1,721,453 research outputs found
Les Nations Unies et des droits de l'Homme à l'approche de la Conférence mondiale sur les droits de l'Homme de 1993
No full textSchmidt Marcus. Les Nations Unies et des droits de l'Homme à l'approche de la Conférence mondiale sur les droits de l'Homme de 1993. In: Revue Québécoise de droit international, volume 8-2, 1993. pp. 243-248
Les Nations Unies et des droits de l'Homme à l'approche de la Conférence mondiale sur les droits de l'Homme de 1993
No full textSchmidt Marcus. Les Nations Unies et des droits de l'Homme à l'approche de la Conférence mondiale sur les droits de l'Homme de 1993. In: Revue Québécoise de droit international, volume 8-2, 1993. pp. 243-248
Tree-microbial biomass competition for nutrients in a temperate deciduous forest, central Germany
No full textAims Our goals were (1) to determine whether tree species diversity affects nutrient (N, P and K) cycling, and (2) to assess whether there is competition for these nutrients between microbial biomass and trees. Methods We measured nutrient resorption efficiency by trees, nutrient contents in leaf litterfall, decomposition rates of leaf litter, nutrient turnover in decomposing leaf litter, and plant-available nutrients in the soil in mono-species stands of beech, oak, hornbeam and lime and in mixed-species stands, each consisting of three of these species. Results Cycling of nutrients through leaf litter input and decomposition were influenced by the types of tree species and not simply by tree species diversity. Trees and microbial biomass were competing strongly for P, less for K and only marginally for N. Such competition was most pronounced in mono-species stands of beech and oak, which had low nutrient turnover in their slow decomposing leaf litter, and less in mono-species stands of hornbeam and lime, which had high nutrient turnover in their fast decomposing leaf litter. Conclusions The low soil P and K availability in beech stands, which limit the growth of beech at Hainich, Germany, were alleviated by mixing beech with hornbeam and lime. These species-specific effects on nutrient cycling and soil nutrient availability can aid forest management in improving productivity and soil fertility
Tree species diversity effects on productivity, soil nutrient availability and nutrient response efficiency in a temperate deciduous forest
No full textThere are contrasting reports whether and how tree diversity influences stand productivity in temperate deciduous forests. Tree species diversity may increase stand productivity in temperate forests through complementary resource use and/or facilitation if the resource considered limits productivity. In unpolluted temperate forests, net primary production is typically limited by nitrogen (N). However, in many parts of Europe high N deposition has alleviated N limitation and there is some evidence that phosphorus (P) and/or potassium (K) limitation has become more widespread. Here, we report on a study where we investigated whether complementarity and/or facilitation increase productivity in a typical German deciduous forest with tree species of beech (Fagus sylvatica), oak (Quercus petraea and Quercus robur), hornbeam (Carpinus betulus) and lime (Tilia cordata and Tilia platyphyllus). We measured biomass production and availability of soil N, P, K, calcium (Ca) and magnesium (Mg) in stands of single species (mono-species stands) and in stands with different combinations of three of the tree species above (mix-species stands). We used nutrient response efficiency (NRE) to evaluate whether a specific nutrient limits tree growth. At a stand level, above-ground net primary productivity did not differ between mono- and mix-species stands. At a tree level, using a neighborhood approach, relative growth rates of beech trees in mono-species stands were smaller than when they were in mix with lime and hornbeam whereas growth of lime trees in mono-species stands was larger than in mix with beech and oak. The NRE curve for beech showed that beech trees in mix-species stands had optimal P and K response efficiencies whereas beech trees in mono-species stands showed P and K limitations. The NRE curve for oak with exchangeable soil K showed that K levels were beyond the optimum NRE and thus K was not limiting oak growth. NRE curves for hornbeam and lime showed no significant relationships with any of the soil nutrients. Hence, nutrient limitation was species-dependent. Our results showed that using both NRE and a neighborhood approach are useful tools in quantifying the effects of individual tree species on a species’ productivity between mono- and mix-species stands. Such tools provide important basis for improving management of typical mix-species, temperate forests
