Hydrological impact of broadleaved forestry in the British uplands: implications for water use and water quality

The impact of oak woodland on the quantity and quality of drainage waters were examined in upland Wales and compared to the effects of commercial conifer (spruce) forestry and unafforested moorland. Interception losses from broadleaved woodland are lower than those from coniferous forestry but higher than losses from moorland vegetation. This may lead to reduced water yields if extensive broadleaved planting occurs in headwater catchments. Soil water chemistry also differed between the three land uses; primarily due to the enhanced deposition of atmospherically-derived ions on to tree canopies. The concentration and flux of the mobile anions SO₄ and Cl increased in the order bulk precipitation < oak throughfall < spruce throughfall. The enhanced anion loading results in the acidification of soil waters and the mobilization of Al in the two forest soils with the effect being most marked at the conifer site. Whilst broadleaved planting is unlikely to result in the same acidification problems associated with coniferous forestry in upland Britain, care should be taken when planting in acid-sensitive environments.