City-wide relationships between green spaces, urban land use and topography

Richard G. Davies, Olga Barbosa, Nicholas Burke, Richard A. Fuller, Kevin J. Gaston, Daniel Lewis, Jamie Tratalos & Philip H. Warren

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Davies, R. G. , Barbosa, O. , Burke, N. , Fuller, R. A. , Gaston, K. J. , Lewis, D. , Tratalos, J. & Warren, P. H. (1). City-wide relationships between green spaces, urban land use and topography. Urban Ecosystems, 11(3), 269–287.

Housing density , index , Normalised difference vegetation , Topography , Tree-cover , Urban form

The growing proportion of human populations living in urban areas, and consequent trends of increasing urban expansion and densification fuel a need to understand how urban form and land use affect environmental quality, including the availability of urban green spaces. Here we use Sheffield as a case study of city-wide relationships between urban green space extent, quality (vegetation cover and tree-cover), and gradients in urban form and topography. The total area of buildings and length of the road network are equally strong negative predictors of extent of green space, while the former predictor is amore important negative influence upon green space quality. Elevation positively influences extent of green space but negatively influences tree-cover. In contrast, slope of terrain positively influences green space quality and is the best predictor of tree-cover. Overall housing density is a more important negative predictor of extent of green space and tree-cover than the densities of individual housing types. Nevertheless, the latter are more important influences upon levels of vegetation cover. Threshold effects of densities of different housing types suggest opportunities for optimising green space quality, with implications for housing policy. Variation in ecological quality of green space may partly reflect different historical intensities of industrial activity.

Main finding
The study provides several results, some will be described here. The authors found that building footprints were a negative influence on green space quality in terms of both tree cover ad overall vegetation cover. Negative effects of housing types on tree coverage as compared to quantity of green space involved some additionally factors at play. For example, high housing densities tend to have semi-detached and terraced housing usually with small garden with a higher proportion of sealed surfaces (i.e.. pavement) incorporated in them. In sum, the authors suggest that housing policy should strongly consider both the housing type and their densities when setting goals for the quantity and quality of urban green space. Additionally, efforts should be made to mitigate the effects high density building through tree preservation and planting new vegetation with developments.

Description of method used in the article
The authors applied statistical methods, inclusive of regression analysis, minimum adequate models, and MasterMap GIS data to measure the overall relationship between the outcome variables (quality and quantity of green space) and predictor variables (urban form and topography). The quality of green space was assessed with degree of vegetation and tree cover, built form included predictors of total housing and building density, density by housing type, length of roads, and number of rode junctions. Topography was indicated by mean elevation and slope of terrain. To spatialize these for statistical analysis, highly urbanized areas in an around Sheffield were measured including areas that had more than 25% residential and industrial zones within a 1x1 km overlay. The data compiled on the variables in question used a 250mx250m sampling grid over the Sheffield area.

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