Natural recovery from accelerated forest ditch and stream bank erosion five years after harvesting of plantation forest on Plynlimon, mid-Wales

摘要

Erosion rates surveyed using 230 erosion pins on 24 occasions over eight years (1994-2001) on forested stream banks, tributaries and forest ditches in the 0.89 km(2) Nant Tanllwyth catchment, part of the Hafren Forest on Plynlimon, mid-Wales, showed statistically significant increases of up to 40 mm a(-1) in mean erosion rates during the two-year period in which environmentally sensitive plot-scale timber harvesting operations took place (1996-97). In the four years following timber harvesting mean erosion rates at all sites recovered to levels that were lower than before the harvesting operations began. This is attributed to increased light levels, following canopy removal, allowing vegetation to colonize exposed banks. There was a statistically significant relationship (p < 0.05) between mean erosion rate in 2000-01 (four years after harvesting) and percentage vegetation cover at erosion monitoring sites in the clearfelled (south tributaries) area though the same relationship did not hold for sites on the mainstream banks or for sites on the north (mature forest) ditch sites. The implications of natural vegetation colonization for management of such streams are discussed. Copyright (c) 2005 John Wiley E Sons, Ltd.