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Soil Erosion and Slope in Primary and Selectivity Logged Rain Forest in Danum Valley, Malaysia.

Clarke, M. A., 2003, Soil Erosion and Slope in Primary and Selectivity Logged Rain Forest in Danum Valley, Malaysia. Ph.D. thesis (Forestry). University of Wales at Swansea.

Slopewash, a combination of rainsplash and overland flow erosion, is one of the principal soil erosion processes in rainforest areas. Conventional theory suggests that slopewash in rain-forest environments should increase systematically with increasing slope angle. If soil and ground cover variables themselves change with slope angle, however, relationships between erosion and slope angle may be more complex. When rain forest is logged, whether and for how long rills and gullies initiated on heavily distributed and compacted terrain components continue to enlarge is critical. This thesis examines these issues on slopes of 0-40[degrees] in primary and selectively logged (in 1988-1989) rain forest at Danum Valley, Sabah (Malaysian Borneo). Measurements were made of: (a) actual erosions, deposition and changes in surface roughness at over 100 pre-existing and new sites over periods of 1-9 years using the erosion bridge (microprofiler) technique; (b) infiltration capacity, overland flow, splash detachment and overland flow erosion at small (30 x 30 cm.) plots at key sites using a rainfall simulation program; (c) ground cover and soil properties; and (d) overland flow occurrence at free-standing slope sites under natural rainfall conditions. Overland flow on primary forest slopes was found to be more widespread and frequent than previously thought. Tentative relationships between overland flow, erosion and slope angle, to higher angles than previous studies and theory have proposed, are presented. The dominance of extreme rainstorms in the temporal pattern of both primary forest and post-logging erosion is demonstrated. Eight to twelve years after logging, landslides along logging roads in higher slope areas and roads (particularly when unsurfaced) are the main sediment sources to the stream network. Erosion rates at skid trails and logged slopes, however, are now close to those in primary forest. Results highlight the importance of organic carbon within the soil to maintain structure and aggregate stability, and, therefore, to increase soil resistance to erosion (Winzeler database online (
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Publication:Borneo Research Bulletin
Article Type:Book Review
Date:Jan 1, 2004
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