Restoration ecology of riverine wetlands .3. Vegetation survey and monitoring optimization

A restoration experiment was carried out in a former channel of the Rhone River, France. To evaluate restoration success or failure, aquatic vegetation was surveyed monthly from March to October, one year prior to and 2 years following restoration. This was done in both the channel restored by the dredging of fine organic nutrient-rich sediments and in a similar reference channel. Whereas both species richness and total vegetational cover per transect of aquatic vegetation showed the same temporal pattern each year in each zone, these two variables exhibited a different pattern in the restored channel after restoration. Species richness generally increased continuously during the first year following restoration, then followed a seasonal pattern during the second year. Total vegetational cover was very low the first year following restoration and remained low afterwards, except in the upstream zone of the restored channel, which was fully colonized by aquatic vegetation the second year. Post-restoration changes were thus very clear in the upstream zone of the restored channel. A multivariate analysis depicted changes in the floristic composition: whereas vegetation composition was quite stable in the reference channel, eutrophic species were replaced by mesotrophic species in the restored channel.