1,721,066 research outputs found
Are Fe and P availabilities involved in determining the occurrence and distribution of Calluna vulgaris (L.) Hull in semi-arid grasslands on calcareous soils?
No full textCalluna vulgaris (L.) Hull is primarily found on acid soils and is generally classified as a calcifuge species. Therefore, its occasional growth in semi-arid grassland on shallow calcareous soils gave rise to the question as to whether special soil conditions, deviating from the typical conditions in calcareous soils, enable this unusual occurrence. In an attempt to answer this question, we analysed selected soil factors, comparing plots where C. vulgaris was growing besides calcicole species (=CF plots) with neighbouring plots where only calcicole species were present (=CC plots). Main emphasis was placed on Fe and P availability because results from growth experiments indicate that the availability of either Fe or P to calcifuges causes calcifuge species to fail on calcareous soils. The results of our investigations do not support the hypothesis that the occurrence of C. vulgaris in semi-arid calcareous grasslands depends on higher Fe and/or P availability. Rather, its growth on carbonate-buffered soils shows that this species is not really calcifuge. Since the CF plots differ from the CC plots either by a lower inclination or by a more northerly exposition, we assume that the primary establishment and this species' distribution pattern in the investigated semi-arid grassland are not dependent on soil chemical factors, but are governed by topography and its consequences for soil humidity and drought stress.Deutsche Forschungsgemeinschaft [Ru 136/10-1, 10-2
Einfluß einwandernder Espen (Populus tremuloides) auf den Stickstoffhaushalt nordamerikanischer Prärieökosysteme
No full textIn einem Grasland-Wald-Ökoton wurde untersucht, ob
der gegenüber dem Graslandboden höhere
Mineralstickstoffgehalt des Waldbodens mit dem Alter
der Bäume, der Bodenfeuchte, der Lufttemperatur oder
dem relativen Lichtgenuß im Wald zusammenhängt. Dazu
wurden diese Faktoren in Espenhainen (Populus
tremuloides) auf Radialtransekten, die in die
angrenzende Prärie verlängert wurden, gemessen. Es
zeigte sich, daß der Stickstoffgehalt mit abnehmender
Bodenfeuchte ansteigt. Nur diese Korrelation war
signifikant. Die Ergebnisse deuten an, daß der höhere
Stickstoffgehalt in Hainböden auf eine geringere
Stickstoffaufnahme der Hainarten bei Bodentrockenheit
zurückzuführen ist. Als Alternative zu dieser Erklärung
wurde die Annahme geprüft, daß die stickstoffärmere
Streu in Wäldern wegen geringerer Evapotranspiration im
Schatten schneller zersetzt wird als die
stickstoffreichere Streu im benachbarten Grasland und
dies zu einem höheren Mineralstickstoffgehalt im
Waldboden führt. Dazu wurde der Einfluß der Streusorte
(Grasgemisch oder Espe), des Biotoptyps (Grasland oder
Espenhain) und der Beschattung (ohne oder mit
künstlicher Beschattung) auf die Raten des
Trockenmasseverlustes und der Stickstoffabgabe der
Streu bestimmt. Je 2 g Ende April gesammelter
Vorjahresstreu wurde in 1 dm2 großen Netzen
Anfang Mai auf die Versuchsflächen ausgebracht. Zur
Messung der Stickstoffauswaschung wurden unter die
Streunetze Beutel mit Ionenaustauschern gelegt. Mit
unbedeckten Austauscherbeuteln wurde die
Stickstoffdeposition bestimmt. Je ein Viertel der
Streunetze und Austauscherbeutel wurden nach 4, 9, 16
und 21 Wochen geerntet. Aus dem Masseverlust der Streu
und der Stickstoffauswaschung wurden die Raten der
Zersetzung, Stickstoffabgabe- und -anhäufung berechnet.
Grasstreu wurde signifikant schneller (k= -1,36) als
Espenstreu (k= -0,44) und beide Sorten jeweils in
unbeschatteten Prärieteilflächen schneller als in
anderen Teilflächen zersetzt. Die Grasstreu fing
weniger Stickstoff aus der Deposition auf und ließ mehr
davon durch als Espenstreu. Eine chemische Analyse der
zersetzten Streu zeigte, daß bei Berücksichtigung der
Deposition beide Sorten Stickstoff verloren hatten.
Dieser Verlust war vermutlich durch Fragmentierung der
Streu, jedoch nicht durch Mineralisation entstanden. Da
entgegen der Annahme Espenstreu trotz Beschattung am
langsamsten zersetzt wurde, wird Streuzersetzung als
Erklärung des höheren Stickstoffgehaltes in Hainböden
verworfen und stattdessen die Annahme beibehalten, daß
Trockenheit die Stickstoffaufnahme im Hain
begrenzt.Variables that contribute to a higher soil mineral
nitrogen content in forest soil than in adjacent
grassland soil were studied in a Canadian
forest-grassland ecotone. For this, the correlations of
soil mineral nitrogen with tree age, soil moisture, air
temperature and light penetration were studied along
transects extending from the centre of aspen groves
(Populus tremuloides) 5 m far into the prairie. Among
all correlations only the increase of nitrogen content
with decreasing soil moisture was significant. The
results indicate that nitrogen uptake by plants and
microbes in the forest is limited at a higher level of
soil moisture than plants and microbes in the
grassland. As an alternative explanation I have tested
the assumption that, because of canopy shading, litter
decomposition in forests is faster than in adjacent
grassland and that therefore the mineral nitrogen
content of forest soil is higher than that of grassland
soil. For this, the effects of litter type (aspen or
grass mix), habitat type (forest or grassland), and
shading (with or without artificial shading) on the
rates of litter mass loss and nitrogen release were
investigated Previous year"s litter was collected in
April and put in 1 dm2 large litter bags in
portions of 2 g. The bags were laid out in the
experimental plots in the first week of May. Bags
containing ion-exchange resin were put under the litter
bags to measure nitrogen release. Uncovered resin bags
were used to measure nitrogen deposition. One fourth of
the litter bags and resin bags were each retrieved
after 4, 9, 16, and 21 weeks. Decomposition rates were
calculated from litter mass loss measurements. Nitrogen
release measurements were converted to rates of
nitrogen retention and nitrogen loss. Grass litter
(k=-1.36) decomposed signifcantly faster than aspen
litter (k=-0.44). Decomposition of both litter types
was fastest in unshaded prairie plots, thus there was a
significant habitat type x shading interaction. Grass
litter captured less and released more nitrogen from
deposition than aspen litter. An analysis of total N
content of litter showed that when deposition was
accounted for both litter types had lost nitrogen. This
nitrogen was probably lost by fragmentation and not by
mineralization. Aspen litter decomposed slower than
grass litter, even in shade. Thus, decomposition is
rejected as an explanation for the higher nitrogen
content in forest soils, but the first explanation
should be retained
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
Design and Analysis of a Population Model for Beaver (Castor canadensis)
Full text link30 pages, 1 article*Design and Analysis of a Population Model for Beaver (Castor canadensis)* (Runge, Michael C.) 30 page
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
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