River corridor plants (Stromtalpflanzen) in Central European lowland: a review of a poorly understood plant distribution pattern

Aim and location In Central European lowlands certain plant species grow mainly or exclusively in the corridors of large rivers. In German-speaking plant geography, they are known as 'Stromtalpflanzen'. The aim of this paper is to review the literature about definitions, explanations and species characteristics and to suggest future directions in research concerning this species group. Results A preliminary list contains 129 ecologically heterogeneous plant species. The mechanisms generating the peculiar distribution pattern may include hydrochory along river corridors, high levels of disturbance by water, variable water availability including inundation and summer drought, warm summers and high nutrient supply on alluvial soils. There is evidence from observational studies for all above mechanisms. However, none of them has been tested experimentally. Demographic data of river corridor plants are limited to very few species, including mainly invasive annuals (Artemisia annua, Bidens frondosa, Cuscuta campestris, Xanthium albinum) and annual (hemi)parasites (Cuscuta campestris, Melampyrum cristatum). Metapopulation studies do not exist to date for European species. Apart from their habitat requirements, river corridor plants were grouped according to their similarities in overall distribution pattern or their distribution within particular river corridors. Main conclusions River corridor plants include a high proportion of threatened plant species. In order to preserve them, and in order to understand the mechanisms generating the peculiar distribution pattern, much more has to be known about their population biology and metapopulation dynamics.