1,720,961 research outputs found
Regeneration and Recruitment for Resilience: Sustaining Aspen Ecosystems Threatened by Climate Change, Ungulate Browse, and Oystershell Scale
No full textQuaking aspen (Populus tremuloides) ecosystems are highly valued in the southwestern United States because of the ecological, economic, and aesthetic benefits they provide. Concerningly, aspen has experienced extensive mortality in recent decades, and there is evidence that many areas in Arizona, USA lack adequate recruitment to replace dying overstory trees. Maintaining sustainable levels of regeneration and recruitment is necessary for facilitating resilience to biotic and abiotic disturbance agents and for maximizing aspen’s ability to adapt in an increasingly uncertain future. However, questions remain about which factors currently limit aspen regeneration and recruitment in Arizona and which strategies are appropriate for promoting aspen sustainability. Moreover, recent outbreaks of an invasive insect, oystershell scale (Lepidosaphes ulmi; OSS) pose a new threat to aspen forest health. Because these are the first documented outbreaks of OSS in aspen ecosystems, there is an urgent need to survey the extent and impacts of these invasions and to better understand the insect’s biology and ecology on aspen in Arizona. To fill these knowledge gaps, we conducted a systematic literature review of aspen in the Southwest to understand how biotic and abiotic factors, including management, influence aspen forest dynamics (Chapter 1). We also sampled aspen populations across Arizona to quantify the sustainability and drivers of aspen regeneration and recruitment (Chapter 2) and impacts and drivers of OSS invasions (Chapter 3). Finally, we used repeated measurements of OSS-infested aspen stands to quantify short-term rates of OSS intensification on trees, OSS spread among trees, and aspen mortality, and we collected OSS from these stands to document the insect’s phenology in northern Arizona (Chapter 4).
We found that many aspen populations in Arizona lack sustainable regeneration and recruitment. The status of recruitment was especially dire, with 40% of study plots lacking a single recruiting stem. Aspen regeneration was less abundant on warmer, drier sites, highlighting the threat that a warming climate poses to aspen sustainability. Aspen recruitment was significantly more abundant in areas with recent fire and more severe fire. The most important factors limiting recruitment were OSS and browsing by ungulates, especially Rocky Mountain elk (Cervus canadensis). OSS was widespread in Arizona and was associated with increased aspen crown damage and mortality. Climate was the most important driver of OSS abundance, with warmer, drier conditions resulting in significantly more OSS. OSS was also associated with less recent fire, presence of ungulate management strategies such as fenced exclosures, and stands with a greater density of aspen saplings. We also found that immature OSS life stages persist throughout the year and that there are two waves of first-instar crawlers in northern Arizona, one throughout the summer and the second in mid-winter. The first wave seemed to be driven by warming temperatures, but the cause of the second wave is unknown and might represent the initiation of a second generation. We also found that OSS causes high levels of mortality and spreads rapidly within aspen stands. We conclude by discussing how our findings can inform contemporary management of aspen and OSS (Chapter 5)
Regeneration and recruitment for resilience: sustaining aspen ecosystems threatened by climate change, ungulate browse, and oystershell scale
Full text linkQuaking aspen (Populus tremuloides) ecosystems are highly valued in the southwestern United States because of the ecological, economic, and aesthetic benefits they provide. Concerningly, aspen has experienced extensive mortality in recent decades, and there is evidence that many areas in Arizona, USA lack adequate recruitment to replace dying overstory trees. Maintaining sustainable levels of regeneration and recruitment is necessary for facilitating resilience to biotic and abiotic disturbance agents and for maximizing aspen’s ability to adapt in an increasingly uncertain future. However, questions remain about which factors currently limit aspen regeneration and recruitment in Arizona and which strategies are appropriate for promoting aspen sustainability. Moreover, recent outbreaks of an invasive insect, oystershell scale (Lepidosaphes ulmi; OSS) pose a new threat to aspen forest health. Because these are the first documented outbreaks of OSS in aspen ecosystems, there is an urgent need to survey the extent and impacts of these invasions and to better understand the insect’s biology and ecology on aspen in Arizona. To fill these knowledge gaps, we conducted a systematic literature review of aspen in the Southwest to understand how biotic and abiotic factors, including management, influence aspen forest dynamics (Chapter 1). We also sampled aspen populations across Arizona to quantify the sustainability and drivers of aspen regeneration and recruitment (Chapter 2) and impacts and drivers of OSS invasions (Chapter 3). Finally, we used repeated measurements of OSS-infested aspen stands to quantify short-term rates of OSS intensification on trees, OSS spread among trees, and aspen mortality, and we collected OSS from these stands to document the insect’s phenology in northern Arizona (Chapter 4).We found that many aspen populations in Arizona lack sustainable regeneration and recruitment. The status of recruitment was especially dire, with 40% of study plots lacking a single recruiting stem. Aspen regeneration was less abundant on warmer, drier sites, highlighting the threat that a warming climate poses to aspen sustainability. Aspen recruitment was significantly more abundant in areas with recent fire and more severe fire. The most important factors limiting recruitment were OSS and browsing by ungulates, especially Rocky Mountain elk (Cervus canadensis). OSS was widespread in Arizona and was associated with increased aspen crown damage and mortality. Climate was the most important driver of OSS abundance, with warmer, drier conditions resulting in significantly more OSS. OSS was also associated with less recent fire, presence of ungulate management strategies such as fenced exclosures, and stands with a greater density of aspen saplings. We also found that immature OSS life stages persist throughout the year and that there are two waves of first-instar crawlers in northern Arizona, one throughout the summer and the second in mid-winter. The first wave seemed to be driven by warming temperatures, but the cause of the second wave is unknown and might represent the initiation of a second generation. We also found that OSS causes high levels of mortality and spreads rapidly within aspen stands. We conclude by discussing how our findings can inform contemporary management of aspen and OSS (Chapter 5)
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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