Relationships between floristic and micro site variability in coniferous forests of the Bavarian Alps

High plant diversity and within-releve 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-releve-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 rei eves does not generally allow a prediction of microsite variability, as the causes of the coexistence of species with con­trasting ecological behaviour can differ.