Influence of Leaf Area and Canopy Structure on Size-Density Relations in Even-Aged Lodgepole Pine Stands

The hypothesis that size-density relationships result from the distribution of constant amounts of population leaf area among varying numbers of trees per unit area, was modified to include the influence of population density on canopy structure. The modification was made possible with the constant-stress model of stem formation. The modified hypothesis was tested in unmanaged, even-aged stands of lodgepole pine (Pinus contorta var. latifolia Engelm.) in northern Utah. Using mean leaf area per tree, mean live-crown length, and mean live-crown ratio, the constant-stress model was used to calculate hypothetical values of mean quadratic diameter (Dq) for those stands with equilibrium levels of leaf area. Linear regression showed that the hypothetical and measured values of Dq were not significantly different (P=0.29). Consequently, the modified hypothesis duplicated the observed relationship between Dq and number of trees per hectare (N) for these stands. Using the modified hypothesis, canopy structure is shown to be responsible for the curvilinear relationship between the log of Dq and the log of N observed for these stands