| With the acceleration of urbanization and rapid economic development,population expansion and other urbanization issues have already seriously affected the cycle system of ecosystems,reducing the urban green space and severely destroying the ecological environment required by animals and plants.As the sub-center in Beijing,the Tongzhou district undertakes the function of easing the population in the central urban area.The increasing construction land and the single type of green space both have seriously damaged green space patterns and habitats of the Tongzhou district.The paper not only studied the evolution of green space patterns and characteristics of habitat quality changes,but also clarified the correlation mechanism between these two to realize the quality optimization of habitats led by green space patterns and pursue corresponding space allocation and policy implementation suggestions.Taking the central urban area of Beijing as the research object,the paper selected three important nodes(2008,2013,2018)from 2008 to 2018 to interpret its remote sensing images,and explore the characteristics of spatiotemporal changes in green spatial patterns by calculating the green space area and landscape pattern index of the central urban area of Beijing.Secondly,the characteristics of habitat quality changes in the study area in three time periods were evaluated and studied through the InVEST model.Then,influences of green space area,landscape pattern index and urban green space construction on the quality of habitats were discussed according to the evolution of green space patterns.Here are the research results:(1)From the perspective of changes in green space area: the comparison of the whole research process showed that the overall green space area of the study area presented a downward trend,which was mainly converted to the construction land.Main changes in specific land types were concentrated on the conversions from cultivated land to construction land and from forest area to construction land.A small amount of water andgrassland has been converted into construction land.However,from 2008 to 2013,the area of farmland transferred to woodland was second only to that of construction land.(2)The evolutions of landscape patterns in green spaces during the research period were different: the fragmentation degree of the overall green space pattern was gradually weakening,which was mainly because the patch area of cultivated land was the largest part of green spaces,and its connectivity was better than that of forest land and grassland patches.However,the total number of patches in green spaces presented a downward trend.Among them,the woodland patches were the most scattered type with severe fragmentation and poor connectivity;the connectivity and integrity of the grassland should be improved;the fragmentation degree of the water area also decreased gradually.(3)The habitat quality of the study area had changed: during the study period,the general habitat quality of cultivated land in Tongzhou district decreased year by year while the quality of low-level habitats increased,which were mainly because of the conversion from cultivated land to construction land;the quality of moderate habitats increased slightly,which mainly reflected in the scattered grassland in urban areas and parks;the increasing forest land and water area resulted in the overall increase in the quality of high-level habitats.(4)The evolution of green space patterns had significant effects on the habitat quality:first,the impact of changes in the green space area on habitats was studied.It was concluded that different green space areas had a certain impact on the quality of different levels of habitats.The changes in grassland area had great influences on the quality of moderate and general habitats;the changes in forest land and water area had significant effects on the quality of low-level habitats,general habitats and high-level habitats;the changes in cultivated land area mainly affected the quality of low-level habitats.(5)Based on the evolution of green space patterns,four indexes were selected to further illustrate the importance of green spaces on the habitat quality.The fragmentation degree,the overall area of patches,connectivity and diversity of green spatial patterns also greatly affected the quality of habitats.The reduction in the overall patch area of green spaces and the type of land used for surrounding patches after fragmentation had reducedthe quality of habitats of Tongzhou district and the survival space suitable for animals and plants;the connectivity was affected by the land around green space patches,making the habitats seriously interfered by humans;the increasing patch diversity index indicated that a certain type of green space patches was increased pertinently in Tongzhou district.(6)This paper studied the influences on the habitat quality of the Tongzhou district under the planning and construction of green spaces.It was found from studies that the planning and construction of large-scale green spaces can greatly promote the evolution of local green spatial patterns in central urban areas.The point-shaped green space,namely,the Eastern Suburb Forest Park had converted the construction land before planning to green space;the construction of the linear green space,namely,the Grand Canal Forest Park had optimized the overall landscape patch integrity,connectivity,and diversity of the Grand Canal;the implementation of the flat green space,namely,the plain afforestation project had increased the forest area of Tongzhou district and slowed down the reduction of green spaces to a certain extent.The green space constructions above all had positive impacts.(7)The paper proposed the habitat optimization form for the Tongzhou district with goals of protecting biodiversity,improving people's living environment,balancing the urban construction and ecological protection.The paper also put forward specific strategies,such as strictly controlling the development boundary of urban construction areas,protecting the ecological background,constructing forest-water ecological corridors and improving the biodiversity of farmland landscapes.Innovations: this paper studied the changes in habitat quality of the Tongzhou district led by green spatial patterns under the construction of a new model.Besides,the habitat quality optimization direction aiming to improve the green space patterns of the Tongzhou district was established,which enriched the research systems of habitat optimization and explored research methods applicable to the habitat quality optimization of Tongzhou district based on the combination of qualitative and quantitative analysis methods. |
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