Interception and water recharge following afforestation: experiences from oak and norway spruce chronosequences in Denmark, Sweden and The Netherlands

The long-term effects of afforestation on hydrological fluxes were investigated using a series of forests of different age planted on comparable soils (chronosequences) in Sweden, Denmark and the Netherlands. Rainfall, throughfall, soil moisture contents and groundwater dynamics were monitored at two oak chronosequences and four spruce chronosequences during a period of one to two years. At all chronosequences, the hydrological fluxes were simulated using a hydrological simulation model. The model was validated on measured throughfall data, soil water contents and Cl fluxes. Afforestation has a clear influence on the water recharge of the considered sites. Water recharge is generally lower under spruce compared to oak. In the spruce stands 530% of the incoming precipitation leads to water recharge to ground and surface water, whereas water recharge in the oak stands ranges between 2035% of the precipitation. In general, water recharge declined with an increase of the stand age. At the oak stands leaching decreased from 35 to 20% of the precipitation in the first 30 years. In the spruce stands the water recharge varied considerable between the four investigated chronosequences but in general, the decline in water recharge was approximately 100-150 mm (10-20%). In both oak and spruce stands, losses by soil evaporation slightly declined. Transpiration slightly increased in the oak stands and transpiration remained fairly stable in the spruce stands. It can be concluded that afforestation leads to a reduction in water recharge compared to agricultural use. This reduction is mainly due to an increase in interception evaporation. The strongest reduction is found when sites are afforested with dense spruce forests. The smallest impact is found in open deciduous forest, which has lower interception evaporation.