Post-glacial vegetation migration in conterminous Montreal lowlands, southern Quebec

Aim This work examines the post-glacial plant migration patterns at a regional scale. Location St Lawrence lowlands and adjacent highlands, southern Quebec. Methods The post-glacial plant dynamics in the St Lawrence lowlands are reconstructed based on fifteen pollen diagrams and seventy-four radiocarbon dates. Results Migratory trends are shown for the first established plant formations (tundra, boreal forest and mixed forest), while the subsequent onset of deciduous forests shows no particular pattern. Main conclusions Several factors are involved in this contrasting behaviour. First, the palaeogeographical context, principally determined by the location of the ice sheet and Champlain Sea, played a major role during the initial stages. The Champlain Sea constituted a barrier to seed dissemination between the Appalachians and Laurentians, favouring the development of Populus instead of Picea in the latter region. Secondly, ecological processes partly determined differences in establishment between conifer-dominated forests and deciduous forests. The former resulted from the successive onset of dominant species (Picea and Abies), while the deciduous forest stages resulted from domination shifts between already established taxa. Thirdly, physiographic traits explain local departures to the general migratory pattern. The major departure comprises of the onset of tundra, boreal forest and mixed forest on Monteregian hills (most of which constituted islands within Champlain Sea) before their establishment in Appalachians.