1,721,225 research outputs found
An introduction to the study of social evolution; the prehistoric period, by F. Stuart Chapin.
No full textFire And Successional Trajectories In Boreal Forest: Implications For Response To A Changing Climate
Get PDFDissertation (Ph.D.) University of Alaska Fairbanks, 2003Because of the key role played by fire in structuring boreal forest ecosystems, interactions between vegetation and fire regime may be an important and dynamic control of forest response to climate change. This research uses a series of field observations and experiments in boreal forests to examine the nature of several potential fire and vegetation interactions, and how such interactions may influence forest response to climate change. Long-term observations of post-fire succession provide information on the timing of tree establishment and the effects of early establishment on subsequent successional trajectories. The role of competitive interactions in driving patterns of early establishment was tested with experimental manipulations of aspen (Populus tremuloides) cover after fire. This research demonstrated that competition by aspen re-sprouts may reduce the success of conifer establishment and favor long-term dominance by deciduous trees. The effects of fire severity on successional trajectories were tested in a series of field experiments that contrasted patterns of seedling establishment across differences in depth of the post-fire organic layer. All species in the experiment responded negatively to decreased fire severity, but deciduous trees were more sensitive in their response than conifers. Thus, variations in burn severity are likely to mediate deciduous establishment in organic-rich stands. Observations of natural tree regeneration in stands that burned at different ages also indicate that a decrease in fire interval can influence the relative abundance of deciduous and coniferous species by reducing conifer establishment. Over longer time scales, changes in biota caused by species migration may influence fire and vegetation interactions. Observations of post-fire regeneration at the current distribution limits of lodgepole pine (Pinus contorta) indicate that continued range expansion of pine could initiate rapid shifts in dominance from spruce to pine within a single fire cycle. Together, these results provide insight into the dynamic feedbacks between fire and vegetation that can lead to high levels of system resilience, while also promoting rapid responses when threshold conditions are crossed. A more complete understanding of these interactions will improve our ability to manage and predict boreal ecosystem responses to a changing climate
Quantifying Variability In The Alaskan Black Spruce Ecosystem: Linking Vegetation, Carbon, And Fire History
Get PDFDissertation (Ph.D.) University of Alaska Fairbanks, 2004The boreal forest is the largest terrestrial ecosystem in North America, one of the least disturbed by humans, and most disturbed by fire. This combination makes it an ideal system to explore the environmental controls over species composition, the relative importance of abiotic factors and floristic composition in governing ecosystem processes, and the importance of legacy effects at a large regional spatial scale. In the boreal region of interior Alaska, Picea mariana (black spruce) is the predominant tree species and spans a wide range of habitats, including north-facing slopes with permafrost, lowland bogs, and high dry ridge-tops. This research uses a combination of site description and analysis from both locally near Fairbanks (54) and across a large region and number of sites (146) to answer questions about the regional variability and biodiversity of the black spruce forest type. Based on the relationships between species composition and environmental factors, topography and elevation were the most important gradients explaining species composition locally in the Fairbanks region, and mineral soil pH was the overriding environmental gradient across interior Alaska. To describe the floristic variability, I separated the black spruce forest type into three floristically-based community types and five community subtypes. Variability in ecosystem properties among black spruce stands was as large as that documented previously among all forest types in the central interior of Alaska. The variability in plant community composition was at least as effective as environmental or abiotic factors and stand characteristics as a predictor of soil C pools in the black spruce forest type of interior Alaska. The variability in species composition at the community subtype-level was related to a combination of environmental factors and fire history. Together, these results provide a foundation for future work in black spruce ecosystems of interior Alaska, and contribute to our understanding of the regional variability and biodiversity of the black spruce forest type.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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