| The ecological green heart of Chang-zhu-tan urban agglomeration is the largest green heart of urban agglomeration at present,which has an immeasurable strategic position.Understanding the carbon storage characteristics of vegetation and its dynamic evolution trend is of great significance to correctly understand the importance of green heart,improve the regional ecological environment of Chang-zhu-Xiangtan urban agglomeration and promote the realization of regional carbon neutrality.Taking Chang-zhu-tan Green-core area as the research objective,the land use information of Green-core area was extracted based on Google Earth Engine platform,and combined with quadrate survey,the inversion model of arbor above-ground carbon storage in Green-core area was established,and the carbon storage characteristics of Green-core area were analyzed:The effects of land use and landscape pattern on carbon storage characteristics were discussed,and the contribution of land use and landscape pattern to carbon storage characteristics was quantitatively analyzed at different urbanization stages.The effects of driving factors on vegetation carbon uptake rate were analyzed.According to the analysis results,guidance and suggestions are provided for the planning and construction of Green-core District.The results of this study are as follows:(1)From 1999 to 2020,carbon storage in the Greenheart region changed significantly,and carbon reserves in the area near the urban core decreased significantly.Carbon storage in the central region continued to rise with the growth of forest vegetation,and carbon sequestration level in the Green-core region was still relatively high.Carbon reserves in the Green-core region decreased first and then increased during the four periods from 1999 to 2020.Carbon storage was 1.24×10~6 t,1.08×10~6 t,0.70×10~6 t,1.40×10~6 t,and carbon density was 34.12 t/hm~2;34.04 t/hm~2,35.81 t/hm~2,57.80 t/hm~2,respectively.(2)The influence of landscape dynamic characteristics on carbon storage characteristics of Green-core was significantly different.In both stages,land use type change was the most important factor contributing to the change of carbon storage of trees,but there were some differences.From 2006 to 2013,the contribution rate of land type change to carbon storage change was 58%,and that of landscape pattern to carbon stock was 36%(84.48%accurate).The contribution of land use was mainly the conversion of forest land into cultivated land and construction land,and the decrease of forest land area led to the decrease of carbon storage in this period.The contribution of landscape pattern is mainly the influence of landscape CONTAG,PD,construction land PD and forest land PD on carbon storage.From 2013 to 2020,the contribution rate of land use change to carbon stock change was 91%,and that of landscape pattern was 4%(accuracy:61.72%).The contribution of land use was mainly unchanged forest land(86%),conversion of construction land to forest land(3%),and conversion of cultivated land to forest land(2%).This phenomenon indicated that the contribution of forest land carbon density increase was greater than that of forest land area increase,and it also meant that there was still a huge potential for carbon sequestration in the future green-heart area.Therefore,in the process of development and construction of Chang-zhu-tan Green Heart,it is helpful for sustainable development and construction of green heart area to insist on returning farmland to forest,planting trees and adhering to the protective development strategy of green heart.(3)Through the analysis of vegetation carbon uptake,it was found that vegetation carbon uptake in Green-core region had significant seasonal and spatial differences.The carbon uptake rate in central and eastern regions was higher than that in western regions,and the peak value of carbon uptake in summer was significantly higher than that in other seasons.Correlation analysis found that in spring,summer,autumn and winter of 2006,2013 and 2020,precipitation,surface temperature,dispersal,elevation and slope,land use area and landscape pattern all had strong correlation with vegetation carbon uptake and affected vegetation carbon uptake level.Principal component analysis found that,The first principal component of factors influencing carbon uptake is mostly the comprehensive effect of land use area and landscape pattern factors,indicating that all factors influencing vegetation carbon uptake work together on vegetation carbon uptake and also influence each other.(4)After the implementation of Green Heart protection policy,the situation of continuous decrease of forest area in Green Heart area was reversed,and the forest area increased by 46.45km~2.The carbon storage level of forest area increased significantly by 9.96 ×104 t annually.The overall landscape of Green Heart developed towards agglomeration.In the future process of urbanization,the plan of landscape sustainability planning strategies should be adopted according to local conditions in view of the spatial heterogeneity of carbon density.In addition to increasing the proportion of forest area near the eastern bank of Xiangjiang River,the woodland aggregation degree and the average patch area were improved.In the Muyun area,Tongsheng Area and the north and southeast area of Tiomao Area,attention should be paid to reducing the aggregation degree of construction land when increasing the area of construction land,maintaining the overall connectivity of green core forest land through "green belt" and "green corridor",improving the landscape composition proportion and spatial aggregation degree of green infrastructure such as forest land,so as to promote the sustainable development of regional landscape.This study is helpful for us to better understand the impact of regional landscape dynamic changes on tree carbon storage in the process of urbanization in Chang-zhu-tan,conducive to understanding the factors affecting vegetation carbon uptake,conducive to understanding the practical significance of green heart protection policy for carbon neutrality,and conducive to urban planning and management to promote the direction of ecological sustainability of Chang-zhu-tan urban agglomeration.Based on the results of this study,the following suggestions are put forward for the planning and development of Green-core area:(1)Increase the connectivity of forest land,increase the connectivity of forbidden development zones in the northeast,and reduce isolated patches;(2)Control the construction area "see the seam and insert the green",greening the roof and improving the green area;(3)Increase the density of wetland water patches in Green-core area,protect the existing small and micro wetlands,and prohibit the encroachment and landfill of wetlands. |
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