| Agricultural-pastoral ecotone in the north is an important link between agricultural and pastoral areas,which plays a unique and irreplaceable role in preventing desertification.It is a natural ecological barrier in the agricultural region of the middle and eastern part of China,and plays an extremely important role in the ecological protection and improvement of our country.Driven by climate change and human activities,especially the unreasonable use of natural resources(such as overgrazing and deforestation),the ecological environment is deteriorated.In 2000,our government successively carried out a series of ecological control projects in key areas of the country,such as returning farmland to forests and grasslands,controlling wind and sand sources in Beijing-Tianjin-Hebei,protecting natural forests and preventing wind-blown sand.Chifeng is a typical area in the agro-pastoral ecotone of northern China.Based on the empirical study of Chifeng City,this paper determined two periods: the period of ecological environment degradation from 1990 to 2000 and the period of ecological environment restoration from 2000 to 2015,and quantitatively studies the changes of ecological environment before and after the implementation of ecological engineering in Chifeng City.From the three aspects of ecosystem structure,ecological environment condition and ecosystem service capacity,this paper evaluates the changes brought about by the ecological control project in the agro-pastoral ecotone of northern China,and provides scientific basis for the development and ecological protection of the agro-pastoral ecotone.The main conclusions are as follows:(1)During the period of ecological degradation,grassland,wetland and bare land in Chifeng City showed a decreasing trend.During the period of ecological restoration,the decreasing trend of grassland and wetland slowed down and the ecological environment improved.Firstly,the forest area of Chifeng increased from 1.92 million hm~2 in 1990 to 1.97 million hm~2 in 2015.Secondly,the grassland area of Chifeng showed a decreasing trend,from 4.23 million hm~2 in 1990 to 4.15 million hm~2 in 2000,and to 4.05 million hm~2 in 2015,and the decreasing trend of grassland slowed down.Furthermore,the area of Chifeng wetland showed a decreasing trend,from0.21 million hm~2 in 1990 to 0.19 million hm~2 in 2000,and to 0.17 million hm~2 in 2015.Wetland declined slowly.In addition,Chifeng farmland area showed an increasing trend,from 2.05 million hm~2 in 1990 to 2.19 million hm~2 in 2015.Finally,Chifeng’s urban area showed an increasing trend,from 0.21 million hm~2 in 1990 to 0.23 million hm~2 in 2015.(2)During the period of ecological degradation,the ecological environment of Chifeng City deteriorated.During the period of ecological restoration,the ecological environment of Chifeng City has improved significantly.EI in 1990,2000 and 2015 were 70.58,61.21 and 68.35,respectively.The ecological environment was good.It showed that the vegetation coverage was high and the biodiversity was rich,which was suitable for human life.From 1990 to 2015,the degree of ecological environment change was-2.23,and the degree of ecological environment change was slightly worse.From 1990-2000 to 2000-2015,EI changed from negative to positive,indicating that the ecological environment of Chifeng City improved significantly in 2000-2015.(3)During the period of ecological degradation,the wind-proof and sand-fixing capacity,carbon sequestration capacity of ecosystem and habitat quality of Chifeng City showed a downward trend.During the period of ecological restoration,the wind-proof and sand-fixing capacity and habitat quality of Chifeng City increased significantly,and the declining trend of carbon storage was alleviated.Firstly,from 1990 to 2000,the wind-proof and sand-fixing capacity of Chifeng showed a downward trend,from 9309.69t/km~2 in 1990 to 522.96 t/km~2 in 2000.After the implementation of projects such as returning farmland to forests and three North shelterbelts,the capacity of wind-proof and sand-fixing increased to 5621.06 t/km~2.Secondly,the total carbon reserves in Chifeng from 1990 to 2015 showed a decreasing trend.From 1990 to 2000,the total carbon reserves decreased from 807.99 Tg C to 799.10 Tg C.By 2015,the total carbon reserves will be reduced to 790.65 Tg C,the decreasing trend slowed down.Furthermore,from 1990 to 2015,Chifeng’s ecological environment quality showed a trend of decreasing first and then improving.Overall,the percentage of Chifeng in good condition reached 84.17%. |
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