While the sessile oak (Quercus petraea) may be widely distributed across Europe, it is somewhat rare on the NE Iberian Peninsula, its southern distribution and xeric limit. Understanding the relationship this forest has with not only climate factors but also with past human activity is important. This study aims to analyze the species composition and structure of sessile oak forests that form the xeric limit populations as well as examine the effect environmental factors have on them. The work was focused on the southernmost sessile oak forest, the Montseny Massif populations, which have a marked environmental Mediterranean influence. The sessile oak forest types were defined from field inventories and a cluster analysis classified the inventoried stands into five forest types. The compositional differences among the forest types were the result of past land uses and the intensity of forestry activity 50 y ago. Furthermore, the species composition is influenced by environmental factors, because more hydric stress promotes Mediterranean species. The study concludes that sessile oak are recovering from past forestry activity.