1,720,972 research outputs found
Integrating small mammal personality and population abundance into forest regeneration predictions for a managed, mixed species forest in Maine, USA
No full textOn studying the patterns of individual-based tree mortality in natural forests: A modelling analysis
No full textEste estudio fue financiado por las becas de investigación chilenas Fondo Nacional de Desarrollo Científico y Tecnológico (Fondecyt n.° 1191816) y Fondo de Fomento al Desarrollo Científico y Tecnológico (Fondef n.° ID19110421); National Science Foundation Center for Advanced Forestry Systems (Premio n.° 1915078) y National Science Foundation RII Track-2 FEC (Premio n.° 1920908). Asimismo, agradecemos a todos los investigadores y asistentes de campo que participaron en la recopilación de datos de campo a lo largo de los años.This study was supported by the Chilean research grants Fondo Nacional de Desarrollo Cientifico y Tecnologico (Fondecyt No. 1191816) and Fondo de Fomento al Desarrollo Cientifico y Tecnologico (Fondef No. ID19110421); National Science Foundation Center for Advanced Forestry Systems (Award No. 1915078), and National Science Foundation RII Track-2 FEC (Award No. 1920908). We would also like to thank all the researchers and field assistants involved on collecting the field data over the years
Evaluation of modeling strategies for assessing self-thinning behavior and carrying capacity
No full textFondo Nacional de Desarrollo Cientifico y Tecnologico (FONDECYT), Grant/Award Number: 1151495Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT), Número de subvención/adjudicación: 115149
Évaluation du potentiel de croissance et de qualité des tiges de bouleau jaune (betula alleghaniensis Britton) dans une forêt dégradée
No full textCette étude s'insère dans un contexte de restauration des forêts, proposée comme action sylvicole à accomplir dans le cadre de l'aménagement écosystémique des forêts québécoises. Les pratiques sylvicoles autrefois effectuées ont eu comme conséquence la dégradation de plusieurs forêts, dont celles du domaine de la sapinière à bouleau jaune. Sur certaines stations productives de la région de Charlevoix / bas-Saguenay, la présence du bouleau jaune est limitée, soulevant un questionnement quant à leur capacité réelle à faire croître et constituer une ressource de qualité avec cette espèce. L'objectif de cette étude était de faire état de cette capacité, en se basant sur les caractéristiques de l'arbre, la structure de la forêt et les conditions plus permanentes de la station et du climat. La région présentant cette problématique fut comparée à la région de Portneuf faisant partie du même domaine bioclimatique, mais où la ressource présente une croissance et une qualité plus intéressante. Malgré cette différence, les résultats démontrent que le bouleau jaune possède un potentiel de croissance et de qualité intéressant dans la région de Charlevoix / bas-Saguenay, ce qui peut ainsi justifier des efforts de restauration dans cette région
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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Alterations in Douglas-fir crown structure, morphology, and dynamics imposed by the Swiss needle cast disease in the Oregon Coast Range
Get PDFPlants respond to defoliation in many different and complex ways, depending on their growth habit and form as well as the extent and duration of the defoliation. Tree crowns have been shown to be quite sensitive to disturbances such as defoliation, however quantitative relationships have rarely been developed, making the true biological meaning of crown condition assessments quite difficult to decipher. The sudden emergence of Swiss needle cast (SNC) in the Oregon Coast Range prompted investigation of the response of Douglas-fir crown structure, crown morphology, and foliage dynamics to extended defoliation. Using data from permanent plots and 82 destructively sampled trees, hypotheses regarding the response of trees to defoliation were tested with linear and nonlinear models. Responses of crowns were investigated at multiple levels including the needle, branch, tree, and stand scales. At the individual-needle level, SNC has resulted in foliage that is smaller in length, width, and projected area; lower in dry mass; and higher in specific leaf area. The disease has influenced the foliage age structure by increasing the proportion in the younger age classes with greater SNC severity. The disease has also resulted in crowns that have a greater proportion of their current and 1-year-old needles located higher in the crown than Abstract approved Douglas A. Maguire normal, while the 2-, 3- and 4-year-old needles are shifted towards the crown base relative to healthy trees. At the branch-level, the disease has modified growth patterns as well as dry matter production and allocation. The number of secondary lateral branches on a primary branch declined in response to the disease, as did the foliated branch length and diameter for a given position in the crown. The ratio of branch length to branch diameter, however, increased with disease severity, which suggests altered elongation patterns. Branches in the lower portion of the heavily diseased crowns were elongating faster than normal, while elongation of branches in the mid-crown was slower. Elongation of branches in the upper crown was unaffected. The disease significantly reduced branch foliage dry matter and area for a given position in the crown and diameter. Branches, however, allocated more dry matter to higher order branches, but less dry matter to primary branch