Can seed removal through soil erosion explain the scarcity of vegetation in the Chinese Loess Plateau?

摘要

Seed removal by water erosion may explain the sparse vegetation cover in systems like the Chinese Loess Plateau, which is characterized by severe soil erosion. The seeds from 16 species found on the plateau were examined in relation to the likelihood of their removal by erosion, as tested by rainfall simulation experiments. The experiments were performed over 1-m~2 plots with slopes of 10°, 15°, 20° and 25° for 60 min at intensities of 50 mm h~(-1) 100 mm h~(-1) and 150 mm h~(-1) respectively. Seed loss occurred at simulated rainfall intensities of 100 mm h~(-1) and 150 mm h~(-1) with total seed loss rates of 26-33% and 59-67%, respectively. Most seeds were displaced, even at 50 mm h~(-1). The degrees of seed loss and displacement varied among species. These data, in combination with data from our former research on propagule, seedling and population development in these species, indicate that the species with high seed loss rates either compensate by having a soil seed bank that produces seedlings during the growing season or reproduce by vegetative propagation; the species with no seed loss are still sparsely distributed. Seed germination and seedling survival seem to be more important than seed loss in determining establishment in these regions of the Loess Plateau. Seed translocation by water erosion, however, contributes to the observed distribution of vegetation in this geographic region.