Threats of natural forest wetlands in a changing environment

Paper concerns a study with changes of vegetation and habitats of hydrogenic sites in Bialowieza Primeval Forest. The spontaneous succession of natural bog, swamp and riparian forests were presented in context of menace environment changes. Remembering that surveys of vegetation are a reliable tool for monitoring temporal variations of the forest environment, those below methods were used in investigation. Spontaneous vegetation dynamics of wetlands forest communities were studied by re-sampling of releves recorded in the 1960s and 1970s. Vegetation sampling was carried out according to Braun-Blanquet's phytosociological method. Changes in species composition and habitat conditions were evaluated in terms of average species ecological indicator values and ordination method. Dynamics of ground flora vegetation according to habitat gradient was expressed by using the Detrended Correspondence Analysis method. The measuring of breast high diameters was repeated in two vegetation types. Ground water table was monitored from 1985 in the alder swamp forest site. The results of floristic changes and ground water table were referred to measured environmental variables including climatic conditions (temperature and precipitation). The climatic parameters have carried out from 1950 by Institute of Meteorology and Water Management in meteorological station situated on Bialowieza glade. Species composition changed considerably between today and reference studies. According to average ecological indicator values, besides ash-alder riparian forest Fraxino-Alnetum, habitat conditions became drier and richer in nutrients. The obtained results indicate changes in water and fertility conditions of wetlands, although those changes were not occurred in every communities in the same level. The effect of these changes are a decreasing number and abundance of oligotrophic and bog species as well as an increasing number and abundance of eutrophic species. Observed vegetation and ground water table changes could be caused by the rise of air temperature, especially in winter season.