Empirical modelling of windthrow risk and hazard mapping using Geographic Information Systems

• Main Author: Lanquaye, Clayfield Odarkor
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/13989

There has been a history of wind damage (windthrow) in Weyerhaeuser's North Island Timberlands (NIT) north of Campbell River on Vancouver Island, British Columbia. Identification of the location and type of stands most at risk is needed to target mitigative measures. This study investigated the relationship between windthrow damage along cutblock edges and stand, ecosystem, management, wind and topographic variables. Windthrow occurrence along cutblock boundaries was mapped using aerial photographs. Using ArcView Geographic Information System (GIS), a total of 22,304 forested segments were obtained and used to study the relationship between cutblock edge windthrow and other stand level variables within NIT. Damage declined from 13% of segments within the first 25m of cutblock boundaries to 1 % of segments in the band between 50 and 75m from the cutblock boundary. Western redcedar (Thuja plicata Donn) dominated stands suffered the least loss from windthrow compared to those dominated by other species. The proportion of segments damaged increased with topographic exposure, mean annual windspeeds, boundary exposure to the south, soil fertility, block size and stocking. Logistic regression models were fit using stand, site, ecosystem, wind and management variables to predict probability of damage. The best-fit models had a predictive accuracy of 68-72%. One of these models was selected to produce a windthrow hazard map for the NIT. A comparison between the resultant model and one developed in an earlier study 75 km to the north revealed that empirical models are reasonably portable within this area of Vancouver Island.