Total wood, sapwood, and heartwood in branch bases of three conifers

Abstract

Branches were cut from forest-grown, 15- to 85-year-old Picearubens, Pinusstrobus, and Tsugacanadensis trees. For 1139 branches we measured (i) cross-sectional sapwood, colored heartwood, and total wood areas at the branch base, (ii) dry weight of the needles and wood, and (iii) age. Branch age was a poor predictor of wood areas at the branch base. Regression analysis showed that branch wood dry weight was the best predictor of total wood area. Sapwood area was predicted equally well by needle dry weight or as a percentage of total wood area. The prediction was improved by using needle dry weight plus total wood area as variables. The mean ratio of sapwood area to needle dry weight was 0.72 mm2/g for Picearubens, 1.19 mm2/g for Tsugacanadensis, and 1.62 mm2/g for Pinusstrobus. Colored heartwood formed in the center of all branches older than 8 years. Heartwood area was a greater proportion of total wood area in older branches than in younger branches of any given tree, although absolute heartwood area was as variable as total wood area. The best estimates of heartwood area were obtained by subtracting estimates of sapwood area from total wood area. Heartwood area of the oldest branches (8–46 years) from each tree was 7–96% of total wood area at the branch base.