The North American woody species, Prunus serotina Ehrh., is an aggressive invader of forest understories in Europe. To better understand the plant invasion process, we assessed understorey plants and Prunus serotina seedlings that have colonized a 35‐year‐old replicated common‐garden experiment of 14 tree species in south‐western Poland. The density and size of established (> 1 year old) P. serotina seedlings varied among overstorey species and were related to variation in light availability and attributes of the understorey layer. In a multiple regression analysis, the density of established P. serotina seedlings was positively correlated with light availability and understorey species richness and negatively correlated with understorey species cover. These results suggest that woody invader success is adversely affected by overstorey shading and understorey competition for resources. Simultaneously, however, invader success may generally be positively associated with understorey species richness because both native and invasive plant colonization respond similarly to environmental conditions, including those influenced by overstorey tree species. Identification of characteristics of forests that increase their susceptibility to invasion may allow managers to target efforts to detect invasives and to restore forests to states that may be less invasible.

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Acidophilous oak forests of the Wielkopolska region (West Poland) against the background of Central EuropeThis monograph gives the phytosociological characteristics of acidophilous oak forests from the classQuercetea robori-petraeae(Aulacomnio androgyni-Quercetum, Molinio caeruleae-Quercetum, andCalamagrostio arundinaceae-Quercetum) and the closely related forest communities from the classesQuerco-Fagetea(Potentillo albae-Quercetumand acidophilous forms ofGalio sylvatici-Carpinetum) andVaccinio-Piceetea(Querco roboris-PinetumandSerratulo-Pinetum) in the Wielkopolska region and adjacent areas. The report is based on 1655 relevés selected from 59 published or unpublished studies. The analysed and revised syntaxa are described in accordance with the International Code of Phytosociological Nomenclature. The distribution of the documented localities of all associations and subassociations in the study area is shown in cartograms on the ATPOL grid (squares of 10 km x 10 km). The classical phytosociological methods are complemented with multivariate ordination methods (detrended correspondence analysis and/or principal component analysis) and analyses taking into account Ellenberg indicator values. The natural geographical and site differentiation of all the plant associations is presented, and stages of degeneration are distinguished in some of them. The separation of degenerated forms and substitute forest communities has allowed a clearer classification of the studied syntaxa. This study shows that the analysed associations can be subdivided into 16 subassociations and 23 variants. For 5 subassociations, nomenclatural types are designated here. The most common association in the study area isCalamagrostio arundinaceae-Quercetum, but most of its relevés represent various stages of degeneration. Among communities from the orderQuercetalia roboris, patches ofAulacomnio androgyni-QuercetumandMolinio caeruleae-Quercetumare rare. On the basis of this detailed study, a coherent system of classification of acidophilous oak forests from the orderQuercetalia roborisin Central Europe is proposed. The results are important for biodiversity conservation and sustainable forest management.

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