Compact Change Of Urban Land Use And Its Impact On Riparian Habitat Quality

Under the background of new urbanization in China,compact city is considered as one of the main strategy to alleviate urban spread and promote the sustainable development of cities,but its ecological environment benefits are still unclear.The riparian habitat is located on the boundary of the intersection of aquatic and terrestrial ecosystems.Due to the complex fringe effect,it often has higher biodiversity,landscape and economic value,and also,is more sensitive to the disturbance of urban land construction.In cities,continuous green habitat corridors are often rare and precious,therefore,riparian habitats are of great significance to conserve and maintain urban biodiversity.Studies has shown that urban sprawl on watershed scale has a significant negative impact on riparian habitats,but it is unclear which urban development model can support the biodiversity of riparian zone more effectively.Does compact land use have a potentially positive impact on riparian habitat quality compared with the dispersion or expansion model,or also inhibit the development of biodiversity in riparian zone? Figuring out the above scientific issues has certain theoretical and practical value for urban land and riparian habitats planning and conservation with the orientation of improving riparian biodiversity in the future.Under the above background,this thesis takes Wuhan section of Hanjiang River small watershed as the object,analyzes the connotation of urban land compactness and riparian habitat deeply after reviewing the literature related to compact city theory,land use compactness evaluation and riparian habitat quality evaluation.the evaluation index system of urban land compactness and riparian habitat quality was constructed,and the riparian habitat quality evaluation under the background of urban development was carried out.Moreover,the correlation analysis and ranking analysis were used to reveal the influence mechanism of urban land compact development on riparian habitat quality.The research results of this paper mainly include:(1)The evaluation system of urban land use compactness was established with the perspective of comprehensive and intensive land use development,,which consists of three dimensions of land use intensity,land use form and land use layout.The spatial analysis of land use compactness in Wuhan section of Hanjiang small watershed was carried out with a grid scale of 500m×500m.The result has shown that the land use compactness in small watershed has a significant spatial aggregation characteristics,the number of grids in noncompact and low-compact level is the largest,accounting for 52.23% of the total grids.At present,the development of urban land in the Fourth Ring Road is relatively compact,with76.1% of the grid in the compact and highly compact level.(2)Based on the structure of riparian habitat and the spatial process of the impact of urbanization on it,an evaluation index system of urban riparian habitat quality was established,which was composed of four dimensions and 18 factors: base habitat,indicator habitat,potential habitat and habitat threat.37 sample sites were selected to carry out field survey.The results showed that 46% of the sample points were in the "good" and "fairly good" grades,and they are mainly concentrated in the areas outside the Third Ring Road,the rest of the sample points in the "general" grade are 8,"poor" and "quite poor" grade sample points are 12.The habitat quality grade distribution of riparian zone is bounded by the Third Ring Road,showing obvious spatial differentiation between the downtown and suburban.The differences of habitat quality of riparian zone are mainly reflected in the riparian width,the complexity of micro-topography,the richness of native herbs,the coverage rate of trees,the number of birds,the land use status outside riparian zone,the area of habitat unit outside riparian zone and the intensity of human activities.(3)Spearman correlation analysis,function fitting analysis and RDA analysis were used to explore the impact of urban land use compactness change on riparian habitat quality at reach and sub-watershed levels.The results showed that:(1)On both scales,the comprehensive habitat quality of riparian zone decreased significantly with the increase of land use compactness.However,the function fitting curve showed that the negative impact of moderately compact land use development model on riparian habitat was moderate.(2)The impact of urban land use compact change on riparian habitat has significant scale effect.The impact of land use compact change on the sub-watershed scale was significantly higher than that on the reach scale,both in terms of comprehensive habitat quality and individual habitat quality indicators.(3)Indicator habitat quality is the most significant factor affected by land use compact change.(4)On both scales,development and utilization intensity,proportion of residential land and plot ratio are the dominant factors affecting the change of riparian habitat quality.On the reach scale,road network density also dominates the change of riparian habitat quality.On the sub-watershed scale,mixed land use degree has a significant impact on riparian habitat quality.(5)The compact change of land use form and layout had little effect on riparian habitat,and the fractal dimension index was positively correlated with it.It is proved that under the same development intensity,improving the urban land form and layout compactness is an effective strategy for collaborative urbanization and riparian biodiversity improvement.(4)Combined with the above analysis results,the riparian habitat planning strategy under the background of urban compact development is proposed,which mainly includes:(1)The urban catchment units should be restored and reconstructed by integrating land development impact and natural hydrological process;(2)Based on the habitat connectivity on the longitudinal scale,riparian zone planning is divided into habitat closure type,habitat conservation type,habitat restoration type and habitat reconstruction type;(3)According to the corresponding relationship between hydrological units and urban planning units at different levels,strategies are provided for the connection between riparian habitat planning and urban planning.Finally,from three aspects of land use intensity control,land use form control and land use layout control,this thesis puts forward some strategies for the compact planning of urban land use in small watershed with the purpose of improving the performance of riparian habitat services.