Typology of plant species in tributary streams of the Vienne and Gartempe rivers (Limousin, France)

The distribution of aquatic macrophytes (phanerogams, bryophyta, lichens an d algae) was studied in two rivers in the Limousin region of France, the Ri ver Vienne and the River Gartempe. At each of 106 representative sites, env ironmental factors were recorded as well as a range of physico-chemical par ameters. In this study, two different approaches were used to assess relati onship between macrophytes and their habitat. Firstly, a multivariate analy sis helps to point out the individual species ecology; for instance, some s pecies were found in areas of high ammonium concentrations (Callitriche ham ulata and Ranunculus peltatus) whereas others were associated with raised n itrate concentrations (Callitriche platycarpa, Leptodictyum riparium). Seco ndly a sigmatist phytosociological study was undertaken in order to underst and the determinism of plant communities and, in particular, an association between Callitriche hamulatae and Myriophyllum alterniflorum plus two comm unities belonging to Callitrichetum hamulatae. Both approaches were complem entary, one concerned with the individual species ecology but with a risk o f masking genuine groupings, whilst the other sought to record inter-plant communities whose ecology might not be said to be only the sum of species e cologies associated within each plant community involved.