Colonization potential of an endangered riparian shrub species

Riparian areas and their plant communities are threatened due to human exploitation and habitat loss. Conservation of riparian vegetation requires knowledge on limiting factors in the biology of species preventing its spread along suitable areas. It needs to be assessed if an endangered species is trapped in an extinction vortex or whether it can recover from its current bottleneck situation by management measurements. We investigate the recovery potential of an endangered riparian shrub species of European rivers, the German tamarisk, Myricaria germanica, by combining field and lab experiments on seed production, germination and wind dispersal with a modelling approach on species distribution. While the seed potential is high, wind-mediated dispersal is average, with a majority of seeds falling next to the mother shrub. The modelled dispersal kernel shows highest goodness-of-fit with a polynomic function. Including this kernel in a model on the future distribution of the species based on identification of suitable habitat, limited spread to new areas in Switzerland after 20 and 50 dispersal events is predicted. Given the current limited distribution of the German tamarisk in Switzerland, conservation efforts are required to allow for the formation of new riparian habitat. Additionally, connectivity along river networks has to be enhanced to help the species to escape the extinction vortex it is trapped in.