Vegetation and future natural development of plantations with the Black poplar hybrid Populus×euramericana Guinier introduced to Central Europe

Plantations of the Black poplar hybrid Populus×euramericana Guinier, introduced to Europe, are widely spread especially in floodplains. Within the Spree forest (NE Germany) as a representative investigation area, poplar stands were investigated with regard to stand history, stand structure, species composition, and spontaneous tree rejuvenation. The study presented here, follows the hypothesis, that from the investigation of vegetation, structure, and history of anthropogenous forest stands, dominated by alien tree species, future development scenarios with regard to natural forest stands can be derived. As the main results, (1) two poplar forest communities are differentiated, the Salix cinerea–Populus×euramericana community (SPC) and the Calamagrostis canescens–Populus×euramericana community (CPC). Although these forest communities have several vegetation characteristics in common (e.g. low canopy cover, occurrence of alien species in the herb layer), their different species composition indicates different soil water conditions, similar to the naturally occurring swamp (Alnion) and floodplain forests (Alno-Ulmion). (2) Different site conditions of the poplar forest communities are not only reflected by the different total species compositions but also by the different species pool and frequency of the tree rejuvenation. (3) Within the SPC, different soil water conditions are also indicated by different species compositions on the level of sub-communities. On the contrary, former land use, stand age and stand structure are closely correlated with different species compositions within the CPC, thus indicating different stages of succession at the level of sub-communities. From the stand history and the results of vegetation analysis, including records of species and individual numbers of naturally rejuvenated trees, scenarios of the future natural development of these anthropogenous poplar forests can be derived. It is concluded, that vegetation changes as an effect of former (e.g. grassland) and present day land use (cultivation of alien poplar) are reversible with regard to the future development of natural forests.