Contribution à la connaissance de la végétation rupicole des hautes vallées de l'ubaye et de l'ubayette. (Alpes cottiennes)

Summary The study of the saxatile vegetation of the alpine zone in the Upper Ubaye Valley shows a very sharp demarcation from a phytogeographical point of view.The saxatile groupings on limestone show septentrional affinities. It is interesting to note that the associations described have at least as much relationship to the Swiss Alp groups as to those of The Maritime Alps in fact closer.In our opinion, the explanation is not to be found in very different climatical or ecological considerations but in the presence of important barrier-mountains which have deprived the Upper Ubaye Valley of alien postglacial immigrants.There endemism is apparent but less important than in the neighbouring zone of The Maritime Alps; here it concerns surviving endemic species proceeding from an old native preglacial or interglacial element.These characters are to be found more in the northern areas of Queyras, Embrunais and Briançonnais, regions which have an incontestable relationship with our district.