The late Quaternary history of lodgepole and jack pines

Lodgepole and jack pines (Pinuscontorta Dougl. ex. Loud. and Pinusbanksiana Lamb.), components of the North American boreal forest, have pioneering roles after major disturbances such as fire or glaciation. These species are closely related and hybridize in western Canada, but their fossil records and contemporary variation patterns suggest they had completely different late Quaternary histories. Several taxonomically recognized geographic races of lodgepole pine apparently survived the last glaciation without drastic modification, the northern races either persisting in far-northern refugia or migrating from the south. The uneven influence of jack pine on northern lodgepole populations implies repeated genetic contacts, but less marked introgression in the other direction could be of post-Pleistocene origin. Jack pine occupied its entire range after the last glacial maximum and lacks taxonomically recognized races. In the Great Lakes region, however, the presence of regionally distinct populations suggests the species had at least two Midwestern refugia. This hypothesis is contrary to the widely held view that jack pine occupied most or all of its range from a well-documented refugium in southeastern North America, but is supported by limited fossil evidence that pine persisted in the Midwest during the last glaciation.