Forest Investment Account

Abstract of FIA Project 6067003

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Windthrow Hazard Mapping using GIS, Weyerhaeuser West Island Timberlands

Author(s): Mitchell, Steve
Subject: British Columbia, Forestry, Silviculture/Forest Management Systems, Technology/GIS/Modeling/Remote Sensing
Series: Forest Investment Account (FIA) - Land Base Investment Program - Innovative


WIT: Damaging winds impact seriously on the intent and implementation of integrated resource planning. In BC, the coastal region is most affected and there has been a history of wind damage in Weyerhaeuser's operations on Vancouver Island and the adjacent mainland. Windthrow occurrence along cutblock boundaries was mapped using aerial photographs. Using ArcView Geographic Information System (GIS), buffers 25m deep were created adjacent to cutblocks harvested between 1990 and 2001 for 6 sample mapsheets. Each of these buffers was divided into 25*25m segments. A total of 22,000 forested segments were obtained and used to study the relationship between cutblock edge windthrow and other stand level variables within the West Island Timberlands operating area (Port Alberni). Nineteen percent of segments had at least 40% of segment area damaged and 20% loss of canopy. Douglas-fir and cypress dominated stands suffered the least loss from windthrow compared to those dominated by other species. Hemlock stands had the highest loss. Segments with high topographic exposure, windward facing boundaries, boundary projections, older stands, and stands with higher site index were more likely to be wind damaged. Regression models were fit using stand, site, ecosystem, wind and management variables to predict probability of damage. Variables representing fetch with retention patches accounted for are included. The best-fit models had a predictive accuracy of 72%. One of these models was selected to produce windthrow hazard maps for the operating area. A dataset was built for segments on the perimeter of retention patches. Severe damage was more frequent in larger patches, but was less frequent in segments on the lee side of patches.

For further information, please contact Steve Mitchell, University of British Columbia (

Updated September 08, 2005 

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