Developing ecoregion-based height-diameter models and reference-age invariant polymorphic height and site index curves for black spruce and jack pine in Manitoba
Eight different height-diameter models, five height prediction models with stand variables as predictors and six height and site index models were selected, examined, compared and developed for black spruce (Picea mariana [Mill.] B.S.P.) and jack pine (Pinus banksiana Lamb.) in Manitoba. Eight different height-diameter models were fitted using nonlinear modeling techniques and compared in each of the five ecoregions in Manitoba: Churchill River Upland (Ecoregion 88); Hayes River Upland (Ecoregion 89); Lac Seul Upland (Ecoregion 90); Lake of the Woods (Ecoregion 91); Mid-Boreal Lowland (Ecoregion 148). Results suggested that the Weibull-type and Chapman-Richards models were the most suitable models. Differences of the height-diameter relationship among and between ecoregions were tested. Testing results suggested that height-diameter models significantly differred between ecoregions, indicating ecoregion-based or 'local' height-diameter models are needed for prediction purposes. The ecoregion-based height-diameter models developed in this study may provide more accurate information for developing forest growth and yield models. Five height prediction models were examined with the addition of stand density variables into the base height-diameter model. Adding stand variable resulted in increased prediction accuracy. Six height and site index models were examined and compared for black spruce and jack pine based on the provincial stem analysis data and the most suitable models were selected for Manitoba and the provincial height and site index prediction tables were produced.