Seed removal on loess slopes in relation to runoff and sediment yield

Overland flow and sediment transport can carry away seeds at the soil surface and in the soil, cause a secondary seed dispersal event, lead to seed redistribution, and influence the spatial distribution of seedling renewal, which plays an important role in vegetation restoration and succession. The objectives of this study were to investigate the process of seed loss on loess slopes and its relationship to the yield of runoff and sediment, the effects of rainfall intensity, slope gradient and seed morphology on seed removal.Rainfall simulation experiments were carried out in 1 m2 plots on 10°, 15°, 20° and 25° loess slopes for a 60-minute duration with intensities of 50 mm/h, 100 mm/h and 150 mm/h, respectively. A mixture of 75 seeds from 16 species on the Chinese hilly-gullied Loess Plateau had been placed in these plots, and we measured the number of seeds lost, the distance seeds displaced, the runoff rate and amount, and soil loss rate and amount.Results showed that the accumulated seed loss rates in the rainfall process were closely related to the corresponding sediment yield, and even more closely related to the runoff amount. The seed removal obviously increased with rainfall intensity but did not obviously change with slope gradient, and results varied among species. At 50 mm/h rainfall, there was almost no seed loss on the four slopes, but 30–45% of the seeds moved from their original position. However, 79.5% and 86.4% of the seeds were eroded at 100 mm/h and 150 mm/h, respectively. Of these, 46.9% and 20.4% of the seeds were displaced, and 32.6% and 66.0% of the seeds were lost. Total seed removal was also affected by the seed amount and position on slopes, species composition of the seeds, and slope length. It was suggested that seed removal during water erosion events can affect seed redistribution and, consequently, species composition and vegetation spatial distribution.

Research Highlights► Seed loss rate was closely related to sediment yield and more closely related to runoff amount. ► Seed removal was positively associated with the intensity of rainfall. ► The effect of slope gradient on seed removal had no clear pattern. ► Seed removal varied among species due to their seed morphology. ► Seed removal by water erosion has the potential to explain species distribution on eroded slopes.