Gene flow in a pioneer plant metapopulation (Myricaria germanica) at the catchment scale in a fragmented alpine river system.

River alterations for natural hazard mitigation and land reclamation result in habitat decline and fragmentation for riparian plant species. Extreme events such as floods are responsible for additional local species loss or population decline. Tributaries might provide refugia and subsequent source populations for the colonization of downstream sites in connected riverine networks with metapopulations of plant species.