The impact of the growth of new plantation forestry on evaporation and streamflow in the Llanbrynmair catchments

Abstract. Annual water balances (1983-1995) for the Cwm and Delyn catchments at Llanbrynmair Moor in mid-Wales have been used to quantify the hydrological effects of the land use change in the Cwm from moorland to forestry. Initially, the actual evaporation (precipitation minus streamflow) of the Cwm catchment declined rapidly relative to the Delyn, due to the disruption of the vegetation by ploughing the ground in preparation for planting the trees. It then increased, more quickly than expected, to greater levels than for the original moorland since in the early stages of forest growth a dense understorey of dwarf shrubs contributed to both interception and transpiration.