Relationships between tree slenderness coefficients and tree or stand characteristics for major species in boreal mixedwood forests

Abstract

The slenderness coefficients of trees, defined as the ratio of total height to diameter at 1.3m above ground, have been widely used as an index of the resistance of trees to windthrow. For many European coniferous species, slenderness coefficients have been intensively studied, but very little information is available for the tree species in boreal mixedwoods of Canada. By applying correlation analysis and graphical approaches to permanent sample plots data from Alberta, the relationships between slenderness coefficients and tree or stand variables were investigated for the five major species in boreal mixedwoods. Tree slenderness coefficients were found to be negatively correlated with tree diameter at breast height (DBH), height, crown length and age, but positively correlated with stand density level, species composition, and site index values. For three coniferous species, the results were consistent with those found for European coniferous species in literature. However, for the two deciduous species, no similar studies were found for comparison. The graphical results indicated that about 50% of the sampled stands of the data had a slenderness coefficient over 100 and may be at high-risk for windthrow. Models were also developed to predict slenderness coefficient values from (i) DBH only and (ii) DBH and stand variables combined. The negative decay function was found to be the best for this prediction purpose. Potential applications of these models include selecting windfirm residual trees in a partial cutting and developing windthrow hazard rating systems.