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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.
Suction apparatus with porous ceramic cups have been installed under the root system of meadow vegetation in two long-term experiments set up to study nitrogen budget and the effect of liming. Under appropriate conditions (due to sprinkling), concentration of ammonium-nitrogen and nitrate-nitrogen were low in soil solution. Optimum pH of the meadow soil, as a result of liming, reduces nitrate leaching.
This paper presents results of abundance field research, distribution and habitat and phytocoenotic preferences of Trisetum sibiricum on the Gutowo Meadows (Urszulewo Plain, NE Poland), in a locality outside the continuous range of distribution. The species grown in wet, not used meadows, in places overflooded by beavers, partially afforested. The research was carried out in 2013 and the results were compared with analogical data from 2000–2002. Currently a higher abundance of species (circa 1600 tufts), a larger area of the locality (circa 2.5 ha), larger phytosociological spectrum and a larger share of hygrophilous species in species composition of the examined phytocoenoses was revealed. In 2013 a share of Trisetum sibiricum was noted in 12 plant communities from seven classes (Phragmitetea australis, Scheuchzerio-Caricetea nigrae, Bidentetea tripartiti, Molinio-Arrhenatheretea, Artemisietea vulgaris, Alnetea glutinosae and Querco-Fagetea), and in 2000–2002 – only in seven plant communities from three classes (Scheuchzerio-Caricetea nigrae, Molinio-Arrhenatheretea and Artemisietea vulgaris). Formerly the species was listed mainly in phytocoenoses of Angelico-Cirsietum oleracei and currently most often in phytocoenoses of Junco-Molinietum.
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