1,720,997 research outputs found
Vegetation, climate and fire-dynamics in East Africa inferred from the Maundi crater pollen record from Mt Kilimanjaro during the last glacial-interglacial cycle
No full textThe pollen, charcoal and sedimentological record from the Maundi crater, located at 2780 m elevation on the south-eastern slope of Mt Kilimanjaro, is one of the longest terrestrial records in equatorial East Africa, giving an interesting insight into the vegetation and climate dynamics back to the early last Glacial period. Our sediment record has a reliable chronology until 42 ka BP. An extrapolation of the age-depth model, as well as matching with other palaeo-records from tropical East Africa, suggest a total age of about 90 ka BP at the bottom of the record. During the last Glacial the distribution as well as the composition of the vegetation belts classified as colline savanna, submontane woodland, montane forest, ericaceous belt, and alpine vegetation changed. The early last Glacial is characterized by high amounts of Poaceae and Asteraceae pollen suggesting a climatically dry but stable phase. Based on the absence of pollen grains in samples deposited around 70 ka BP, we assume the occurrence of distinct drought periods. During the pre-LGM (Last Glacial Maximum) a higher taxa diversity of the ericaceous and montane zone is recorded and suggests a spread of forest and shrub vegetation, thus indicating a more humid period. The taxa diversity increases steadily during the recorded time span. The decent of vegetation zones indicate dry and cold conditions during the LGM and seem to have been detrimental for many taxa, especially those of the forest vegetation; however, the early last Glacial seems to have been markedly drier than the LGM. The reappearance of most of the taxa (most importantly Alchemilla, Araliaceae, Dodonea, Hagenia, Hex, Myrsine, Moraceae, Piperaceae) during the deglacial and Holocene period suggest a shift into humid conditions. An increase in ferns and the decrease in grasses during the Holocene also indicate increasing humidity. Fire played an important role in controlling the development and elevation of the ericaceous zone and the tree line. During the Holocene no increased anthropogenic impact around the Maundi crater can be observed, since neither higher fire activity nor a spread of hemerophilic plants is recorded. This pollen archive reveals shifts in the upper vegetation zones (ericaceous zone and montane forest zone) of at least 1100 m but underlines the role of Mt Kilimanjaro as a glacial refuge for montane forest species similar to that of the Eastern Arc Mountains. (c) 2012 Elsevier Ltd. All rights reserved.German Research Foundation (DFG) [BE 2116/X-1]; University of Bayreut
Soil microbial C and N turnover under Cupressus lusitanica and natural forests in southern Ethiopia assessed by decomposition of C-13- and (15) N-labelled litter under field conditions
No full textNatural forests in Ethiopia are frequently replaced by Cupressus lusitanica plantations, but little is known about consequences of this land use change for soil C and N dynamics. The objectives of the study were: (i) quantification of microbial incorporation of litter-derived C and N under field conditions, (ii) identification of forest management effects on microbial incorporation of litter-derived C and N and (iii) elucidation of soil moisture effects on microbial utilization of litter-derived C and N. Natural litter in the Munessa forest was replaced by C-13 and (15) N labelled litter and its degradation was studied over 2 years. Microbial incorporation of litter-derived C and N was measured by chloroform fumigation extraction and stable isotope analysis. Most of the C-13 and (15) N tracer remained in the litter or was incorporated into bulk soil, whereas soil microbial biomass showed minor incorporation. Silvicultural management practices influenced microbial litter-derived C utilization with increased microbial incorporation under wet soil conditions under plantations. Thinning of Cupressus trees led to increased litter decomposition during dry soil conditions. Soil humidity is the main influencing factor for microbial turnover of litter-derived C in this ecosystem. Fast-growing tree plantations had no negative effects on microbial C and N turnover when compared to natural forests
In situ 15N and 13C labelling of indigenous and plantation tree species in a tropical mountain forest (Munessa, Ethiopia) for subsequent litter and soil organic matter turnover studies
No full text
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
A 16-ka delta O-18 record of lacustrine sugar biomarkers from the High Himalaya reflects Indian Summer Monsoon variability
No full textWe investigated a late glacial-Holocene lacustrine sediment archive located at 4,050 m a.s.l. in the small carbonate-free catchment of Lake Panch Pokhari, Helambu Himal, Nepal. A delta O-18 sugar biomarker record was established by applying novel compound-specific delta O-18 analysis of plant sugar biomarkers (Zech and Glaser in Rapid Commun Mass Spectrom 23:3522-3532, 2009). This method overcomes analytical challenges such as extraction and purification faced by previous methods aimed at using delta O-18 of aquatic cellulose as a paleoclimate proxy. The delta O-18 results for sugar biomarkers arabinose, xylose and fucose agree well and reveal a pronounced trend towards lower delta O-18 values during the deglaciation and the onset of the Bolling/Allerod interstadial. By contrast, the period of the Younger Dryas is characterized by higher delta O-18 values. The early Holocene again reveals lower delta O-18 values. We suggest that our lacustrine delta O-18 record reflects coupled hydrological and thermal control. It is strongly related to changes in the oxygen isotopic composition of paleo-precipitation and resembles the delta O-18 records of Asian speleothems. With respect to the 'amount effect,' the record is interpreted as reflecting the Indian Summer Monsoon intensity. The precipitation signal is, however, amplified in our record by evaporative O-18 enrichment that is controlled by the ratio of precipitation to evaporation. We suggest that our delta O-18 record reflects the variability of the Indian Summer Monsoon, which was strong during the Bolling/Allerod interstadial and early Holocene, but weak during the Younger Dryas stadial. This interpretation is corroborated by a pollen-based index for Lake Panch Pokhari that estimated the strength of the Indian Summer Monsoon versus the strength of the Westerlies. Millennial-scale synchronicity with the Greenland delta O-18 temperature records highlights the previously suggested strong teleconnections between the Asian Monsoon system and North Atlantic climate variability
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
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