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
Tree Species Shape Soil Bacterial Community Structure and Function in Temperate Deciduous Forests
No full textAmplicon-based analysis of 16S rRNA genes and transcripts was used to assess the effect of tree species composition on soil bacterial community structure and function in a temperate deciduous forest. Samples were collected from mono and mixed stands of Fagus sylvatica (beech), Carpinus betulus (hornbeam), Tilia sp. (lime), and Quercus sp. (oak) in spring, summer, and autumn. Soil bacterial community exhibited similar taxonomic composition at total (DNA-based) and potentially active community (RNA-based) level, with fewer taxa present at active community level. Members of Rhizobiales dominated at both total and active bacterial community level, followed by members of Acidobacteriales, Solibacterales, Rhodospirillales, and Xanthomonadales. Bacterial communities at total and active community level showed a significant positive correlation with tree species identity (mono stands) and to a lesser extent with tree species richness (mixed stands). Approximately 58 and 64% of indicator operational taxonomic units (OTUs) showed significant association with only one mono stand at total and active community level, respectively, indicating a strong impact of tree species on soil bacterial community composition. Soil C/N ratio, pH, and P content similarly exhibited a significant positive correlation with soil bacterial communities, which was attributed to direct and indirect effects of forest stands. Seasonality was the strongest driver of predicted metabolic functions related to C fixation and degradation, and N metabolism. Carbon and nitrogen metabolic processes were significantly abundant in spring, while C degradation gene abundances increased from summer to autumn, corresponding to increased litterfall and decomposition. The results revealed that in a spatially homogenous forest soil, tree species diversity and richness are dominant drivers of structure and composition in soil bacterial communities
Distribution patterns of vascular plant taxa in the federal states of Lower Saxony and Bremen, Germany, with respect to their naturalisation and threat status
No full textDistribution patterns of vascular plant taxa in the federal states of Lower Saxony and Bremen, Germany, with respect to their naturalisation and threat status Detailed knowledge about the spatial distribution of richness centres is a prerequisite for the development of national strategics for the conservation of vascular plant species. However, different groups of plant taxa may have different relevance depending on their naturalisation and threat status. In this study we investigate the spatial distribution of plant species richness centres in the area of the federal states of Lower Saxony and Bremen, based on data from the plant survey of Lower Saxony (Niedersachsisches Pflanzenarten-Erfassungsprogramm). Our analyses include: 1.) The complete floristic list (1819 taxa) 2.) Three groups of taxa defined by their naturalisation status (1509 indigenous taxa, 160 archaeophytes, 145 established neophytes), 3.) Two groups of taxa defined by their threat situation (unthreatened versus threatened taxa, including 643 taxa which have been Red Listed with status I, 2, 3, G or R). Based on the complete floristic list, a clumped distribution pattern was observed. Site conditions in the Quaternary coastal and lowland areas arc relatively homogeneous and, with exception of the major stream valleys of the Weser, Aller, and Elbe, relatively species-poor. The upland area with its heterogeneous site conditions shows the overall highest taxonomic richness. The large group of indigenous taxa shows a distribution very similar to that of the complete floristic list. Archaeophytes are concentrated in the coastal area of Bremen, the Weser and Aller plains, the old moraine loess landscapes, and in smaller cities. High diversity of established neophytes is mainly found in congested urban areas and several other small-scale centres of diversity. Red List species are mainly indigenous (91 %), 8 % are archaeophytes and only 1 % are neophytes. Their diversity centres are spatially highly differentiated: at the coast only the islands in the North Sea are small hotspots, while in the lowlands relatively large hotspots are situated in the Wend land, the Luneburg Heath, and the Elbe-Weser triangle north of Bremen. In the uplands, the area around Gottingen, the uplands of the Weser and Leine valleys, and the Harz mountain margins are well-defined hotspots of Red List taxa. Many of these endangered species are presumably specialists adapted and limited to natural and semi-natural habitats
