The impact of forest harvesting on water yield: Modelling hydrological changes detected by pollen analysis

Abstract

Forest harvesting practices have been shown to have a hydrological impact that is akin to bushfire regeneration. Fine resolution fossil pollen studies in the upper Delegate River basin, East Gippsland, Australia, have revealed large changes in the reproductive activity of aquatic plants synchronous with the onset of harvesting activities. This paper seeks to establish an explanation for these changes by applying a 2-parameter regional bushfire yield trend model to the wet eucalypt forests above the pollen core site. Using histories of piecemeal coupe (harvesting plot) development, the model was used to reconstruct annual runoff yields between 1970 and 1991 assuming zero harvesting. The results indicated a progressive reduction in simulated annual yields (relative to the zero disturbance scenario) attaining between 20 and 55% loss by 1987/1988. Given the historic rate of harvesting, over a 50% reduction of water yield is expected to occur by 2005 due to factors including enhanced forest transpiration. Such hydrological changes would have significant implications for downstream fauna and flora and for stream dynamics. © 1994 Taylor & Francis Group, LLC.