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There are three basic approaches to windthrow risk assessment: observational, mechanical and empirical. The diagnostic framework used in the FS 712 Field Cards and introduced in Lesson 2 of this course extends the observational approach by adding calibration and feedback steps. This makes it semi-empirical and semi-quantitative.

Using the capabilities of GIS for assembling large datasets, empirical models of windthrow risk can be built using stand-level information contained in forest cover maps and topographic maps.

Once models are built, they can be entered into the GIS for production of landscape-level maps. The following screens describe the process and results of a study on northern Vancouver Island. Read the paper by Mitchell, Hailemariam and Kulis for background on this study.

The purpose of presenting this method in this course is to make participants aware of the potential of using GIS to build empirical models and maps, and to set the stage for a development planning exercise. Most forest companies are now using GIS for drafting, but few are using them for analysis. Even without building empirical models, maps of windthrow patterns are very useful for observational evaluation of windthrow risk, and can contribute to improved planning by identifying orientation and recurrence of damaging winds, and locations subject to recurring damage.

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