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Some ombrotrophic peatlands in temperate regions have been characterized by a process of rapid densiflcation of their forest cover for several decades. This phenomenon is particularly marked in southern Quebec (Canada), where a number of peatlands now contain mixed forest stands. The present study aimed to document the woody encroachment dynamics of a peatland colonized by Larix laricina (Du Roi) K. Koch and Acer rubrum L. The specific objectives were to characterize the contemporary dynamics of the forest cover through analysis of dendrometric, dendrochronological, and aerial photographs, and to reconstruct the evolution of tree species present in situ since the peatland's origin through botanical identification of ligneous remains collected in excavations of the peat as well as macro fossil analysis of a sedimentary core. The vegetation cover underwent rapid transformation beginning in the 1970s, first by the densiflcation of L. laricina, followed by the expansion of A rubrum. This transformation followed several millennia during which the peatland continuously presented a shrub-dominated cover with a few scattered coniferous trees. The rapid expansion of a mixed forest cover is a unique event in the peatland's history. Acer rubrum progressively replaced L. laricina and, in the more or less long-term, should become the dominant species. Key words: dendrochronology, Acer rubrum L., Larix laricina (Du Roi) K. Koch, paleoecology, woody encroachment, ecological succession, peatland Plusieurs tourbieres ombrotrophes des regions temperees sont caracterisees par un processus de densiflcation rapide de leur couverture forestiere. Ce phenomene est bien marque dans le sud du Quebec (Canada) ou plusieurs tourbieres comportent des peuplements forestiers mixtes. Cette etude visait a documenter le processus de boisement d'une tourbiere dominee par larix laricina (Du Roi) K. Koch et Acer rubrum L. Les objectifs speciflques etaient de caracteriser la dynamique contemporaine du couvert forestier a l'aide d'analyses dendrometriques, dendrochronologiques et de photographies aeriennes, et de reconstituer devolution des especes arborescentes presentes in situ depuis l'origine de la tourbiere via l'identiflcationbotanique de pieces de bois prelevees dans des excavations de la tourbe et de l'analyse macrofossile d'une carotte sedimentaire. Le couvert vegetal de la tourbiere s'est transforme rapidement a partir de la decennie 1970, d'abord par une densiflcation de L. laricina, suivie d'une expansion d'A rubrum. Ceci fait suite a plusieurs millenaries pendant lesquels la tourbiere a toujours presente une structure arbustive avec la presence eparse d'arbres coniferiens. L'expansion rapide d'un couvert forestier mixte est un evenement unique dans l'histoire de la tourbiere. Acer rubrum supplante progressivement L. laricina et devrait, a plus ou moins long-terme, devenir dominant pour former une erabliere rouge sur tourbe. Mots-cles : dendrochronologie, Acer rubrum L., Larix laricina (Du Roi) K. Koch, paleoecologie, processus de boisement, succession ecologique, tourbiere, Introduction Certain anthropic disturbances that take place on the periphery of peatlands (e.g., land drainage for agricultural use, urbanization) often result in a lowering of the water table and drying [...]