Abstract
A set of multivariate methods was used to evaluate the influence of the successional age of the ecosystem on the frequencies of individual species (log-linear analysis) and the community composition (PCA, cluster analysis), and to assess the differences in characteristic indicator values between successional stages (discriminant analysis, Scheffé test). Significant successional changes become evident in the community composition, but after the successional elimination of certain species right at the initial stage, the changes are mostly of quantitative character. The results of the analysis at the species and community level show good agreement. There is no convergence in community composition as succession proceeds. Four groups with different successional strategies are distinguished in the field layer species: post-disturbance, early, intermediate and late species. The characteristic indicator values show that the field layer vegetation becomes more shade-tolerant and less hydrophilous as the succession proceeds. Two types of succession mechanisms are distinguished: (1) "general processes" — changes due to various population processes (migration, regeneration from seed bank) and to increased shade, and (2) "site-dependent processes". In Järvselja the last type is represented by the increase of the role of hydrophilous species in the clear-cut area, probably due to the increase of moisture when the total transpiration rate decreases. Post-disturbance species are mostly characteristic of swamp forests. In the course of secondary succession, the abundance of hydrophilous species decreases.