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The relationship between tree height and leaf area: sapwood area ratio
N McDowell1, H Barnard2,3, B Bond4
1Department of Forest Science, Oregon State University, 97331, Corvallis, OR, USA. nate.mcdowell@orst.edu.
Oecologia
|May 27, 2017
Summary
The leaf area to sapwood area ratio (Al:As) decreases as trees grow taller, a finding consistent across multiple species. This ratio adjustment may help trees maintain hydraulic function despite increased height.
Area of Science:
- Plant physiology
- Forest ecology
- Biophysics
Background:
- The leaf area to sapwood area ratio (Al:As) is a key plant trait influencing water transport.
- Theory predicts Al:As must decrease with tree height to overcome hydraulic limitations.
Purpose of the Study:
- To test the hypothesis that Al:As declines with increasing tree height.
- To investigate the relationship between tree size, hydraulic conductance, and Al:As across multiple species.
Main Methods:
- Measured whole-tree Al:As in Douglas-fir across a wide range of heights and ages.
- Conducted a meta-analysis of 13 published whole-tree studies on Al:As and tree height.
- Analyzed the relationship between Al:As slope, precipitation, and maximum potential height.
Main Results:
- Al:As significantly declined with increasing height in Douglas-fir.
- Meta-analysis confirmed a consistent reduction in Al:As with height across most species studied (P<0.05).
- Two species showed an increase in Al:As with height; the slope was unrelated to precipitation but correlated with maximum potential height.
Conclusions:
- The decrease in Al:As with tree height is a common phenomenon, likely a homeostatic mechanism.
- This adjustment may compensate for reduced whole-plant hydraulic conductance in taller trees.
- Understanding this relationship is crucial for predicting forest dynamics and water use efficiency.
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