Structure and syntaxonomy of beech forests from Gresolet Valley (E Pyrenees). Six communities related to beech forest from Gresolet Valley (Alt Bergucda) arc compared, based in their structure and synsystematics. A new subassociation (pinetosum sylvestris) of Helleboro-Fagetum is proposed. The results of a multivariate analysis discriminate pine and hazel dominated forests against typical beech forests, but do not among the last ones. The importance of dynamic factors, besides local factors as environmental and edaphic humidity, in the patch distribution of these communities in the valley is suggested. Geomorphological processes and man intervention (mostly forestry activities) account among the principal causes of the evolution of these forests.