Juying Jiao, Weijie Yu, Yu Chen Institute of Soil and Water Conservation, CAS & MWR

1. The Third World Conference of WASWAC NEW CHALLENGES AND STRATEGIES OF SOIL AND WATER CONSERVATION IN THE CHANGING WORLD SUSTAINABLE MANAGEMENT OF SOIL AND WATER RESOURCE Seed Removal Due to Overland Flow on Abandoned Cropland in the Chinese Hill and Gully Loess Plateau Juying Jiao, Weijie Yu, Yu Chen Institute of Soil and Water Conservation, CAS & MWR

2. Background ——Soil erosion is an increasing environmental problem globally, and the Chinese Loess Plateau suffers the most severe soil erosion in the world.

3. ——The soil erosion on the Loess Plateau causes the loss of cropland and degraded ecosystem onsite, the siltation of rivers and reservoirs offsite, and potential flooding in the lower reaches of the Yellow River.

4. ——Vegetation is the prerequisite in the restoration of degraded ecosystem, and it was proved that natural recovery of vegetation is an effective approach to control soil erosion in this region. —— Soil erosion in turn interferes with natural recovery of vegetation by impacting the whole growth stages of plant in the degradation ecosystems. —— Seed is the basis of natural vegetation restoration, and the seed stage is particularly vulnerable to environmental conditions within the life cycle of plants.

5. —— In arid and semiarid regions with the potential to trigger strong soil erosion processes, consequently result in seed removal in soils and on soil surfaces. Mineral particle loss Soil erosion Soil nutrients loss Seed removal (redistribution & loss) Secondary seed dispersal Spatial colonization patterns of seedling Vegetation restoration and succession

6. —— The objectives of this study were to: 1) evaluates seed redistribution patterns through the comparison of soil seed banks in eroded, deposited and trap micro-sites, 2) characterizes seed loss by using runoff plot, 3) explores the effect of vegetation coverage and rainfall on seed loss along three abandoned slopes in the Chinese Hill and Gully Loess Plateau.

7. Methods Forest-steppe region Warm temperate continental monsoon climate Average annual precipitation 505 mm Loessial soils

8. Three abandoned Slopes A1 Upslope B1 Upslope A2 Middle slope C1 Upslope A3 Down slope B2 Middle slope C2 Middle slope B3 Down slope C3 Down slope Southern-aspect slopes， Similar vegetation composition， Similar period of time since agricultural abandonment， Slope angles of 25-30°， Vegetation cover of 25-30%.

9. Soil seed loss and seed rain In each slope position

10. Soil seed bank tussocks as trap micro-sites bare inter-plant areas as eroded micro-sites fish-scale pits as artificial deposited micro-sites Three micro-sites: 1 slope ×3 quadrats (20 m ×20 m) × 3 micro-sites × 20 soil cores ×3 soil layers (0-2, 2-5 and 5-10 cm) Soil cores were collected using a soil auger (diameter 4.8 cm) in late March of 2011. Seeds were identified by seedling emergence method.

11. Rainfall & vegetation Rainfall data were obtained from the An’sai Ecological Experimental Station of Soil and Water Conservation. For the erosive rainfall event, rainfall depth and average intensity exceed 12 mm and 0.04 mm min-1, respectively (Xie et al., 2000). Vegetation coverage was examined using the traditional ocular method after each erosive rainfall event. Seed loss rate was regard as the ratio of seed loss density to total seed density (including the seeds that entered the system through seed rain and mean soil seed bank of the three micro-sites). Differences in densities and species quantities of soil seed banks across the three micro-sites were examined via one-way ANOVA.

12. Results Soil seed bank __ micro-sites and soil layers Soil seed bank densities: fish-scale pit > tussock > inter-plant area. The effect of soil erosion on soil seed bank was mainly for top soil layers.

13. Soil seed bank __ species

14. Soil seed bank __ plant functional groups

15. Seed loss __species

16. Seed loss rate

17. Seed loss density & erosive rainfall The significant exponent relationships (P＜0.05) between seed densities of loss and erosive rainfalls over the two years was not consistent. It might be caused by varied densities in seed rains during the rainy season(2352 and 1966 seeds m-2 in 2011 and 2012 ), the more abundant seeds inputted, the greater loss of seeds was caused under same rainfall condition.

18. Seed loss density & vegetation coverage Seed densities of loss did not show relationship with vegetation coverage during each erosive rainfall event. Other vegetation characteristics (e.g., spatial distribution patterns of vegetation and plant shoot architectures) may play a key role. Besides, the more or less presence of fish-scale pits in a runoff plot and the differences of soil seed bank densities among all plots could influence the results.

19. Conclusions 1 Soil erosion resulted in seed redistribution and caused seeds to concentrate in soils or on soil surfaces in trap or deposited micro-sites. 2 Overland flow could not result in large numbers of seeds loss and soil erosion is not the limiting factor for natural vegetation recovery in the seed stage. 3 The pioneer species, A. scoparia, was dominate in soil seed bank and it is necessary to further investigate whether this speciescan slow down the speed of vegetation succession. 4 Other factors, such as seed germination and seedling survival capacities maybe the limiting factor for natural vegetation recovery, need be studied further.

20. Thanks for your attentions！ In this study, soil erosion caused seeds to concentrate in soils or on soil surfaces under tussock areas and in fish-scale pits at varying levels. But it did not remove large quantities of seeds from the abandoned slopes. Seed loss was affected by several field-related factors and by erosive rainfall in particular. In conclusion, Soil erosion is not the limiting factor for natural vegetation recovery in the seed stage. Other factors, such as seed germination and seedling survival capacities, must be studied further.