The effect of broadleaved woodland on Chalk groundwater resources

The impact of broadleaved woodland on chalk groundwater resources, in Hampshire, UK, was assessed with a comparative study of beech woodland at Black Wood near Micheldever and grass at Bridgets Farm near Winchester. At both sites, parallel estimates of evaporation and detailed studies of the changes in soil water content and the direction of water movement were made. Beneath both sites, a reduction in soil water content was observed during the summer to a depth of 6 m. However, total water potential measurements showed that upward movement of water was only occurring in the upper 2 m of the profile, whilst drainage was occurring below this point. Drainage continued even when soil moisture deficits existed in the upper part of the profile. Seasonal differences between woodland and grass do exist, however annual differences in evaporation and drainage are insignificant. The similarity of evaporation from and drainage below the broadleaved woodland and grass sites contrasts markedly with several other studies that show greater drying below woodland. Unlike other comparisons, this study was made within a large block of woodland and both sites were on chalk. The relevance of woodland size and chalk substrate are discussed.