Assessment Of Engineering Measures For Restoration Of Degraded Grassland In Typical Steppe Region Of Inner Mongolia

The grassland degradation induced by natural and human factors is an important problem Inner Mongolia.It affects the sustainable social development in the region and the ecological security in northern China.This situation has stimulated the government to initiate a series of ecological restoration and construction projects,and a series of engineering measures has been developed for this purpose.In order to understand the effects of different engineering measures on the production and ecological functions of the degraded grassland,and select green and efficient engineering measures,we assessed the long-term economic and environmental efficiency of four engineering measures for restoring grazing-or mowing-induced grassland degradation,i.e.,natural recovery,harrowing,shallow ploughing and fertilization,in the typical steppe region of Inner Mongolia.The effects of these different engineering measures on grassland ecosystem services were compared,the engineering benefits of these different measures were evaluated.The main results were as follows:1)Natural recovery,shallow ploughing and harrowing could all improve the vegetation and soil conditions of the long-term grazing degraded grassland,,rehabilitate the ecosystem functions and services of degraded grassland.2)Shallow ploughing could promote an rapid improvement of grassland production.The economic benefits generated in the first 7 years following the implementation of this restoration measure was much higher than that from natural recovery or harrowing.The improvement of soil organic carbon(SOC)content by shallow ploughing within the first 9 years was better than other measures;However,The ecological benefits from shallow ploughing,such as nutrient storage,water retention and wind erosion prevention,became less than that of natural recovery 10 year after the implementation of these restoration measures;3)The effect of harrowing was between that of natural recovery and shallow ploughing.The effects of harrowing on grassland production and carbon sequestration were not as good as shallow ploughing within the first 9 years following the implementation of the engineering measures.Then,the production and ecological benefits such as wind erosion prevention of the harrowing were better than that of shallow ploughing.4)The economic benefits from natural recovery exceeded that of shallow ploughing seven years after the implementation of these measures.After 23~26 years following implementation of these measures,soil organic carbon reserves reached a relatively stable state in grassland under natural recovery,and had better ecological benefits,such as nutrient cycling,water conservation,and wind erosion prevention,than other measures.5)Fertilization improved plantproductivity in the long term mowing grassland,however,it was not cost-benefit effective.Moreover,no obvious improvement in soil nutrients was observed,and soil organic carbon even declined,turning the grassland soil as a carbon source,with the application of chemical fertilizers.Therefore,we must be cautious in applying fertilizer as a measure for restoring degraded grassland.For the long-term grazing degraded typical steppe of Inner Mongolia,selection of restoration measures should be based on the restoration target.Shallow ploughing could be selected for quick recovery of grassland production,thus achieving better economic benefits in the short term;while natural recovery was superior to other measures for the restoration of long-term ecological security.