Questions: 1. How does species richness of recipient communities affect Reynoutria invasion? 2. How does Reynoutria invasion change host community structure? 3. Are there any differences in habitat preferences among three closely related Reynoutria taxa? 4. How does the genetic structure of Reynoutria populations change along the course of a river?
Location: River Jizera basin, north Bohemia, Czech Republic.
Methods: Nine 0.25 km2 plots were chosen along the river. Within each plot all main habitat types were determined and sampled using the Braun-Blanquet scale to determine the invasibility of various communities. The patches invaded by Reynoutria taxa and surrounding Reynoutria-free vegetation in the same habitat type were sampled as relevé pairs to compare the composition of invaded and non-invaded vegetation. In addition, to characterize the genetic structure of Reynoutria populations along the river, 30 samples from different clones were collected.
Results and conclusions: 1. The species richness of communities has no influence on the success of Reynoutria invasion in the area studied. The combination of environmental conditions and propagule spread is more important to the invasion success than the number of species in the host community. 2. Reynoutria invasion greatly reduces species diversity. 3. R. japonica invaded more habitat types than R. sachalinensis and R. × bohemica. The hybrid R. × bohemica outcompetes the parental taxa at sites where both taxa co-occur. 4. Isozyme analysis revealed phenotype variability in the hybrid in contrast to the parental taxa. Different hybrid phenotypes are distributed randomly on the middle and lower reaches of the River Jizera; one of them dominates and the other three occur occasionally. This pattern supports the hypothesis that sexual reproduction occasionally occurs within Reynoutria taxa.
Nomenclature: Ehrendorfer (1973).