Modeling crown volume of lodgepole pine based upon the uniform stress theory

A new model was proposed based on the uniform stress theory to predict crown volume of lodgepole pine (Pinus contorta var. latifolia Engelm.). Uniform stress theory states that trees tend to develop a balance between the size of the stem and the bending moment applied at the stem, to maintain mechanical stability. Bending moment is produced when trees receive a drag created by friction as wind acts on the crown. Data from permanent sample plots of natural stands of lodgepole pine across Alberta, Canada were used for model construction. Mean wind speed was estimated for each plot based on the Canadian Wind Energy Atlas. Diameter at breast height, a measure of leverage from the center of the crown to breast height, and wind speed were used as predictor variables. The new models explained 69.4 and 60.6% of total variation for crown volume and crown radius, respectively, when lodgepole pine trees were sampled from various subregions. Inclusion of relative depth to zero plane displacement and stand relative density resulted in virtually no improvement of the regression. The prediction of crown size with these models could be used for modelling mortality and growth of individual trees, and estimation of crown cover of stands.