1,721,084 research outputs found
The response of photosynthesis and stomatal conductance of forest trees exposed to elevated CO2: δ13C and δ18O tree ring analysis
No full textTree rings indicate different drought resistance of a native (Abies alba Mill.) and a nonnative (Picea abies (L.) Karst.) species co-occurring at a dry site in Southern Italy
No full textClimate changes induced by the anthropogenic alteration of the atmospheric radiative balance are expected to change the productivity and composition of forest ecosystems. In Europe, the Mediterranean is considered one of the most vulnerable regions according to climatic forecasts and simulations. However, although modifications in the inter-specific competition are envisaged, we still lack a clear understanding of the ability of the Mediterranean vegetation to adapt to climate changes. We investigated how two co-occurring tree species commonly used in afforestation programmes, the native Abies alba Mill. and the nonnative Picea abies L. Karst., adapt to climate change by assessing their growth performance and physiological responses in relation to past climate variability. Growth was addressed by analysing tree-ring width and carbon and oxygen stable isotopes. Statistical relationships between isotopic value and monthly climate data suggest that the two species underwent ecophysiological adaptation to Mediterranean climatic constraints. These adaptations are also expressed in the ring-width data. Based on the carbon isotope ratio reflecting the stomatal response to drought, we found that the precipitation in the first period of the growing season, i.e. early spring, is a major factor influencing the annual growth of A. alba, which although native, proved to be sensitive to drought. P. abies, on the other hand, showed a higher tolerance to summer drought stress. These findings should help define criteria for sustainability and effective forest conservation in the Mediterranean region. © 2008 Elsevier B.V. All rights reserved
Climatic significance of Carbon and Oxygen signals in tree rings cellulose and plant organic matter of different tree species
No full textDrought response strategies of Arbequina, Arbosana and Koroneiki olive cultivars revealed by ring growth, wood anatomy and d13C dynamics
No full textThe olive tree (Olea europaea L.), a key crop in Mediterranean climates, is
increasingly affected by climate variability. Over the last several decades, the
Umbria region of central Italy, with its long-standing olive-growing tradition, has
experienced a rise in extreme summer droughts, severely impacting water
availability. This makes it an ideal case study for investigating olive tree
responses to climatic stress. In this study, we examined the adaptive strategies
of three economically important cultivars – Arbequina, Arbosana, and Koroneiki
– grown as mature trees (7 years old) between 2020 and 2023. We combined
dendrochronological techniques, wood anatomical analyses, and intra-seasonal
d13C profiling to assess growth dynamics, structural adjustments, and ecophysiological
responses across four growing seasons. Our results revealed
distinct cultivar-specific strategies in response to climate variation. In
Arbequina and Arbosana, d13C values showed significant correlations with
current-year spring and summer climate conditions, as well as with conditions
during the preceding winter, reflecting a more isohydric behavior. In contrast,
Koroneiki exhibited a more anisohydric strategy: its d13C values were primarily
influenced by precipitation from the previous winter, indicating a reliance on
stored carbon reserves to support early-season growth. Wood anatomical traits
further supported these differences. Koroneiki exhibited higher vessel density
and a greater proportion of lumen area, traits that enhance water transport
efficiency. It also achieved the highest stem basal area and fruit production
among the three cultivars, reaching 10.2 kg/tree in 2023. These characteristics
highlight Koroneiki’s potential as a drought-resilient cultivar suited for future
orchard designs in Mediterranean regions increasingly affected by heat and
water stress
Climatic sensitivity of δ18O in the wood and cellulose of tree rings: Results from a mixed stand of Acer pseudoplatanus L. and Fagus sylvatica L.
No full textThe oxygen isotope composition in tree rings is commonly used to assess the impact of climatic factors on tree growth. However, the relationships between environmental variables and δ18O in whole wood and the wood components (e.g., cellulose, lignin) are still not completely clear - particularly for deciduous species. It is currently common procedure to consider only one wood constituent, a process that saves time. To test whether the δ18O of cellulose relates better to environmental variables than that of whole wood, we measured the oxygen isotopic composition of tree ring whole wood and cellulose, for the period 1916-1950, for two different broad-leaved species (Fagus sylvatica L. and Acer pseudoplatanus L.) on Monti Picentini (Southern Italy). Data show that δ18O in cellulose is enriched (4.7 ± 1.1‰) compared to the corresponding whole wood. The relationship between the δ18O of the cellulose and of whole wood is generally poor, especially for A. pseudoplatanus suggesting that the sources of variability for δ18O differ strongly between the whole wood and the cellulose constituents. Furthermore, we find that the cellulose fraction correlates strongly with climatic variables, while the whole wood fraction generally does not. Monthly temperature during the growing season is strongly correlated with δ18O of cellulose for F. sylvatica (r = 0.82) and A. pseudoplatanus (r = 0.63) but not with δ18O of whole wood. We found a relevant difference in the isotopic signals of the two species that could be related with difference in seasonal timing of growth. In contrast to F. sylvatica, early spring conditions have an influence on A. pseudoplatanus at our study site. This is evidenced by the high correlation between δ18O of cellulose and April and May precipitation, and the positive relationship between tree ring width and March and April mean annual temperature. The different climatic sensitivities of the two investigated species suggest that physiological properties, i.e. root system and stomatal conductance responses, or a variation in the proportions of wood constituents play an important role for the oxygen isotopic signal. We conclude that, even when partially obscured by site parameters (soil depth and structure, nutrient availability, etc.), δ18O in the cellulose compartment strongly reflects climate information. Our study suggests that cellulose extraction is a necessary step in studies seeking to investigate the climatic signatures in the δ18O of broad-leaved species. © 2008 Elsevier B.V. All rights reserved
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
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