Ecological diversity of birds in relation to the structure of urban green space

A functional network of green space is important for the maintenance of the ecological dimension of a sustainable urban landscape. We used avian ecological diversity as a proxy for evaluating the functionality of different types of urban green space. The urban landscape of the municipality of Örebro in Sweden was stratified into four strata (City centre, Residential, Greenway and Periphery). Bird species found in these strata were classified into four ecological groups with decreasing degree of specialisation (woodpeckers, hole-nesters, forest birds and urban birds). Overall there was lower bird species richness in the City centre and Residential areas compared to the Greenway and Periphery. Woodpeckers, hole-nesters and forest birds showed an increasing trend in the number of species as well as individuals from the City centre to the Periphery while urban birds showed the opposite trend. The amount and quality of green space as well as natural vegetation increased from the City centre to the Periphery. Species richness of woodpeckers, forest birds and hole-nesters were positively correlated with tree density while urban birds showed an inverse correlation. There was no dead wood in City centre, Residential and Greenway in contrast to the Periphery, which held some dying trees, stumps and old windthrows. Our findings emphasise the importance of urban green space with natural structures to maintain high ecological diversity. Finally, we discuss how conflicts between habitat for biodiversity maintenance and other functions of green space could be handled by zoning.