The Morpho-Ecological Character of Coastal Sand Dunes on the Northern Tombolo, Les Iles-De-La-Madeleine, Quebec

Abstract

There are marked differences in the morphology and vegetation of the west (Dune du Nord) and east (Dune du Sud) coast dunes of Les Iles-de-la-Madeleine in the southern Gulf of St. Lawrence. The west coast dunes consist mainly of blown-out foredunes succeeded inland by large parabolic dunes. Vegetation is dominated by Ammophila breviligulata with <40% cover, except for the rich flora of cranberry bog communities that occur in deflation hollows at the base of the parabolic scarps. One section of Dune du Nord has more stable, heath-covered dunes that have been extensively modified by deflation, creating a complex topography. On the east coast, the stable dunes support species rich heath and grassland vegetation with higher cover (60-100%). The southern part is a wide complex of progradational ridges, now being overridden on the seaward side by a narrow blown-out strip dominated by A. brevliligulata. To the north, the topography is simple, with A. brevliligulata on the foredune that is quickly succeeded by grassland vegetation on a narrow dune flat. This contrast in morpho-ecological conditions between the two coasts is related to the differences in wave energy described by Owens (1977), wind regime, and existing topography. The present research paper provides a Canadian example of Hesp's (1988) model of the surfzone and wave energy interaction with dune morphology and ecology.