Simulating The Impact Of Urban Expansion On Ecosystem Patterns And Ecosystem Carbon Storage For The Chang-Zhu-Tan Urban Agglomeration

Rapid urbanization promotes socio-economic development,but also generates many ecological and environmental problems,such as loss of biodiversity,alteration of terrestrial carbon cycle,destruction of landscape patterns,and resulting in the continuous decline of regional ecological services.Studying the impact of urban expansion on ecological patterns and ecosystem services can help rational and effective urban planning and management,and promote regional sustainable development.This study takes Chang-Zhu-Tan urban agglomeration as the study area,adopts the logistic-cellular automata land use change simulation model,establishes the urban expansion simulation model based on the urban expansion from 2008 to 2013,validates the model accuracy with the urban expansion from2013 to 2018,and simulates the urban expansion in 2025 on this basis.Based on this model,we simulate the urban expansion changes in Chang-Zhu-Tan urban agglomeration in 2025 under four urban expansion intensity scenarios: natural growth,rapid economic development,ecological protection and comprehensive development with or without the protection of green heart policy,and use Fragstats4.2 landscape pattern index calculation software and In VEST ecosystem service assessment model to quantify the impact of urban expansion on regional ecosystem pattern and ecosystem services(in terms of carbon storage)under different scenarios.The results of the study are as follows.(1)Urban sprawl is influenced by elevation,slope,distance to rivers,distance to provincial roads,distance to national roads,distance to highways,distance to city centers,distance to district and county centers,and distance to railroad stations.The constructed logistic-CA model has a Kappa coefficient of 0.75,which has high accuracy and can be used to simulate the urban expansion process of Chang-Zhu-Tan urban agglomeration.(2)During the period of 2018-2025,the urban expansion rate under the scenario with or without the political protection of the green center is: rapid economic development scenario > comprehensive development scenario > natural growth scenario > ecological protection scenario.The land use structure changes significantly,with a large expansion of construction land,a large decrease in the area of arable land,and a small decrease in the area of forest land,grassland,and water bodies.The proportion of landscape area occupied by the largest patches of construction land increases,and by 2025 the dominant land types in Chang-Zhu-Tan are construction land and cropland;the landscape fragmentation of each type in the study area decreases,but the overall landscape fragmentation increases,indicating that while construction land expands to urban areas in a concentrated manner,it also encroaches on the scattered cropland and grassland around the towns,and the more gentle areas of woodland are encroached upon,making the cropland and grassland more concentrated.Woodlands are concentrated to mountainous areas with higher and steeper elevations,and human activities have seriously affected the distribution of each land use type,making the dominance of a single land class landscape weaken.(3)During 2018-2025,the total carbon stock in the study area shows a decreasing trend.The carbon stocks of different land use types are directly related to their carbon density and area,with the strongest carbon sequestration capacity of forest land and the largest area share of cropland,indicating that the sources of carbon stocks in the study area are mainly forest land and cropland,and the changes between land uses have a direct impact on the changes of carbon stocks in urban clusters;the total carbon stocks under the no-greenheart policy protection scenario are larger than those under the greenheart policy protection scenario,while the total carbon stocks under both The total carbon stock in the no-greenheart policy protection scenario is larger than that in the green heart policy protection scenario,while the total carbon stock in the two scenarios is: ecological protection scenario > natural growth scenario > comprehensive development scenario > rapid economic development scenario,and the rapid economic development scenario has the largest loss of total carbon stock among the four urban expansion intensity scenarios.