Conducting sapwood area, foliage area, and permeability in mature trees of Piceasitchensis and Pinuscontorta

Abstract

The relationships between foliage area and sapwood area between trees and within the crowns of 20 P. sitchensis (Bong.) Carr., provenance Queen Charlotte Island, British Columbia [Canada] (10 in a control plot and 10 in a plot fertilized with K and P 8 yr before harvest) and 10 P. contorta Dougl., provenance Ladysmith trees were examined [Scotland, UK] using a physiological analysis based on Darcy''s law. Foliage area index on the fertilized P. sitchensis plot was higher than on the control. The variation of foliage area density with depth in the canopies followed a normal distribution. Relationships between foliage area and sapwood basal area were linear but the slopes were different for the 2 spp. There was no significant difference between the control and fertilized P. sitchensis trees. The relationship between foliage area and the product of sapwood area and permeability was linear and data from the 3 plots fell on the same line. Sapwood area, permeability, and their product decreased with depth through the crowns of the trees. Within the crowns, relationships between cumulative foliage area and sapwood area, and between cumulative foliage area and the product of sapwood area .times. permeability were different with species and treatment. A single linear relationship resulted when the product of cumulative foliage area above an internode .times. the internode length was plotted against sapwood area .times. permeability for the internode. This suggests that it is the drop in potential across a node and internode rather than the gradient of potential across the internode that is related to the flux of water through tree crowns. The data support the hypothesis that the relationship between foliage area and sapwood area depends on permeability of the sapwood and the local climate through its influence on transpiration rate, particularly via average water vapor pressure deficit of the air and stomatal conductance.