Festucetalia valesiacae communities and xerothermic vegetation complexes in the Central Alps related to environmental factors
Schwabe, Angelika; Kratochwil, Anselm
An important theme of this paper is to search for more generalities of pattern and diversity on the level of vegetation complexes. For this purpose the landscape sections chosen as investigation areas not only represent different mosaic habitats but have been selected according to climatic gradients and different human impact to test, e. g., hypotheses of correlations between vegetation structure and these gradients. As test areas dry physiotopes in the Central European Alps were chosen (Valle d'Aosta, Valais, Vinschgau [= Valle Venosta], Valtellina, Oberinntal/Engadin, Rhein near Chur). After a census of all plant communities present there and - if necessary - vegetation analysis with classical relevés, altogether about 150 vegetation-complex relevés, each covering landscape sections of about 0.5 ha, have been sampled. After classification and ordination of the vegetationcomplex data sets it was possible to typify the complexes and to differentiate the valley regions by these complexes. Using precipitation and temperature data for a CCA of the complex relevés it was possible to determine significant correlations with a meso-xerothermic and a meso-xerohygric gradient. This was the basis for deriving a landscape ecological differentiation of the valley areas. The DCA for the grassland communities and for the vegetation complexes results in a similar structure, but the individuality of the valley regions becomes much clearer in the vegetation-complex ordination. Characteristic structures of plant species diversity and vegetation type diversity can be generalized on the one hand for the Festucetalia valesiacae communities and on the other hand for the dry grassland vegetation complexes. For both, significant positive correlations were found between humidity and high species/community diversity, which is consistent with the hypothesis of resource-limitation of phytodiversity. Mainly Trifolio-Geranietea communities contribute to the higher community richness of the more mesohygric complexes. The communities and complexes of the subcontinental, dry inner valleys show decreased species/community diversity but are rich in rare, stenoecious species and vegetation types. Vegetation complexes of the different valley regions (consisting mainly of corresponding but also of shared vegetation types) have a similar diversity pattern. Definable successional traits characterize xerothermic complexes of the different valleys. Shallow rocks are naturally free from forest, but many areas, especially in the more humid regions, are severely endangered by succession processes. The inner-alpine dry vegetation is part of the Eurasian thermomontane vegetation complexes and has a high conservation value.