Sapwood and inner bark quantities in relation to leaf area and wood density in Douglas-fir

Abstract

The relationships between leaf area and sapwood and inner bark quantities (widths, areas, and volumes) were studied in an attempt to understand the design criteria for sapwood quantity in eighteen 34-year-old Douglas-fir (Pseudotsuga menziesii) trees with a wide range of leaf areas, sapwood areas, and dry masses of leaf, xylem, bark, and branch. Cumulative leaf area increased from the tip to the base of the crown, and then was constant; none of the other variables had the same distribution, and so whereas there were many significant correlations, none of the factors can be related to leaf area in a simple, causal manner. Leaf area/sapwood area was extremely variable from tree to tree at a given height, and within a tree from height to height. Sapwood width was relatively constant from the tip down the stem, supporting the hypothesis that sapwood quantity in this species is related to radial gas diffusion causing either a lethal buildup of CO2 or a lethal depletion of O2 at the sap/heart boundary. However, there was no significant correlation between leaf area and either total sapwood density (dry weight/green volume) or the average latewood density in the sapwood which were used as proxies for radial diffusion rate; further research on actual radial gas diffusion in green wood may be informative.