The Role of Forest Fragmentation in Accelerating Soil Erosion in Mountainous Basin

Abstract Soil erosion is one of the most severe global threats to watershed sustainability. Fragmented forests lead to increased surface runoff, accelerating erosion, particularly in watersheds characterized by rugged terrains. Therefore, understanding the impact of forest fragmentation on soil erosion rate is crucial for effective forest and watershed management. This study applies the revised universal soil loss equation model to predict the annual average soil erosion rate and then combine it with the sediment delivery ratio to estimate sediment yield. Forest fragmentation is analyzed using a land use/land cover map derived from Landsat image, which classifies the landscape into five categories: interior, patch, transitional, edge, and perforated. The results show that the Zhoushui River Basin experiences a severe impact from soil erosion, with a mean rate of 108.47 t ha −1 yr −1 and a mass sediment load of 206.03 × 106 t yr −1 downstream, despite forests covering 76.04% of the total area. The RUSLE-SDR model shows predicted sediment yields that align closely with observed sediment discharges in the sub-basins, with a percent bias ranging from 0.75% to 24.96%. Soil erosion is particularly severe in areas affected by forest fragmentation, averaging over 100 t ha −1 yr −1 . Among the different fragmentation classes, patches experience the highest erosion rates at 266.18 t ha −1 yr −1 , followed by transitional areas at 225.72 t ha −1 yr −1 . Interior areas have the lowest erosion rate at 114.10 t ha −1 yr −1 , while edge and perforated classes experience rates of 136.63 and 188.76 t ha −1 yr −1 , respectively. These findings would be helpful for prioritizing forest management across different forest fragmentation classes. Given the complex factors influencing on soil erosion, it is necessary to implement additional control measurements along with forest planting, particularly engineering solutions, to effectively mitigate soil erosion and sediment loads.