ARE THE BANKS A SOURCE OF RECOLONIZATION AFTER DISTURBANCE - AN EXPERIMENT ON AQUATIC VEGETATION IN A FORMER CHANNEL OF THE RHONE RIVER

Recolonization of vegetation on 1 m(2) quadrats was surveyed after a m ajor disturbance induced by a restoration experiment, carried out by d redging in a former river channel. Various spatial and temporal patter ns of recolonization were determined by the analysis of vegetation (re -)establishment on adjacent quadrats located along transects from one bank to the other in several zones. Most species, except emergent spec ies that remained on bank quadrats (e.g. Phalaris arundinacea), initia lly (re-)established on the banks and later expanded towards the cente r of the channel (e.g. Callitriche platycarpa). Several species (re-)e stablished simultaneously on both bank and center quadrats, and this i n all three zones (e.g. Nasturtium officinale, Potamogeton pusillus). This suggests that the fine sediment contains a propagule bank. New sp ecies (not observed prior to restoration) generally established on the center quadrats first (e.g. Groenlandia densa), suggesting immigratio n via propagule drift. At the channel scale, several species (re-)esta blished first upstream and then downstream (e.g. Nasturtium officinale ), confirming the role of propagule drift from upstream habitats. Few species (re-)established downstream first (e.g. Callitriche platycarpa ). Recolonization patterns of dominant species (location and timing of (re-)establishment) are related to biological traits such as the effi ciency and means of reproduction.