Dispersal of Plants in Fragmented Landscapes

Abstract

The decline of plant species and populations during the last decades is obvious in the man-made landscape in Central Europe (Korneck & Sukopp 1988). Although many nature reserves were established, the decline is going on. The most obvious reasons outside nature reserves are change of land use, drainage, and pollution by nutrients. Some changes, e.g. hydrological conditions in the agricultural landscape, do also affect nature reserves (Grootjans & van Diggelen 1995). A less obvious reason, however, not less important, is, that many plant species lack any possibilities to reestablish populations under suitable or restored conditions. Plants have different regeneration strategies to reestablish: One is a short- or long-term persistent diaspore bank, another one is the (re-) invasion of suitable sites by dispersal. Recently it was shown, that many species of the Northwestern European flora only have a transient or short-term persistent diaspore bank (Thompson et al. 1996). Exceptions are many weeds, ruderal, and pioneer species which tend to have a long-term persistent diaspore bank. This is one of the main causes why extinct plant populations cannot reestablish once conditions are suitable or restored (Bakker et al. in press). That means for many species that dispersal is the bottle-neck in regeneration. Additionally, in the actual man-made landscape, high dispersability will be still more important for our species-rich seminatural ecosystems because of increasing fragmentation and isolation by large distances between them. Therefore, we want to focus on the following questions in this review:.