The Mixedwood Growth Model (MGM) is a deterministic, distance-independent, individual tree growth model developed by the University of Alberta for the western Canadian boreal forest. MGM simulates the growth of five major boreal species—white spruce, lodgepole pine, trembling aspen, black spruce, and jack pine—in pure or mixed stands. The model starts with a tree list or stand summary data. MGM then uses growth and survival functions to project the list of trees into the future. Outputs include yield tables and charts portraying averages and totals for the conifer and hardwood components including estimates of above ground tree biomass. The Stand Visualization System can also be used to provide visual snapshots of stand structure at specific points in time.
MGM is well suited for modelling both natural and managed stands including simple, even-aged stands, mixed species stands, as well as more complex (multi-age/multi-cohort/vertically structured) stands created through partial harvesting practices such as understory protection or other tending practices.
Development of MGM has been supported by industry, provincial and federal governments, and the Forest Resource Improvement Association of Alberta (FRIAA). This work has focused on several key needs:
- Yield estimation in support of forest management plan development (both natural origin and managed stands)
- Estimation of mean annual increment (MAI) from performance survey data
- Developing and evaluating response curves for understory protection and other tending practices
- Rationalizing and understanding the effects of silviculture on managed stand yields
Refining and improving MGM has been an ongoing focus of the MGM Development Team at the University of Alberta. The current version of MGM, released in July 2019, represents a substantial update that includes new climate sensitive tree survival functions, implementation of the “GYPSY” site index curves for Alberta, and support for additional species (i.e. jack pine and black spruce). This release has undergone extensive validation and behavioural testing and is currently undergoing a formal review by the Government of Alberta.
Current model development includes enhancement to model tree improvement, validation and/or re-calibration of the tree list generator, inclusion of a white spruce release response function and an update to the maximum size-density functions.
User support is available and training workshops are offered. periodically. Contact Mike Bokalo (email: Mike.Bokalo@ualberta.ca) for support, for information on upcoming workshops, or to arrange a workshop.
The model is publicly available. Information on downloading and installing MGM, along with model documentation and other related materials can be found on the MGM website at http://www.mgm.ualberta.ca.
Figure 1. Conifer and deciduous mean annual increments (MAIs) at age 90 based on MGM simulations initiated using age 12-15 data from 299 WESBOGY long term study plots grouped by aspen (Aw) and spruce (Sw) treatment densities.
PC April 22, 2020