The "Gestion, Naturalité, Biodiversité (GNB)" project was built to enhance knowledge concerning the effects of forest management on biodiversity in temperate european forest and look for further explaining factors behind the "management" effect. Managed and unmanaged stands on similar stations were compared for 7 taxonomic groups : vascular plants, birds, lignicolous fungi, bryophytes, carabidea, saproxylic coleopteridea, bats. The magnitude of the effects was analysed in addition to their significancy. We present (i) the effects of management on stand structure and biodiversity ; (ii) the effects of stand structural variables on biodiversity ; (iii) for each taxonomic group, the best model explaining species richness.