Abstract: Grassland ecosystem is the largest terrestrial ecosystem in China,and plays an important role in maintaining the ecological safety of Northern China.In this paper,the maps of steppe degradation in the Xilingol Biosphere Reserve of Inner Mongolia in 1985 and 1999 were drafted,based on remote sensing data and field survey.The changes of steppe ecosystem values were estimated by selecting the ecosystem functions such as soil erosion control,soil nutrient maintaining,nutrient cycling,C storage,and O₂ production.The total valuation of the steppe ecosystem services in 1987 and 1999 was 28.24×10⁸ Yuan RMB and 26.75×10⁸ Yuan RMB,respectively,with a decrease of 5.28%,while the valuation of the steppe ecosystem services per unit area in 1987 and 1999 was 2.99×10³ Yuan RMB·hm^-2 and 2.83×10³ Yuan RMB·hm^-2,respectively,with a decrease of 5.35%.The results indicated that owing to over-grazing,the steppe became more and more degraded,and the functions and ecosystem services of the steppe were also decreased.To restore the degraded steppe,keeping the densities of human and livestock under the carrying capacity of the steppe region should be the most essential solution.

Key words: Gap regeneration, Mixed-broad-leaved Korean pine forests, Tree diversity, Gap structure, Stand dynamics