| In the semi-arid region of Northwest China,along with population growth,natural landscape had been replaced by artificial landscape,habitat fragmentation,poor landscape connectivity,and decline in biodiversity.Constructing multi-level spatial ecological network is an important guarantee for maintaining ecological security in the western semi-arid region.The stability of low-level ecological source areas depended on high-level ecological source areas,and high-level ecological source areas were of great significance for maintaining the stability of hierarchical ecological network.The destruction of high-level ecological sources easily affected the surrounding low-level ecological sources,to affect the stability of low-level ecological networks,trigger cascade failure of hierarchical networks,leading to the collapse of the entire network.Therefore,this paper took Baotou,a typical semi-arid city in Northwest China,as the research area.With the support of GIS spatial technology,using the analysis methods of landscape ecology and complex network theory,the hierarchical ecological network of Baotou city was extracted.The main conclusions were as follows:(1)During the decade of 2006-2016,the characteristics of urban landscape had undergone profound changes,and the acceleration of urbanization had led to the fragmentation of ecological landscape.During the decade 2010-2016,the landscape changed in Baotou City showed a point distribution,mainly distributed in the farming area with dense cultivated land and broken grassland and the edge of different landscape alternation.Baotou City had not yet formed a dominant landscape,landscape fragmentation intensified.On the scale of type,the walking and juxtaposition index and separation index of grassland landscape decreased by 15.98 and 1.12 in 2006-1016,respectively.The shape index of construction land increased by 55.3 and the cohesion index decreased by 4.59.The shape index and segregation index of cultivated land increased by 79.5 and 447.74,respectively.(2)Grassland landscape was the main part of Baotou's ecological landscape.On the scale of landscape,the similarity percentage index and dispersal and juxtaposition index of landscape in Baotou are higher,while the landscape segmentation index was lower.On the scale of type,the proportion of grade 1-7 was higher,the patch density was lower and the aggregation index was higher.The proportion of grade 8-12 was low,the landscape segmentation index was high,the landscape was fragmented and the connectivity was poor.Per the extracted grassland landscape network,the characteristics of ecological network were analyzed by using degree and degree distribution to evaluate node degree,average path length and clustering coefficient.It was found that the number of grassland patch nodes with a degree of 6 in the grassland landscape network was 5.There were two nodes with a maximum degree of 8 and an average path length of 1.6061.The grassland landscape network had obvious non-uniformity.(3)The potential ecological network of Point-line-plane interweaving layers was formed on the city scale.The first layer consisted of eight potential ecological sources,eight potential ecological corridors and seven nodes.The second layer consists of 31 potential ecological sources,35 potential ecological corridors and 28 ecological nodes.The third layer consists of 123 potential ecological sources,151 potential ecological corridors and 47 ecological nodes.The hierarchical ecological network structure was evaluated by calculating the alpha,beta and gamma indices.With the increase of the number of ecological sources and corridors,the more loops available for material flow in the network,the better the average connectivity of ecological sources.In the second and third layer networks,the proportion of sources with high connectivity was less.Based on the index of topological structure analysis in complex networks,the topological properties of the extracted layer 1,2 and 3 ecological networks were analyzed.(4)The pattern of ecological network played an important role in maintaining regional ecological security.Based on existing research,it was of great significance to accurately simulate the evolution of landscape ecological network space.In this paper,the ANN model was used to extract the neighborhood rules of cellular automata,and the MCR model was used to construct the cumulative consumption resistance surface.Based on the MCR-ANN-CA model,the spatial evolution of landscape ecological network in Baotou City is simulated.The results were of high accuracy.Comparing the simulation results of MCR-ANN-CA model with that of CA-Markov model,the KIA indices of the two models were 0.89 and 0.87,and the relative errors were 3.10%and 5.31%,respectively.The MCR-ANN-CA model had higher simulation accuracy for the evolution process of landscape ecological network space in Baotou City. |
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