Forest Investment Account

Abstract of FIA Project Y051298

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Windthrow risk in mixed-species complex structured stands

Author(s): Coates, K. David
Imprint: Victoria, B.C. : B.C. Ministry of Forests, 2005
Subject: Forest Investment Account (FIA), Windfall (Forestry), Winds, Mathematical Models
Series: Forest Investment Account (FIA) - Forest Science Program


Predicting the effects of forest management on long-term forest dynamics involves a complex suite of factors, especially when partial cutting systems are employed that retain variable levels of canopy trees in time and space. Foresters have long believed that partial cutting increases the risk of windthrow. Our research directly addresses how harvest intensity (% basal area removal) and the proximity to a logging created edge affects risk of wind damage in complex structured mixed-species forests. We used a model selection approach to test competing hypotheses on wind damage risk. The best overall model predicted susceptibility to windthrow as a function of storm severity, tree size, prior harvest level (interacting with tree size) and proximity to an edge. There were clear species and tree size differences in susceptibility to windthrow, however, we found no evidence that harvest intensity, as measured by the level of basal area removal, increased the risk of windthrow for any tree species. Proximity to an edge did increase the risk of windthrow for some species. Our results clearly refute the presumption that risk of windthrow increases as you open up the stand. Introduction Wind events affect all forests and in many is the predominant natural disturbance agent. Quantifying the impact of wind on trees has focused on damage to existing individuals and the recruitment of new cohorts (refs). Wind disturbance studies either view wind events as a natural disturbance agent that needs to be understood in order to predict forest dynamics or as a damaging event that compromises forest management objectives. Different methodological approaches, the range of variability in the intensity of individual storm events, the difficulty of Coates et al. - 3 quantifying storm intensity and the differing site-specific factors involved have resulted in little generalization about how wind events affect individual trees (Everham 1995). Canham et al. (2001) introduced an approach to develop functional relationships between storm severity and susceptibility of trees to windthrow after hurricane events for unmanaged northern temperate forests of northeastern and north-central North America. Their approach took advantage of the inherent variability in storm intensity across an affected area to simultaneously estimate both local storm severity and parameters of a function that quantified species-specific variation in susceptibility to windthrow as a function of storm severity and tree size. The resulting predictive models can be easily incorporated into stand-level forest dynamics models that allow exploration of the consequences of changes in storm frequency, storm intensity, and forest composition on wind damage risk and future forest conditions. We propose to expand this approach to include how forest management, and in particular partial cutting systems that retain variable levels of canopy trees in time and space, affect windthrow susceptibility of individual trees. In northern latitude forests greater attention is being paid to maintaining structural diversity in managed stands (Arnott and Beese 1997; Coates et al. 1997; Aubry et al. 1999; Vyse 1999; McClellan et al. 2000; Harvey et al. 2002; Lieffers et al. 2003). The risk of wind damage, however, in managed structurally complex stands is poorly understood (Moore et al. 2003). Our research directly addressed how partial cutting affected the probability of wind damage in complex structured mixed-species forests. Our specific objectives were to evaluate how: (1) harvest intensity (% basal area removal) and (2) the proximity to a logging created edge affects windthrow risk of individual species.

For further information, please contact K. David Coates, BC Ministry of Forests (

Updated September 08, 2005 

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