The article presents a portion of results obtained during monitoring of bog alder forest ecosystems Ribeso nigri-Alnetum S o l.-G ó rn. (1975)1987 (=Carici elongatae-Alnetum typicum K o c h 1926) which undergo transformations as a result of water drainage in the vicinity of the open pit brown coal mine Bełchatów taking place since 1975. The most common symptom of forest community degeneration in the drained habitats is xerophytisation, i.e. the replacement of hygrophilous plant species by mesophilous or even xerophilous species. Xerophytisation of hygrophilous communities results directly in their regression.