elongation. At the tree-level, the disease has led to crowns that are shorter than normal, while the largest measured standing width remains unaffected. Crown radii and maximum branch diameter profiles suggested that changes within the crown might be occurring at different levels due to variations in SNC damage within the crown. The number of primary interwhorl branches decreased with greater disease severity. SNC also significantly reduced total foliage and branchwood dry matter. Overall, the vertical distribution of foliage dry matter was less skewed and more uniform with increased disease severity. At the stand-level, SNC has significantly increased crown recession rates, woody litterfall, the specific leaf area of the litter, and growth efficiency. The disease caused a decline in foliage litterfall rates as well as leaf area index. In addition, the seasonal distribution of foliage litterfall was altered, with a greater amount occurring in the summer than normal. Crown condition, as assessed by foliage retention and the crown sparseness index, varied with SNC and other site factors. Within-tree variability of foliage retention was significantly higher than between-tree or between-plot variability. Although assessments of foliage retention were found to be highly variable, the sample size required to attain a sufficiently precise estimate for a given tree and stand are lower than the sample sizes currently being collected. The crown sparseness index was found to be significantly less variable than foliage retention and was primarily influenced by stand factors such as age and stand density. Defoliation caused significant changes at the individual needle, branch, tree, and stand levels, complicating efforts to accurately predict growth responses to defoliation. This detailed analysis of crown and foliage dynamics helps to establish links among current SNC studies. For example, growth losses associated with SNC are due to the reduction of foliage area, but also to changes in the size and vertical distribution of the needles. In addition, crown assessment indices such as foliage retention and crown length to sapwood area ratio represent different aspects of crown condition. Crown attributes are sensitive to the direct and indirect effects of SNC, which have important implications for tree growth and stand management. Important direct effects include the premature loss of foliage, while important indirect effects of SNC include changes in the within-crown light environment. Integrating measures of crown condition into forest models, therefore, represents an important step towards incorporating physiological-mechanisms into models for predicting growth responses to environmental changes such as tree disease and for understanding the complex responses of tree morphology and growth
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Development of a hybrid modeling framework for intensively managed Douglas-fir plantations in the Pacific Northwest
Get PDFForest growth models in the Pacific Northwest are predominantly empirical. Predictions of yield under alternative silvicultural regimes cannot rely completely on field trials; yet empirical growth models are often inadequate for extrapolating untested regimes and genotypes. The limitations of current models include (1) long time-steps (e.g. 5-10 years); (2) insufficient detail for characterizing crowns; and (3) inability to capture physiological mechanisms. The overall goal of this dissertation was to test the ability of a hybrid model (empirical + process-based) to predict the growth of intensively managed plantations.
The first step of model development was to refine current characterizations of Douglas-fir crown structure across several silvicultural treatments. The effects of fertilization, thinning, precommercial thinning, vegetation control, and disease intensity (Swiss needle cast) were found to influence important structural attributes of the crown. Among the crown attributes affected, maximum branch size and total- and nonfoliated-crown profile were the most dynamic attributes. Conversely, treatments had no effect on the number of branches or on branch angle. Equations based solely on bole and crown variables predicted crown structural attributes reasonably well across these varied stand conditions.
Annualized empirical equations for individual tree diameter and height growth were developed next and found to outperform similar models with a longer time-step. The parameters of these empirical equations showed very few meaningful relationships with physiography, soil, or climate, suggesting that representation of key physiological processes was a necessary next step.
Individual branch growth and mortality were significantly influenced by fertilization, thinning, precommercial thinning, vegetation control, and Swiss needle cast. Dynamic equations developed from this dataset significantly improved predictions of crown recession, compared to a traditional empirical approach. The improvements, however, had a relatively minor impact on short-term stand volume growth.
The combination of these equations into a hybrid framework showed improvements in leaf area index and periodic annual increment when compared to other stand-level hybrid models. At the individual tree-level, the use of both empirical and mechanistic components was necessary to achieve a level of bias slightly better than that of a purely empirical approach. Beyond growth predictions, this hybrid model offers many other uses
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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