Study On Land Use Change And Ecological Service Value In The Three Gorges Reservoir Area

Land-Use and Land-Cover Change(LUCC)is one of the important components of global environmental change research.LUCC not only affects the regional ecological structure,but also changes the regional ecological service function.Therefore,study on LUCC and its ecological service functions is essential for the sustainable development of regional economy and ecological environment security.From 1990 to 2015,with the rapid economic development,the construction of the Three Gorges Project and the increase of population of the Three Gorges reservoir area,human activities have caused major changes in the LUCC in this area and triggered a series of ecological and environmental problems,such as resources shortage,the lack of environmental carrying capacity,and the intensification of human-land conflicts,which have led to changes in the value of ecological services.In the past,most scholars mainly involved the analysis of land use evolution in one region or the analysis of the value of ecological services in a certain area.However,there are relatively few studies on the comprehensive analysis of these two parts and they are mainly concentrated in the economically developed areas in the southeastern coastal areas.Therefore,taking the Three Gorges reservoir area as the research object,studying the land use type change and ecological effect in this area can not only make up for the limitations of spatial scale analysis,but also promote and optimize land use in this area,and provide scientific support for ecological civilization construction.This paper applies RS and GIS technology to process the remote sensing image data of the six phases of the Three Gorges reservoir area in 1995,2000,2005,2010 and 2015,and analyzes the evolution characteristics and temporal and spatial variation of five different land use types(cultivated land,forest land,grassland,water area,construction land)in the Three Gorges reservoir area for 25 years;and then evaluates the quantitative change and spatial difference of ecological service value in the Three Gorges reservoir area combined with the elevation and slope distribution pattern;besides,this paper also analyzes the quantitative change and spatial variation of ecological service value in the Three Gorges reservoir area over the past 25 years by taking land use change and ecological service value as the entry point.Based on this,the Ca-Markov model is used to simulate the land use spatial pattern of the Three Gorges reservoir area in 2025,and estimate the quantity and pattern change of ecological service value in 2025,in order to provide technical support and scientific basis for the sustainable economic development and ecological environment construction of the Three Gorges reservoir area.The main results are as follows:(1)From 1990 to 2015,the main land use type in the Three Gorges reservoir area was forest land,and the proportion of the area in the total area was over 50%,showing a trend of decreasing first and then increasing;the cultivated land and grassland increased first and then decreased,and the water area decreased first and then increases,while the construction land continued to increase.The land use type has obvious slope and elevation difference in spatial distribution.In terms of slope,the forest land is concentrated in the area with slope more than 15°,the cultivated land is mainly distributed in the area less than 25°,and the construction land is concentrated below 10°.In the region,the range of grassland distribution is large,and each slope zone has a proportional distribution.In terms of elevations,the forest land is mainly distributed in the area of 460-1167 m above sea level,and the cultivated land is concentrated in the area of 175-794 m above sea level and the water area and construction land are concentrated in the area below 460 m above sea level,and the grassland is concentrated in 460-1167 m.In the past 25 years,the overall dynamics of land use in the Three Gorges reservoir area showed a trend of rising first and then decreasing slowly with time.From 2000 to 2005,the overall dynamic degree reached the highest value,the landscape changed drastically,and the land type changed greatly.The change rate of forest land and cultivated land showed an increasing trend in different periods.The dynamic degree of water area was small,and the change rate of construction land was the fastest,which was much higher than other land use types.The land use degree(237.84)change in the last 25 years in the Three Gorges reservoir area was slightly higher than the national average(231.92),and the comprehensive index of land use degree is relatively stable throughout the whole period,and it is at a medium-level utilization,while the change in utilization degree generally shows a downward trend.Dynamic pattern with positive "W" type.(2)From 1990 to 2015,the value of ecological services in the Three Gorges reservoir area decreased first and then increased.The overall net increase was 5.319 billion yuan,with an average annual increase of 212 million yuan.Among them,the value of forestland ecological services accounted for more than 70%,which is the main part of the value of ecosystem services in the reservoir area.The ecological service value of the Three Gorges reservoir area has obvious differences in slope and elevation: the ecological service value per unit area of each slope section increases with the increase of slope,and the >25° slope section has the highest unit area ecological service value and highest total ecological service value in different time periods;the value of ecological service per unit area increases with height.Besides,the high altitude area has a higher ecological service value per unit area,and the 1167-1616 m elevation belt has the highest ecological service value.During the study period,the contribution rate of individual services in the Three Gorges reservoir area did not change much.The total contribution rate of biodiversity function,soil conservation function and hydrological regulation function was close to half of the total service value,while the total contribution rate of aesthetic value and food production was less than 12%,which indicated that the ecosystem of the Three Gorges reservoir area is dominated by service functions such as regulation and support.In terms of the value of each individual service,the increase in ecological service functions is mainly raw material production,gas regulation,climate regulation,water temperature regulation,waste treatment,the ecological functions of soil conservation,biodiversity and aesthetic value,while the decrease is food production functions.(3)Using the Ca-Markov model to predict the land use pattern and ecological service value of the Three Gorges reservoir area in 2025,the results show that the LUCC situation in the Three Gorges reservoir area in the next decade is: the area of forest land decreased greatly from 60.31% in 2015 to 52.61% in 2025,but it is still the largest land use type in the Three Gorges reservoir area;and cultivated land,grassland,waters and construction land increased from 28.26%,5.67%,3.00%,and 2.75% in 2015 to 31.15%,7.16%,4.22%,and 4.86% in 2025 respectively.In 2015-2025,the value of total ecological services in the Three Gorges reservoir area showed a downward trend,that is,from 131.846 billion yuan in 2015 to 129.835 billion yuan in 2025,a total reduction of 2.008 billion yuan,an average annual reduction of 0.15%.Judging from the composition of the ecological service value of each land use type,although the proportion of the value of local ecological services has changed,the structure is basically stable.During the study period,the complex changes in the value of ecological services in the Three Gorges reservoir area were mainly reflected in the increase in the value of ecological services in cultivated land and waters,while the value of ecological services in forests and grasslands decreased.The forest land is a type of land use that contributes a lot to the ecological service value of the Three Gorges reservoir area.However,the forest area of the Three Gorges reservoir area is reduced due to the development and construction of the Three Gorges reservoir area.Therefore,there is a slight decrease in total ecological service value.