de alimento para los herbívoros nativos. Este trabajo evalúa la dieta estacional de Lama guanicoe vinculada a la vegetación, los tipos de hábitat y el manejo forestal en Tierra del Fuego. Se realizaron censos de vegetación (n = 206) y se estudió la dieta de L. guanicoe mediante recolección de heces y análisis micro-histológico (n = 4 en cuatro áreas, durante las cuatro estaciones). Las áreas abiertas tuvieron la mayor riqueza específica, mientras que los valores más bajos correspondieron a bosques primarios de Nothofagus pumilio. La dieta de L. guanicoe incluyó 25 especies y 13 géneros de plantas y un musgo (Sphagnum spp.). Nothofagus pumilio (21,6 %), Carex spp. (17,2 %), Misodendrum spp. (10,6 %) y Deschampsia spp. (8,6 %) fueron los ítems más frecuentes en la dieta. Se registraron diferencias estacionales tanto en la composición como en la amplitud del nicho trófico: el consumo de pastos fue continuo durante todo el año, el ramoneo de árboles disminuyó en invierno y aumentó el consumo de arbustos perennes. Este estudio confirma que el guanaco utiliza una amplia variedad de ambientes, incluyendo bosques cosechados. En verano y primavera los bosques de Nothofagus spp. fueron los principales sitios de alimentación para los guanacos, dependiendo más del alimento en áreas abiertas durante el invierno. El conocimiento de las interacciones planta-herbívoros nativos en paisajes con manejo agro-forestal podría mejorar los planes de manejo hacia un uso ecológicamente sustentable.Fil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Borrelli, Laura. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentin

Flowering and seeding patterns in unmanaged and managed Nothofagus pumilio south Patagonian forests

Regeneration is the success key for the silvicultural treatment implemented in natural seed produced forests. Most of the studies assumed that regeneration is limited by environmental factors and herbivory, but few considered other limiting factors, such as limitants during the flowering and seeding process as bird or insect foraging. It is necessary a whole cycle approach study to understand the bottlenecks in the full regeneration processes. The aim of this work was to analyze the flowering and the seeding patterns in managed and unmanaged stands of Nothofagus pumilio forests, including the pre-dispersion insect and bird foraging analysis, and the abscised biomass production along one growing season. Our results showed that a high percentage of pollinated flowers success in produce fruits (68-79%), independently to the seed rain production and the forest management of the stand (2.2 to 14.7 million.ha-1). The premature abscission of fruits was the main loss factor (13-25%), while biotic factors (insect and bird foraging) was not greatly (less than 5%). The other important loss factor was the large percentage of empty seeds observed in all the treatments (21- 32%), which was significantly greater in primary unmanaged stands. More studies are necessary to explain the causes of these two main loss factors, and self-incompatibility studies to quantify its influence in empty seed production, as well as to extend this kind of studies in long periods of time to include seeding years with different seed rain production.Facultad de Ciencias Agrarias y Forestale

Ecuaciones del grosor y volumen de corteza a diferentes alturas utilizando variables de fácil medición

The objective of this work was to develop equations of thickness profile and bark volume at different heights with easy-measurement variables, taking as a study case Nothofagus pumilio forests, growing in different site qualities and growth phases in Southern Patagonia. Data was collected from 717 harvested trees. Three models were fitted using multiple, non-lineal regression and generalized linear model, by stepwise methodology, iteratively reweighted least squares method for maximum likelihood estimation and Marquardt algorithm. The dependent variables were diameter at 1.30 m height (DBH), relative height (RH) and growth phase (GP). The statistic evaluation was made through the adjusted determinant coefficient (r2-adj), standard error of the estimation (SEE), mean absolute error and residual analysis. All models presented good fitness with a significant correlation with the growth phase. A decrease in the thickness was observed when the relative height increase. Moreover, a bark coefficient was made to calculate volume with and without bark of individual trees, where significant differences according to site quality of the stands and DBH class of the trees were observed. It can be concluded that the prediction of bark thickness and bark coefficient is possible using DBH, height, site quality and growth phase, common and easymeasurement variables used in forest inventories.Ecuaciones del grosor y volumen de corteza a diferentes alturas utilizando variables de fácil medición El objetivo de este trabajo fue desarrollar ecuaciones de perfil del grosor y el volumen de corteza para diferentes alturas utilizando variables de fácil medición, tomando como caso de estudio los bosques de Nothofagus pumilio, creciendo en un gradiente de calidades de sitio y fases de crecimiento en Patagonia Sur. Se tomaron datos de 717 árboles. Se ajustaron tres modelos utilizando regresión múltiple, no lineal, y modelo lineal generalizado, mediante la metodología paso a paso, el algoritmo de Marquardt y de máxima verosimilitud. Las variables dependientes fueron el diámetro a 1,30 m de altura (DAP), altura relativa y la fase de crecimiento. Todos los modelos presentaron buen ajuste con una correlación significativa con la fase de crecimiento. Se observó una disminución en el espesor de corteza con el aumento de la altura relativa. Por otra parte, se desarrolló un coeficiente de corteza para calcular el volumen sin corteza de árboles, en donde se observaron diferencias significativas con la calidad de sitio y clases de DAP de los árboles. La predicción del espesor de la corteza y el coeficiente de la corteza es posible utilizando el DAP, altura, calidad de sitio y la fase de crecimiento, variables de fácil medición en inventarios forestales.Laboratorio de Investigación de Sistemas Ecológicos y Ambientales (LISEA

Canopy composition and site are indicative of mineral soil conditions in Patagonian mixed Nothofagus forests

Key message: Canopy composition in mixed Patagonian Nothofagus forests has an impact on soil properties like cationic exchange capacity and pH, while most soil variables changed with site [P, cation exchange capacity (CEC), soil moisture (SM), resistance to penetration (R)]. Site conditions and canopy composition need be considered together to better understand the distribution of Nothofagus species.Context: Forests can influence soil development, changing main soil properties by several mechanisms, but this has never been investigated in mixed Nothofagus forests. Such influences can be strongly variable depending on local site conditions, and the interactions between both factors need to be clearly established.Aims: To reveal the effect on physical and chemical mineral soil properties in mixed Nothofagus forests of canopy composition and their interactions with site conditions.Methods: Two sites and threemixed forest types, with different proportion of deciduous-evergreen,were selected in coastal andmountain sites. We evaluated forest structure, litterfall and physico-chemical properties of mineral soil (N= 60), and analyzed these factors with general linear models and multivariate statistics [multi-response permutation procedure (MRPP), principal component analyses (PCA)].Results: Basal area and litterfall were significantly influenced by forest type × sites. CEC and pH value varied among forests types and sites, but sites also influenced other variables (P, SM, R). Multivariate analyses reveals a much stronger effect of site conditions than that of species mixture.Conclusion: Forest soil studies must consider environmental factors on different spatial scale and canopy species composition to better understand their influence on soil dynamics in mixed Nothofagus forests.Fil: Toro Manríquez, Mónica del Rosario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Promis, Álvaro. Universidad de Chile; Chil