The distribution of and factors influencing the vegetation in a gully in the Dry-hot Valley of southwest China

The Dry-hot Valley of the Jinsha River in southwest China is an ecologically fragile zone in which gully erosion is one of the most important environmental problems due to the high sediment yield from the gully. The vegetation, which impacts the erosion processes of the gully, is important to the ecological environment. In this study, we investigated the vegetation in gully n1 of Yuanmou County, which is a typical area of the Dry-hot Valley. A total of 82 vegetation quadrats on a relatively gentle section of gully n1 (slope was mostly less than 45°) and nine points on a steep slope (slope higher than 70°) were investigated in 2012. The vegetation indices, in addition to the soil conditions and topography, were measured through field investigations and the gully Digital Elevation Model (DEM). On the gully sidewall, almost no vegetation grew in the steep slope, whereas the slope gradient and the slope aspect exhibited a weak relationship with the vegetation indices when the slope was less than 45°. On the gully bed, the runoff path was the most important factor that affected the vegetation. The average vegetation cover inside the runoff path was 5.2%, whereas the average vegetation cover outside the runoff path increased to 56.3%. The vegetation strongly impacted the soil moisture during the rainy season. However, this relationship was not observed during the dry season, which indicates that the water conservation effects exerted by the vegetation cannot last a long time in the Dry-hot Valley. The active part of gully n1 has a vegetation cover (average 16.9%) that is significantly lower compared with the stable parts of the gully (55.1%). This finding indicates that the vegetation in the gully is not only impacted by the soil and the topography in the area of vegetation growth but also influenced by the runoff processes upstream of the gully heads.