Wednesday, August 8, 2007 - 3:20 PM

COS 88-6: Structure and physiology of the world's tallest trees, Part 2: Structural indicators of tree growth potential

Stephen C. Sillett, Humboldt State University and Robert Van Pelt, University of Washington.

The rate at which tree height increases slows as trees grows taller.  For example, 60-m-tall Eucalyptus regnans and 70-m-tall Sequoia sempervirens both grow 43 cm yr-1 in height in 2006, but 90- and 110-m-tall trees of the same species at the same sites grew only 27 and 8 cm yr-1, respectively.  Tree growth, however, is far more than an increase in height, because growth occurs across the entire surface of a tree’s cambium.  Accurate quantification of whole-tree dimensions has now been achieved for many individuals of the 3 tallest tree species (S. sempervirens, E. regnans, and Pseudotsuga menziesii).  For example, all branches, limbs, and trunks were non-destructively measured for size, structure, and location on 70 P. menziesii trees 50 to 650 years old in Washington.  Principal components analysis of 24 tree-level variables revealed two orthogonal dimensions of structure that accounted for 71.3 and 12.4 % of the total variation.  The first dimension represented a gradient of overall tree size and structural complexity that was positively correlated with stand age (R2 = 0.99).  The second dimension represented a gradient of tree growth potential that was positively correlated with measured growth of main trunks at breast height during the 5-yr period after trees were mapped (R2 = 0.39).  The strongest determinant of growth potential was the ratio of a tree’s total cambium surface area to projected leaf area.  A tree’s growth potential may thus be unrelated to either size or structural complexity and depend instead on factors related to whole-tree carbon balance.