MORPHODYNAMICS OF VEGETATION-STABILIZING DUNES IN THE MU US DUNE FIELD, CHINA

Better understanding of the morphodynamics of partially vegetated dunes will help interpret their environmental significance and predict their future changes in mobility. Field observations and model simulations indicate that crescentic dunes can be transformed into parabolic dunes by increasing vegetation, but more real-world case studies of high spatial resolution are needed to document this transformation in detail. Most parts of Mu Us dune field in north central China experienced significant vegetation increase since the early 2000s, and high-resolution satellite imagery provides opportunities to study dune morphodynamics over time.

As vegetation stabilized the barchan and transverse dunes in the study area, anchoring of sands on barchan horns was an important process, as previously reported. Vegetation growth of lower stoss faces was also important, however, limiting sand supply and causing erosion higher on the stoss face. As a result, dune height was lowered and the stoss face was elongated, creating a pan-like form which was an intermediate stage to parabolic dune development. Although dunes all tended to change to parabolic-like forms, they did not always become well-defined parabolic dunes before full stabilization. Dunes artificially fixed by planted shrubs, with original shape preserved, simulating an extreme case of dunes “frozen” by rapid establishment of vegetation cover. These observations lead to generalized conceptual models for vegetation-stabilized dune development, in which vegetation growth rate and sand transport intensity are critical.

Dune migration rates were mostly reduced by vegetation influence. However, some barchans, reduced in mass by losing sand supply, actually migrated faster and faster as their size became smaller. At current rates, even the largest active dunes would completely turn over through migration in < 200 yr. Individual dunes can be stabilized and change form quite rapidly under present climate condition. Therefore, even very short-term disturbance can be recorded by dune morphodynamics. However, the dunefield as whole will take much longer to stabilize at the current rate of about 0.6% of additional vegetated area per year, and overall dunefield stabilization/activation is related to longer-term climatic or land use change.