EN
The changes in grassland communities of north-western Poland are presented on the basis of phytosociological investigations conducted within 1964-2000. The greatest attention was paid to the role of grasslands utilization as influencing their plant cover, the threats resulting from anthropopression, and the problems of active protection of the most valuable grassland communities. The Western Pomerania is the second region in Poland in respect of polders establishment. Following the dewatering of lowland bogs, large polders of 200-400 ha were used to establish the cultivated grasslands. Within 1970-1999, i.e., during intensive utilization of grasslands, they were dominated by sown fodder grasses: Alopecunis pratensis, Dactylis glomerata, Festuca pratensis, and Phleum pratense. In contrast, in river valleys of, e. g., the Ina and Wolczenica rivers, semi-natural, extensively utilized grasslands of rich floristic composition remained. The Cirsio-Polygonetum plant association forming four subassociations, i.e., Cirsio-Polygonetum gracilis, C.-P. caricetosum fuscae, C.-P. avenastretosum, and C.-P. deschampsietosum, commonly occurred. The moor grass (Molinietum coeruleae) plant association occurred frequently. Beginning from 1990, the plant associations listed above have been frequently secondarily dominated by rush associations of the orders Phragmitetetalia or Magnocaricetalia due to the lack of conservation of water lifting and drainage devices and desisted cuttings of the sites to become too humid or marshy. The original plant association changes into simplificated associations belonging to the Caricetum acutiformis, C. gracilis, C. ripariae, Phalaridetum arundinaceae, and Phragmitetum communis associations. In the Caricetum gracilis association, Carex disticha, a species previously infrequently found, often occurs. On the contrary, Polemonium coeruleae, a plant earlier recorded on this area, was not encountered. The naturalistically most valuable plant associations remained in some river valleys, where the grasslands were extensively utilized, including those with Trol- lius europaeus located on the well-head peatland in the Chociel river valley (the basin of the Parsęta river) in the Central Pomerania. The greatest population of Trollius europaeus may be found here. This species of a high vitality, occurs in different associations of the order Molinietalia, i. е., Cirsio-Polygonetum, Molinietum coeruleae, Filipendulo-Geranietum, and Scirpetum silvaticae. Apart from Trol- lium europaeus, over 430 vascular plant species grow in the valley, including dan- gered and protected species. The grasslands are dangered by firing of non-cut areas, expansion of other species, including, e.g., Carex cespitosa, Cirsium oleraceum, Deschampsia cespitosa, and Filipendula ulmaria, as well as by the lack of utilization. The naturalistic values of the valley indicate the need of protecting it legally as the Ecological-Cultural Society in Bobolice and the botanists from different centers of Poland suggest.