Plantations, river flows and river salinity

Summary Large-scale plantation development will exert additional pressure on a water resource system that is already under considerable stress. Tree planting will reduce river flows and recharge to groundwater and, in certain circumstances, may lead to short-term worsening of river salinity prior to any improvement. Reductions in flow will be particularly problematic during dry spells, when water resources are sorely stretched. Most of the likely hydrologic impacts of afforestation can be predicted using current catchment models, but new field data are needed to test and improve their accuracy. Reductions in river flow induced by afforestation can be minimised with careful planning, and various strategies to minimise impact are recommended. It is argued that a regulatory framework needs to be erected to control the development of new plantations in order to complement other policies to preserve water resources, such as the cap on diversions in the Murray-Darling Basin and recently introduced legislation on farm dams. Given the future need to allocate additional river flows to the environment, new allocations of water to plantations should be offset by up-front transfers of water from other uses. We argue that water use by plantations should be factored into the water economy of catchments.