Recovery of riverine vegetation after experimental disturbance: A field test of the patch dynamics concept

The Patch Dynamics Concept predicts different recovery patterns of communities after disturbance according to the spatial and temporal heterogeneity of the habitat. The aim of this study was to test the predictions arising from the Patch Dynamics Concept on the recovery of macrophyte communities after an experimental disturbance. The test was based on the comparison of the vegetation recovery in three stations located on former channels of the Rhone River, France, differing by their temporal heterogeneity, which was estimated by the frequency of flood scouring. In each station the experimental disturbance was set up by uprooting 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 biological traits of the species occurring in this station are considered as r-strategies. The species colonizing the experimental sets were not necessarily present on the sets before the disturbance, but occurred regularly on other sites of the station. The rapidity of the community recovery demonstrates the high resilience of this ecosystem. According to the unpredictable character of its recolonization, the macrophyte community of this station could be said to be 'founder controlled' with competitive lottery for establishment. The station with intermediate temporal heterogeneity was overgrown by some r-selected species but the community recolonization was predictable and this station had intermediate resilience. Its species richness was low (6 species). The less frequently disturbed station presented low resilience with a slow recovery of its community (more than 5 months); the species richness was low (4 species) and the traits of some species were related to K-strategies while others were related to r-strategies. The macrophyte community of this station could be said to be 'dominance controlled'. Different patterns of recovery of the macrophyte communities of former channels of the Rhone River could be depicted according to their temporal heterogeneity; these patterns were consistent with the hypotheses arising from the Patch Dynamics Concept. However, the competitive lottery appeared to be limited at the scale of our experiment.