Windthrow is a natural phenomenon affecting forests throughout British Columbia. Every year hundreds of hectares of trees are blown over in uncut stands and along cutblock boundaries and road allowances. At recurrence intervals of 10 to 20 years, thousands of hectares of forest are windthrown by gale or hurricane force winds. This damage results in considerable loss of revenue and disrupts long-term management plans. Windthrown timber that is not salvaged can also create a fire hazard and can produce habitat conditions that increase the risk of insect epidemics. For example, the spruce bark beetle (Dendroctonus rufipennis) can very rapidly spread from windthrown trees into adjacent stands where it can cause extensive damage.
As integrated management plans for forests become more complex and diverse, the potential effects of wind damage need to be considered more carefully. The feasibility of some treatments may be questionable on certain sites because of a high windthrow hazard. Smaller opening sizes, wildlife corridors, and streamside management zones are often prone to wind damage and require careful layout and edge stabilization treatments in high hazard areas.
The Forestry Commission in the United Kingdom has developed a quantitative windthrow hazard classification scheme for identifying where wind damage is most likely to occur, however, not enough is currently known about wind zones in B.C. forests to implement a similar system. A more qualitative approach toward a windthrow hazard classification system is all that is currently possible, given that very little windspeed data has been collected in our forests and that very little is known about the threshold forces required to overturn the wide range of species and crown classes that comprise stands in B.C. Even so, a classification scheme to stratify degrees of risk of wind damage that is based upon observations, experience, and the physical principles governing the windthrow process should serve as a good starting point to develop management strategies to reduce the risk of windthrow.
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Updated October 15, 2009