The use of line transects for an accurate description of river bank vegetation

Abstract

The last decades, considerable efforts have been made to increase the habitat diversity of river banks along navigable waterways. In particular the construction of nature friendly bank protections aimed to preserve or restore ecological gradients, enhancing habitat diversity. To evaluate the ecological gain obtained so far, monitoring studies are performed. The use of the quadrat method is widespread in the vegetation monitoring of river banks. However, when monitoring narrow river banks, this method has serious restrictions. A possible alternative could be the use of a line transect method. Both methods were compared by calculating weighted averages of Ellenberg indicator values of all species present in a sample area, to determine the most appropriate method. We observed that the Ellenberg indicator value for moisture was the most appropriate variable to describe changes perpendicular to the waterline. When comparing both methods through time, they seemed to produce similar results in the case of species poor vegetation types such as reedbeds or some grassland types. Nevertheless the line transect method produced a much better description of the spatial gradient complexity. The use of the most efficient monitoring method is determinant to accurately evaluate the present gradients and the gradients after an intervention has taken place.