Understanding windthrow: Silvicultural implications

Abstract

Windthrow is a damaging agent that can be of paramount importance in silviculture. Windthrow depends on a number of factors interacting with each other. This paper tries to incorporate windthrow concerns into the silvicultural decision making process by understanding the windthrow process and its interaction with silviculture. The forces involved in the windthrow process are reviewed. The effects of natural factors on these forces are examined and the potential impact of silviculture on these factors is discussed. Some available hazard rating systems are reviewed, trying to underline their applicability in the Eastern Canadian context. Climate affects the severity and frequency of storms. However, wind speed in a particular stand is influenced strongly by local topography. Soil and root characteristics determine the sturdiness of the anchoring system. Many stand-related factors, such as stand height, age, density and stem form, can also exert an influence on the resistance to uprooting. Silviculture can modify the vulnerability to windthrow by acting on these factors. In stands at risk, stripcutting, thinning or the creation of new margins can cause important losses. The impact of stem form also indicates the need for an early control of stand density. Among the hazard rating systems available, the British system seems the most complete but would require some adjustments for use in the Eastern Canadian context. Key words: windthrow, uprooting, blowdown, wind