Häufigkeit und Ausbreitungsdynamik von Neophyten in der Region Basel: Anlass zur Besorgnis oder Bereicherung?

Abstract

The «Flora of Basel und Surroundings 1980–1996» (BRODTBECK et al. 1999) presents an excellent opportunity for an evaluation of non-native species in the region of Basel (an area of 795 km²). The number of alien species, their taxonomic composition and geographic origin in the flora of Basel is similar to what has been reported for exotic species in the flora of Switzerland. We considered 323 naturalized or semi-naturalized alien species. Almost 50% of them are extremely rare or rare, only a small number is actually spreading, including five of the species considered in Switzerland as invasive and a potential threat to the indigenous flora. We use the distribution pattern of aliens in the «Flora of Basel» for a test if species traits allow to predict the success of exotics. Among the traits evaluated, only the dispersal type tended to have some predictive value. However, time since introduction was significantly correlated with the success of alien species. With the exception of particular cases, the non-indigenous flora cannot be considered generally as a problem, but rather as enrichment to our flora. Nevertheless, since time is an important factor for the success of exotic species, the role of aliens in our flora and probably also their problematic aspects are expected to increase in the future.