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

English Abstract:

Gray birch (Betula populifolia Marshall) is a tree species native to North America, with a continuous distribution range extending east to west from Novia Scotia to southern Ontario, and south to New Jersey and Pennsylvania. It is a fast-growing, short-lived pionneer species that prefers poor, dry soils. Present notably on abandoned fields, the species can colonize diverse habitats. Little paleoecological information about the postglacial dynamic of gray birch is available, largely due to the fact that it is virtually impossible to identify its pollen in pollen assemblages. In order to document its past presence, we examined all sites within and beyond the species’ current distribution range in eastern North America that have been subjected to macrofossil analyses. Periods during which the species was present were estimated based on available ¹⁴C data. In total, more than 20 sites with gray birch remains were inventoried. The first occurrences date from the Late Glacial and Early Holocene. Gray birch was present during the period when the first forests formed, and fires were more frequent than they are today. Few sites show a long continuous presence of gray birch in macroremains assemblages during the Holocene. These sites are situated in pine barrens where fires seem to have always been frequent. Several ombrotrophic peatlands are characterized by gray birch establishment during approximately the last hundred years, very probably due to drier hydrological conditions in response to anthropic activities (agriculture, urbanization), conditions that favor the species’ expansion.