Vegetation changes in beech and spruce stands in the Orlické hory Mts. in 1951-2001

Plant cenological surveys on the basis of Braun-Blanquet's seven-point scale were made on 34 research plots in the course of studies of vegetation changes in beech and spruce stands in the Orlicke hory Mts. over period of 1951-2001. The acquired data were processed not only by traditional plant coenological methods but also by numerical analyses (agglomerative and divisive classification, ordination, species diversity). The results document marked changes that occurred in species-rich spruce communities of the association Athyrio alpestre-Piceetum (Aa-P) as well as in species-poorer communities of the associations Vaccinio myrtilli- -Piceetum (Vm-P), Calamagrostio villosae-Piceetum (Cv-P) and Deschampsio flexuosae-Piceetum (Df-P). The developmental trend of these communities in 1971-1991 converged on types very poor in species (Df-P association). On the contrary, the period 1991-2001 was characterised by a marked increase in the number of species, especially in the herb layer. An increase in coverage and number of tree species seedlings was very high after the productive seed years 1992 and 1995. The acceleration of changes in beech stands in 1971-1991 led to a species number diminution in herb-rich types of the association Dentario enneaphylli-Fagetum (De-F), and/or to their transition to species-poorer acidophilous types Calamagrostio villosae-Fagetum (Cv-F). Similarly like in spruce stands the number of species in beech stand releves increased in 1991-2001. But a majority of typical species of herb-rich beech stands returned to the communities under study very slowly.