La variabilité alloenzymatique des hêtraies dans les sous-domaines medio- et eu-atlantiques d'Europe

One hundred and four beechwoods located in the Atlantic range of western Europe have been analysed for four polymorphic enzymatic markers. The most diverse populations are mainly found in southern regions (Spain, Pyrenees, Aquitaine), the Pyrenean ones being characterized by the greatest diversity. Allelic variations are noticeable from west to east and then towards the north; they are mostly independent from ecological parameters. Only one locus (peroxydases 1) seems to depend on selection effect (greater polymorphism at high altitude); however, the very important total diversity of Pyrenean beechwoods may be a response, at least partly adaptative, to the large variety of microhabitats found within mountain populations.