Water Relations of Mountain Ash (Eucalyptus regnans F. Muell.) Forests

Abstract

Measurements of the vertical gradients of water potential and stomatal resistance were made in adjacent mature and regrowth forests of mountain ash to follow diurnal and seasonal behaviour. The vertical gradient of water potential at dawn in either forest was shown to be consistent with the theoretical static head of -0.1 bar m^-1 but the daytime gradients in the regrowth forest were steeper (down to - 0.45 bar m^-1) than in the mature forest which did not fall below -0.27 bar m^-1. Stomatal resistance measurements could not be related to height but, consistent with the water potential data, the leaves of the mature forest had higher resistance to water loss than did those of the regrowth. The observations are discussed in relation to the problems of water supply to the leaves of tall trees and the possible contribution of stomatal control to the established water yield characteristics of mountain ash forests.