Shrub encroachment enhances the infiltration capacity of alpine meadows by changing the community composition and soil conditions

Due to global changes and anthropogenic disturbances shrubs are widely encroaching into alpine meadows, which may have profound impacts on the ecohydrological functioning of these key ecosystems. This phenomenon is particularly alarming in the alpine meadows of the Qinghai-Tibetan Plateau, the headwaters for many of Asia's largest rivers. However, little is known about the extant in which shrub encroachment alters the infiltration capacity of those soils. Here we examined the effects of shrub encroachment on the plant community and soil infiltration processes by contrasting vegetation and infiltration variables between three areas: a reference alpine meadow, an alpine meadow lightly encroached by smaller shrubs, and an alpine meadow heavily encroached by larger shrubs. We found that shrub encroachment reduced herbaceous plants aboveground biomass by 10-24 g m(- 2) and root biomass by 1346-2239 g m(- 2). The sedge functional group was gradually replaced by forbs. Initial infiltration rates gradually increased with shrub encroachment, and were approximately doubled and tripled at the earlier and later stages of encroachment, respectively. Overall, shrub encroachment improved the soil infiltrability by changing soil conditions and inhibiting herbaceous species due to the reduction of surface mattic epipedon and the formation of dead root channels. These findings suggest that the rapid transformation of alpine meadows into shrublands could have drastic effects on the surface runoff and stream flow dynamics of the Qinghai-Tibetan Plateau.