|Dengler, J: Variabilität von Artendichte und Artenzusammensetzung auf unterschiedlichen räumlichen Skalenebenen - Exemplarische Untersuchungen aus Trockenrasen und Konsequenzen für das Probedesign von Biodiversitätsuntersuchungen. In: Bültmann, H., Fartmann, T., Hasse, T. [Eds.]: Trockenrasen auf unterschiedlichen Betrachtungsebenen., Arbeiten aus dem Institut für Landschaftsökologie Münster, 15, 73-81 (2006)|
|Key words: Floristic similarity, homogeneity, scale dependence, spatial autocorrelation, species- area relationship|
Variability of species density and species composition on different spatial scales exemplary results from dry grasslands and consequences for the sampling setup in biodiversity studies. The article deals with three questions: (1) In which manner do species densities vary on different spatial scales? (2) What are the implications of these ndings for biodiversity studies? (3) Does homogeneous vegetation with respect to species density and species composition exist? These questions are analysed in different dry grassland communities from three European regions (Brandenburg/Germany, Öland/Sweden, Curonian Spit/Russia). The analyses were conducted by use of (a) species-area data (nested plot design, plot size range > 104) and (b) relevés of exactly located plots. With increasing logarithm of the plot size, the mean standard deviation of the species richness increases but its coef cient of variation (CV) decreases exponentially for all communities studied. This regular decline of the CV can be used to determine the number of replicates at different plot sizes that are necessary to achieve a given accuracy. Within visually homogeneous stands, the species density shows no spatial structuring whereas the floristic similarity between pairs of plots decreases signi cantly with increasing distance. This nding emphasises the fact that there is no absolute floristic homogeneity in real vegetation stands.