Indices de qualite de station du sapin baumier dans le sous-domaine ecologique de la sapiniere a bouleau blanc humide

Balsam fir (Abies balsamea (L) Mill.) site indices (height at 50 years at stump height) were estimated for the principal ecological types of the boreal and humid balsam fir-white birch climatic subdomain in central Quebec. Ecological types consisted of units homogeneous as to their geomorphological deposit, their drainage class and vegetation dynamic. Mean site index varied from 15.9 m for rich mesic seepage sites to 9.4 m for very thin and poorly drained sites. To the three productivity classes generally used for boreal balsam fir stands in Quebec (Linteau 1955), our results demonstrated the need to recognize a fourth class to distinguish operational groups. Rich mesic seepage sites are clearly more productive than other mesic sites with which they were grouped in the past. The proposed classes are: 1) I+ (SI > 15 m) comprising rich seepage sites; 2) class I-, comprising mesic sites (SI from 13.5 to 15 m); 3) class II (SI from 10.5 to 13.4 m) which comprises sites that possess moderate growth limitations including imperfectly drained sites, thin (< 50 cm) mesic sites and coarse textured dry sites; 4) and class III (SI < 10.5 m) comprising poorly drained sites. Growth studies of four ecological types based on permanent plots of similar densities, show the same relative order in productivity as the one established with their site indices. Mean annual growth of these somewhat understocked plots were 2.9, 2.0 and 1.5 m3/ha/year for classes I+, I- and II respectively. The principal ecological variables that influenced fertility of these boreal sites were drainage class and the presence of seepage. Soil depth and, to a point, soil texture were not very significative variables in this humid climatic zone. It must also be emphasized that all site indices of ecological types showed high variability.