Persistence of colonizing plant species along an inferred successional sequence on a subarctic coastal dune (Quebec, Canada)

Coastal dune systems have been extensively studied in various parts of the world, but few investigations have been made in the Subarctic where tempera tures remain relatively low during the short growing season. Here, we repor t the results of a study performed on a subarctic coastal dune system on th e east coast of Hudson Bay, Canada. We determined the spatiotemporal dynami cs of some important substrate characteristics, described the spatial dynam ics of the vascular plant community, and followed temporal changes in the p opulations of the two major plant species, Leymus mollis (Poaceae) and Lath yrus japonicus (Fabaceae), along a toposequence, from the embryo dunes to t he stabilized dune. Thr observed spatial changes in substrate characteristi cs were consistent with those reported in studies of lower-latitude dune sy stems, but they were generally of lesser magnitude. Thr subarctic climate a ppears to have unusual effects on me spatial gradient of substrate salinity and water content. For instance, salinity did not vary along the toposeque nce early in the season while the bay was still partly frozen, bur it showe d a significant gradient during the summer, with lower salinity values on t he stabilized dune. Life-form turnover. from the upper beach to the stabili zed dune,was lower than what has been reported for lower-latitude dune syst ems because of the rarity of annual plant species. Although the density and biomass of Leymus and Lathyrus ramets decreased along the toposequence, bo th species persisted onto the stabilized dune where they were the most freq uent 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, wi th characteristics quite different from those of lower-latitude coastal dun e systems.