TAG is a whole-stand growth and yield model for trembling aspen, developed with data from British Columbia, Alberta, Saskatchewan, and Manitoba. Its structure is similar to that of the interior spruce model at http://forestgrowth.unbc.ca/scube, and the one for loblolly pine at http://forestgrowth.unbc.ca/lobdyn. Published in:
García, O. Building a dynamic growth model for trembling aspen in Western Canada without age data. Canadian Journal of Forest Research 43(3), 256-265, 2013. DOI 10.1139/cjfr-2012-0366. Preprint.
There is also a supplementary info file in the Journal website. A more detailed report with computer code, etc., is available here.
The spreadsheet version runs on Microsoft Excel, LibreOffice, and OpenOffice. Use the link above to download a zip archive containing the spreadsheet, a README text file, and pdf Help. To run, unzip somewhere, and execute TAG.xls. You may have to lower macro security to Medium, and allow Enable Macros when prompted. Once the spreadsheet opens, click on HELP at the top for instructions.
Here are two short video tutorials: Demo 1, Demo 2 (made with Wink). These show the loblolly pine model, but are also applicable to TAG.
The TAG spreadsheet is open-ended, in that you can use the standard tools to extend it with special-purpose entries, to produce graphs, or to customize it in other ways.
A very different implementation uses the boxes and arrows of System Dynamics. Here is a model file that can be loaded into the free version of Vensim. This can be useful for experimentation, and may help to better understand the structure of the model. The software can display graphs or tables for any of the variables, with inputs and parameters being changed through the keyboard or graphical sliders in real-time. This introduction to the theory might be useful.
The site index / height growth component is also available in the SiteSheets program.
The software is open source (MIT license).
Please contact Oscar García (firstname.lastname@example.org) for any questions or comments.
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