The relationship between tree height and leaf area: sapwood area ratio
- Cite this article as:
- McDowell, N., Barnard, H., Bond, B. et al. Oecologia (2002) 132: 12. doi:10.1007/s00442-002-0904-x
- 1.4k Views
The leaf area to sapwood area ratio (Al:As) of trees has been hypothesized to decrease as trees become older and taller. Theory suggests that Al:As must decrease to maintain leaf-specific hydraulic sufficiency as path length, gravity, and tortuosity constrain whole-plant hydraulic conductance. We tested the hypothesis that Al:As declines with tree height. Whole-tree Al:As was measured on 15 individuals of Douglas-fir (Pseudotsuga menziesii var. menziesii) ranging in height from 13 to 62 m (aged 20–450 years). Al:As declined substantially as height increased (P=0.02). Our test of the hypothesis that Al:As 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 Al:As with increasing height (P<0.05). However, two species (Picea abies and Abies balsamea) exhibited an increase in Al:As with height, although the reason for this is not clear. The slope of the relationship between Al:As and tree height (ΔAl:As/Δh) was unrelated to mean annual precipitation. Maximum potential height was positively correlated with ΔAl:As/Δh. The decrease in Al:As with increasing tree size that we observed in the majority of species may be a homeostatic mechanism that partially compensates for decreased hydraulic conductance as trees grow in height.