1,720,978 research outputs found
Effects of NPK fertilisation in arid southern Mongolian desert steppes
No full textFew studies have been performed on the importance of nutrient availability for plant productivity at < 200 mm annual precipitation and available meta-analyses have produced contradicting results. Here, we present data from a 3-year experiment on the effects of NPK-fertilisation under ambient precipitation in dry Central Asian steppes. The study site had an annual mean precipitation of ca. 160 mm and represented an intensively grazed montane desert steppe. One year of NPK-fertilisation at levels equivalent to 10 and 20 gN/m(2) (100 and 200 kg/ha) increased above-ground mean standing crop in a moist year to 1130 and 1490 kg dry mass/ha, respectively, compared to the 615 kg/ha from the control. The absolute increase was smaller in subsequent drier years, but the crop again more than doubled under fertilisation. The effects were most pronounced for the main fodder plants Agropyron cristatum and Allium polyrrhizum, which benefited from fertilisation more than other less palatable species. Both species also showed increased levels of foliar N. Fertilisation enhanced flowering activity on the community level, and soil analyses revealed that nutrients accumulate in the soil. Effects are therefore expected to be long lasting. Our results imply that nutrient shortage may co-limit plant growth at well below 200 mm annual precipitation. Considering that predominantly nomadic land use is known to result in nutrient withdrawal, our data raise concerns of a largely unnoticed potential pathway to pasture degradation
Inter-annual rainfall variability in Central Asia – A contribution to the discussion on the importance of environmental stochasticity in drylands
No full textDrylands are characterised by pronounced climatic fluctuations, especially in regard to precipitation. We tested the relationship between mean precipitation and variability values using monthly data from climate stations in both arid and semi-arid parts of Central and High Asia. Total annual and growing season precipitation values were also compared in order to produce results relevant to plant biomass productivity and thus land use. Our study confirmed the well known observation that variability increases with lower overall precipitation levels. The observed correlation indicated that growing season precipitation variability increased dramatically where mean precipitation levels fell below similar to 100 mm. This sheds new light on the transition between regimes with more regular rainfall patterns and those with episodic rainfall; a focus on the growing season indicates a stronger relation between rainfall sums and rainfall variability compared to annual values. We therefore encourage future analysis for other parts of the world to improve our understanding of the relationship between climatic conditions and productivity in drylands. (C) 2010 Elsevier Ltd. All rights reserved.DFG; GTZ; FWF [P14992]; German Academic Exchange Servic
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
Population ecology of Stipa species in Mongolian drylands/ von Katrin Ronnenberg
No full textDie Ökologie von Stipa- (S. krylovii, S. gobica und S. glareosa) und kodominante Arten wurde in der Süd-und Zentralmongolei untersucht. In Trockengebieten ist Pflanzenwachstum wasserlimitiert, dennoch kann Beweidung zu Nährstoffaustrag und zu Produktivitätssenkung führen. In einer Dünge-und Bewässerungsstudie erhöhte Düngung die Biomasse-, Infloreszenz- und Samenproduktion aller Arten. Bewässerung zeigte erstaunlicherweise keinen Effekt auf Biomasse und senkte sogar die Samenlebensfähigkeit von S. krylovii. In Populationen geringer Individuendichte könnte kleistogame Bestäubung, die bei Trockenheit stattfindet, effektiver sein als chasmogame Fremdbestäubung. Im Labor keimen die meisten dominanten Taxa schnell. Allerdings erhöhte S. krylovii seine Keimrate durch Kaltstratifikation, besonders die Samen aus feuchteren Ursprungsgebieten. Nur ein ungewöhnlich starker Sommerregen löste in-situ Keimung aus. Es ist wichtig, die Stipa-Steppen zu erhalten. Sexuelle Reproduktion ist selten, daher wäre eine Wiederbesiedlung von degradierten Flächen schwierig. Der heutige Beweidungsdruck beschleunigt die natürliche Bodenerosion
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
Reproductive Ecology of Two Common Woody Species, \u3ci\u3eJuniperus sabina\u3c/i\u3e and \u3ci\u3eArtemisia santolinifolia\u3c/i\u3e, in Mountain Steppes of Southern Mongolia
Full text linkThe present study describes the reproductive ecology of the prostrate shrub Juniperus sabina and the dwarf shrub Artemisia santolinifolia in dry mountain steppes of southern Mongolia. Whereas stands of the juniper are located at the drought limit of the genus’ distributional range, the genus Artemisia is typical of central Asian drylands. Both species produce large numbers of reproductive organs. For Juniperus sabina, however, only 2.5% of the morphologically intact seeds were found to be viable. Correspondingly, neither seedlings nor saplings were found in the field, and recruitment by reseeding happens at most rarely under the present climatic conditions.
Instead, clonal growth is apparently the main mode of reproduction of the juniper. RAPD fingerprinting demonstrated that patches of J. sabina were constituted by a single genet. As mean current growth rates were between 1.8 and 6.8 cm/a, the largest patches found in the study area are estimated to have a minimum age of 769 to 2,941 years. Thus, seedling establishment might have taken place under more favorable climatic conditions as they occurred e.g. 1800 yr BP, whereas in dry phases such as today survival is mainly guaranteed by clonal growth.
In contrast to that, more than 90% of the achenes of Artemisia santolinifolia were found viable. Achenes are not dormant, however, increasing temperatures positively affected time needed for germination (32° \u3e 20/10° \u3e8/4 °C). Germination is possible in both, light and darkness. The higher the osmotic stress the slower is germination and the fewer achenes remain viable.
Therefore, it can be concluded that Artemisia santolinifolia seeds are well adapted to germinate under a wide variety of conditions, allowing the plant to colonize open sites rapidly and enabling it to invade further stands providing open space is available.
Since both species grow in the same habitat, A. santolinifolia is a possible candidate for replacing J. sabina provided that the climatic conditions are not reversing again so that chances of sexual reproduction for juniper increase
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
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