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 inc lude paired catchment studies, storm-induced mass movement surveys, and sur face erosion plot experiments from both natural and simulated rainfall-runo ff. Road surface erosion data exist only for indurated conglomerate, granit ic, 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 an d gravelled road surface-ditch, cutbank and sidecast. Sediment generated fr om infrequent storm-induced landslides over entire forest road networks ran ge from c. 40 to 8000 t km(-1) road, or one to three orders of magnitude gr eater than combined surface road erosion processes. Young roads tend to hav e greater landslide susceptibility. Despite predicted increases in sediment yields from road surfaces during forest establishment and harvesting activ ities, annual sediment yields from catchments appear to be within natural l evels. Copyright (C) 2001 John Wiley & Sons, Ltd.