Comparison of hydraulic behaviour of unvegetated and vegetation-stabilized sand dunes in arid desert ecosystems

Revegetation was one of most successful measures to restore desert sand dunes and to improve regional eco-environments in the Tengger Desert, Northwest China. The potential for soil moisture replenishment by precipitation in the revegetation restored desert ecosystems is influenced strongly by the hydraulic properties of the surface soils. Steady-state infiltration rates from tension disc infiltrometer were measured at revegetation restored desert soils (VS) and unvegetated sand dunes (SD), respectively. Results indicated that the site specific VS and SD hydraulic properties differed significantly. Compared with SD, the long term VS has the effect of decreasing the hydraulic conductivity of the surface soil, while increasing the capillary effect on the infiltration rate. Averagely, the hydraulic conductivity of VS was 0·43 times of SD at the near saturation conditions. At VS, tension infiltration were dominated by capillarity effect more than that of SD, which were ascribed to the differences in soil properties where the former has a higher amount of finer particles, organic matters content and lower bulk densities. Accordingly, the hydraulically functioning mean pore sizes were larger at SD, where the gravity effect dominated the tension infiltration process. Therefore, in the study area under the pulse precipitation events in the growing seasons, VS contains more soil water by capillarity effect than SD does, which would contribute to shallow rooted herbage and cryptogam water consumption. Nevertheless, looking at the whole soil profile, for the actual rainfall water regimes, VS has insignificant effects on the soil profile water regime, with unchanged deep fluxes.