Regional studies support foresters' perceptions that site indices, the measure of forest site productivity in British Columbia, are underestimated in old-growth stands. When old-growth (total age > 140 years) stands regenerate following harvest, site index estimates generally rise. As a result of these regional studies, a province-wide study was initiated to derive adjustments, or corrections, for old-growth site indices with application guidelines for timber supply planning. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), western hemlock (Tsuga heterophylla (Raf.) Sarg.), lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and interior spruce (Picea glauca (Moench.) Voss, P. engelmannii Parry ex. Engelm., and P. glauca x P. engelmannii) were examined in this study. Data came from paired plots installed in old-growth stands and adjacent logged and regenerated (LAR) stands of the same productivity. Site index was estimated for both the old-growth and LAR plots and comparisons were made. Equations to correct the old-growth site index for each species were derived using the two site indices from the plot pairs. No equation was derived for western hemlock due to poor sampling success. The analysis shows that on average, the old-growth site indices were being underestimated. Correction equations and application guidelines are provided. The results of this study should be useful in forest level planning until more reliable methods of estimating site index become available for old-growth stands.
Nussbaum, A.F.. 1998. Site Index Adjustments for Old-growth Stands Based on Paired Plots. British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Working Paper (FLNRORD). WP37
Topic: FLNRORD Research Program
Keywords: Growth, Yield
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