from Part V - Cloud forest water use, photosynthesis, and effects of forest conversion
Published online by Cambridge University Press: 03 May 2011
ABSTRACT
Hydraulic characteristics of the common Hawaiian tree species, Metrosideros polymorpha, were compared in cloud forest, dry forest, bogs, and along an altitudinal gradient to understand how habitat plays a role in the evolution of plant hydraulic features. Plants of intermediate altitudes within the cloud forest zone suffered 50% reduction of hydraulic conductivity at higher water potentials than did low-and high-altitude plants, indicating that plants from cloud forest habitats are more susceptible to cavitation. Xylem area per unit leaf area increased with altitude, and was relatively high in dry forest and bogs, suggesting that more xylem is necessary to support leaf gas exchange in plants stressed by drought, waterlogging, or high altitude. Further, transpiration, leaf traits, and forest structure were examined at an extremely wet cloud forest site (>5000 mm of precipitation per year) to evaluate physiological limitations associated with waterlogging as a mechanism for reduced canopy leaf area. Leaf area index (LAI) and stand basal area were lower on level, waterlogged sites than on moderately sloped, well-drained sites. Stand transpiration varied from 79–89% of potential evapotranspiration (PET) for sloping sites and from 28–51% of PET for level sites. Leaf area index was a good predictor of stand transpiration. Whole-tree transpiration was lower at level sites with waterlogged soils, but was similar to that for trees on level sites when normalized by leaf area. […]
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