Indicadores del decaimiento en bosques de Nothofagus pumilio en el norte de la Patagonia, Argentina

Abstract Forest decline is associated with partial or total crown mortality in a large percentage of trees at the stand level. While forest decline has been reported on a global context, the relationships between the external conditions of trees and their radial growth have rarely been reported. This study relates the intensity of decline with radial growth in 294 Nothofagus pumilio trees in northern Patagonia. The selected external indicators of decline were crown mortality, bark health, the incidence of boring insects and woodpeckers, as well as the presence of hemiparasite plants, fungi and lichens. High percentages of crown mortality are significantly related to decreasing radial growth of remaining trees. This relationship is more reliable when basal area increments rather than ring widths are used as estimates of radial growth. Bark health and abundance of cavities, resulting from the activities of boring insects and woodpeckers, were also significantly inversely related to growth. In contrast, no statistically significant relationships were found between growth and the presence of hemiparasites, fungi or lichens. Based on these results, we recommend the use of the following external indicators (1) crown mortality, (2) bark conditions and (3) cavities from boring insects and/or woodpeckers, to comprehensively characterize the Nothofagus pumilio forest decline in Patagonia.Resumen El decaimiento forestal está frecuentemente asociado a la mortalidad parcial o total de las copas en un alto porcentaje de individuos de un rodal. Si bien el decaimiento ha sido documentado a escala global, las relaciones entre las condiciones externas de los árboles y su crecimiento radial raramente han sido exploradas. El presente trabajo relaciona la intensidad del decaimiento con el crecimiento radial en 294 árboles de Nothofagus pumilio en el norte de la Patagonia. Los indicadores externos del decaimiento analizados fueron la mortalidad de la copa, la sanidad de la corteza, la incidencia de insectos barrenadores y pájaros carpinteros, así como la presencia de plantas hemiparásitas, hongos y líquenes. Los resultados indican que elevados porcentajes de mortalidad de copa están significativamente relacionados con la disminución del crecimiento radial promedio, siendo esta relación más notoria cuando se usa como medida del crecimiento radial el incremento en área basal en lugar del ancho de los anillos. El deterioro de la corteza y la abundancia de cavidades producto de las actividades de insectos barrenadores y de pájaros carpinteros también estuvieron significativa e inversamente relacionados con el crecimiento. Por el contrario, el crecimiento y la presencia de hemiparásitas, hongos o líquenes no mostraron relaciones significativas. A partir de estos resultados, se propone utilizar en la estimación de la sanidad forestal los indicadores externos (1) mortalidad de copa, (2) deterioro de la corteza y (3) cavidades de insectos y/o pájaros carpinteros, como una medida integral del decaimiento forestal de Nothofagus pumilio en la Patagonia

Climate and Nothofagus pumilio Establishment at Upper Treelines in the Patagonian Andes

The upper treeline provides a unique opportunity for documenting changes in forest dynamics in the context of current environmental fluctuations. Documenting the response of forests to present environmental changes will be very useful in developing and validating vegetation models that predict plant responses to global changes resulting from human activities. It is generally suggested that the expansion of the upper treeline is limited by cold temperatures, so warmer conditions are expected to induce an advance of forests into alpine vegetation. Significant changes in temperature and precipitation have already been documented in regional studies along the Patagonian Andes during the last decades. Across Patagonia, there are strong relationships between changes in climate and variations in the Southern Annular Mode (SAM). The atmospheric circulation indexes, act as climate packages summarizing climatic information since they combine changes in environmental variables. In order to complement previous studies in the northern Patagonia treeline, we have conducted a this study in the southern Patagonian Andes to: (1) characterize the patterns of Nothofagus pumilio establishment in the upper treeline along a precipitation gradient, (2) to establish the relationship between variations in regional climate and tree establishment and (3) to determine the influence of continental and hemispheric-scale climatic forcing on tree establishment at regional scale. Our studies suggest that the location of the upper treeline of the N. pumilio forest in the Patagonian Andes is sensitive to changes in climate variations. The temperature increment has facilitated the tree recruitment, however, the rate of seedling establishment appears to be more strongly modulated by the interaction between temperature increase and variations in precipitation. The expansion of the upper treeline has been limited to 5–10m from the abrupt treeline. This comparatively reduced advance of the forest in the alpine grassland is regulated by other biotic and abiotic factors rather than the temperature increase. While the recent expansion of the upper treeline in northern Patagonia was regulated by temperature and precipitation variations associated with the different phases of the Pacific Decadal Oscillation, the establishment above the upper treeline in the southern Patagonian Andes was facilitated by climatic variations induced by the positive trend of the SAM during the last decades

Dendrochronological Advances in the Tropical and Subtropical Americas: Research Priorities and Future Directions

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain

Recent growth increase in endemic Juglans boliviana from the tropical Andes

The spatial coverage of tree-ring chronologies in tropical South America is low compared to the extratropics, particularly in remote regions. Tree-ring dating from such tropical sites is limited by the generally weak temperature seasonality, complex coloration, and indistinct anatomical morphology in some tree species. As a result, there is a need to complement traditional methods of dendrochronology with innovative and independent approaches. Here, we supplement traditional tree-ring methods via the use of radiocarbon analyses to detect partial missing rings and/or false rings, and wood anatomical techniques to precisely delineate tree-ring boundaries. In so doing we present and confirm the annual periodicity of the first tree-ring width (TRW) chronology spanning from 1814 to 2017 for Juglans boliviana (‘nogal’), a tree species growing in a mid-elevation tropical moist forest in northern Bolivia. We collected 25 core samples and 4 cross-sections from living and recently harvested canopy-dominant trees, respectively. The sampled trees were growing in the Madidi National Park and had a mean age of 115 years old, with certain trees growing for over 200 years. Comparison of (residual and standard) TRW chronologies to monthly climate variables shows significant negative relationships to prior year May-August maximum temperatures (r = −0.54, p < 0.05) and positive relationships to dry season May-October precipitation (r = 0.60, p < 0.05) before the current year growing season. Additionally, the radial growth of Juglans boliviana shows a significant positive trend since 1979. Our findings describe a new and promising tree species for dendrochronology due to its longevity and highlight interdisciplinary techniques that can be used to expand the current tree-ring network in Bolivia and the greater South American tropics.This work was supported by the U.S. National Science Foundation (NSF) projects AGS-1702789, OISE-1743738 and AGS-1903687. MEF was partially supported by Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), PICT-2019-01336 PMO BID (Argentina). G.M.S. thanks U.S. National Science Foundation for support (AGS-1703035 and AGS-1903690).Peer reviewe