Planting shrubs is a common measure to control mobile sand in semi-arid area. In order to understand effects of shrubs on development of soil crusts and its mechanism, an investigation on development properties of soil crusts outside and inside shrub communities and a field experiment on effects of falling dust, adding litter, and inoculating bio-crust were conducted in 2006—2007 in Horqin Sandy Land. Results show that 1) falling dust and adding litter and inoculating bio-crust can obviously promote formation and development of soil crusts in mobile sand land; 2) it is more beneficial to development of soil crusts in wet and shade environment than in arid and sun environment, and development of soil crusts is more sensitive to moisture than to illumination; 3) shrubs can markedly promote development of soil crusts in mobile sand land because "fertile island" effects appear after shrubs are planted in mobile sand land, and soil crusts format there and then extend gradually around shrubs; and 4) effects of shrubs on development of soil crusts result mainly from the function of reducing wind speed, holding dust and producing litter, so that resulting in a visible increase of fine particles, organic matter and nutrients in soil, and promote visible amelioration of local microenvironment.

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