The forest vegetation of the upper Oise valley (Belgium and France): an integrated phytosociological approach.

The forest vegetation of the upper Oise valley (Belgium and France): an int egrated phytosociological approach. - From its springhead close to Chimay ( Belgium) until it reachs the Thierache hills (department Aisne, France), th e Oise river has carved its course through the primary mounts of Ardennes, where the substrate composed by schists and sandstones is almost covered by forests. Forest vegetation of this hydrological geomorphological complex i s studied according to a phytosociological method that integrates different spatiotemporal organization levels ("integrated" synusial phytosociology) : 1) synusiae : arborescent, shrubby and herbaceous synusiae were respectiv ely distributed into 6, 6 and 10 synusial associations; 2) phytocoenoses : 11 coenassociations were provisionally recognized; 3) teselas: 3 sigmassoci ations were provisionally distinguished; 4) catenas: the whole forest compl ex seems to belong to a same geosigmassociation. Our results show the high floristical and phytosociological diversity of the upper Oise valley, as we ll as its spatial arrangement from a local scale (synusiae and phytocoenose s) to a regional one (teselas and catenas). The position of this region as a phytogeographical junction is emphasized.