Scientia silvica extension series, no. 23

Knowledge of ecological characteristics of sites and growth of trees on different sites is fundamental for silvicultural decision-making and planning. With the biogeoclimatic ecosystem classification in place in British Columbia, silvicultural management has been given an ecological foundation; however, relationships between growth and site quality have not yet been fully investigated, particularly for high-elevation tree species and sites. One of the contributing factors for this situation is limited knowledge of forest productivity in the high-elevation Mountain Hemlock (MH) and Engelmann Spruce - Subalpine Fir (ESSF) biogeoclimatic zones. Consequently, the management and planning in the high-elevation forest is fraught with difficulties and uncertainties. Current harvest rates of old-growth forest stands and the method and distribution of cuttings in these zones suggest that there needs to be more recognition of the uppermost elevation limit for harvesting. Subalpine fir (Bl), Engelmann spruce (Se), and lodgepole pine (Pl) are important timber crop species in the interior high-elevation forest which is represented predominantly by the subalpine boreal ESSF zone. This zone extends from 49° to approximately 57° N latitude and from approximately 900 to 1,700 m in the north, from 1,200 to 2,100 m in central BC, and from 1,500 to 2,300 m in the south. In view of this relatively wide climatic and edaphic amplitude, a large variability in productivity is expected. The objective of this study was to quantify relationships between site index (height @ 50 yrs @ bh) of Bl, Se, and Pl, and three ecological determinants of site quality: climate, soil moisture, and soil nutrients. Quantitative relationships between site index and these measures provide predictive models for estimating site index. Additionally, we compared the site indices of the three study species to each other to examine their early height growth performance on the same sites.Forestry, Faculty ofForest Sciences, Department ofReviewedFacult