Modelling the soil moisture deficits developed under grass and deciduous woodland: The implications for water resources

The area of deciduous woodland in the UK is increasing as a result of Government policy, and studies suggest that this might result in reduced streamflow and groundwater recharge. Measurements of soil water content were carried out (a) at a site on a sandy loam soil, (b) under land covers of grass, and (c) in deciduous woodland. The data show that both the field capacity and wilting point of the soils were much less under the woodland than those under grass. In 1997, soil moisture deficits were developed down to a depth of 1 m under grass and in excess of 3 m under the deciduous woodland. A simple daily water-balance model was able to simulate the observed soil water contents and emphasised the importance of interception losses from the deciduous woodland canopy For a 25-year period, the model predicted that the mean annual runoff and soil drainage for the woodland was less than half those for grass.