In the Upper Doubs Valley, at the end of the Middle Ages, man simultaneously destroys forests to extend his agricultural space and uses trees as necessary raw materials and a key source of energy. This represents a paradoxical situation for which he must find solutions. In the Middle Ages, woods are indeed both shaped by nature and by mankind. This study first describes the natural wood environment of this era and examines the effect of climate on a land that is the result of a long evolution from the Quaternary period. Then, it studies the impact of man from the Mesolithic era to the Middle Ages. It analyzes the chronology of deforestation and its link to demography in the context of wars and various crises in the lower Middle Ages. Deforestation is studied in its political, social, technical and ecological aspects and the way the newly created farmland is used is analyzed. The forests that man erases in the lower Middle Ages remain however, a vital resource for him, in particular for the growing manufacture. Therefore, man needs to solve this contradiction (i.e. to destroy and to build) for the following reasons: first, logging is a source of social and political conflicts, then it is about to destroy a fragile ecological balance. The consequences are the creation of restrictions and laws that are significant of a need for him to protect the environment. This situation is the precursor of problems and conflicts that contemporary man is now facing and which he still tries to solve
