The palaeoecological record of gray birch (Betula populifolia) in eastern North America

Gray birch (Betula populifolia Marshall) is a pioneer tree species that generally colonizes both poor, dry soils and disturbed sites. Its current range appears to be expanding, and it has been observed to establish gradually and often massively in ombrotrophic peatlands. We examined data from sites within and beyond its continuous range that have been subjected to macrofossil analyses to determine whether this species was more abundant during certain periods since deglaciation. The most abundant macroremains were found in the eastern United States and date from the early Holocene (11 700 – 7000 cal. BP). Gray birch was present in mixed forests in which fires were probably more frequent than today. Only a few sites, located in pine barrens that experienced recurrent fires, show a continuous presence of the species during the middle and late Holocene. Palaeoecological data suggest that the colonization of peatlands by gray birch is a recent phenomenon (20th century), and one unique in peatland history. Anthropic disturbances seem to create conditions that foster this species, which could consequently increase its range in the coming decades.