Late-Holocene Expansion of Eastern Larch (Larix laricina[Du Roi] K. Koch) in Northwestern Québec

Abstract

The Holocene expansion of eastern larch (Larix laricina[Du Roi] K. Koch) at the edge of its geographical range in northwestern Québec was reconstructed using pollen and macrofossils from peat deposits. BecauseLarixis a poor pollen producer, the total pollen sum of 300–500 grains per spectrum was supplied by an additional survey of 2000 grains. However, the use of 2000 pollen counts did not give a betterLarixrecord. The combination of both pollen and macrofossil analyses offered greater opportunities to estimate the time of arrival of eastern larch at the edge of its distributional range. Along the study transect, eastern larch established east of 75° W long before 2000 yr B.P. but not sooner than 5000 yr B.P., whereas it arrived much later, after 1500 yr B.P., in most sites west of 75° W within a migration corridor around 57° 45′ N. The macrofossil record is completely different between the eastern sites, with high frequencies and densities, and the western sites where larch occurs sporadically with few remains only, concentrated in the upper part of the peat profiles. The colonization pattern of eastern larch was patchy in time and space, as suggested by the available macrofossil records, present distributional pattern in the area, and age structure of extant populations. The establishment of disjunct larch populations in the westernmost sites most likely proceeded from long-distance transport. The spatial–temporal pattern of eastern larch west of 74° W may have been influenced by the site conditions associated with late deglaciation in central northern Québec.