-In this study, forest ecosystems were analysed with regard to the occurrence and ecological range of non-indigenous plant species. Pine forests in the NE German lowland, which naturally and anthropogenically occur on a broad range of different sites, were taken as an example. The analysis is based on a data set of about 2 300 vegetation plots. The ecological range was assessed applying Ellenberg's ecological indicator values. Out of a total of 362 taxa recorded in the pine forests, only 12 non-indigenous species, including trees, shrubs, annual and perennial herbs, and one bryophyte were found. They commonly grow on sites with relatively high nitrogen availability and soil reaction values. Most species are native to North America. Taking into account that a high proportion of the investigated pine forests is of anthropogenic origin and will naturally develop towards broad-leaved forests with beech and oak, it is hypothesised that most of the observed invasions are reversible.

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