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Marshy pine forests have a relatively broad range of distribution across Europe but are very scattered. The typical Vaccinio uliginosi-Pinetum association is mainly restricted to nature reserves, because bog forests have been drained in many unmanaged sites where they naturally occur. Changes in the vegetation of natural forest associations in protected areas of NE Poland were studied with respect to environmental changes and ongoing autogenic successional processes in Vaccinio uliginosi-Pinetum associated plant communities. Changes in the species composition of natural communities after ca. 40 years were monitored on 14 releves in nature reserves. Most plots (nine) were located in the Bialowieza National Park with the rest in nature reserves in the Augustow and Knyszyn forests. The re-sampling of phytosociological releves was done by the same method originally used by Braun-Blanquet. The groundwater table and depth of organic layer were measured close to each releve edge. The collection of vegetation data for the two periods (old - new releves) included such parameters as: species richness, cover of layers, ecological indicator values, number of occurrences and cover coefficients of species and particular taxonomical groups. The analysis of vegetation changes in natural communities of marshy pine forest indicated that four more species were present than in the past. The largest changes in species richness occurred in the moss and herbaceous flora. The mean number of trees, shrubs and herbaceous species per plot increased significantly. Notable changes in the vertical structure of forest communities were visible. There was also an increase of ca. 20% in the secondary layer of tree canopy cover and a concomitant decrease in the moss layer. The depth of the soil organic layer reached 150 cm. The groundwater table exhibited large seasonal fluctuations in height between spring (mean of 24.3 cm) and summer (mean of 86 cm). There were changes in all the measured parameters describing the species composition of the Vaccinio uliginosi-Pinetum association. Tree species Picea abies, Betula spp. and Quercus robur, all increased in abundance over the period between sampling and re-sampling, either through increased presence in the lowest layer of stands in new releves or, in the case of Quercus robur, previously unreported occurence in the shrub layer. Many species characteristic of bog communities disappeared or significantly decreased in abundance, whereas some species typical of mineral soils became more common. The vegetation in repeatedly sampled plots became more chacteristic of wet sites than the initial bog sites over the 40 year period between sampling.

The habitat of ash-alder swamp forest, was studied in a phytosociological context. A census of changes in the species composition of natural communities was performed 40 years after the original survey had been carried out in 31 releves located in natural forests. The study sites were localized in Augustow and Bialowieza nature reserves.Re-sampling of releves followed the same Braun-Blanquet assumptions as previously. The chemical characteristics from nine soil cores were also analysed, and the peat thickness and ground water table level were measured close to every vegetation sample. Phytosociological surveys were conducted in both spring and summer. Comparative analysis of vegetation data from the two periods (old - new releves) was performed for selected variables: species richness, layers cover, ecological indicator values, number of occurrences and cover coefficients of species and syntaxonomical groups.The analysis of changes in the natural communities of vegetation occurring on ash-alder swamp forest habitat over the last 40 years indicated that decreasing humidity has caused the succession of ash-alder swamp forest to moist variants of oak-lime-hornbeam forest. An increase in cover of the understorey layer (and parallel decrease in cover of the moss layer) was evident in every sample. The species richness increased significantly over time, but this was mainly caused by the increasing number of species in the herbal flora. The species richness increasing significantly, but it was mainly caused by increasing of species number in herbal flora.