The effects of clear-felling established forestry on stream-flow losses from the Hore sub-catchment

The effects on streamflow of clear-felling a substantial part of the established forestry within the Hore sub-catchment at Plynlimon were estimated by a regression comparison of pre-and post-felling rainfall/runoff relationships and by a model based on evapotranspiration estimates from plot studies of established forestry and heather moorland. Increases in streamflow were predicted using both methods, with those using the regression method being substantially larger than those using the model. The largest increases using the regression method occurred about 5 years after the end of felling, and amounted to 10.5% of the measured annual flow. On a seasonal basis, the largest increases using the regression method occurred during the latter half of the year, whilst the model predicted the largest increases during the summer months. These patterns are explained in terms of forest transpiration and canopy interception.