Competitive abilities and related strategies in four aquatic plant speciesfrom an intermediately disturbed habitat

1. High species richness in disturbed habitats is commonly attributed to th e coexistence of species with diverse competitive abilities and, more gener ally, to the coexistence of different plant strategies sensu Grime (1977, 1 979). The present study tests this assumption for the case of intermediatel y disturbed, species-rich macrophyte habitats. 2. Four species, Sparganium emersum, Hippuris vulgaris, Groenlandia densa a nd Luronium natans that coexist solely in one flood-disturbed, cut-off chan nel of the Upper Rhone River (France) were selected for this study. Apart f rom this common, disturbed habitat, they presented different distribution p atterns within the floodplain. The present study aimed to establish both a hierarchical ranking of their competitive abilities and their respective st rategies according to the C-S-R-model. 3. The study was carried out during one growth season in a de Wit experimen tal design with supplementary monitoring of growth characteristics. Whereas a clear ranking of species competitiveness could not be established, the e xperiment revealed differences in their traits and strategies. 4. S. emersum possesses the traits of a competitor, whereas the other speci es present intermediate secondary strategies, with a C-R-strategy in G. den sa, a C-S-strategy in H. vulgaris, and a C-S-R or S-R-strategy in L. natans . These strategies are well matched to the distribution of the species with in the floodplain, since the distribution of S. emersum reaches far into we akly disturbed and undisturbed, and supposedly competition intensive sites, whereas Luronium occupies a habitat that is both disturbed and relatively nutrient-poor. Only the presence of Hippuris in disturbed habitats seems no t to correspond to the established strategy, but this might be explained by its need for only moderately intensive competition and by particularities of its regeneration strategy. The revealed differences in strategy may also make it possible to interpret the patchy pattern in vegetation cover withi n disturbed habitats.