1,721,248 research outputs found
Pflege- und Ausbaumaßnahmen an Gräben der Singener Aachniederung - Ihre Auswirkungen auf Vegetation und Diasporenbank
Full text linkSubstitutes for grazing in semi-natural grasslands - do mowing or mulching represent valuable alternatives to maintain vegetation structure?
No full textQuestion Which management treatments are suitable to replace historically applied grazing regimes? How and why does vegetation structure change following changes in management? Location Semi-natural calcareous dry grasslands in southwest Germany. Methods We analysed changes in floristic and functional composition induced by different management treatments (grazing, mowing, mulching, succession) in long-term experimental sites. First, floristic and functional distances between the initial conditions and the following years were determined. Second, we used RLQ analyses to include data on abiotic conditions, vegetation composition and functional traits in one common analysis. Finally, we applied cluster analyses on RLQ species scores to deduce functional groups. Results In contrast to the historical management regime of grazing, all alternative management treatments led to changes in floristic and functional composition, depending on their intensity with respect to biomass removal. The distance analyses showed that mulching twice per year and mowing did not lead to strong changes in floristic or functional composition. However, RLQ analysis clearly provided evidence that only the grazed sites are in equilibrium, indicating that vegetation change still goes ahead. Conclusions The current study clearly shows that RLQ is a powerful tool to elucidate ongoing processes that may remain hidden when separately analysing floristic and functional data. Alternative management treatments are not appropriate to sustain the typical disturbance dynamics of species-rich semi-natural grasslands. The less frequent an alternative management treatment is with respect to biomass removal, the less the floristic and functional structure can be maintained
An unexplored side of regeneration niche: seed quantity and quality is determined by the effect of temperature on pollen performance
Full text linkIn 1977, Peter Grubb introduced the regeneration niche concept, which assumes that a plant species cannot persist if the environmental conditions are only suitable for adult plant growth and survival, but not for seed production, dispersal, germination and seedling establishment. During the last decade, this concept has received considerable research attention as it helps to better understand community assembly, population dynamics, and plant responses to environmental changes. Yet, in its present form, it focuses too much on the post fertilization stages of plant sexual reproduction, neglecting the fact that the environment can operate as a constraint at many points in the chain of processes necessary for successful regeneration. In this review, we draw the attention of the plant ecology research community to the pre-fertilization stages of plant sexual reproduction, an almost ignored but important aspect of the regeneration niche, and their potential consequences for successful seed production. Particularly, we focus on how temperature effects pollen performance and determines plant reproduction success by playing an important role in the temporal and spatial variations in seed quality and quantity. We also review the pollen adaptations to temperature stresses at different levels of plant organization and discuss the plasticity of the performance of pollen under changing temperature conditions. The reviewed literature demonstrates that pre-fertilization stages of seed production, particularly the extreme sensitivity of male gametophyte performance to temperature, are the key determinants of a species’ regeneration niche. Thus, we suggest that previous views stating that the regeneration niche begins with the production of seeds should be modified to include the preceding stages. Lastly, we identify several gaps in pollen-related studies revealing a framework of opportunities for future research, particularly how these findings could be used in the field of plant biology and ecology
How substrate depth shapes spontaneous plant colonisation on Mediterranean green roofs: A case study
No full textGreen Roofs (GRs) have been recognized by the EU as key Nature-based Solutions providing environmental and human benefits in cities. Mediterranean GRs (MGRs) are still rare and little is known about the successional dynamics and environmental factors shaping plant community composition. In the current study, we monitored spontaneous plant communities colonising two MGRs different in substrate depths and composition, and year of installation in the city of Genoa (NW Italy). Taxonomic composition variation over time was described using Non-Metric Multidimensional Scaling (NMDS) and species turnover rates. A nested ANOVA was used to test differences in plant biomass. Finally, functional composition variations were investigated by calculating CSR ecological strategies of species using the StrateFy tool, which identifies competitive (C), stress-tolerant (S) and ruderal (R) plant strategies. Both the taxonomic and functional structure of spontaneous plant communities were strongly dependent on MGR characteristics, with S species usually dominating on MGRs with shallower substrate, while deeper MGRs were also able to support more C species. However, the temporal variation in biomass and CSR strategy distributions indicates that substrate effects might be modulated by external interactive factors such as climate conditions and human disturbance. Our results show that, although described as extreme habitats, MGRs can support resilient, heterogeneous and dynamic spontaneous plant communities and that substrate plays a key role in driving their temporal evolution. From a planning perspective, our study demonstrates the importance of implementing a functional trait-based approach for species selection in MGRs, considering substrate-related factors and management practices
Mycorrhizal infection indicates the suitability of different management treatments for nature conservation in calcareous grassland
No full textThe vegetation composition of calcareous grasslands in Central Europe is mainly determined by the applied management treatments and the nutrient status of the ecosystems, but these factors cannot clearly be separated. Recently several authors reported a shift in growth-limiting plant nutrients from nitrogen to phosphate. Therefore, we tested the interaction between management and plant available phosphate in a long-term experiment in Southern Germany with different management treatments applied to calcareous grassland. We measured mycorrhization rates, which are assumed to be high at low phosphate availability, to explore the interaction between management, phosphate availability and vegetation composition. By correlating mycorrhization rates to vegetation and soil data we found that treatments involving nutrient removal show a greater degree of mycorrhization than treatments leading to nutrient enrichment. According to decreasing suitability for grassland conservation, the six different management treatments could be ranked as mowing, followed by mulching (twice a year, once a year and every second year), burning and undisturbed succession. It was shown, that mycorrhizal infection rates (1) can be used to evaluate different management treatments for their suitability to conserve the initial vegetation composition, and (2) may provide information about the processes of adaptation to the current management, namely to differences in plant available phosphate. However, as discussed for the undisturbed succession treatment, it might not be sufficient to look at the degree of mycorrhization only. These are related to phosphate availability, but to detect adaptation processes to management, the degree of mycorrhization should be analysed together with plant's internal nutrient relocation patterns
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
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