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Rooftops as butterfly habitats in Singapore’s HDB housing estates
Author
Zhou, Diana Jing Ying
Supervisor
Lum, Shawn K. Y.
Abstract
Exploring ways to increase wildlife habitats in urban areas of Singapore is important in the conservation of the island’s flora and fauna. With an estimated 82% of Singapore residents living in Housing and Development Board (HDB) flats, bringing wildlife into HDB housing estates serve also to enrich residents’ nature experience. As the local population is expected to increase by 30% over the next two decades, land use conflicts between socio-economic development needs and nature conservation will undoubtedly intensify. Conservation of wildlife by habitat preservation will in turn face mounting land area limitations. A complementary solution would be to integrate wildlife habitats into the urban fabric and for this purpose green roofs are becoming an increasingly attractive option to alleviate various detrimental impacts of urbanisation. Rooftops of HDB buildings in particular are largely empty flat spaces able to be converted into green roofs suitable for habitation by a range of species. The rooftop space therefore represents untapped potential to boost wildlife habitats in residential heartlands without consuming additional land area.
To test the hypothesis that green roofs can support wildlife even in heavily developed neighbourhoods, an experimental green roof was set up in the densely populated Tampines housing estate. Butterflies were chosen as the study subject as they are one of the best-studied taxa in Singapore and charismatic organisms able to gather the support of local residents for conservation efforts. As the experimental green roof was intended to be a butterfly habitat, nine species of butterfly larval host and nectar plants were selected for planting on the rooftop. Over the course of the study, surveys were conducted at least three times a week to record butterfly species richness and abundance as well as recruitment of caterpillars to the green roof.
Seventeen weeks of surveys recorded 317 individuals comprising of 7 butterfly species from 3 families, Pieridae, Papilionidae, and Nymphalidae. Species abundance on the green roof was dominated by three species of generalists, namely Eurema hecabe contubernalis, Papilio demoleus malayanus, and Danaus chrysippus chrysippus. The absence of specialist butterfly species indicates that habitat specificity of butterflies is predictive of the species which will come to inhabit rooftop habitats. This study has thus demonstrated that generalist butterfly species are better able to adapt to and utilise green roofs. Along with knowledge of butterfly populations in the vicinity of designated green roofs, planning can focus on catering to species which could be retained on these artificial habitats.
Results of this study revealed that the experimental green roof was able to support viable butterfly populations comparable to surrounding ground-level green spaces. It also performed better in terms of butterfly species richness than extensive green roofs with a monoculture of Sedum mats. Species richness on the experimental green roof was however lower than that of a nearby, semi-urban park. This is possibly due to several local variables such as age of the green roof, sunlight intensity, floral area, and vegetation diversity and structural complexity. External factors such as landscape configuration and connectivity to and proportion of surrounding green spaces could also influence dispersal to the green roof from ground-level habitats. Altogether, this study demonstrated that green roofs hold an ecological advantage over conventional bare roofs and their installation on HDB buildings should be adopted as a means to create additional wildlife habitats to mitigate habitat loss and to conserve and enrich urban biodiversity in land scarce Singapore.
To test the hypothesis that green roofs can support wildlife even in heavily developed neighbourhoods, an experimental green roof was set up in the densely populated Tampines housing estate. Butterflies were chosen as the study subject as they are one of the best-studied taxa in Singapore and charismatic organisms able to gather the support of local residents for conservation efforts. As the experimental green roof was intended to be a butterfly habitat, nine species of butterfly larval host and nectar plants were selected for planting on the rooftop. Over the course of the study, surveys were conducted at least three times a week to record butterfly species richness and abundance as well as recruitment of caterpillars to the green roof.
Seventeen weeks of surveys recorded 317 individuals comprising of 7 butterfly species from 3 families, Pieridae, Papilionidae, and Nymphalidae. Species abundance on the green roof was dominated by three species of generalists, namely Eurema hecabe contubernalis, Papilio demoleus malayanus, and Danaus chrysippus chrysippus. The absence of specialist butterfly species indicates that habitat specificity of butterflies is predictive of the species which will come to inhabit rooftop habitats. This study has thus demonstrated that generalist butterfly species are better able to adapt to and utilise green roofs. Along with knowledge of butterfly populations in the vicinity of designated green roofs, planning can focus on catering to species which could be retained on these artificial habitats.
Results of this study revealed that the experimental green roof was able to support viable butterfly populations comparable to surrounding ground-level green spaces. It also performed better in terms of butterfly species richness than extensive green roofs with a monoculture of Sedum mats. Species richness on the experimental green roof was however lower than that of a nearby, semi-urban park. This is possibly due to several local variables such as age of the green roof, sunlight intensity, floral area, and vegetation diversity and structural complexity. External factors such as landscape configuration and connectivity to and proportion of surrounding green spaces could also influence dispersal to the green roof from ground-level habitats. Altogether, this study demonstrated that green roofs hold an ecological advantage over conventional bare roofs and their installation on HDB buildings should be adopted as a means to create additional wildlife habitats to mitigate habitat loss and to conserve and enrich urban biodiversity in land scarce Singapore.
Date Issued
2014
Call Number
LC4713.2 Yeo
Date Submitted
2014