Habitat requirements of Myriophyllum alterniflorum DC. in river stands of the Upper Palatinate Forest, Bavaria

Biodiversity loss is, at present, one of the most severe global environmental issues. However, more demanding species are put at greater risk than generalists. Knowledge of the habitat requirements of threatened species is essential for defining the levels at which nature conservation efforts should prospectively operate. This study describes the habitat niche of the macrophyte species Myriophyllum alterniflorum DC., based on its occurrence along environmental gradients of sediments, flow velocity, turbidity, depth and shade on five brooks of the Upper Palatinate Forest, Bavaria. To examine the transregional validity of our results, we first carried out an analysis on the Pfreimd River and defined the outcomes as a reference. We then defined a transfer system for the other four brooks with M. alterniflorum occurrences, repeated the analysis and compared the results. We found a general pattern of preferred habitat conditions in combination with a regional aspect influencing the species distribution in each brook. We, suggest a broader formulation of habitat characteristics when aiming to describe a transregional pattern. Instead of preferences, we defined local extinction criteria for this species, namely: i) sediment with saprobic fraction, ii) stagnation of flow velocity, iii) strong turbidity iv) shading > 75% and v) water depth > 100 cm. Furthermore, we found that eutrophication is less effective under high-flow conditions. With its high demands on water quality, M. alterniflorum overlaps with the requirements of other endangered species. Therefore, conservation efforts should focus on promoting high-quality habitats, which include sustainable land management approaches at the catchment level.