Patterns of macrophyte distribution within a Breton brook compared with other study scales

In order to assess macrophyte organisation processes and patterns, with particular reference to corridor effects and connectivity, macrophyte distributions and floristic assemblages were studied within a whole brook system divided into 208 consecutive 50-m-long units in summer. The results were compared with four 5-m-long plots of the downstream part of the brook, and with 196 stations located on the river basin. Four main types of longitudinal distribution were emphasised: macrophytes could be upstream-specific ortolerant, downstream-specific, -tolerant or mainly downstream, ubiquitous or confined to one tributary. The ecological tendencies of some macrophytes were pointed out from ecological profiles. Vegetational groups were determined by correspondence analysis: sunny upstream areas were dominated by heliophilous vascular spring hydrophytes while shaded upstream areas were characterised by aquatic bryophytes; in the larger downstream brooks, three layers were observed: helophytes, vascular rheophytes and aquatic bryophytes. The comparison with the two other levels showed how mapping was useful to emphasise species distribution. A possible misinterpretation of macrophyte ecology was pointed out when studying ecological profiles in a particular brook versus a stratified sampling on the river basin. The intermediate position of the brook in regard to the general typology of the river watercourse, and also its particularities due to general eutrophication of main course were shown. Then the relationships between the species distribution and the levels of organisation or human management were discussed and placed within the topics of fluvial corridor functioning, connectedness and connectivity. The use of other concepts such as ecotones, river continuum concept or functional sectors in hydrosystems was then attempted to understand some distribution and organisation features, and to forecast further research.