Optimising water co-benefits from forest carbon mitigation

Forests can contribute to climate change mitigation through (1) protection and enhancement of existing carbon stocks, (2) increasing carbon stocks and (3) substituting forest products for energy production or energy intensive building materials. Payments for forest carbon mitigation are occurring under various arrangements in different jurisdictions and the scale of future activity could be large. The likely impacts of broad-scale forest-mitigation on water yield and quality are not understood. Various approaches to water management using carbon mitigation have been examined in south-western Australia, a region with a drying Mediterranean climate and limited potable water supplies. The impacts on water yield and water quality of (1) deforestation and thinning of natural forests, and (2) reforestation of farmland have been studied. Approaches to reforestation have concentrated on Eucalypts and Pinus spp. and include total reforestation of watersheds, integration of strips of trees with farmland and 3–5 year rotations of trees interspersed with cereal cropping. Mitigation has been through both sequestration and bioenergy production and has occurred on both productive and abandoned land. Forest cover profoundly affects water yield and quality, not only through changes in watershed water balance, but also on the release of dissolved salts into the landscape