International audience This study consists of an analysis of charcoal accumulations resulting from the exploitation of salt springs in Franche-Comté. The aim is to mark transformations in the vegetation cover and evaluate the human impact on the forest. Three main phases illustrate forest changes. The first evidences Quercus (deciduous oak) and/or Fagus exploitation which depends on altitude. The second shows development of Fagus exploitation and the last consists of a Quercus-Carpinus one in plains and foot hills. An extension of the acquisition area, due to progressive depletion of forest mass may be at the origin of these results.