THE HOLOCENE DYNAMICS OF JACK PINE AT ITS NORTHERN RANGE LIMIT IN QUEBEC

1 The postglacial history of jack pine (Pinus banksiana Lamb.) at its northernmost distribution limit in the upper boreal forest, along the Grande Riviere de la Baleine (northern Quebec), was reconstructed by using radiocarbon-dated conifer macrofossils found in dune palaeosols. 2 Black spruce (Picea mariana (Mill.) BSR) was the first conifer species to colonize the area at 6000 BP, immediately after deglaciation. Jack pine first invaded the sandy terraces at 3050 BP, apparently at a low density. The species most likely survived for several centuries at this low density before experiencing a regional expansion between 2400 and 1750 BP. 3 From the period of regional expansion of jack pine to the present, mixed and monospecific stands of jack pine and black spruce developed concurrently, indicating that both species responded positively to fire and climate conditions. 4 The regional expansion of jack pine was not followed by a northward spread of the species into the forest tundra. The formation and expansion of the forest tundra during the last 3000 years restricted jack pine to the boreal forest. A lower fire frequency with colder conditions in the forest tundra may have been responsible for the inability of jack pine to expand northwards.