ESQUISSE ÉCOLOGIQUE DES COMTÉS DE L'ISLET ET DE KAMOURASKA

Abstract

The vegetation of the region south of the St. Lawrence estuary, more specifically L'Islet and Kamouraska counties, is described in relation to soils and physiographic features.In the first part, a climatic, geologic, geomorphic, and phytogeographic approach is made, summarizing known data for the region. The second part is devoted to the natural vegetation, particularly in its primeval state.On the estuarian lowlands, in the southwest part, the dominant feature is a sugar maple forest which maintains itself in good condition along the coast as far as Saint-Roch-des-Aulnaies. Farther to the northeast, maples are restricted to the Champlain terraces, along the appalachian foothills. The perpetuation of the maple woods is relatively precarious on account of the cold climate. In many cases, maple woods seem to be a relic vegetation. White spruce often reclaims hills where maples have been cut down, especially when the parent-material of the soil has a low calcium content. In the northeast, spruce is the dominant feature of the landscape, on account of the siliceous rocks and a slightly colder climate.On the seashore, the sandy beach facies is characterized by a lyme-grass fringe, and the alluvial mud-flat facies is characterized by salt-water cord-grass. The latter constitutes the original phase of the silty clay soils of the lower plain. In the fresh-water section of the estuary, the alluvial muds, under tidal influence, are characterized by American bulrush and wild rice.Because of its fertile soils, the upper clay plain of the lowlands is entirely under an agricultural régime. Some reliquary fragments of forest allow us to reconstruct the primeval vegetation. In the southwest, a stand, of red maple, associated with American elm, possibly covered these flat and poorly drained soils. In the northeast, there might have been a spruce–sphagnum type of vegetation.The upper Appalachian Plateau has a rolling topography. A maple forest grows on the glacial till of the hills, where limestone delays podsolization. More often a mixed wood occurs, with white spruce, red maple, balsam fir, aspen, and white birch. The depressions are characterized by a black spruce forest, often associated with American larch and eastern white cedar. It seems that red pine and white pine have been characteristic elements of fluvioglacial soils. A coniferous forest is dominant on all sites in the northeastern part of the Plateau.