Response of soil erodibility of permanent gully heads to revegetation along a vegetation zone gradient in the loess-table and gully region of the Chinese Loess Plateau.

Revegetation has been proven to significantly affect soil erodibility of gully heads, and climate conditions are expected to affect soil erodibility by determining the vegetation characteristic. However, there are crucial scientific/knowledge gaps regarding the change in the response of soil erodibility of gully heads to revegetation along a vegetation zone gradient. Therefore, we selected the gully heads with different restoration years along a vegetation zone gradient encompassing the steppe zone (SZ), forest-steppe zone (FSZ), and forest zone (FZ) on the Chinese Loess Plateau to clarify the variation in soil erodibility of gully head and its response to soil and vegetation properties from SZ to FZ. Furtherly, we systematically and comprehensively reveal driving factors of changes in soil erodibility in three vegetation zones. Results showed that: (1) Vegetation and soil properties were affected positively by revegetation and differed significantly in three vegetation zones. (2) Soil erodibility of gully heads in SZ was significantly higher than in FSZ and FZ, by 3.3 % and 6.7 % on average, respectively, and it showed a significantly different decrease with restoration years in three vegetation zones. (3) Standardized major axis analysis proved that the sensitivity of response soil erodibility to vegetation characteristics and soil characteristics presented a significant difference as the revegetation proceeded. Vegetation roots were the primary driver in SZ, but soil organic matter content dominated the change in soil erodibility in FSZ and FZ. (4) Structural equation modeling indicated that climate conditions played an indirect role in regulating soil erodibility of gully heads by mediating vegetation characteristics. This study offers essential insights for assessing the ecological functions of revegetation in the gully heads of the Chinese Loess Plateau under different climatic scenarios.