Using trees to manage local and regional water balances

In this chapter we review some of the key aspects to consider when planning revegetation strategies that use trees to manage local and regional water balances. We commence by reviewing how trees use water and how they respond to environmental conditions, including drought, waterlogging and salinity. Understanding these responses are critical when selecting suitable species for managing the water balance in specific landscape locations. After providing definitions of typical ground water systems we introduce the principle of ecological optimality and use this to explore available design options to manage the water balance using trees in dryland catchments (typically, 300—600 mm mean annual rainfall). We conclude that the prospects for lowering watertables by revegetation with perennial vegetation would appear to be best in local groundwater systems, or where annual rates of groundwater inflow are considerably less than annual transpiration losses