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We evaluated the Mixedwood Growth Model (MGM) at a whole model scale for pure and mixed species stands of aspen and white spruce in the western boreal forest. MGM is an individual tree-based, distance-independent growth model, designed to evaluate growth and yield implications relating to the management of white spruce, black spruce, aspen, lodgepole pine, and mixedwood stands in Alberta, British Columbia, Saskatchewan, and Manitoba. Our validation compared stand-level model predictions against re-measured data (volume, basal area, diameter at breast height (DBH), average and top height and density) from permanent sample plots using combined analysis of residual plots, bias statistics, efficiency and an innovative application of the equivalence test. For state variables, the model effectively simulated juvenile and mature stages of stand development for both pure and mixed species stands of aspen and white spruce in Alberta. MGM overestimates increment in older stands likely due to age-related pathology and weather-related stand damage. We identified underestimates of deciduous density and volume in Saskatchewan. MGM performs well for increment in postharvest stands less than 30 years of age. These results illustrate the comprehensive application of validation metrics to evaluate a complex model, and provide support for the use of MGM in management planning. [ABSTRACT FROM AUTHOR]

Abstract: In 1992, the Western Boreal Growth and Yield Association (WESBOGY) began a long-term study to evaluate the dynamics of regenerated aspen (Populus tremuloides Michx.)—white spruce (Picea glauca (Moench) Voss) mixedwood stands following manipulation of aspen to a range of densities. In this study six levels of aspen (0, 200, 500, 1500, 4000stemsha−1 and natural) and three levels of spruce (0, 500 and 1000stemsha−1) densities have been created. Data from four locations demonstrate substantial variation in initial aspen densities following clearcutting of aspen dominated stands. After 9 years densities begin to converge with the highest rates of mortality associated with high starting densities. A model was developed that shows a significant relationship between the proportion of trees surviving to the end of a year and the density at the beginning of the year. Size-density relationships based on quadratic mean root collar diameter, mean tree volume and mean tree height are presented. Three to four years following spacing of aspen to densities ranging from 200 to 4000stemsha−1 there were no significant effects of density on aspen size. In addition, spacing of the aspen had no significant effect on spruce height at year 9 (3–4 years after spacing), but spruce root collar diameter (RCD) was significantly smaller in the unspaced compared to the spaced plots. The ratio of height to root collar diameter (HDR) for white spruce showed a significant and clear response to aspen density and increased with increasing aspen density. [Copyright &y& Elsevier]

A large number of height-diameter functions were evaluated using felled tree data for white spruce (Picea glauca (Moench) Voss) grown in Alberta's boreal forests. The logistic-type function was found to produce the most satisfactory fits. Residual analyses were conducted to identify the error structure of the model. A weighting factor of w[sub i] = 1/Ĥ[sup 3/2, sub i] was found appropriate for satisfying the equal error variance assumption. Regional differences in the height-diameter models were examined and tested using the nonlinear extra sum of squares method. It was found that height-diameter models were different among different ecoregions. Incorrectly applying a height-diameter model fitted from one ecoregion to different ecoregions resulted in overestimations between 1.10% and 29.05%, or underestimations between 1.92% and 21.92%. [ABSTRACT FROM AUTHOR]

Investigates the development of an individual tree-height increment models for white spruce and aspen growing in the boreal mixed-species in Alberta. Selection of a base height-increment function; Incorporation of tree and stand level variables using the parameter prediction approach.

Investigates the relationships between tree slenderness coefficients and tree characteristics in boreal mixedwood forests. Application of correlation analysis and graphical approaches; Negative correlations of tree slenderness with heights, crown length and age; Percentage of tree slenderness coefficient values.