Spatial pattern of soil erodibility factor (K) as affected by ecological restoration in a typical degraded watershed of central China.

Long-term ecological restoration of degraded habitats can alter their near-land surface characteristics and thus affect soil erodibility factor (K). In this study, we used geostatistics coupled with structural equation modeling (SEM) to investigate the spatial patterns of K and quantify its relationship to potential impact factors (spatial location, topography, plant, and soil characteristics) in a restored watershed in the Danjiangkou Reservoir region of central China. Results showed that the K values in this watershed ranged from 0.026 Mg h Mj-1 mm-1 to 0.057 Mg h Mj-1 mm-1 and generally increased with soil depth. Across the watershed, the K values in the surface soil (0-10 cm) were the highest in the mid-stream region, followed by the downstream and upstream regions. No obvious pattern in the relationship between K and the slope was found in either the 0-10 cm or 10-30 cm soil layer. Among the four land-use types, the K values followed the rank of shrubland > terrace and slope farmland > woodland. SEM results indicated that the variation in K in this restored watershed was closely related to soil texture and soil organic matter (SOM) content. The external environmental variables (spatial location, topography, and plant) significantly influenced indirectly soil erodibility through their effects on the intrinsic soil characteristics (particularly the SOM) at both depths (R2 of 0.67 and 0.33, respectively). Although soil texture was shown to be an important direct-effect factor (with path coefficients of 0.72 and 0.90, respectively), its external interpretation was the weakest among all the direct-effect factors (R2 of 0.12 and 0.02, respectively). These results showed that afforestation, increasing soil organic fertility, and reducing tillage should be promoted in the future.