Abstract
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.
Highlights
The Mixedwood Growth Model (MGM) [1] is a deterministic, distance-independent, individual tree-based stand growth model developed for the western Canadian boreal forest
The scatter plots illustrate that, for the mature Alberta Sustainable Resource Development (ASRD) dataset, MGM is generally unbiased, with the amount of scatter around the 1:1 line varying by species group
The only noteworthy concerns are the poor prediction of the minor deciduous component and an overestimate of spruce density (RMB = −11.58%)
Summary
The Mixedwood Growth Model (MGM) [1] is a deterministic, distance-independent, individual tree-based stand growth model developed for the western Canadian boreal forest. As MGM was developed, various growth and mortality relationships were published, typically accompanied by tree-level and stand-level validation [5]. In response to a growing need to characterize yield trajectories for mixed and pure post-harvest stands subject to silvicultural interventions, new and improved growth and mortality functions that better account for the interactions between trembling aspen and white spruce have been developed. This manuscript provides the first peer-reviewed journal publication examining the whole model behavior of MGM, where the component relationships and their interactions are validated at the stand level
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