Forest age-induced changes in evapotranspiration and water yield in a eucalypt forest

Water yields in a regrowth eucalypt forest were found to increase initially and then to decline below pre-treatment levels during the 16-year period w hich followed the logging of a moist old-growth eucalypt forest in Eastern Australia. Both regrowth and old-growth stands were dominated by Sydney Blu e Gum (Eucalyptus saligna Smith) and Silvertop Stringybark (Eucalyptus laev oyinea R. Baker). Using a paired-catchment approach we observed significant reductions in five of six gauged catchments, and were able to associate th eir magnitude with forest growth rate, canopy cover and soil depth. Regular yield declines were interrupted for a period in some catchments, possibly due to foliar insect attack. Yield reductions of up to a maximum 600 mm per year in logged and regenerated areas were in accord with water yield reduc tions observed in Mountain Ash (Eucalyptus regnans F.J. Muell.) regeneratio n in Victoria. This study therefore represents the first confirmation of th ese Maroondah Mountain Ash results in another forest type that has also und ergone eucalypt-to-eucalypt succession. Baseflow analysis indicated that ba seflow and stormflow both increased after logging, with stormflow increases dominant in catchments with shallower soils. The lower runoff observed whe n the regenerating forest was aged 13-16 years was principally a consequenc e of lower baseflow. (C) 2001 Elsevier Science B.V. All rights reserved.