1,721,109 research outputs found
Stemflow chemistry and epiphytic lichen diversity in dieback-affected spruce forest of the Harz Mountains, Germany
No full textIn the German Harz Mountains, epiphytic lichen diversity was found to be higher in a Picea abies forest affected by pollution-caused dieback than in a comparable healthy stand. Although amount and chemical composition of incident precipitation did not differ between the stands, element concentrations of S, H+, K, Fe, Mn, and Al in stemflow were significantly lower in the dieback-affected plot than in the healthy one. These lower concentrations are attributed to reduced interception and reduced leaching due to needle loss. Cover of Hypogymnia physodes decreased with increasing concentrations of many elements in stemflow and bark. Among these parameters, S concentration of stemflow is considered to influence directly H. physodes. Cover of the extremely toxitolerant Lecanora conizaeoides was less affected by chemical variables, but a significant dependence of cover on S concentration of stemflow, resulting in an optimum regression curve, could be established in this case. Total number of lichen species per sample tree decreased as concentrations of several elements increased, indicating that most lichen species had similar habitat requirements as H. physodes
The significance of stemflow chemistry for epiphytic lichen diversity in a dieback-affected spruce forest on Mt Brocken, northern Germany
No full textEpiphytic lichen diversity in a boggy stand of Norway spruce (Picea abies) was studied in the eastern Harz Mountains, northern Germany. Spruce trees at wet sites were affected by forest dieback, whereas trees on drier sites remained unaffected. Lichen diversity was higher on dieback-affected trees than on healthy ones. The foliose lichen Hypogymnia physodes was significantly more frequent on dead trees, whereas the crustose, extremely toxitolerant Lecanora conizaeoides occurred more frequently on healthy trees. Stemflow concentrations of NH4+ NO3-, PO3-, and SO42- were lower on affected trees. This is attributed to reduced interception from the atmosphere due to needle loss. Cover of H. physodes decreased with increasing mean SO42- concentration in stemflow. The total of lichen species per sample tree also decreased with increasing SO42- concentration in stemflow, indicating that most species reacted in a similar way as H. physodes. Cover of L. conizaeoides increased with increasing SO42- concentration, but decreased at higher SO42- concentrations. Bark chemistry had a minor influence on lichen diversity. (C) 2002 The British Lichen Society. Published by Elsevier Science Ltd. All rights reserved
Relevance of element content of bark for the distribution of epiphytic lichens in a montane spruce forest affected by forest dieback
No full textElement content in the bark of Norway spruce (Picea abies) was measured in a montane forest heavily affected by forest dieback and compared to that in a nearby intact stand. Bark contained less S, K, Fe, Mn. Pb, Cu, and H+ and more N, Ca, Mg, and Zn in the dieback-affected stand than in the intact one. Diversity of epiphytic lichen vegetation was higher in the dieback-affected stand than in the intact one. Cover of the foliose lichen Hypogymnia physodes was negatively correlated with Mn and Cu content of bark. Cover of the extremely acidophytic species Lecanora conizaeoides decreased with increasing Mg and increased with increasing Cu content of bark. The measurements support the hypothesis that chemical site factors are decisive for the high lichen diversity in dieback-affected montane spruce forests. (C) 2001 Elsevier Science Ltd. All rights reserved
Does water-holding capacity of bark have an influence on lichen performance in dieback-affected spruce forests?
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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
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
Effects of manganese on the viability of vegetative diaspores of the epiphytic lichen Hypogymnia physodes
No full textSoredia of the lichen Hypogymnia physodes cultivated with Bold's basal medium on agar plates for 8 days exhibited decreasing growth rates along with increasing Mn concentrations above 3 mM. Ca and Mg added separately or in combination, alleviated Mn toxicity. The chlorophyll a and b content of the soredia was reduced under the influence of Mn and was positively correlated with the rate of grown soredia. Trebouxia cells of the soredia grown with excess Mn were smaller than control cells, had reduced chloroplasts and were partly collapsed; fungal hyphae were shortened and strongly swollen. Disintegrated cell walls occurred both in algal and fungal cells. Excess Mn was sequestered in extracellular encrustations together with phosphate as corresponding anion. Intracellularly, Mn was accumulated in polyphosphate granules both in algal and fungal cells. Mn uptake was correlated with significant loss of Na, Mg and Ca, particularly from the mycobiont. Fungal cell walls also lost significant amounts of P. The same damage symptoms occurred in cells of soredia both grown or not, but the former had a higher share of intact cells. Damaged cells of both types of soredia had equally increased Mn concentrations, whereas the total Mn content was higher in not grown soredia than in the grown ones due to the greater amount of damaged cells in the former. The Si-Mn ratio in cell walls of intact Trebouxia cells was significantly higher than in collapsed cells. The experimental evidence of Mn sensitivity of If. physodes soredia corresponds to studies of epiphyte vegetation in montane spruce forests of northern Germany that revealed decreasing cover values of H. physodes with an increasing Mn content of the substrate. (C) 2002 Elsevier Science B.V. All rights reserved
Long-distance transported sulphur as a limiting factor for the abundance of Lecanora conizaeoides in montane spruce forests
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