Water Balance of an Australian Subtropical Rainforest at Altitude: the Ecological and Physiological Significance of Intercepted Cloud and Fog

Abstract

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, south-eastern Queensland. Mean annual rainfall of the site is approximately 1125 mm, but is variable and often less than 900 mm. Tree transpiration rates are low and depletion of the large soil moisture reserves enables extraction for lengthy periods of time, permitting survival during extended dry seasons (May–November). Fog deposition to the forest provides the equivalent of an additional 40% of rainfall to the site as measured using a conventional rain gauge. A frequently wet canopy results in reduced transpiration rates and direct foliar absorption of moisture alleviates water deficits of the upper crown leaves and branches during the dry season. These features of this vegetation type may enable long-term survival at what could be considered to be a marginal rainforest site.