THE CONTRIBUTION OF THE BERRY OAKS TO TAXONOMY AND ECOLOGY

Microscopical observations of the morphology of the twigs, leaves and peduncles of 419 Oak trees were carried out in the sympatric and allopatric populations of Berry (Central France). Nineteen characters, divided into a total of 82 classes, were measured on each tree. Multivariate analysis of the data displayed 3 distinct poles connected by a few intermediates. These 3 poles correspond to Quercus robur L., Quercus petraea (Matt.) Liebl., and Quercus pubescens Willd. Multivariate analysis and the linear correlation of the characters allowed the discriminating taxonomic criteria to be distinguished. The variation in peduncle and petiole lengths was studied at both the tree and population level. These analyses displayed discontinuities between Sessile and Pedunculate Oaks and allowed comparisons to be made with other studies made in France and elsewhere. Similarly a phytoecological study allowed the study plots to be correlated with the taxonomic study. It was thus possible to provide evidence for the xerothermophilic nature of Downy Oaks and the hygrophilic nature of Pedunculate Oak. Sessile Oak appeared to be particularly tolerant of dry and acidic conditions. The very rare intermediates at Berry were only present on neutral, mesophilic sites and completely absent on xero-acidophilic or hydromorphic sites. The Oak population distribution, then, appears to be related to ecological site types i.e. taxonomic speciation and ecological segregation are closely linked. The distribution of Pedunculate Oak, present to a certain extent in a number of ecological sites, is likewise discussed. Although interspecific gene exchange at Berry appears very limited today, the hypothesis of introgression appears, after all, to be plausible.