| Based on the analysis of land use type change,landscape pattern change,desertification degree change,the relationship between vegetation cover change and climate change,the relationship between vegetation cover change and groundwater,and the relationship between vegetation distribution and soil characteristics,this thesis explores the changes of natural environmental conditions in Ulan Buh Desert.Combining the natural resources,environment and socio-economic conditions of the study area,applying the conceptual model of"sensitivity resilience pressure",selecting appropriate evaluation indicators to analyze the ecological vulnerability of Ulan Buh Desert,and combing the regulation methods of ecological environment with different degrees of vulnerability in the study area in combination with its important influencing factors,It provides a scientific basis for the construction of ecological environment and the development of characteristic economy in the study area.The results show that:(1)Over the past 30 years,with the increase of population,the acceleration of urbanization and the increase of demand for development,the area of cultivated land,grassland and construction land has increased continuously and steadily,especially the area of grassland and cultivated land has increased rapidly.The total area of grassland increased by 737.99 km~2,the total area of cultivated land increased by 565.49 km~2,and the total area of construction land increased by 34.85 km~2.The area of sandy land and saline-alkali land has decreased,the proportion of sandy land has decreased from 46.92%in the initial stage to 37.89%,the area has decreased by 1281.15 km~2,and the proportion of saline-alkali land has decreased from 1.5%in the initial stage to 0.73%.From the patch type,the landscape fragmentation of forest land,grassland,cultivated land and construction land showed a downward trend from 1989 to 2019,and the degree of aggregation was higher and higher.The aggregation degree of saline-alkali land and sandy land tends to decrease,the number of patches becomes more and the area decreases,the development and utilization of forest land,cultivated land,construction land are relatively regular,and the integration degree of forest land and grassland is improved.(2)The degree of desertification in the south of Ulan Buh Desert is more serious than that in the north.The severely and extremely severely desertified land is mainly distributed from the middle to the south of Ulan Buh Desert.Mild and moderate desertification land is mainly distributed in the northeast.From 1989 to 2019,the proportion of serious desertification area decreased from 41.76%to 13.51%,the area decreased by 4005.52km~2,and most of it was transformed into severe desertification.From 1994 to 1999,the average value of desertification index ADI decreased from 3.25to 2.94,which shows that the overall degree of desertification has improved from 1989 to2019.By analyzing the driving and influencing factors of desertification,the contribution rate of human factors is 56.63%.(3)The vegetation coverage of Ulan Buh Desert decreases from north to south in space.The areas with high vegetation coverage are mainly distributed in the north of Ulan Buh Desert,with farmland as the main body.The area with increased vegetation coverage accounts for 85.90%of the total area.Correlation analysis and partial correlation analysis show that average temperature,precipitation and wind speed have a significant impact on NDVI in Ulan Buh Desert.The residual analysis shows that the improvement and destruction of vegetation by human activities coexist.The vegetation change in Ulan Buh Desert from 1989 to 2019 is the result of the interaction between climate change and human activities,with a contribution rate of 35.05%.The contribution rate of human activities to vegetation restoration was 59.81%.(4)Through the superposition analysis of the spatial distribution of vegetation species and the groundwater depth contour,it is found that Artemisia sieversiana and Artemisia ordosica have a wide range of adaptability to the groundwater depth,and grow in the areas with the groundwater depth contour of 2.5-57.5m and 22.5-70m respectively.Through the distribution of soil subclasses and the spatial distribution of vegetation types,it can be seen that the soil subclasses in the growth areas of Artemisia ordosica,Artemisia sieversiana,Haloxylon ammodendron and Nitraria sibirica are mostly aeolian sandy soil,and the soil nutrients are low.(5)From 1989 to 2019,the overall ecological vulnerability of Ulan Buh Desert changed for the better.From 1989 to 1999,the ecological vulnerability situation intensified,and the ecological vulnerability situation has significantly improved since1999 to 2019,especially from 2004 to 2014.Since 2004,Ulan Buh Desert has been seriously desertified,the area of desertification has been continuously reduced,and the control of saline-alkali land has achieved remarkable results.The ecological vulnerability of land use type and desertification degree showed a trend of deterioration first and then improvement from 1989 to 2019.The ecological vulnerability of severe desertification has a trend of deterioration after stabilization during 1989-2004.During 2004-2019,the desertification vulnerability began to improve year by year,and the proportion decreased from 50.05%to 13.52%by 2019.Severe desertification and extremely severe desertification have a good correlation with the change of wind speed,and the correlation coefficients are 0.7675 and 0.8891 respectively.Among the three meteorological factors,precipitation and wind speed have a greater impact on ecological vulnerability in the study area.(6)In view of different ecological vulnerability areas in Ulan Buh Desert,reasonable utilization of regional resources should be carried out.Areas with slight and mild ecological vulnerability can be utilized by rational development,moderate ecological vulnerability areas can be exploited in a combination of conservation and development,and in areas with severe and extremely severe ecological vulnerability,protection is the main way to use resources. |
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