Productivity of black spruce and Jack pine stands in Quebec as related to climate, site biological features and soil properties

The relationships between site quality indices (SQI) (estimated height at age 50) of black spruce and Jack pine and site characteristics were investigated over a large territory in the boreal forest of Quebec. The relationships with degree-days (DD) and parent material, which are considered as permanent site factors, were significant for both species. Linear regressions with these two parameters as independent variables explained about 40% of the variability in site quality indices for black spruce and Jack pine. The addition of soil chemistry and biological data to this model indicated a significant contribution of exchangeable Mg concentrations or Al:CEC molar ratios in the forest floor and lichen cover to the prediction of site quality indices. Inclusion of these variables increased the model R^2 up to 60% for both species. Whether these variables reflect permanent site conditions or conditions related to the history of the sites is unknown.