Influence of slope steepness on ground coverage of natural grasses and soil moisture in the Loess plateau

摘要

Restoration of natural vegetation on steep slope in the gullied-hilly area of Loess Plateau is important for soil erosion control. The objective of this study was to find out the relationship between vegetation coverage /aboveground biomass and slope steepness, and the possible relations among vegetation, topographic characteristics and soil moisture. Vegetation and soil water were sampled on sites with different slope steepness ranging from 5-45° along two topographic transects. Each transect composed of two opposite slope aspects (east-west and south-north). Aboveground biomass was obtained by harvesting the current year live and dead plants and oven dried. Soil moisture was measured on moderate (10-15°), steep (20-25°) and steepest (43-45°) sites of each aspect to a depth of 3 m. Vegetation coverage and aboveground biomass were linearly related to slope steepness on east (p<0.0001), south (p<0.001) and west (p<0.0001) slopes. The slope steepness alone could explain more than 90% of ground coverage variations on the east, south and west slopes. On northern facing slope, the coverage and aboveground biomass were decreased slower than those on other aspects with increasing slope steepness. The soil moisture at the sites of northern facing slope was greater than those of other aspects. soil moistures on certain soil profiles at relatively moderate areas with higher aboveground biomass were lower than those on steeper areas with smaller aboveground biomass. This trade off relationship between above ground biomass and soil moisture may maintained the soil water balance both at moderate and steepest sites on all aspects and made the ecosystem sustainable in the water stressed typical steppe area under natural conditions.