Common alder (Alnus glutinosa) decline has been observed in most of European countries since 1993. In Poland decline of alder trees has been observed during the last 6 years. Alder Phytophthora was recorded, however, only from one sampling area in the middle of the country. Species of Armillaria, Fusarium, Mucor, Penicillium and Trichoderma were also isolated from diseased trees. Inoculation of alder stem pans, leaves and seedlings with Phytophthora isolates resulted in the development and spread of necrosis. Studies will be continued in the nearest years.

Phytophthora cambivora was isolated from the bark lesions of two 10- and 15-year-old of analysed alder trees. Additionally, Botrytis cinerea, 3 Fusarium species, Mucor spp., P. alni and Trichoderma spp. were recovered from diseased tissues. Isolates of P. cambivora from six plant species, used for inoculation of alder seedlings and plant parts, cause dthe development of necrosis. Isolate from Chamaecyparis lawsoniana was the weakest pathogen whereas those from Abies alba, Acer pennsylvanicum and Alnus glutinosa were the strongest.

The paper presents phytosociological and hydrological results of field investigations carried out in old excavation in Mikołów - Gniotek town (the Silesian Upland) in June 2002. Owing to renunciation of building works, primary succession led to form riparian black alder forest Fraxino-Alnetum W. Mat. 1952 of anthropogenic origin. Vegetation of the area is mostly determined by water conditions indepentently of occurrence of sandy and silty clays in the soil.