La végétation forestière du secteur nord-ouest de la vallée du Saint-Laurent, Québec

Abstract

The forest vegetation of the north-west section of the St. Lawrence Valley in Quebec was sampled within 68 quadrats. The location of the quadrats was selected by means of a stratified random sampling plan. Ordination (detrended correspndence analysis) and cluster analysis (Twinspan) allowed the identification of 11 forest community types. The ecological factors most closely associated with the distribution of these communities are soil drainage and richness. These two factors are strongly related to the types of surface deposits. Communities dominated by Acer saccharum are found on well drained and nutrient-rich moraines. On the contrary, communities dominated by Acer rubrum and the majority of coniferous forests are found on poorly drained and nutrient-poor soils. Two floristically distinct community types, the Flaxinus-Tilia americana forests and the Tsuga canadensis-Acer saccharum forsts, are found on poorly drained marine deposits with edaphically identical lower horizons. However, the pH and major cation concentrations of the upper soil horizons are much lower under the cover of the hemlock forest than under the cover of the ash-basswood forests.