| Land use/Land cover(LULC)change is the consequence of human social and economic activities and natural environmental conditions on the Earth’s terrestrial ecosystem,and serves as the linkage between humans and nature.The Lijiang River basin belongs to a typical karst region with fragile ecological environment.Since 2000,due to the acceleration of urban construction,strengthening of tourism development and improvement of socio-economic activity,the Lijiang River basin has been experienced in significant changes in LULC,intense disturbances with land ecology,declines in ecosystem services and increasingly serious environmental issues.These problems directly affect the sustainable development of the entire basin and have become a bottleneck restricting local economic and social development and land ecological security.However,the spatiotemporal-changes characteristics of LULC change in the Lijiang River basin are still not clear and the ecosystem services and their values in the basin are not documented.Therefore,in this study,the LULC change,ecosystem services and their values,and land ecological security were systematically investigated in the Lijiang River basin in the last two decades(2000-2019)by using multisource remote sensing images,3S technology and spatial analysis and statistical method.Specifically,the spatiotemporal evolution characteristics and driving mechanism of LULC change were explored,the ecosystem services and their values were estimated based on land use change,the spatiotemporal differences and spatial agglomeration characteristics of the functions and values of ecological services were analyzed,the land ecological security status and their differences among counties were evaluated in the Lijiang River basin during the study period.In addition,the distribution of land use types and their ecological service value in the basin in 2025 were predicted,based on the constraints of land ecological security.The main results showed that:(1)The LULC change was significant in Lijiang River basin with an annual land use change rate of 0.17%.During the study period,the cultivated land area decreased by205.44 km~2,the forestland increased 41.49 km~2,the construction land increased by 237.57km~2,the grassland,water and unused land decreased by 42.92 km~2,6.96 km~2 and 23.74km~2,respectively.Moreover,an accelerating trend was found in the change of cultivated land and construction land.The increase of construction land mainly came from cultivated land and forestland,which contributed 80.87%and 13.12%,respectively.The LULC changes were obviously different for each district and county in the basin.The annual change rate was higher in the five districts of Guilin city(LC>0.3)than in the counties(LC<0.15).The lang use change rates were relatively large in the low elevation zone,low slope zone and near river area with frequent interference from human activity.The degree of landscape fragmentation increased,the degree of aggregation was reduced and the degree of patch combination was relatively high in the Lijiang River basin.The agricultural technology level,urbanization level and population were the main driving factors of the change in cultivated land and construction land in the basin.(2)The ecosystem service value decreased by 369.08×10~6 yuan in the Lijiang River basin during the study period with average annual decrease of 19.43×10~6 yuan.After 2010,the decrease had an increasing trend.From the perspective of secondary ecological service types,the values of ecosystem services was as follows:aesthetic landscape(10027.38×10~6-10101.19×10~6 yuan)>hydrological regulation(9643.68×10~6-9903.88×10~6 yuan)>climatic regulation(7337.25×10~6-7383.18×10~6 yuan)>soil conservation(2988.02×10~6-3006.42×10~6 yuan)>gas regulation(2920.07×10~6-2871.89×10~6 yuan)>biodiversity(2791.09×10~6–2810.10×106 yuan)>environmental purification(2355.78×10~6-2372.38×10~6yuan)>food production(1017.03×10~6-957.19×10~6 yuan)>raw material production(799.77×10~6-(792.42×10~6 yuan)>nutrient cycling maintenance(314.52×10~6-306.30×10~6yuan)>water supply(429.60×10~6-346.14×10~6 yuan).From the perspective of land type,the forest land,water bodies and cultivated land contributed the highest value to ecosystem service functions,with the contribution rates exceeding 75%,15%and 6%,respectively.The highest value of ecological services was found in 200-500 m elevation zone(>19400.00×10~6 yuan)and 15°-25°slope Zone(>12300.00×10~6 yuan),while the value of ecological service function of 0～200 m elevation zone(decreased by 321.07×10~6 yuan)and 2°-6°slope zone(decreased by 246.54×10~6 yuan)varied relatively greatly.The ecological service value per unit area was relatively large in the high elevation zone and high slope zone,while the changes in ecological service value per unit area were relatively large in the both low elevation zone and low slope zone.The largest value of ecosystem services per unit area was found in Lingchuan County(more than 24,000 yuan per hectare),and the smallest was in Diecai District(less than 3,800 yuan per hectare).During the study period,only Xiufeng District has increased the value of ecosystem services by 3,583.82yuan per hectare in the basin.The largest decrease of ecosystem service value came from Qixing District with a decrease of 7,617.32 yuan per hectare.The smallest decrease of the ecosystem service value came from Xing’an County with a decrease of 309.37 yuan per hectare.The supply service,regulation service,support service and cultural service varied greatly among the counties in Lijiang River basin.Based on the grid scale of 100m×100m,the values of different components of the ecosystem service have obvious spatial aggregation.The distribution range,degree and change trend of spatial agglomeration are different.(3)The overall status of land ecological security was poor in Lijiang River basin.Every five years between 2000 and 2019,the ecological security status of land in the basin was in the sensitive level,sensitive level,critical level,critical level,and sensitive level.There were significant differences of the land ecological security status among the subsystems.The land ecological security status has improved for the subsystems of driving force,impact and response,while that got worse for the subsystems of pressure and state.The changes in land ecological security status were obviously different in different districts and counties of the basin during the study period.The status of land ecological security has been changed from dangerous level to sensitive level in Diecai District,Xiufeng District and Xiangshan District,indicating the ecological status of the land has improved in these districts The ecological status of the land was fluctuated between sensitive level and the critical level in other districts and counties within the basin.The ecological status of the land was at the sensitive level for all districts and counties in 2019,with the best in Xiufeng District(0.3660)and the worst in Qixing District(0.3062).The status of land ecological security varied greatly in the subsystems in each district and county,fluctuating among the dangerous level,the sensitive level,the critical level and the good level.The natural population growth rate,GDP per capita,population density,fertilizer use per unit cultivated area were the main factor affecting the land ecological security in the Lijiang River basin.(4)Under the constraints of land ecological security,the construction land will further expand in the basin in 2025,increasing by 250.40km~2 compared to 2015.In 2025,the cultivated land and water body increased under the status of protection,increasing by 93.54km~2 and 3.81 km~2,respectively.But the forest land will decrease by 326.72 km~2,mainly due to the significant transformation of non-public welfare forests around towns into construction land in the Lijiang River basin.The ecosystem service value of the basin continues to decline,decreasing by 1729.05×10~6 yuan compared to 2015.The C value of land ecological security is 0.5136,which has slightly increased compared to 2015,but the land ecological security status is still in the critical level.The results from this study have significant theoretical and practical implications for promoting regional economic development,achieving coordination between human and natural systems,and seeking scientifically sound land use planning and management in the Lijiang River basin.They can provide scientific support for regulating and managing the land ecological security patterns in the basin.It is recommended to enhance the ecosystem service functions,improve the land ecological security status,and promote the sustainable development of the ecological,social,and economic aspects of the Lijiang River basin,including the protection and compensation of forest land,the protection and restoration of the Lijiang River aquatic ecosystem,and the establishment of a permanent basic farmland and cultivated land protection system in the Lijiang River basin. |
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