1,721,172 research outputs found
Author Correction: Mature Andean forests as globally important carbon sinks and future carbon refuges
No full textAuthor Correction: Widespread but heterogeneous responses of Andean forests to climate change
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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
Mature Andean forests as globally important carbon sinks and future carbon refuges
No full textAbstract It is largely unknown how South America’s Andean forests affect the global carbon cycle, and thus regulate climate change. Here, we measure aboveground carbon dynamics over the past two decades in 119 monitoring plots spanning a range of >3000 m elevation across the subtropical and tropical Andes. Our results show that Andean forests act as strong sinks for aboveground carbon (0.67 ± 0.08 Mg C ha −1 y −1 ) and have a high potential to serve as future carbon refuges. Aboveground carbon dynamics of Andean forests are driven by abiotic and biotic factors, such as climate and size-dependent mortality of trees. The increasing aboveground carbon stocks offset the estimated C emissions due to deforestation between 2003 and 2014, resulting in a net total uptake of 0.027 Pg C y −1 . Reducing deforestation will increase Andean aboveground carbon stocks, facilitate upward species migrations, and allow for recovery of biomass losses due to climate change.Abstract It is largely unknown how South America’s Andean forests affect the global carbon cycle, and thus regulate climate change. Here, we measure aboveground carbon dynamics over the past two decades in 119 monitoring plots spanning a range of >3000 m elevation across the subtropical and tropical Andes. Our results show that Andean forests act as strong sinks for aboveground carbon (0.67 ± 0.08 Mg C ha −1 y −1 ) and have a high potential to serve as future carbon refuges. Aboveground carbon dynamics of Andean forests are driven by abiotic and biotic factors, such as climate and size-dependent mortality of trees. The increasing aboveground carbon stocks offset the estimated C emissions due to deforestation between 2003 and 2014, resulting in a net total uptake of 0.027 Pg C y −1 . Reducing deforestation will increase Andean aboveground carbon stocks, facilitate upward species migrations, and allow for recovery of biomass losses due to climate change
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
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The Ecophysiology of Photosynthetic Heat Tolerances in Tropical Plants
No full textTemperature governs several biological processes from molecular to macroecological scales. Underlying many ecological processes is the assumption that fitness is constrained by the physiological limits of species’ metabolic function. The thermal limits of metabolic function, termed thermal tolerances, are often assumed to directly translate into the environmental conditions that define species’ abiotic thermal niches. When species exceed their physiological thermal tolerances, it is expected to negatively impact fitness, and may therefore provide a basis for understanding the environmental constraints on species distributions. Given the rising temperatures caused by climate change, heat tolerances are of particular interest for understanding these constraints. Heat damage in plants has the potential to influence growth rates, which are tied to fitness and contribute to ecosystems services like carbon sequestration that modulate climate change. Photosynthesis is a temperature-sensitive metabolic process, and photosynthetic heat tolerances can be readily assessed, but provide only incomplete information for understanding whole-plant fitness. Understanding the effect of thermal damage on plant growth is necessary if heat tolerances are to predict species thermal niches, their geographic distributions, or their responses to climate change. This dissertation investigates the ecophysiology of heat tolerances in order to advance their use in linking ecological patterns to physiological processes. In the first chapter we provide an introduction to heat tolerances and a review of existing heat tolerance literature. In this review, we call attention to the different sources of methodological variation likely to bias estimates of plant heat tolerances. Using the newly assembled database of heat tolerances, we illustrate current the methodological biases that may prevent heat tolerances from being integrate into ecological contexts. We also discuss how environmental conditions like a) growth temperature, b) drought, c) light, d) salinity, and e) ontogenetic stage can cause variation in estimates of heat tolerance. Finally, we propose a standardized terminology to facilitate interpretation of heat tolerance data among studies. One issue limiting the use of heat tolerances to understand species distributions is mixed support for the hypothesis that hotter climates select for higher heat tolerances. Furthermore, the limited heat tolerance data that exist indicate some taxonomic groups have distinct ranges of heat tolerances. In the second chapter we hypothesized that phylogenetic structure may help to explain variation in heat tolerances, resolve the conflicting effects that climate has been observed to have on heat tolerances, and advance the use of heat tolerances in broader ecological contexts. To address our hypothesis, we measured the heat tolerances for 123 species of ferns, gymnosperms, magnoliids, monocots, and eudicots grown in a common climate at Fairchild Tropical Botanic Garden and the John C. Gifford Arboretum in Miami, FL USA. Phylogenetic analysis using Blomberg’s K indicated that species’ heat tolerances are not phylogenetically conserved, but data from the five groups we studied suggest there may be some evolutionary constraints on plant heat tolerances at coarse phylogenetic resolutions that are potentially related to leaf thermoregulation. Phylogenetic independent contrasts of heat tolerance and climatic data for 102 species revealed limited support for the hypothesis that climate can predict species heat tolerances. We also re-analyzed the effect of climate on heat tolerances using a