Plant population processes in the course of forest succession in abandoned meadows. I. Variability and diversity of floristic compositions, and biological mechanisms of species turnover

Abstract

Within Białowieża Forest the studies on the rate and nature of changes in meadow vegetation on the sites no longer mown were conducted for 15 years (1974-1988). The successional processes were analysed at various organizational levels by applying hierarchi­cal system of study areas, varying in size (Figs. 1, 2). Changes in plant landscape were studied on 15 ha, those in phytocoenoses - 4 × 1 ha, populations - 24 × 200 ml, and those in the individual development - 6 × 25 m². Forest re-colonized abandoned meadows at a various rate through: a) gradual transformation of meadow phytocoenoses into tall­herb, and later brushwood communities, which went on for c. 15 years; b) formation of the mosaic of monospecific aggregations of a few, among 124, components of meadow communities, such aggregations persisted for 5-15 years; c) the development of tree biogroups (forest outpost) directly in the meadow sod. This diversity resulted from the habitat heterogeneity (microrelief, water level) and variety of colonization strategies among the species present prior to the succession. They vary in their role in the successional process and can: I) stimulate the changes in the structure of meadow phytocoenoses and lead to the formation of new communities (promotors), 2) limit species turnover due to their long-lived aggregations (inhibitors), 3) play no crucial role in the vegetation transformation (indifferents).