Relationships between floristic and micro site variability in coniferous forests of the Bavarian Alps
High plant diversity and within-relevé variance of indicator values in a large phytosociological dataset suggest that stands of montane coniferous forest communities of the Alps (suballiance Galio-Abietenion) possess mosaic structures of field layer vegetation caused by small-scale heterogeneity in microhabitats. In order to test this hypothesis in two representative stands species abundances, humus and soil morphology, pH, matrix potential and microtopography were recorded in linear transects of 1 m2 quadrats. Data were analysed by correspondence, cluster, simple and multiple correlation analysis. The hypothesis was confirmed in the Galio-Abietetum equisetetosum community, where a pattern of dry acidic mounds and moist hollows explained much of the heterogeneous plant distribution. In the Adenostylo-Abietetum vaccinietosum community soil parameters were less variable and showed only a loose relationship to species composition. Pattern diversity, as measured by inter-relevé-similarities and the Dahl index of uniformity, is considerably higher in the Galio-Abietetum community. On the ground of these findings different explanations of the observed diversity are put forward. In the Galio-Abietetum the contrast between highly acidic organic topsoil and well-buffered mineral soil results in a distinct microsite pattern, whereas base indicators in the Adenostylo-Abietetum appear as successional relics in an environment largely homogenized by an acid forest floor. Thus, a similiar species diversity and variance of Ellenberg indicator values in phytosociological relevés does not generally allow a prediction of microsite variability, as the causes of the coexistence of species with contrasting ecological behaviour can differ.