Distribution patterns of vascular plant taxa in the federal states of Lower Saxony and Bremen, Germany, with respect to their naturalisation and threat status
No full textDistribution patterns of vascular plant taxa in the federal states of Lower Saxony and Bremen, Germany, with respect to their naturalisation and threat status Detailed knowledge about the spatial distribution of richness centres is a prerequisite for the development of national strategics for the conservation of vascular plant species. However, different groups of plant taxa may have different relevance depending on their naturalisation and threat status. In this study we investigate the spatial distribution of plant species richness centres in the area of the federal states of Lower Saxony and Bremen, based on data from the plant survey of Lower Saxony (Niedersachsisches Pflanzenarten-Erfassungsprogramm). Our analyses include: 1.) The complete floristic list (1819 taxa) 2.) Three groups of taxa defined by their naturalisation status (1509 indigenous taxa, 160 archaeophytes, 145 established neophytes), 3.) Two groups of taxa defined by their threat situation (unthreatened versus threatened taxa, including 643 taxa which have been Red Listed with status I, 2, 3, G or R). Based on the complete floristic list, a clumped distribution pattern was observed. Site conditions in the Quaternary coastal and lowland areas arc relatively homogeneous and, with exception of the major stream valleys of the Weser, Aller, and Elbe, relatively species-poor. The upland area with its heterogeneous site conditions shows the overall highest taxonomic richness. The large group of indigenous taxa shows a distribution very similar to that of the complete floristic list. Archaeophytes are concentrated in the coastal area of Bremen, the Weser and Aller plains, the old moraine loess landscapes, and in smaller cities. High diversity of established neophytes is mainly found in congested urban areas and several other small-scale centres of diversity. Red List species are mainly indigenous (91 %), 8 % are archaeophytes and only 1 % are neophytes. Their diversity centres are spatially highly differentiated: at the coast only the islands in the North Sea are small hotspots, while in the lowlands relatively large hotspots are situated in the Wend land, the Luneburg Heath, and the Elbe-Weser triangle north of Bremen. In the uplands, the area around Gottingen, the uplands of the Weser and Leine valleys, and the Harz mountain margins are well-defined hotspots of Red List taxa. Many of these endangered species are presumably specialists adapted and limited to natural and semi-natural habitats
History of vegetation and land use in the Reinhardswald forest (Hesse, Germany)
No full textDer Reinhardswald in Nordhessen ist mit einer bewaldeten Fläche von 18.500 ha eines der größten zusammenhängenden Waldgebiete im nördlichen deutschen Mittelgebirgsraum. In dem stark von Buntsandstein geprägten Naturraum sind ausgedehnte Hainsimsen-Buchenwälder (Luzulo-Fagion sylvaticae) an den steileren Hängen zum Wesertal und bodensaure Eichenmischwälder (Quercion roboris) sowie bodensaure Fichtenwälder (Vaccinio-Piceetea) als nutzungsbedingte Ersatzgesellschaften auf der schwach geneigten Hochfläche zu finden. Durch die Auswertung zahlreicher historischer Quellen sowie durch archäologische Geländebegehungen sind die Siedlungs- und die Waldnutzungsgeschichte des Reinhardswaldes sehr gut erforscht. Es fehlte jedoch bislang eine ergänzende palynologische Untersuchung, um tiefere Einblicke in seine Vegetationsgeschichte zu erlangen. Erst durch eine Bohrung im Quellmoor „Federbruch“ konnte geeignetes Material dafür gewonnen werden. Die Analyse des 333 cm langen Bohrkerns ergab einen Einblick in 10.000 Jahre holozäner Waldgeschichte vom Ende des späten Boreals bis in die Neuzeit. Dabei folgte den im Boreal weit verbreiteten Hasel-Kiefern-Wäldern der Einzug wärmeliebender Baumarten, u. a. mit Eiche, Ulme, Linde und Esche. Ein deutlicher menschlicher Einfluss ließ sich im Reinhardswald trotz früherer archäologischer Befunde in angrenzenden Naturräumen erst mit bronzezeitlichen