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The phytogeographical districts of the study area - © 2004 by Paul Diederich

Study area - The Boulogne district

The Boulogne district (Boul.) is a large depression, mainly occupied by sand, clay and marl belonging to the upper Jurassic, and bordered by a cuesta belonging to the Cretaceous. The region is geologically very heterogeneous. The climate is relatively oceanic. Several large forests bear a rich lichen flora comprising several atlantic or oceanic species; two main vegetation types can easily be recognized: the neutrophilous Quercus-Fraxinus-Carpinus woodland, usually dominated by Hyacinthoides non-scripta, and the widespread, much more humid Quercus-Fraxinus-Alnus woodland with the ground layer invaded by Carex pendula or Carex remota. Large limestone quarries harbour a rich flora of saxicolous lichens.