MGM is a “height-driven model” that uses provincial site index curves (height-age-site index models) to predict the maximum potential height increment for each tree. Then, trees are ranked by social status (diameter) to determine competition-adjusted height increment, diameter increment, and survival. Dominant trees grow quickly and are more likely to survive. Suppressed trees grow slowly and are less likely to survive. Under this approach, tree-level height, diameter, tree factor*, basal area, and volume are updated annually using competition-adjusted growth information. Then, tree-level characteristics are summarized for each stand to determine stand-level height, diameter, density, basal area, and volume. User-defined merchantability criteria are applied after tree-level growth is complete.
MGM’s growth and survival relationships are based on data from across the western boreal (Table M1). Recent submodel updates have been published in Strimbu et al. (2017), Cortini et al. (2017), Comeau (2021a), Comeau (2021b), and Oboite and Comeau (2021). Regional variants of MGM are also available for Alberta, Saskatchewan, Manitoba, and northeastern British Columbia. These variants allow the use of local species codes, site index curves, and taper equations (Table M2).
Table M1. Data origin for MGM’s height increment, diameter increment, and survival submodels by species. These submodels apply to all regional variants.
|Modeled Species||Height Increment||Diameter Increment||Survival|
|White Spruce||Alberta (Stadt unpubl.)||Alberta (Stadt unpubl.)||Alaska to Manitoba (Cortini et al. 2017)|
|Lodgepole Pine||Alberta||Alberta||Alaska to Manitoba (Comeau 2021a)|
|Jack Pine||Alberta, Saskatchewan, and Manitoba (Strimbu et al. 2017)||Alberta, Saskatchewan, and Manitoba (Strimbu et al. 2017)||Alaska to Manitoba (Comeau 2021a)|
|Trembling Aspen||Alberta (Stadt unpubl.)||Alberta (Stadt unpubl.)||Alaska to Manitoba (Cortini et al. 2017)|
|Black Spruce||Alaska to Manitoba (Oboite and Comeau 2021)||Alaska to Manitoba (Oboite and Comeau 2021)||Alaska to Manitoba (Comeau 2021a)|
Table M2. MGM’s site index and taper equations by regional variant.
|Regional Variant||MGM Region Code||Site Index Curves||Taper Equations|
|Alberta||1||GYPSY Site Index Curves (Huang et al. 2009)||Natural Subregion Taper Equations (Huang 1994)|
|British Columbia||2||British Columbia Provincial Site Index Curves†||BEC Taper Equations (Kozak 1994)|
|Saskatchewan||3||Saskatchewan Provincial Site Index Curves‡||Saskatchewan Provincial Taper Equations (Gal and Bella 1994)|
|Manitoba||4||Saskatchewan Provincial Site Index Curves‡||Saskatchewan Provincial Taper Equations (Gal and Bella 1994)|
† Ministry Recommended site index curves in SiteTools 4.1 (BCMFLNRO 2017). White spruce use Goudie (1984) with an age correction. Lodgepole pine use Thrower (1994). Jack pine use Huang (1997) with an age correction. Trembling aspen use the Nigh et al. (2002a) provincial equation, and black spruce use the Nigh et al. (2002b) provincial equation.
‡ White spruce use Hu and Garcia (2010). Jack pine use Fang (2007). Lodgepole pine use Cieszewski et al. (1993). Trembling aspen use the Nigh et al. (2002a) BWBS equation, and black spruce use the Huang et al. (1997) Central Mixedwood equation.
MGM requires fully enumerated tree-level measurements (i.e. species, height, and DBH) within representative area-based plots (preferred). These tree-level measurements should include trees <1.3m tall. Synthetic “treelists” may also be developed for juvenile stands (Trees < 25 years) using MGM’s Treelist Generator and plot summary statistics. MGM’s Treelist Generator requires trees/ha, maximum height, average height, average DBH, the standard deviation of height, and the standard deviation of DBH for each species.
MGM also requires accurate site index estimates for white spruce, lodgepole pine, jack pine, trembling aspen, and black spruce. Site index may be calculated using local height-age information and the regional site index model(s) from Table M2. For more information about site index estimation, please see the documentation for the regional site index models. Approximate site index estimates may also be determined using local ecosite guides.
Mean Climate Moisture Index (Hogg et al. 2013) from 1981-2010 is also required to run MGM. Climate Moisture Index (CMI) must be calculated using ClimateNA (Wang et al. 2016) Version 6.11 data and the MGM CMI Solver. Please see the MGM CMI Solver section on the Download page to get ClimateNA Version 6.11, the MGM CMI Solver, and instructions to calculate CMI. (Note: Stand-level latitude, longitude, and elevation (m) are required to run ClimateNA Version 6.11. Only ClimateNA Version 6.11 data may be used to calculate CMI for MGM.)
If you are initializing MGM with tree-level measurements, please see the MGM Make Stands section on the Download page for a utility that prepares tree data for MGM, identifies common data errors, and creates MGM Stand Worksheets. The MGM Make Stands User’s Guide also includes detailed instructions and formatting rules to prepare tree data for MGM. Contact firstname.lastname@example.org for additional site index, CMI, and data-handling support.
MGM outputs charts and yield tables that portray averages and totals for the conifer and deciduous components. Tree-level data may also be exported from MGM for in-depth analyses. In addition, MGM can also output stand-level graphics through a linkage to the Stand Visualization System (SVS). Please see the MGM Record Extractor and the MGM Batch Macro sections on the Download page for utilities that covert long-form MGM outputs into a tabular format for data analysis.
* Tree factor is the number of trees per hectare that are represented by each tree in a treelist (i.e. the relative weight of each tree), based on the area of the sample plot. Tree Factor = 10,000 m2 / sample plot area (m2)
Last Modified: December 13, 2021