subset of our study species that were most unlikely to experience heat tolerance down-regulation, which confirmed the inability of climate to predict species heat tolerances. We conclude that there are weak phylogenetic and climatic constraints on the heat tolerances of plants. In the third chapter, we attempt to develop a mechanistic explanation for the variation in heat tolerance among species. Given that plants exhibit unique thermoregulatory traits that influence leaf temperatures, and that leaf temperatures can be decoupled from ambient air temperatures, we hypothesized that photosynthetic heat tolerances are adapted to extreme leaf temperature as opposed to coarse climatic variables. We measured thermoregulatory traits, maximum leaf temperatures and two different metrics of photosynthetic heat tolerances for 19 plant species growing at Fairchild Tropical Botanic Garden (Coral Gables, FL, USA). The first metric of heat tolerance is termed Tcrit and is defined as the temperature that causes an initial decrease in the quantum yield of photosynthesis. The second metric of heat is termed T50 and is defined as the temperature that cause as a 50% reduction in the quantum yield of photosynthesis. The thermoregulatory traits measured at the Garden were used to parameterize a leaf energy balance model and predict maximum in situ leaf temperatures across the geographic distributions of 13 species. The maximum observed leaf temperatures and maximum predicted in situ leaf temperatures were positively correlated with only heat tolerances. The breadth of species’ thermal safety margins (the difference between heat tolerance and leaf temperature for T50) was negatively correlated with T50. Our results provide observational and theoretical support for the hypothesis that photosynthetic heat tolerances are adapted to extreme leaf temperatures, but refute the assumption that species with higher PHTs are less susceptible to thermal damage. Tree growth is an important predictor of tree survival and component of the global carbon sink that is potentially negatively influenced by thermal damage. In the fourth chapter, we investigate the ability of heat tolerances to predict annual growth for eight tropical tree species. More specifically, we test the hypotheses that 1) species with higher heat tolerances are more likely to experience decelerating growth rates across multiple years; and 2) thermal safety margins are capable of predicting species’ annual growth rates. Our results suggest that only species with a combination of high leaf temperatures and low heat tolerances are expected to experience thermal damage, but that thermal damage is unlikely drive changes in species’ growth. Instead of heat tolerances, our results point to optimal temperatures for photosynthesis, not respiration, as a promising physiological mechanism explaining species growth rates. Nevertheless, Tcrit may provide a limited ability to explain growth deceleration when photosynthesis ceases, while and T50 may act as a thermal constraint on leaf size.</p
Widespread but heterogeneous responses of Andean forests to climate change
Full text linkGlobal warming is forcing many species to shift their distributions upward, causing consequent changes in the compositions of species that occur at specific locations. This prediction remains largely untested for tropical trees. Here we show, using a database of nearly 200 Andean forest plot inventories spread across more than 33.5° latitude (from 26.8° S to 7.1° N) and 3,000-m elevation (from 360 to 3,360 m above sea level), that tropical and subtropical tree communities are experiencing directional shifts in composition towards having greater relative abundances of species from lower, warmer elevations. Although this phenomenon of ‘thermophilization’ is widespread throughout the Andes, the rates of compositional change are not uniform across elevations. The observed heterogeneity in thermophilization rates is probably because of different warming rates and/or the presence of specialized tree communities at ecotones (that is, at the transitions between distinct habitats, such as at the timberline or at the base of the cloud forest). Understanding the factors that determine the directions and rates of compositional changes will enable us to better predict, and potentially mitigate, the effects of climate change on tropical forests.Fil: Fadrique, Belén. University of Miami; Estados UnidosFil: Báez, Selene. Escuela Politécnica Nacional; EcuadorFil: Duque, Álvaro. Universidad Nacional de Colombia; ColombiaFil: Malizia, Agustina. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional; ArgentinaFil: Blundo, Cecilia Mabel. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional; ArgentinaFil: Carilla, Julieta. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional; ArgentinaFil: Osinaga Acosta, Oriana. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional; ArgentinaFil: Malizia, Lucio Ricardo. Universidad Nacional de Jujuy. Facultad de Ciencias Agrarias; ArgentinaFil: Silman, Miles. University Wake Forest; Estados UnidosFil: Farfán Ríos, William. Universidad Nacional San Antonio Abad del Cusco; Perú. University Wake Forest; Estados UnidosFil: Malhi, Yadvinder. University of Oxford; Reino UnidoFil: Young, Kenneth R.. University of Texas at Austin; Estados UnidosFil: Cuesta C., Francisco. University of Amsterdam; Países BajosFil: Homeier, Jurgen. Universität Göttingen; AlemaniaFil: Peralvo, Manuel. Consorcio para el Desarrollo Sostenible de la Ecorregión Andina; EcuadorFil: Pinto, Esteban. Consorcio para el Desarrollo Sostenible de la Ecorregión Andina; EcuadorFil: Jadan, Oswaldo. Universidad de Cuenca. Facultad de Ciencias Agropecuarias; EcuadorFil: Aguirre, Nikolay. Universidad Nacional de Loja. Programa de Investigación Biodiversidad y Servicios Ecosistémicos; EcuadorFil: Aguirre, Zhofre. Universidad Nacional de Loja. Programa de Investigación Biodiversidad y Servicios Ecosistémicos; EcuadorFil: Feeley, Kenneth J.. University of Miami; Estados Unidos. Fairchild Tropical Botanic Garden; Estados Unido
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
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