Distribution and vitality of xylem rays in relation to tree leaf area in Douglas-fir

The factors that determine sapwood width and volume in a tree are not known . This study asked whether sapwood width is related to a need for stem stor age sites. Experiments were conducted on 12 34-year-old Douglas-fir [(Pseud otsuga menziesii (Mirb.) Franco] trees with a 6-7 fold range of leaf areas and leaf area/sapwood volumes. Because of declining ray frequency but const ant average ray area, ray volume declined for the first 6-10 growth rings, then remained constant, and did not vary with height (breast height vs. 10 nodes from the top). Fewer of the ray parenchyma cells had nuclei in inner than outer sapwood. Inner sapwood had ray parenchyma with smaller rounder n uclei than did outer sapwood, and there was no effect of height. There was a positive relationship between leaf area and the relative volume of ray in outer sapwood at breast height (r = 0.646, p = 0.02), supporting the hypot hesis that Douglas-fir trees with larger leaf areas have higher ray volume than do trees with smaller leaf areas. However, correlations of leaf area/s apwood volume with leaf area at either height were not significant, nor wer e correlations of either leaf area or leaf area/sapwood volume with measure s of ray vitality (nuclear frequency in outer sapwood, or the ratio of nucl ear frequency in the middle/outer sapwood or in inner/outer sapwood). These latter correlations give no evidence that Douglas-fir trees determine thei r sapwood volume based on a need for quantity of vital xylem rays.