The Holocene closing of the ‘ice-free’ corridor: A biogeographical perspective

Abstract

Biogeographical corridors are continuous areas of similar habitat that connect two biogeographical regions and allow the migration of fauna and flora. Examples of Quaternary faunal radiation between the Nearctic and Palearctic biogeographic regions and between Beringia and the Great Plains indicate that the ‘ice-free’ corridor region of western Canada must have been such a route for grazing animals. Today, boreal forest and extensive peatlands in the ice-free corridor region separate the open vegetation of the grasslands and arctic tundra. However, it is likely that open vegetation existed between Beringia and the plains, creating a biogeographic corridor during some Pleistocene glacial stages and during glacial non-glacial transitions such as the Late Glacial-Early Holocene. Between 12,000 and 10,000 BP the corridor supported a herb and shrub dominated vegetation that included Populus trees and probably reflected a climate that was relatively warm in the summer and dry. Vertebrate paleontological evidence indicates that the corridor vegetation supported grazing fauna. The most recent closing of the biogeographic corridor occurred with the development of the present boreal forest, which is dominated by plants unsuitable for grazing. The development of forest was initiated by a rapid northward spread of Picea glauca and P. mariana from the eastern plains and western mountains at 10,000 BP. By 8000 BP the Picea forests in the corridor were as dense as at present. The extensive peatlands that typify much of the corridor today developed by ∼5000 BP and provide an additional impediment for the movement of some grazing animals.