Study On The Structural Evolution Of Settlements And Ecological Spatial Network In Oujiang River Basin

Urbanization is a social development trend.Promoting green development and promoting harmonious coexistence between man and nature is the general tone of ecological civilization construction in the new era.At the macro level,the relationship between human and nature can be expressed as the relationship between construction land and natural landscape such as woodland,water body and grassland in the land use type.The Oujiang River Basin is characterized by complex and diverse terrain,developed regional social economy,and typical and special characteristics and rules of urban and rural settlements and ecological environment.Therefore,this paper selects the Oujiang River Basin as a test area to explore the evolution characteristics of its settlements and ecological spatial network structure.Based on the land use data of 2000,2010 and 2020,the settlement spatial network is constructed for Wenzhou section and Lishui section of Oujiang River Basin respectively.Several network evaluation indexes,such as node degree and aggregation coefficient,are selected to analyze the structure and evolution characteristics of the settlement spatial network,and explore its driving factors from the perspective of nature and social economy.Ecosystem service value estimation,morphological spatial pattern analysis model and minimum resistance model were used to estimate the ecosystem service value of Oujiang River Basin,identify the ecological source,construct the ecological network,and select α,β,γ index to evaluate the ecological network structure.The relationship between settlements and ecological networks in the Oujiang River basin is summarized.The main conclusions of this paper are as follows:(1)The spatial network of settlements in Wenzhou District of the Oujiang River Basin is closely connected;The change of network structure in the first 10 years is greater than that in the last 10 years.The spatial development of settlements is unbalanced.The settlements along the Oujiang River main stream,especially in the south,are more widely distributed and more concentrated,while the settlements along its tributaries are small and scattered.With the continuous development of settlements in Wenzhou area,the scale and external radiation capacity of settlements have been continuously enhanced.Topographic and economic factors are the main factors affecting the formation of settlement structure in Wenzhou area.The lowlying and flat areas are widely distributed,and the more developed areas are,the stronger the centrality of settlement.(2)The spatial network of settlements in Lishui District of the Oujiang River Basin is scattered on the whole.The spatial development of settlements is unbalanced and affected by topography obviously.The subnetwork structure in the northeast is more complex,while the subnetwork structure in the southwest is small and simple.The settlement scale of each subnetwork continues to grow,and the ability of external radiation continues to strengthen,but the development speed is slower than that of Wenzhou District.Topographic and economic factors are the main factors affecting the formation and evolution of settlement structure in Lishui District,and the restrictive effect of topographic is more obvious.The settlement scale is larger in the low-lying flat area,while the settlement scale is scattered and small in the complex terrain area.(3)The ESV coefficient per unit area of Oujiang River Basin is the highest.During the study period,the ecological environment of the basin remained stable on the whole,and the distribution change of ecosystem service value was not obvious.The contribution of forest land to ecosystem service value is the largest,and the absolute value of change is also the largest.The main service functions of the Oujiang River Basin ecosystem are climate regulation,hydrological regulation,soil conservation and biodiversity protection.In addition to water resources supply and hydrological regulation,the value of other service functions showed a continuous decreasing trend in the past 20 years,with a small decreasing range.(4)Based on the land use data in 2020,forest land,water body and grassland are selected as prospects for MSPA analysis according to the ESV estimation results.The results show that the ecological source area is widely distributed in the mountainous and hilly area of the Oujiang River Basin,and the ecological environment of the basin is good.The landscape core area accounts for 57.8% of the basin area.Landscape type,distance from road,elevation and slope were selected as resistance factors to establish the comprehensive resistance surface of species migration,and construct the ecological network of Oujiang River Basin.It is more concentrated in the north of the basin than in the south.The results showed that there were more closed loops and more alternative paths for species migration in the ecological network.The network structure is complex and the anti-interference ability is strong.The connection level of the network structure is complex.The distribution and characteristics of ecological environment and ecological network in Oujiang River Basin are mainly determined by terrain and climate.Meanwhile,economy and policies are also important influencing factors.(5)In general,there is an inverse correlation between settlements and ecological networks in the Oujiang River Basin.However,settlement spatial network and ecological network are not completely unrelated.The upstream is the birthplace of the Oujiang River,which is an important ecological source with large topography and small scale settlement network.In the middle reaches,ecological corridors are dense in the north and south,and ecological source areas are widely distributed.Ecological source areas and ecological networks are widely distributed in the north of the lower reaches.The south is flat and the river surface is widened,which has developed into a large-scale Wenzhou settlement network.