Sediment pathways in a tropical forest: effects of logging roads and skid trails

Abstract

AbstractSignificant erosion occurred from recently constructed forest logging roads and skid trails in a small headwater catchment in Peninsular Malaysia. Soil loss was estimated by measuring dimensions of all significant rills and gullies along the road, as well as by measuring height of preserved soil pedestals in sidecast and fill material and on skid trails. Estimates of surface erosion from logging roads and skid trails were 272 ± 20 t ha−1 year−1 and 275 ± 20 t ha−1 year−1 respectively. However, owing to lack of connectivity of skid trails to the stream, much of the sediment mobilized on skid trails was stored either on adjacent hillslopes or the trails themselves, rather than being transported to the stream system, as was the case for the road. Steeper skid trails (>20% gradient) had slightly higher erosion rates (320 ± 24 t ha−1 year−1) than trails with gentler gradients (245–264 t ha−1 year−1). Some 60% of the soil loss on logging roads comes from erosion of the running surface. Disturbed cut and fill material along the road supplied the remaining 40% of the soil loss from roads. Roads and skid trails had no designed drainage systems; runoff discharged onto the hillslope at 25 major discharge nodes from the logging road (690 m total length) and at 34 nodes from skid trails (2300 m). Sediment pathways were either fully or moderately connected to headwater channels at 64% of the logging road nodes, but at only 26% of the nodes emanating from skid trails. A detailed sediment budget revealed that 78% of the soil loss from the road system (including log landings) was delivered to the stream in the first 16 months after logging began. Most (90%) of the deposition from skid trails occurred below just three discharge nodes. Runoff from and onto skid trails often exacerbated the sediment connectivity to channels. Clearly, sediment discharge from logging roads was more highly connected to the stream than discharge from skid trails. Once in the channel, much of this sediment was temporarily stored in the floodplain and behind woody debris. Copyright © 2004 John Wiley & Sons, Ltd.