Ecological Restoration of Headwaters in a Rural Landscape (Normandy, France): A Passive Approach Taking Hedge Networks into Account for Riparian Tree Recruitment

摘要

The safeguard of riparian ecosystems is a major field of study in the understanding and maintenance of the ecological health of rivers. Vegetation communities found on these ecotones ensure essential functions such as limitation of river bank erosion and protection of rivers from pollutants. The aim of our study is to investigate the potential for natural regeneration of trees on river banks after passive restoration. We have also studied the influence of landscape on recolonization through the analysis of the influence of hedge networks. Our study takes place on headwaters in Normandy (France) on Vallee-Aux-Berges, a stream, which has been passively restored for the last 6 years. As passive restoration removes stresses (heavy trampling and grazing) caused by cattle on river banks, we expect it to help the growth of natural plant communities. The condition of this stream-from the start of restoration work to the present-is compared to another one in the same catchment considered to be ecologically healthy. Our results suggest that passive restoration leads to an increase in tree cover on river banks and contributes to the improvement of the banks' physical integrity. Landscape structure seems to be a major factor for this recolonization: the more the stream is surrounded by hedge networks, the more the recolonization by trees on banks is effective. These results indicate that the influence of landscape structure should be considered in future restoration management in similar headwaters.