WATER-BALANCE OF AN AUSTRALIAN SUBTROPICAL RAIN-FOREST AT ALTITUDE - THE ECOLOGICAL AND PHYSIOLOGICAL SIGNIFICANCE OF INTERCEPTED CLOUD ANDFOG

A water balance study of a small subtropical rainforest catchment (10 ha, 1000 m altitude) was conducted at Gambubal State Forest, near the headwaters of the Condamine River, 200 km south-west of Brisbane, sout h-eastern Queensland. Mean annual rainfall of the site is approximatel y 1125 mm, but is variable and often less than 900 mm. Tree transpirat ion rates are low and depletion of the large soil moisture reserves en ables extraction for lengthy periods of time, permitting survival duri ng extended dry seasons (May-November). Fog deposition to the forest,p rovides the equivalent of an additional 40% of rainfall to the site as measured using a conventional rain gauge. A frequently wet canopy res ults in reduced transpiration rates and direct foliar absorption of mo isture alleviates water deficits of the upper crown leaves and branche s during the dry season. These features of this vegetation type may en able long-term survival at what could be considered to be a marginal r ainforest site.