The Relationship between Tree Height and Leaf Area: Sapwood Area Ratio

The leaf area to sapwood area ratio ($A_{1}\colon A_{\text{s}}$) of trees has been hypothesized to decrease as trees become older and taller. Theory suggests that$A_{1}\colon A_{\text{s}}$must decrease to maintain leaf-specific hydraulic sufficiency as path length, gravity, and tortuosity constrain whole-plant hydraulic conductance. We tested the hypothesis that$A_{1}\colon A_{\text{s}}$declines with tree height. Whole-tree$A_{1}\colon A_{\text{s}}$was measured on 15 individuals of Douglas-fir (Pseudotsuga menziesii var. menziesii) ranging in height from 13 to 62 m (aged 20-450 years).$A_{1}\colon A_{\text{s}}$declined substantially as height increased (P=0.02). Our test of the hypothesis that$A_{1}\colon A_{\text{s}}$declines with tree height was extended using a combination of original and published data on nine species across a range of maximum heights and climates. Meta-analysis of 13 whole-tree studies revealed a consistent and significant reduction in$A_{1}\colon A_{\text{s}}$with increasing height (P