Kobresia meadow degradation and its impact on water status

Abstract

AbstractAlpine Kobresia meadows are valuable pasture resources on the central and eastern Qinghai‐Tibetan Plateau that are also important in preserving local and regional water. Kobresia pygmaea is the dominant species forming a typical turf layer resistant to disturbance; however, overgrazing may have exceeded that resistance. An integrated approach, including field monitoring, soil sampling, stable isotope hydrology, and physical modelling, was used to evaluate the hydrological consequences of meadow degradation with respect to normal meadow, degraded crust, and bare soil. Multiple evidence confirms that the soil moisture condition worsens when the meadow degrades. Bare soil has the coarsest soil texture, rapid infiltration, and low soil moisture in the root zone, and soil evaporation rate is high compared to normal meadow especially in dry periods. Crusted meadow soil has the lowest surface infiltration and a larger exposure of the leaf surface because of low plant cover over a dark surface, which favours high transpiration. Crusted meadow also has a drier condition in the root zone. These suggest that degradation is a positive feedback process in which leaf and soil exposure to radiation strengthen water demand for transpiration and facilitate non‐productive water loss, leaving the root zone (0–20 cm) dry and subject to further soil erosion. This positive process suggests that recovery of the Kobresia meadow is a long‐term task which has to consider the different levels of degradation and the effects of local climate change, in order to adapt the rangeland management practices, to the needs of meadow conservation and restoration.