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

The slenderness coefficients of trees, defined as the ratio of total height to diameter at 1.3 m above ground, have been widely used as an index of th e resistance of trees to windthrow. For many European coniferous species, s lenderness coefficients have been intensively studied, but very little info rmation is available for the tree species in boreal mixedwoods of Canada. B y applying correlation analysis and graphical approaches to permanent sampl e plots data from Alberta, the relationships between slenderness coefficien ts and tree or stand variables were investigated for the five major species in boreal mixedwoods. Tree slenderness coefficients were found to be negat ively correlated with tree diameter at breast height (DBH), height, crown l ength and age, but positively correlated with stand density level, species composition, and site index values. For three coniferous species, the resul ts were consistent with those found for European coniferous species in lite rature. However, for the two deciduous species, no similar studies were fou nd for comparison. The graphical results indicated that about 50% of the sa mpled stands of the data had a slenderness coefficient over 100 and may be at high-risk for windthrow. Models were also developed to predict slenderne ss coefficient values from (i) DBH only and (ii) DBH and stand variables co mbined. The negative decay function was found to be the best for this predi ction purpose. Potential applications of these models include selecting win dfirm residual trees in a partial cutting and developing windthrow hazard r ating systems.