1,721,011 research outputs found
Variation in the access to deep soil water pools explains tree-to-tree differences in drought-triggered dieback of Mediterranean oaks
Full text linkIndividual differences in the access to deep soil water pools may explain the differential damage among coexisting, conspecific trees as a consequence of drought-induced dieback. We addressed this issue by comparing the responses to a severe drought of three Mediterranean oak species with different drought tolerance, Quercus pubescens L. and Quercus frainetto Ten., mainly thriving at xeric and mesic sites, respectively, and Quercus cerris L., which dominates at intermediate sites. For each species, we compared coexisting declining (D) and non-declining (ND) trees. The stable isotope composition (δ2H, δ18O) of xylem and soil water was used to infer a differential use of soil water sources. We also measured tree size and radial growth to quantify the long-term divergence of wood production between D and ND trees and non-structural carbohydrates (NSCs) in sapwood to evaluate if D trees presented lower NSC values. The ND trees had access to deeper soil water than D trees except in Q. frainetto, as indicated by significantly more depleted xylem water values. However, a strong δ2H offset between soil and xylem water isotopes observed in peak summer could suggest that both tree types were not physiologically active under extreme drought conditions. Alternative processes causing deuterium fractionation, however, could not be ruled out. Tree height and recent (last 15-25 years) growth rates in all species studied were lower in D than in ND trees by 22 and 44%, respectively. Lastly, there was not a consistent pattern of NSC sapwood concentration; in Q. pubescens, it was higher in ND trees while in Q. frainetto, the D trees were the ones exhibiting the higher NSC concentration. We conclude that the vulnerability to drought among conspecific Mediterranean oaks depends on the differential access to deep soil water pools, which may be related to differences in rooting depth, tree size and growth rate
La variación intraespecífica en el uso del agua del suelo explica el decaimiento de bosques causado por sequía en especies de robles en el sur de Italia
Full text linkEl decaimiento de los bosques debido al cambio climático es un fenómeno global que afecta a
muchas especies de árboles, principalmente en áreas propensas a sequías, como la región
mediterránea. En el sur de Italia varias especies de robles muestran fenómenos de decaimiento
desde principios de siglo debido al estrés inducido por sequía. Si bien el fenómeno se extiende a
rodales enteros, el daño (desecación a nivel del follaje, reducción del crecimiento, etc.) no afecta por
igual a todos los individuos. Por lo tanto, existen mecanismos intraespecíficos que explican la
variabilidad de la vulnerabilidad a la sequía y que aún no se comprenden completamente. El objetivo
general del estudio fue verificar si la variabilidad en dicha vulnerabilidad puede estar relacionada
con diferencias en el acceso al agua entre individuos de la misma especie. El estudio se realizó en
dos sitios en decaimiento (Gorgoglione y San Paolo Albanese), durante la sequía estival más
extrema de la última década (2017), comparando las respuestas de tres robles mediterráneos que
presentaban diferentes necesidades ecológicas con respecto a la disponibilidad hídrica: Quercus
pubescens, Quercus cerris y Quercus frainetto. Para cada especie comparamos pares de individuos
dominantes mostrando mucha (decaídos) o poca (no decaídos) defoliación. Sobre estas categorías
se analizó la señal isotópica de oxígeno (δ18O) e hidrógeno (δ2H) del agua contenida en el xilema de
las ramas y en el suelo. También caracterizamos el crecimiento radial para detectar divergencias a
largo plazo entre árboles decaídos y no decaídos. Finalmente, se midió la concentración de
carbohidratos no estructurales (NSC) en la albura para evaluar las diferencias entre árboles. Al
comparar los isótopos estables del agua en el suelo y en el xilema, encontramos diferencias
significativas entre individuos decaídos y no decaídos en Q. cerris y Q. pubescens, pero no en Q.
frainetto. Los árboles no decaídos utilizaron agua menos enriquecida, derivada de fuentes de agua
más profundas, lo que sugiere que disponen de un sistema de raíces más profundo capaz de
asegurar un suministro de agua en caso de sequía extrema. La tasa de crecimiento radial promedio
de los árboles decaídos, que eran en general menos altos, fue un 44% menor que la de los no
decaídos. Encontramos concentraciones más bajas de NSC en árboles decaídos de Q. pubescens, la
especie que forma un sistema radical menos profundo. Estos resultados no apoyan la idea de que el
decaimiento está relacionado con la escasez de reservas de carbono. La vulnerabilidad a la sequía
entre individuos de una misma especie depende, entre otros factores, del acceso a los recursos
hídricos disponible a distintas profundidades del suelo
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
Growth, wood anatomy and stable isotopes show species-specific couplings in three Mexican conifers inhabiting drought-prone areas
No full textAn improved understanding of how tree species will respond to warmer conditions and longer droughts requires comparing their responses across different environmental settings and considering a multi-proxy approach. We used several traits (tree-ring width, formation of intra-annual density fluctuations - IADFs, wood anatomy, Δ13C and δ18O records) to retrospectively quantify these responses in three conifers inhabiting drought-prone areas in northwestern Mexico. A fir species (Abies durangensis) was studied in a higher altitude and slightly rainier site and two pine species were sampled in a nearby, lower drier site (Pinus engelmannii, Pinus cembroides). Tree-ring-width indices (TRWi) of the studied species showed a very similar year-to-year variability likely indicating a common climatic signal. Wood anatomy analyses done over 3.5 million measured cells, showed that P. cembroides lumen area was much smaller than in the other two species and it remained constant along all the studied period (over 64 years). Instead, cell wall thickness was widest in P. engelmannii and this species presented the highest amount of intra-annual density fluctuations. Climate and wood anatomy correlations pointed out that lumen area was positively affected by winter precipitation for all studied species, while cell-wall thickness was negatively affected by this season's precipitation in all species but P. cembroides. Stable isotope analysis showed significantly lower values of Δ13C for P. cembroides and no significant δ18O differences between the three species, although they shared a common decreasing trend. With very distinct wood anatomical traits (smaller cells, compact morphology), P. cembroides stood out as the better adapted species in its current environment and could be less affected by future drier climate. P. engelmannii and A. durangensis showed high plasticity at wood anatomical level, allowing them to promptly respond to seasonal water availability but likely gives few advantages on future climate scenarios with longer and frequent drought spells
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