Influence of soil geography on the occurrence and intensity of gully erosion in the Hengduan Mountain region

Abstract

How to assess gully erosion at large spatial scales is a major challenge, and few previous regional-scale studies have identified the vegetation and topography as the main factors of gully erosion, while little attention has been paid to the effects of soil properties on the regional gully occurrence and intensity. The Hengduan Mountain region has high pedodiversity owing to its significant horizontal and vertical zonation, and gully erosion is an important soil loss process in this region. This study aimed to identify the occurrence, intensity, and key influencing factors of gully erosion in the different soil zones of the Hengduan Mountain region. A total of 2,300 investigation quadrats were randomly set around the region with the size of 1 km × 1 km, and the gully erosion within each quadrat was investigated using Google Earth images. Approximately 25.5 % of the quadrats contained gullies (Qeg), 96.1 % of which was concentrated in 13 major soil groups. The annual temperature, vegetation, and slope were the key factors that influenced the occurrence of gullies in the alpine (>3,700 m a.s.l.), middle mountain (2,000–3,700 m a.s.l.), and low mountain (<2,000 m a.s.l.) soil zones, respectively. The average gully density (GD) and number of gullies (GN) were 2.22 km km−2 and 20.4 in the region, respectively, and both the average GD and GN of each main soil group exhibited significant exponentially decreasing relationships with the soil properties, including the soil organic matter (SOC) and silt content (0.43 < R2 < 0.76, P < 0.001). Within a specific soil zone, the vegetation (NDVI) and topography (elevation and slope) became the key influencing factors on GD and GN. These results show that, at the regional scale, gully erosion is initially controlled by the geographic pattern of the soil. Within the same soil zone, the vegetation and topography (slope and elevation) predominantly influence the occurrence and intensity of gully erosion.