Trends and cyclical changes in natural fir-beech forests at the north-western edge of the Carpathians

The vegetation of natural fir-beech forests on the western edge of the Carpathians was repeatedly surveyed in 1972(4) and 1994(5) on 34 plots in the Razula and Salajka reserves. Concurrently repeated whole-area dendrometric measurements of all live and dead trees were made together with maps of forest development stages. The maps were used to compare vegetation changes. The objective was to assess the tree layer dynamics, to discern vegetation development trends from cyclical changes, and to assess the changes of site conditions through phytoindication. The fir (Abies alba) population showed disrupted continuity of development associated with its pronounced withdrawal and replacement by beech (Fagus sylvatica). Rather than a cyclical change, the phenomenon is a trend that can be expected to become more dominant in the future. The reason for the interchange of the two species is seen in a fading response to the medieval colonization of Carpathian ridges connected with the exploitation of local forests for grazing and intensive litter raking. The herb layer was significantly modelled by changes occurring over time and by the dynamics of forest development stages. Species diversity in Razula was observed to increase. Salajka exhibited an invasion of acidophilous taxa (Luzula luzuloides, Vaccinium myrtillus) and decreased frequency of demanding taxa (Galeobdolon montanum, Dentaria enneaphyllos, Galium odoratum). Changes in the coverage of Dryopteris filix-mas, Rubus idaeus and Senecio ovatus were interpreted as cyclical changes. No significant shifts were found in the species diversity between the stages. The herb layer at a disintegration stage was homogenized and exhibited the lowest tendency to gain relative control of the undergrowth; the tendency was highest at the optimum stage. The stages of forest development exhibited changes in soil nitrogen and soil reaction.