Home About us Contact
|
Home About us Contact | ||
|
|
||
Ellenberg Values (ellenberg + value)
Selected AbstractsShrub effects on herbs and grasses in semi-natural grasslands: positive, negative or neutral relationships?GRASS & FORAGE SCIENCE, Issue 1 2008A. Pihlgren Abstract The present study investigated how the abundance and sexual reproduction of herbs and grasses relates to the presence of shrubs of Rosa dumalis in three semi-natural pastures in Sweden. Shrubs may affect grassland plants negatively by competition, positively by serving as grazing refuge, or neutrally. At different distances from shrubs of R. dumalis, data were collected on plant abundance, frequency of reproductive shoots, vegetation height and litter depth. In one grassland, data were collected on seedling density and frequency of reproductive shoots in the presence and absence of grazing. The shrubs functioned as grazing refuges with taller vegetation, deeper litter and higher probability of reproduction by plants. The overall number of plant species remained the same at all distances from shrubs. Most species showed a neutral relationship with shrubs. Proportionately, 0·08,0·26 of the species showed a negative pattern to shrubs and 0·14,0·30 a positive pattern. Seedling density was negatively correlated with litter depth and peaked at 60,90 cm from shrubs. Establishment of seedlings of small-seeded species was negatively related to shrubs probably because of thicker litter layer close to shrubs. The observed patterns were compared with different functional traits, such as Ellenberg values, plant height, growth form and Raunkiaer life form. Plant height from data in the literature was the trait that best explained the relationship of plant species to shrubs because tall species were more common in proximity to shrubs. It was concluded that shrubs increase the heterogeneity in grasslands and that intensive shrub-clearing may negatively affect biodiversity. [source] Hemeroby, urbanity and ruderality: bioindicators of disturbance and human impactJOURNAL OF APPLIED ECOLOGY, Issue 5 2002M. O. Hill Summary 1Species vary according to whether they benefit from or are harmed by disturbance and intensive human activity. This variation can be quantified by indices of disturbance and unnaturalness. 2An urban flora was characterized by comparing quadrat data from cities with several large data sets from the countryside. Existing scales of species response to disturbance and unnaturalness, ruderality (a plant's ability to survive in disturbed conditions) and hemeroby (a measure of human impact) were contrasted with derived scales based on the number of associated annuals and aliens and with ,urbanity', defined as the proportion of urban land in the vicinity of each quadrat. 3Species presence data were available from 26 710 quadrats distributed through Great Britain, with urban sites only in central England. Satellite imagery was used to measure the proportion of urban land cover in the vicinity of each quadrat; 2595 quadrats were located in 1-km squares having at least 40% cover of urban land. 4The 20 species having highest urbanity were all alien to Britain, comprising 12 neophytes and eight archaeophytes. 5Of the 20 most frequent species in quadrats situated in 1-km squares with at least 40% urban land cover, 18 were natives. The two exceptions were Artemisia vulgaris , an archaeophyte, and Senecio squalidus , a neophyte. 6Both ruderal and hemerobic species, as usually defined, include many non-urban arable species. The hemeroby scale of Kowarik (1990 ), designed for Berlin, does not work well in Britain. 7The proportion of associated annuals (annuality) and the proportion of associated neophytes (alien richness or xenicity) can be developed into good indices. The annuality scale is very well defined because annuals tend to occur with other annuals. Plants with high annuality are mostly arable weeds. 8Urban specialists in central England are, with a few exceptions, character-species of the phytosociological classes Artemisietea , Galio-Urticetea and Stellarietea . Most of them have numerous non-urban associates and they do not form a very well defined group. They have intermediate levels of annuality combined with relatively high levels of xenicity. 9While it is possible to develop indices of hemeroby, urbanity and ruderality, these concepts are relatively complicated. Annuality and xenicity are simpler measures that can complement Ellenberg values, but definitive values for Great Britain would require additional data from southern England. [source] Extending Ellenberg's indicator values to a new area: an algorithmic approachJOURNAL OF APPLIED ECOLOGY, Issue 1 2000Mark O. Hill Summary 1.,Ellenberg's indicator values scale the flora of a region along gradients reflecting light, temperature, continentality, moisture, soil pH, fertility and salinity. They can be used to monitor environmental change. 2.,Ellenberg values can be extended from central Europe, for which they were defined, to nearby parts of Europe. Given a database of quadrat samples, they can be repredicted by a simple algorithm consisting of two-way weighted averaging, followed by local regression. 3.,A database of British samples was assembled from two large surveys. Ellenberg values were repredicted. 4.,Except for the indicator of continentality, the correlation of repredicted and original values was in the range 0·72 (light) to 0·91 (moisture). The continentality indicator could not be adequately repredicted by the algorithm, and is unusable in Britain. 5.,Discrepancies between original and repredicted values can be attributed to various causes, including wrong original values, differing ecological requirements in Britain and central Europe, biased sampling of the British range of habitats, and the occurrence of small plants in shaded or basic microhabitats within well illuminated or predominantly acid quadrats. 6.,The repredicted values were generally reliable, but a small proportion was clearly wrong. Wrong values were due to either inadequate sampling of species' realized niches in Britain or sampling with quadrats that were too large and included species that were not close associates. [source] Dynamics of species-rich upland hay meadows over 15 years and their relation with agricultural management practicesAPPLIED VEGETATION SCIENCE, Issue 3 2007C.N.R. Critchley Stace (1997) Abstract Questions: Has the species-rich vegetation of upland hay meadows been maintained under low intensity management imposed by an agri-environment scheme? Is the target plant community re-establishing where it has been modified previously by intensive agricultural practices? What combinations of management practices and soil properties are associated with changes towards or away from the target community? Location: The Pennines, northern England, UK. Methods: A survey of 116 hay meadows in 1987 was repeated in 2002 by recording plant species in permanent quadrats. Changes in community variables (species richness, Ellenberg values, upland hay meadow community coefficients) were analysed in species-rich, modified species-rich and degraded grassland types. Redundancy Analysis and Generalised Linear Models were used to show the relationship between management practices and soil properties and change in species composition and community variables. Results: Few sites contained the species-rich grassland type, and here forb richness declined. In the modified species-rich type, total and grass species richness increased but Ellenberg N-values also increased. Total and grass species richness increased in the degraded type and the community coefficient increased. Management was weakly related to change in species composition but showed clear relationships with the community variables. Re-establishment of the target species-rich community was more likely with late cutting, in the absence of cattle or prolonged spring grazing, and at lower soil nutrient status. Conclusion: The species-rich community was not maintained but some reversion occurred in degraded grassland. Inorganic fertiliser application and intensive spring grazing should be avoided and cutting delayed until late July. [source] | ||||||||||