To establish a link between ecological site quality and forest productivity in the Sub-Boreal Spruce zone of the Prince Rupert Forest Region, site index and site data from 93 lodgepole pine stands and 77 interior spruce stands were obtained and analyzed. The stands studied were distributed across 2 climatic regimes (biogeoclimatic subzones), 8 soil moisture regimes, and 5 soil nutrient regimes. These regimes were used as categorical variables to stratify the stands and in the regression analysis. Some combinations of soil moisture and nutrient regimes were poorly represented.
Site index of lodgepole pine and interior spruce changed with soil moisture and nutrient regimes, but not with climate. The pattern of change in site index in relation to soil moisture was similar for both species, but differed in relation to soil nutrients. Site index of interior spruce was significantly lower than that for lodgepole pine on nutrient-deficient sites. Of the six types of regression models developed, the edatope model showed strong relationships between site index and soil moisture and nutrient regimes (R 2 >0.80, SEE <1.6 m) for both lodgepole pine and interior spruce. This model was used to draft site index isolines which were then superimposed onto edatopic grids. Estimates of soil moisture and soil nutrient regimes were found to be good predictors of lodgepole pine and interior spruce site index over a large area. Additional sampling of sites that were poorly represented and testing against independent data sets are recommended.
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Updated May 29, 2009