UBC Theses and Dissertations
Impacts of tree improvement programs on yields of white spruce and hybrid spruce in the Canadian boreal forest Ahmed, Suborna Shekhor
Local and regional timber shortages may be ameliorated via planting improved stocks with higher yields. In this dissertation, I addressed an important knowledge gap on the impacts of tree improvement programs on yields of white spruce (Picea glauca (Moench) Voss) and hybrid spruce (Picea engelmannii Parry ex Engelmann x Picea glauca (Moench) Voss) plantations across the boreal and hemiboreal forests of Canada using meta-modelling approaches. In particular, I used meta-data for white and hybrid spruce provenance trials extracted from the literature to: (i) forecast provenance yields over time for broad spatial and temporal extents; (ii) model yields of provenances relative to standard stocks (termed “gain”) over time; and (iii) test alternatives for forecasting each provenance at a location using available repeated-measures data. In the first study, provenance height over time trajectories were modelled by incorporating the effects of climatic variables, provenances and site characteristics into mixed-effects nonlinear models via a random coefficients modelling approach. Height trajectories were strongly affected by planting site and provenance climates, along with planting site characteristics. The height trajectory meta-model was incorporated into an existing growth and yield model, which can be used to predict provenance yields for long temporal and large spatial extents. In the second study, the impacts of the particular gain definition (i.e., selection age, proportion of top performers) were examined using the model from the first study, and one definition was selected. A meta-model of gain as a function of plantation age, planting density, and planting site climate was developed. Planting site climate strongly affected these gain trajectories. The gain definition and trajectory model can be used to evaluate potential gains of using improved white and hybrid spruce stocks. Forecasts are needed to evaluate provenance (or progeny) performance at harvest, often 80 or more years from planting. In the third study, three alternative procedures (population-averaged, subject-specific, and autocorrelation) to forecast repeated measures for a particular progeny at a location were compared and evaluated by virtually removing some repeated measures. The subject-specific forecasts were best with accuracies similar to the measurement precision using standard height measurement devices given five or more prior measurements.
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