Extending sapwood - Leaf area relationships from stems to roots in Coast Douglas-fir

Studies of allometric relationships between leaf area and the cross-sectional area (CSA) of sapwood in the stem have shed light on the structural and functional relationships between water-conducting and photosynthetic tissues. The purpose of this study was to test whether sapwood-leaf area relationships could be extended from stems to roots in coast Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Twelve trees were felled, their stumps were excavated, and the CSA of sapwood and heartwood were estimated for individual roots, entire root systems, and stem section. Root sapwood CSA was greater than sapwood CSA throughout the stem, and the ratio of leaf area to sapwood CSA (A(l):A(s)) was accordingly lower for root sapwood. The relationship between sapwood CSA and leaf area was more variable in roots and at groundline compared to crown base. Root A(l):A(s) decreased with relative tree height (tree height/mean stand height). The strong allometric relationship between leaf area and the CSA of sapwood in the stem generally holds when extended to roots. The greater CSA of sapwood in roots versus stems may reflect differences in their roles in supporting the tree.