Not all green is as good: Different effects of the natural and cultivated components of urban vegetation on bird and butterfly diversity

Abstract

It has been suggested that provision of greenery can ameliorate the hostility of the urban environment for wildlife, but greenery can either be in the form of regenerating or remnant patches of natural vegetation, or as cultivated tree, shrub, and ground cover. We test if natural and cultivated greenery differed in their effects on bird and butterfly diversity in the tropical city-state of Singapore, while accounting for the effects of traffic density. Natural vegetation cover was positively correlated to both bird and butterfly species richness. Cultivated tree cover was positively correlated to bird species richness. Meanwhile, ground cover was weakly negatively correlated to bird species richness and overall cultivated greenery cover was weakly positively correlated to butterfly species richness. Increasing road lane density also negatively impacted both bird and butterfly species richness, while there was substantial evidence for an interaction effect between road lane density and cultivated tree cover on bird species richness. Cultivated and natural forms of greenery favoured different assemblages of bird and butterfly species. After controlling for the confounding effects of alpha diversity on community dissimilarity, cultivated greenery was found to produce homogeneous bird and butterfly communities in the urban landscape. Therefore, not all forms of greenery benefit urban biodiversity to the same extent. Management of urban areas to support bird and butterfly wildlife would need to maximise natural or semi-natural cover and only resort to highly-manicured, artificial greenery as a second option, while planning road networks carefully to optimize road lane density.