Long-term vegetation dynamics in the Sumava Mts. natural spruce-fir-beech forests

In 1972(74)-1996(98), repeated phytocoenological surveys of natural mixed forest remainders were made on permanent plots in the Sumava Mts. in the south-western part of the Czech Republic. The surveys were made in localities with subsoils poor in nutrients (Boubin-Milesice-27 plots) and in a locality with nutrient-rich subsoil (Stozec-15 plots). Vegetation dynamics were studied according to the year of measurement and the nutrient capacity of the geological bedrock. We used the indices of floristic similarity, the calculation of plant communities' characteristics (Shannon-Wiener's index, equitability index), the calculation of taxa characteristics (fidelity, average cover, constancy) and multivariate ordination analyses-indirect (DCA) and direct (CCA). Changes in environmental conditions were studied between the years of measurement and between the localities using bioindication-by the calculation of Ellenberg indicator values (EIV) for plant communities. Over 24 years both the nutrient-poor site and the nutrient-rich site showed a considerable reduction in the tree layer cover and conversely the advancement of shrub layers. The coverage degree of dominants in the main tree layer (Fagus sylvatica, Picea abies and Abies alba) markedly decreased. Abies alba also exhibited a pronounced drop in constancy. On the other hand, the lower tree layer and shrub layers in Boubin-Milesice exhibited a distinctive invasion of Fagus sylvatica. An increase in the frequency of Sorbus aucuparia and a decrease in the frequency of Ulmus glabra were determined too. Herb layer changes were highly significant between the 1970s and the 1990s with qualitative changes being greater than quantitative changes. The number of species and Shannon-Wiener's index increased. A significant difference was recorded between the nutrient-poor and the nutrient-rich sites in the values of the quantitative similarity of releves with other differences being insignificant. The nutrient-poor sites exhibited herb layer homogenisation. A significant increase of EIV for light was found on both site types. The changes in phytocoenoses were interpreted partly as developmental trends (caused by indirect impact of man-e.g. fluctuations in game populations since the 18th century, the impact of air pollution); partly as cyclical changes connected with the developmental cycle of the natural temperate forest.