Abstract
Unlike fire or insect outbreaks, for which a suppression program can be implemented, it is impossible to prevent a windstorm event or stop it while it is occurring. Reducing stand susceptibility to windstorms requires a good understanding of the factors affecting this susceptibility. Distinct species- and size-related differences in stem windthrow susceptibility are difficult to obtain because it is impossible to distinguish their relative effects from those of wind intensity. Using a damage assessment database (60 20-metre radius plots) acquired after an exceptional wind storm in Western Quebec in 2007, we developed an approach in which proportions of windthrown sugar maple poles were used as bio-indicators of wind intensities affecting the plots. We distinguished between single and interactive effects of wind intensity, species, stem size, and local basal area on stem windthrow susceptibility. The best logistic regression model predicting stem windthrow included the wind intensity bio-indicator, species, basal area, and the species by diameter at breast height (DBH, 1.3 m) interaction. Stem windthrow probability generally increased with DBH and decreased with basal area. Species wind-firmness was ordered as: yellow birch > sugar maple = eastern hemlock = American beech > ironwood > basswood = other hardwoods = other softwoods. Our method remained an indirect method of measuring wind intensity and its real test would require a comparison with anemometer measurements during a windstorm. Despite its indirect nature, the method is both simple and ecologically sound. Hence, it opens the door to conducting similar windthrow studies in other ecosystems.
Highlights
Windthrow represents one of the most important catastrophic natural disturbances in shade-tolerant hardwood stands of North America (Bormann & Likens, 1979; Canham & Loucks, 1984; Foster, 1988; Seymour et al, 2002)
It has been generally observed that 1) larger stems are more vulnerable than smaller ones (Peterson, 2007), 2) softwood species are more vulnerable than hardwoods (Foster, 1988; Scott & Mitchell, 2005), and 3) early-successional species are more vulnerable than late-successional species (Foster, 1988; Everham & Brokaw, 1996; Rich et al, 2007)
We argue that it is impossible that a stem windthrow probability decreases with wind intensity; we can no longer consider this model as valid
Summary
Windthrow represents one of the most important catastrophic natural disturbances in shade-tolerant hardwood stands of North America (Bormann & Likens, 1979; Canham & Loucks, 1984; Foster, 1988; Seymour et al, 2002). As with other natural disturbances, windthrow affects ecosystem elements, such as stand structural complexity (Hanson & Lorimer, 2007; Fukui et al, 2011; Kneeshaw et al, 2011) and soil characteristics (Clinton & Baker, 2000; Simon et al, 2011), which have key roles in ecosystem processes (Putz et al, 1983). It affects forestry operations by reducing timber volume availability and by drastically changing harvest schedules, which both bring economic losses. In forests, where many species and diameter classes may be found, such generalities are not sufficient to develop prevention practices that are aimed at decreasing stand susceptibility to windstorms
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