Assessing land degradation as the impact of deforestation due to the expansion of oil palm plantation in Rokan Hulu, Riau

Abstract

In Riau province, Sumatra much of the deforestation has been associated with the extension of oil palm plantations on soils that are particularly vulnerable to soil erosion and land degradation. Most of the deforestation in Riau occurred on highly erodible Ultisols, on slopes steeper than 7 degrees and under a high and erosive rainfall regime, which, when taken together can result in a high risk of soil erosion and land degradation. Land degradation depends on soil erodibility, climatic factors expressed as rainfall erosivity, and slope conditions. This research aims to determine the impact of deforestation, particularly on the risk of land degradation. The rate and extent of deforestation was determined using remote sensing data published from reliable sources. The risk of land degradation assessed through soil erosion analysis in Riau Province by using published soil survey information and data to calculate soil erodibility and by combining this with other factors such as rainfall erosivity for the region and an assessment of slope factors. The estimation of the risk of land degradation has been achieved by a quantitative assessment of the potential soil erosion loss by applying the USLE (Universal Soil Lost Equation) to discrete land facets within Riau Province. The result of this study indicates that slight and moderate risk erosion class were dominant over most of the study area with 239,389 ha (47.92 %) and 129,391 ha (26.23 %), respectively. About 25% of the study area was predicted to suffer from erosion risk of more than 60 ton/ha/year.