Review study on near-natural conditions of Central European mountain streams, with particular reference to debris and beaver dams: Results of the “REG meeting” 2000

Abstract

This paper summarises the results of the “Rhithron Ecology Group” meeting in Essen (March 2000), supplemented by a literature evaluation. An extended view of small mountain streams in Central Europe under “potentially natural conditions” is presented. We focus on the potential impact of natural transverse structures (debris dams and beaver dams) on stream morphology, hydrology, habitat composition and communities. Furthermore, impact of other stream morphological features, which are presently lacking in the Central European landscape, is described. We suggest that Central European mountain streams are characterised by a higher proportion of lentic zones under “potentially natural conditions”. Morphological degradation leads to a loss of lentic zones and to an increase of current velocities and corresponding changes in faunal composition, particularly higher abundance and proportion of rheophilic species and a decrease of species preferring lentic zones. This should be regarded in future stream assessment.