Kulturen und der Massenausbreitung der Rotbuche um etwa 1100 v. Chr. feststellen. Weidevieh wurde zu dieser Zeit wahrscheinlich bereits in die Wälder getrieben. Phasen intensiver Waldnutzung ergaben sich im 16. und 18. Jahrhundert (Jhd.). Dabei spielten u. a. der große Holzverbrauch von Eisen- und Glashütten sowie die Waldweide eine starke Rolle. Die historischen Quellen und das Pollenprofil stimmen hierbei sehr gut überein. So kam es im 16. Jhd. zu einer Auflichtung der Waldbestände mit einem deutlichen Rückgang des Baumpollens in Reaktion auf den Wiederanstieg der Bevölkerung nach der Wüstungsperiode des 14. Jhd. Dabei übten Waldweide und ein Vernässungsschub direkten Einfluss auf das Federbruch-Moor aus. Ein weiterer Wiederanstieg der Bevölkerung nach dem Dreißigjährigen Krieg sorgte erneut für ein deutliches Signal anthropogener Nutzung. Trotz starker Auflichtung der Baumbestände auf der Reinhardswald-Hochfläche kam es nicht zu einer vollständigen Entwaldung, da die Eiche als Mastbaum und Bauholz geschont wurde. An den Weserhängen blieben nach historischen Quellen vorratsreiche Buchenbestände erhalten. Somit hat es im Reinhardswald keine flächendeckende Waldverwüstung gegeben. Aufforstungsmaßnahmen mit Kiefer und anschließend mit Fichte im 18. und 19. Jhd. spiegeln sich im Pollendiagramm wider. Die palynologische Untersuchung des Federbruch-Moors ermöglicht somit nicht nur einen umfassenden Einblick in die Vegetationsgeschichte des Reinhardswaldes, sondern konnte auch vergangene Nutzungsintensitäten und Bewirtschaftungsformen umfassend abbilden und bestätigen. Aus den Ergebnissen der Untersuchung lassen sich Konsequenzen für den Umgang mit naturschutzrelevanten Lebensräumen im Reinhardswald (Buchen- und Eichenwälder, Waldmoore) ableiten.The Reinhardswald (near Kassel, Hesse) forms one of the biggest coherent forests in the northern German highlands, with a total area of 18.500 ha. Within the study area, which is mainly characterised by red sandstone bedrock, there are extended woodrush-beech forests (Luzulo-Fagion sylvaticae) located on steep slopes of the river Weser valley. On slightly inclined plateau sites, mixed oak forests (Quercion roboris) can be found, with spruce forests on acid soils (Vaccinio-Piceetea). An intensive study of historical sources, together with archaeological findings, had already developed a comprehensive picture of the (pre)historical land use and settlement history in the area. However, an additional palynological study, which could yield deeper insights into the vegetation history of the Reinhardswald, was missing due to a lack of suitable study sites. Peat coring in the spring mire Federbruch now provided material for pollen analysis. The 333 cm long sediment core offered an insight into 10,000 years of Holocene forest history, from the late Boreal until modern times. Boreal hazel-pine forest is followed by the immigration of nemoral species, such as oak, elm, lime and ash. An intensification of anthropogenic influence, caused by nearby Bronze Age settlements, has been dated to ca. 1100 cal. yrs. BC and was simultaneous with the spread of beech. It is probable that livestock already grazed in the forest around that time. The greatest human influence can be found in the 16th and 18th centuries, with heavy timber use for the maintenance of glass- and ironworks, as well as wood pasture, as driving factors. A decline in forest stands in the 16th century could have been caused by a population increase after a long period of land abandonment in the 14th century. Wood pasture and increasing wetness had local influence on the Federbruch. The next signal for intensive land use in the core was caused by an increase in population after the 30-year-war. Despite opening of the forest, no complete deforestation of the Reinhardswald took place because oak was protected as a source of livestock and timber. According to historical sources, broad beech stands on the Weser-slopes were also retained. Thus, no forest devastation has taken place. In the late 18th until the 19th century the forest underwent afforestation with pine, followed by spruce, as recorded in the pollen diagram. Our investigation on the palynological record of the Federbruch sediment core not only allowed deep insights into the Reinhardswald’s vegetation history but also confirmed more than 3000 years of settlement and land use history. From the results, consequences for an improved management of habitats essential for nature conservation (beech- and oak forest, peat bogs) can be derived
- …
