Site index adjustments for old-growth stands based on veteran trees

Regional studies are supporting foresters’ perceptions that the site indices of British Columbia’s old-growth stands are being underestimated. A province- wide paired-plot study resulted in old-growth site index adjustments for coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), interior spruce (Picea glauca (Moench.) Voss, P. engelmannii (Parry) Engelm., and P. glauca x P. engelmannii), and interior lodgepole pine (Pinus contorta var. latifolia Dougl.). The objective of this study is to develop adjustments for species not covered in the provincial project. Adjustments for the species in the provincial project are also derived for comparison purposes. The data for this study come from temporary and permanent sample plots with a veteran and a main stand component. The site indices for the two components were estimated and an adjustment equation for each species was derived using the two site indices in a linear regression analysis. The veteran component represents an old-growth stand and the main stand component represents a managed stand. The analysis showed that the veteran site indices were being underestimated. Some guidelines on the application of these adjustments to old-growth site indices are provided.