Self-organized vegetation patterning effects on surface soil hydraulic conductivity: A case study in the Qilian Mountains, China

A tension infiltrometer technique was used to determine the effects of vegetation patterning on the hydraulic properties of surface soils in an alpine catchment unit previously used as rain-fed agricultural land but now exhibiting a significantly self-organized vegetation pattern, with a shrub-covered surface on the north-facing slope and a grass-covered surface on the south-facing slope. We hypothesized that the surface soils in the catchment unit had a random pattern with relatively uniform variance before the fencing program began in 2000, because of long-term tillage and crop production, and we found a slightly organized and apparently heterogeneous pattern of Ks after the recovery period. While a relatively higher average Ks was observed on the north-facing slope than on the south-facing slope, the difference was not statistically significant. The surface soil hydraulic pattern in the catchment unit was controlled mainly by terrain-related processes such as runoff sealing and compaction, and vegetation patterning did not contribute as much as we expected to its development. Although the positive feedbacks between vegetation and soil we postulated in this work were not observed, such a positive feedback may exist in the root-zone soil profile, as indicated by the significant differences in physical and chemical parameters of soil profiles on different slope positions, e.g. bulk density, field capacity, total C, N and available P, etc. Assertion of the statement, however, is still subject to debate because of the limited data, and deserves much more detailed research and investigation in the future.