POSTGLACIAL CLIMATIC VEGETATION AND FLUCTUATIONS ON THE NORTHERN COAST OF GASPE PENINSULA (QUEBEC)

The postglacial (ca. 13 000 BP) vegetational and climatic history is reconstructed from the pollen analytical study of the sediments of two lakes located in coastal northern Gaspe Peninsula. J'Arrive Lake (altitude: 56 m) was submerged by the Goldthwait Sea until about 11 400 BP. Euloge Lake, 83 m in altitude and less than 1 km from the shore, escaped the marine invasion. Before 10 400 BP, the vegetation, very scarce at first, evolved to a herb tundra that lasted for over a millenium. A cold climatic oscillation correlative with the Younger Dryas is identified at both sites between 10 700 and 10 400 BP, during this herb tundra phase. After 10 400 BP, dwarf birch and willows colonized the sites, leading to a shrub tundra. The afforestation of the area began only around 9300 BP, with the late arrival of spruce and aspen. This phase was interrupted at 8650 BP by the upsurge of green alder, in response to another cold oscillation. Since 7250 BP, the present forested landscape finally developed in three steps, characterized by (i) a high diversity of forest species until 2500 BP, (ii) a loss of diversity until 1000 BP that favoured spruce and balsam fir, and (iii) an increase of heliophilous trees, shrubs, and herbs. These reconstructions contribute to the late-glacial palaeogeography of Eastern North America through the unravelling of conditions close to the retreating ice.