The usage of grassland significantly affects the microbial and biochemical parameters of soil epipedons. The use of grasslands (by mowing, grazing, and mowing and grazing) affects the dominance of bacteria in abundance relative to fungal populations. This was particularly noticeable when manual mowing was applied. In general, the highest number of microorganisms occurred during spring and summer, which should be associated with the intensity of growth of root systems of grass vegetation. It was noted that the grazing system caused an increase in the enzymatic activity of urease and slightly less dehydrogenases and acid and alkaline phosphatase. Therefore, microbial abundance and enzymatic activity are considered as indicator parameters to evaluate the biological soil environment. They are highly probable estimates of soil fertility and ecosystem biodiversity.

ABSTRACT. Geobotanical studies conducted in spring in 2011-2012 in the Zagórów polder washland, covered by the ecological restoration programme, provided assessment of current nature value of plant communities and indicated potential directions of their further transformations as a result of changes in habitat water content levels. Based on the analyses of 77 relevés of 50-100 m 2 each, prepared following the Braun-Blanquet method, water levels were assessed by phytoindication using moisture indicator values (F) according to ellenBerg et al. (1992). Moreover, nature value of vegetation was assessed based on the botanical structure, geo-historical spectrum, life form structure as well as the nature valuation index in the 10-point scale according to oświt (2000). Based on relevés the area was valuated using the point score method according to Mahon & Miller (2003). An attempt was made to indicate potential directions of changes in vegetation, based on the determination of dependencies between certain parameters assessing its current condition and habitat conditions. Habitat water content connected with the supply of water through a network of culverts, geomorphology of the area and land use, affects the distribution of phytocenoses in the polder and their considerable diversity, which was confirmed by the identification of 19 plant communities from six phytosociological classes. Further maintenance of water relations and land use results in the transformation of plant communities: in the vicinity of culverts -towards the class Phragmitetea, in swamps and around small water bodies -towards communities of the classes Salicetea purpurea or Alnetea glutinosae, at longer distances from culverts in leveled and agriculturally utilised areas -towards the orders Trifolio fragiferae-Agrostietalia stoloniferae and Molinietalia, while in areas at valley margins the succession progresses towards communities of the class Nardo-Callunetea.

One of the habitat types protected within the framework of the NATURA 2000 network due to the presence of species of European importance are fresh meadows from the Arrhenatherion alliance. The maintenance of their characteristic floristic composition depends on habitat conditions and extensive use, while any changes in this respect trigger succession transformations potentially threatening their nature value.The aim of the study was to conduct nature and habitat valuation of one of the largest meadow complexes in the Wielkopolska region, i.e. Wielki Łęg Obrzański, which will make it possible to describe the preservation status of fresh meadows and their habitats.Based on multifaceted analyses of 535 relevés made using the Braun-Blanquet method in the years 2006-2012 and representing the Arrhenatherion alliance, the phytosociological and botanical structure as well as constancy of species in individual variants (floristic types) were determined. Moreover, their habitat conditions were defined, i.e. soil moisture and nitrogen content using the index method according to Ellenberg, while laboratory methods were used to determine the content of organic matter, soil moisture as well as the contents of potassium, magnesium and phosphorus in soil.Floristic composition of fresh meadows from the Arrhenatherion alliance differs due to high heterogeneity of habitat. The presence of fresh meadow phytocenoses both on dried organic soils (the driest forms of flood meadows) and on mineral soils (oak-hornbeam forests) contributes to differences in the floristic composition both in ryegrass meadows and grass-fescue meadows, mainly due to soil moisture and fertility as well as sward use type. This constituted the basis for the identification of lower syntaxonomic units in the internal structure of the plant associations. Five variants were distinguished in Arrhenatheretum elatioris, while the community of Poa pratensis-Festuca rubra was developed in as many as 8 variants.

Abstract. The floristic composition of anthropogenic meadow communities undergoes transformations dependent on utilisation and habitat conditions. One of their consequences includes encroachment into and maintenance in the sward of some expansive plant species e.g. Taraxacum officinale. The objective of the study was to analyse the impact of the occurrence of Taraxacum officinale on the floristic diversity of meadow-pasture communities at varying levels of utilisation and habitat conditions. The effect of Taraxacum officinale presence on changes in the floristic composition of meadow communities was assessed on the basis of results of geobotanical studies carried out by Braun-Blanquet's method. The studies assumed evaluation of plant species proportions in the sward of meadow communities based on the share of Taraxacum officinale, floristic diversity and the natural value index of the sward. The highest share of analysed plant species was determined in extensively utilised meadows and pastures found on periodically dry habitats. Simultaneously, the high numbers of examined plant species exert a negative influence on the floristic diversity index and the natural value of plant communities.

The paper presents results of the studies conducted to determine causes and directions of transformations in vegetation of meadow-pasture communities in the area of the Wielki Łęg Obrzański [Great Obra Floodmeadows]. Multifaceted natural and habitat analyses were conducted on over 1800 relevés prepared in the vegetation seasons of 2005-2009 according to Braun-Blanquet. On their basis the phytosociological and floristic structure was analysed and habitat conditions were determined by phytoindication. Moreover, laboratory methods were applied in soil analyses to determine contents of basic macro-and microelements and groundwater table levels were recorded. Results referred to the documentation and archive literature made it possible to determine causes of transformations in plant communities in that area and outline probable directions in which succession was progressing. A lack of regular land use patterns is seen as the primary cause for the transformation in the flora of the Wielki Łęg Obrzański, particularly in the last 20 years. A considerable limitation of land use in certain sections of this area has led to the initiation of dominance of nitrophilic species such as Urtica dioica, Cirsium arvense, Potentilla anserina or Galium mollugo, while in the thinned sward it led to the development of grass species with very limited economic importance. Another equally important factor affecting the structure of vegetation cover is connected with air and water relations in soils, determined by the drainage system operating there for the last 200 years and by precipitation.