Résumé
Coastal dune systems have been extensively studied in various parts of the world, but few investigations have been made in the Subarctic where temperatures remain relatively low during the short growing season. Here, we report the results of a study performed on a subarctic coastal dune system on the east coast of Hudson Bay, Canada. We determined the spatiotemporal dynamics of some important substrate characteristics, described the spatial dynamics of the vascular plant community, and followed temporal changes in the populations of the two major plant species, Leymus mollis (Poaceae) and Lathyrus japonicus (Fabaceae), along a toposequence, from the embryo dunes to the stabilized dune. Thr observed spatial changes in substrate characteristics were consistent with those reported in studies of lower-latitude dune systems, but they were generally of lesser magnitude. Thr subarctic climate appears to have unusual effects on me spatial gradient of substrate salinity and water content. For instance, salinity did not vary along the toposequence early in the season while the bay was still partly frozen, bur it showed a significant gradient during the summer, with lower salinity values on the stabilized dune. Life-form turnover. from the upper beach to the stabilized dune,was lower than what has been reported for lower-latitude dune systems because of the rarity of annual plant species. Although the density and biomass of Leymus and Lathyrus ramets decreased along the toposequence, both species persisted onto the stabilized dune where they were the most frequent vascular plants. Such persistence appears to be related to the ability of both species to physiologically adjust to local conditions. Because of the climatic context, subarctic coastal dunes constitute unique systems, with characteristics quite different from those of lower-latitude coastal dune systems.