RECOVERY OF RIVERINE VEGETATION AFTER EXPERIMENTAL DISTURBANCE - A FIELD-TEST OF THE PATCH DYNAMICS CONCEPT

The Patch Dynamics Concept predicts different recovery patterns of com munities after disturbance according to the spatial and temporal heter ogeneity of the habitat. The aim of this study was to test the predict ions arising from the Patch Dynamics Concept on the recovery of macrop hyte communities after an experimental disturbance. The test was based on the comparison of the vegetation recovery in three stations locate d on former channels of the Rhone River, France, differing by their te mporal heterogeneity, which was estimated by the frequency of flood sc ouring. In each station the experimental disturbance was set up by upr ooting the aquatic plants in three experimental sets comprising four 1 m(2)-plots. The aquatic plants were surveyed in these sets as well as in their reference sets from July to November 1991. As predicted, the most frequently disturbed station recovered its species richness (19 species) and its vegetation cover in less than two months. The biologi cal traits of the species occurring in this station are considered as r-strategies. The species colonizing the experimental sets were not ne cessarily present on the sets before the disturbance, but occurred reg ularly on other sites of the station. The rapidity of the community re covery demonstrates the high resilience of this ecosystem. According t o the unpredictable character of its recolonization, the macrophyte co mmunity of this station could be said to be 'founder controlled' with competitive lottery for establishment. The station with intermediate t emporal heterogeneity was overgrown by some r-selected species but the community recolonization was predictable and this station had interme diate resilience. Its species richness was low (6 species). The less f requently disturbed station presented low resilience with a slow recov ery of its community (more than 5 months); the species richness was lo w (4 species) and the traits of some species were related to K-strateg ies while others were related to r-strategies. The macrophyte communit y of this station could be said to be 'dominance controlled'. Differen t patterns of recovery of the macrophyte communities of former channel s of the Rhone River could be depicted according to their temporal het erogeneity; these patterns were consistent with the hypotheses arising from the Patch Dynamics Concept. However, the competitive lottery app eared to be limited at the scale of our experiment.