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The analyses of 4 permanent study plots located in the Białowieża forest (NE Poland, at 52º43´ N, 23º50´ E) were carried out 4 times, first time in 1973 or 1974 and next in 1985, 1998, 2008. The paper presents the results of a long–term study on natural forest dynamics in two forest communities: raised-bog pine forest of the association Ledo-Sphagnetum magellanici Sukopp 1959 em. Neuhäusl 1969 and transitional bogs represented by the boreal spruce forest Sphagno girgensohnii-Piceetum Polak. 1962. On each measurement date the DBH of all trees were recognized. At the same time, stems of shrub species as well as tree species with the height lower than 1.3 m were counted within the experimental areas. During the study period the structure of stands changed significantly. The major change observed on raised bog sites was an increase in numbers of Betula spp., Picea abies (L.) H. Karst. and Quercus robur L. After 34th-year of observations the boreal spruce forest stand partly passed the terminal phase and regenerated. New species occurred in the stands, especially in their lower layer, are typical for oak-lime-hornbeam forest, such as e.g. Carpinus betulus L., Q. robur, Acer platanoides L. Rapid development of Corylus avellana L. was also observed. During last decades, the decrease in the number of Pinus sylvestris L. trees has been observed. The results of analyses of stand data in four research periods show that the wetland habitat of the Białowieża forest has been a subject to the processes of succession conditioned by environmental changes such as desiccation through lowering of the water table as well as climatic changes entailing inter alia an increase of the air temperature and a decrease of precipitation.
The paper concerns forest populations of lady's slipper orchid (Cypripedium calceolus L.). The study sites were located in localities with the most numerous populations of Cypripedium calceolus L. in managed forests in Poland. The field studies were conducted in 2012 according to Natura 2000 sites protocols. The aim of studies was the determination of population structure of lady's slipper orchid, especially in indexes reflected number of flowering and fruit plants. The relations between above factors and environmental conditions expressed by ecological indicator values, cover of vegetation layers, species richness, stand age, and intensity of thinning were studies. The obtained results confirmed negative influence of understorey layer and positive influence of density of tree layer on the development of studied orchid populations. The increase in thinning intensity has not significant influence on protection status of Cypripedium calceolus.
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