1,720,954 research outputs found
An Analysis Of Blue Ash (fraxinus Quadrangulata) Regeneration In Southeastern Michigan In The Presence Of Emerald Ash Borer (agrilus Planipennis)
Full text linkAbstract
AN ANALYSIS OF BLUE ASH (FRAXINUS QUADRANGULATA) REGENERATION IN SOUTHEASTERN MICHIGAN IN THE PRESENCE OF EMERALD ASH BORER (AGRILUS PLANIPENNIS)
by
BENJAMIN A. SPEI
May 2016
Advisor: Dr. Daniel M. Kashian
Major: Biological Sciences
Degree: Master of Science
Since the introduction of the invasive bark beetle emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) to southeastern Michigan, most native ash species (Fraxinus spp.) such as white ash (F. Americana), black ash (F. nigra), and green ash (F. pensylvanica) have suffered mortality rates exceeding 99% after infestation. This has led to the loss of seed sources resulting in a depleted seed bank and thus a loss of potential future regeneration. These trends suggest that these species will soon no longer function as important canopy species in North American hardwood forests as EAB continues to spread. Blue ash (F. quadrangulata) is thought to be the most resistant of all native ash species to EAB with observed mortality rates between 30% and 40%. This reduced mortality may be sufficient for mature blue ash trees to persist and maintain a seed bank robust enough to evolve even higher resistance to EAB. While several studies have quantified declining regeneration of other ash species, little research exists describing blue ash regeneration in the presence of EAB. A total of 18 blue ash stands were sampled at 6 different sites in southeastern Michigan near the EAB introduction point. For reference, 18 white ash (F. Americana) stands within the same 6 sites were also sampled. Observed overstory mortality for blue ash ranged between 7.1% and 31.6% and was significantly lower than white ash across all sites. Overstory blue ash was on average significantly older and larger than white ash across all sites and maintained a higher frequency of healthier crowns. Blue ash regeneration densities were found to be abundant at all sizes within all stands. New seedlings (\u3c 3 yrs old) were significantly more abundant for blue ash than white ash across all sites suggesting blue ash has not experienced the same depletion of its seed bank as white ash. Blue ash seedling growth rates were equal to or significantly greater than associate non-ash species at all size classes and at all sites; and equal to white ash seedling growth rates at the majority of sites and size classes with few exceptions. My results show blue ash maintaining a relatively healthy and dominant position in the canopy of several forests in southeastern Michigan. Furthermore, my results suggest that blue ash is still regenerating in a capacity that shows a high probability of canopy replacement by blue ash and thus its continued persistence in the presence of EAB
Ecological factors Driving Aspen (Populus tremuloides Michx.) Stand Stability in a Semi-Arid Montane Region of the Intermountain West
No full textIn the western United States Populus tremuloides Michx., hereafter referred to as aspen, is considered an important forest cover type because of its contribution to local and regional biodiversity, as well as its use for habitat and food for a variety of large and small mammals, songbirds, and game birds. These critical ecosystem services provided by aspen have made many ecologists and resource managers concerned with recent trends of aspen decline across the western U.S. Many ecologists have for decades predicted a trajectory of disappearance while more recently others have suggested that aspen persistence is contingent on local disturbance regimes, management, and or geographical location. The greatest threats to aspen persistence in the West have been identified by researchers as competition with succeeding conifers, browsing by ungulates, and acute drought. In this dissertation, I investigate the relationship between aspen persistence and regeneration ecology with these identified threats focusing primarily on drought and soil moisture but accounting for successional conifer density and browsing pressure. My efforts focus on aspen stands in the Caribou-Targhee National Forest (CNF). In chapter 2, I explore the importance of precipitation as a proxy for potential soil moisture limitation on aspen growth across the CNF using dendrochronological methods. Specifically, I applied a new dendrochronological technique, Blue Intensity (BI), for the extraction of a climate signal in aspen latewood to explore the importance of mid-summer precipitation on aspen growth. Blue intensity is an effective and inexpensive proxy for wood density that has been found to correlate more accurately with climate factors (precipitation, temperature) than ring width, especially in latewood. The results of this analysis showed a positive correlation between mid-summer precipitation and latewood density that supports the first part of my hypothesis; aspen growing on sites with expected soil moisture limitations will produce a climate signal that correlates with precipitation; and the second part of my hypothesis that this signal reveals latewood development is driven by and dependent on soil moisture availability based on precipitation. From these results I conclude that late season growth for aspen on exposed high elevation sites is dependent on precipitation and growth is thus limited by soil moisture availability. In Chapter 3, I investigate the relationship between soil moisture availability and aspen stand persistence by comparing the structure, composition, and regeneration densities of nine aspen stands with nine paired upland aspen stands. Considering the numerous studies published in the last two decades that show evidence of drought being the main inciting factor of aspen decline on xeric sites, I hypothesized that the proximity to perennial streams will lead to higher soil moisture availability and thus increase the probability of aspen persistence on the Caribou-Targhee National Forest landscape. My results for this study partially supported my hypothesis that riparian areas support aspen stands that show evidence of a higher probability of persistence relative to upland aspen stands. The most compelling evidence comes from the significantly higher aspen regeneration densities at the seedling layer (1m height) aspen regeneration densities were still considerably higher in the riparian areas than in the upland areas but this difference was not significant. In this study I used the term “seedling layer” and “sapling layer” to refer to aspen regeneration in different height classes and did not differentiate between regeneration originating from seed versus regeneration originating from suckering. Building off of the results in chapter 3 of significant differences in the density of aspen in the regeneration layer between riparian and upland aspen stands, in chapter 5 I developed a model path analysis using structural equation modeling to explore the relative impacts and interactions of physiographic and ecological factors that affect aspen regeneration densities. Before any analysis of the direct factors influencing soil moisture availability on aspen regeneration, it was important to characterize the clonal diversity of each site. To do this, in chapter 4 I used a traditional approach, with modern techniques, based upon leaf morphology to determine the clonal diversity on each site to be used in a structural equation model (SEM). Overall, I found that there were differences in mean clonal diversity between riparian and upland aspen stands, with riparian stands tending to have higher clonal diversity. The results of the SEM analysis (chapter 5) support my hypothesis that factors affecting soil moisture availability have the strongest effect on regeneration. Specifically, the exogenous factor with the strongest direct effect on aspen regeneration was incident radiation (heatload), and the endogenous factor with the strongest direct effect on regeneration was the percent cover of competitive plant species. Overall, the results of each chapter support my global hypothesis that factors reducing soil moisture availability and increasing site susceptibility to drought have a negative effect on aspen growth and regeneration. My results, however, also emphasize that context is important in determining the collective effect of these factors. Thus, proper assessment of aspen vulnerability in the West requires analyses at multiple scales that can incorporate the relative weights and interactions of elements influencing aspen persistence.doctoral, Ph.D., Natural Resources -- University of Idaho - College of Graduate Studies, 2022-0
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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