Miasto jako przestrzeń rozwoju spontanicznej roślinności drzewiastej

City as a space for the development of spontaneous woody vegetation The paper presents the results of field investigations, which were carried out in the years 2002–2006 in the city of Poznan and its surroundings. The aim of this article is to characterize the phenomenon of trees and shrubs expansion on urban areas after the cessation of direct human impact. The examined plant communities were documented with the aid of classic phytosociological releves. Observed woods and thickets in Poznan were marked in the squares of a side of 1 km. The secondary woods and thickets were noted in various ruderal sites in Poznan, especially in sites after earthworks, on roadsides and embankments as well as in abandoned gardens. In the suburbs they very often occurred on fallow lands. The documented phytocoenoses were aggregations with an unstable and poor species composition of undergrowth. Common species with wide ecological scale dominated among herbaceous plants. Only small group of trees and shrubs (mainly native species) had an important share in secondary woods and thickets. In many patches they were the dominant plants. The Norway maple was in Poznan the most frequently noted tree species.