The relation between geomorphology and forest community types of the Haut-Saint-Laurent, Quebec

Abstract

The highly disturbed community types of the Haut-Saint-Laurent in southern Quebec were classified using an hierarchic approach with three levels: geomorphology, pedology and vegetation. Considered as distinct entities were, on the one hand, the herbaceous and shrub species that made up ecological groups as defined by Meilleur et al. (1992), and, on the other hand, individual tree species. Great importance was given to geomorphological variables because they are one of the most stable ecological factors of the region. We identified 47 community types from 452 sites sampled, based on a TWINSPAN analysis of the vegetation data. Binary Discriminant Analysis (BDA) showed the importance of disturbance on community composition, especially for sites included in the forest mosaic. Other important abiotic parameters included morphogenic features, topography and drainage. The BDA showed that 24 community types were found to be significantly associated with at least one morphogenic feature. The results indicate that the Beech-Hemlock association is a more stable state for mesic sites than the often cited Sugar Maple with Hickory. On glacial deposits, the presence of Thuja occidentalis is significantly associated with grazing practices. The other 23 community types are not significantly associated with any morphogenic features. On one hand, these types tend to be ubiquitous on different deposits with the same drainage class and reveal that their composition was altered through disturbances. On the other hand, some community types are more associated with microclimates as is the case of Sugar Maple with Striped Maple, or with their ecological amplitude limits as is the case of Sugar Maple with Ironwood and Aspen or Sugar Maple with Red Maple and Black Ash. A classification of the stands, given the high number of disturbed communities within the territory, appears difficult to use as a basis for ecological units.