RECOLONIZATION OF CLEARED RIVERINE MACROPHYTE PATCHES - IMPORTANCE OFTHE BORDER EFFECT

Recolonization of two experimentally cleared 9 m(2)-patches by macroph ytes in a former channel of the Rhone River, France, was investigated from May to July 1994. Two patterns of recolonization were recognized: (1) Groenlandia densa, Luronium natans and Potamogeton natans invaded the bare areas by propagation from the adjacent vegetation (border ef fect); (2) Potamogeton pusillus colonized the disturbed areas at rando m, apparently independently from the position of nearby clumps. An int ermediate recolonization pattern was shown by Callitriche platycarpa, Elodea canadensis, Hippuris vulgaris, Ranunculus circinatus and Sparga nium emersum. Species recolonization patterns and associated strategie s were related to species traits, particularly vegetative and sexual r eproduction.