Forest road erosion in New Zealand: Overview

New Zealand research relating to erosion impacts of plantation forest roads, tracks and landings has been carried out since the mid-1970s. Methods include paired catchment studies, storm-induced mass movement surveys, and surface erosion plot experiments from both natural and simulated rainfall-runoff. Road surface erosion data exist only for indurated conglomerate, granitic, schist and pumice terrains, with annual sediment yields up to 15 kg m(-2) for a range of treatments and source types including graded, ungraded and gravelled road surface-ditch, cutbank and sidecast. Sediment generated from infrequent storm-induced landslides over entire forest road networks range from c. 40 to 8000 t km(-1) road, or one to three orders of magnitude greater than combined surface road erosion processes. Young roads tend to have greater landslide susceptibility. Despite predicted increases in sediment yields from road surfaces during forest establishment and harvesting activities, annual sediment yields from catchments appear to be within natural levels. Copyright (C) 2001 John Wiley & Sons, Ltd.