| Timely and effective assessment of the direct and indirect effects of urban expansion on natural habitats in the TACM is of great significance for the maintenance and promotion of regional sustainability and biodiversity conservation.However,at present,there is a lack of the research on assessing the direct and indirect natural habitat losses cause by urban expansion in the TACM.Therefore,this paper aims to simulate and evaluate the direct and indirect effects of urban expansion on natural habitats under different scenarios in the TACM from 2015 to 2050 on a multi-scale and multi-method basis based on the theoretical framework of landscape sustainability science of "pattern-process-impact-sustainability".The main work and findings are as follows:(1)The spatial pattern of natural habitat in the TACM was quantified.There is a large number of natural habitats in the TACM,and the main habitat type is the forest.In 1992,the natural habitat area of the whole region was 108200 km2,which was 82.73%of the total area in the whole TACM.Among the different types of natural habitats,the forest has the largest area of 106700 km2,accounting for 98.62 percent of the total area of natural habitats.On subregions,the natural habitat area on the Chinese side is the largest,with an area of 62500 km2,which is 57.78%of the natural habitat area in the region,followed by the DPRK side,followed by the Russian side.(2)The urban expansion in the TACM during 1992-2015 was reconstructed,and then the urban expansion under different SSPs from 2015 to 2050 was simulated.The study simulates the urban expansion under different scenarios in the TACM from 2015 to 2050 by combining the Shared Socioeconomic Pathways(SSPs)scenario and the zoned Land Use Scenario Dynamics-urban(LUSD-urban)model.It was found that the urban land in the TACM will continue to increase in the future.Urban land area in the whole TACM increased from 463.32 km2 to 868.23 km2,an increase of 87.39%from 1992 to 2015.The proportion of urban land in the total area of the region increased from 0.35% to 0.67%.The urban expansion on the Chinese side is the most obvious,and the urban land area has increased from 280.53 km2 to 603.36 km2,an increase of 1.15 times.During 2015-2050,the urban land area will increase from 868.23 km2 to 1025.78 1386.50 km2,an increase of 18.15%and 59.65%in the TACM under different SSPs.The proportion of urban land area in the total area of the region will increase to 0.78%to 1.06%by 2050.The DPPK’s side will become the main region of urban expansion in the TACM in the future.The urban land area on the Democratic People’s Republic of Korea’s(DPRK)side will grow from 174.78 km2 to 232.46 to 357.58 km2,an increase of 33.00%to 104.59%,with an average annual growth rate of 0.82%and 2.07%,which is 1.50 to 1.71 times the average of the whole TACM.(3)The direct and indirect effects of urban expansion on regional natural habitats in the TACM were evaluated.Based on the LUSD model,the direct and indirect effects of urban expansion on natural habitats are systematically evaluated in the TACM from 2015 to 2050.The results show that,the urban expansion in the whole region led to the loss of regional natural habitat area 234.18km2 during 1992-2015,among which the natural habitat loss caused by the urban expansion on the Chinese side was the most serious,with the loss of 78.48260.82 km2,which was 55.14%-59.26%of the lost area in the whole TACM.However,the loss of natural habitats will be 134.73-472.32 km2 caused by future urban expansion in the TACM under the SSPs during 2015-2050.Compared with 1992-2015,the future loss of natural habitats will be 2.02 times that of in 1992-2015.In the subregions,the DPPK’s side will be the most serious,and the loss of natural habitats 56.25-191.16 km2 resulted from urban expansion under different scenarios,which will be 5.30 times the natural habitat loss in the past.The indirect loss of natural habitat in the whole region will be 2.12 times that of the direct loss caused by future urban expansion.What is more noteworthy is that the indirect effect of the future urban expansion on the natural habitat will be obviously greater than the direct effect.The direct loss of natural habitat caused by urban expansion will be 56.97-153.90 km2 in the TACM,and indirect loss of natural habitat caused by cropland displacement resulting from urban expansion will be 77.76-318.78 km2.Furthermore,the DPRK’s side will experience the most serious indirect loss of natural habitat among the three subregions,decreasing by 38.70-145.08 km2,which will be 2.21-3.15 times greater than the direct loss.Therefore,we suggest that in the TACM,especially on the DPRK’s side,measures such as increasing urban population density and promoting three-dimensional urbanization should be taken to improve the utilization of urban land.Additionally,the occupation of cropland by new urban land should be controlled to protect high-quality cropland Furthermore,important ecological protected areas should be defined based on ecosystem services to reduce the occupation of natural habitat by urban expansion and cropland displacement.In brief,some regulations and policies should be taken to balance urban expansion,cropland displacement,and natural habitat conservation and further promote regional sustainable development. |
