Abstract
Urban ecology is threatened by habitat loss and fragmentation due to increasing urbanization. Green roofs may act as habitats to compensate for loss of green space at the ground level. Here, we assessed greening variables of 11 green roofs for butterflies in Taipei City. Butterfly number, species, and richness on green roofs were lower than parks, but some less common species were observed on green roofs. The nectar plant area, number of nectar plant species and age of green roof were the main positive effectors of butterfly number. The height above ground of green roof had not impact on butterfly survival; supposed high rise buildings are spreading out over city that would be a potential good habitat for butterflies on skyscape. However, since the scale of green roofs was small in Taipei, we adopted a habitat suitability index (HSI) method to determine optimal value of selected greening variables to attract more butterfly number on green roofs. HSI curves' findings suggested that achieving a nectar plant area of more than 25 m2 and not less than 10 nectar plant species would greatly benefit butterfly number; meanwhile, the age of green roof was higher than 38 months, butterfly number is expected to increase rapidly. We confirmed that carefully design green roof could play a good habitat for butterflies in Taipei city.
Highlights
The increase of human populations in city centers and urban sprawl has eliminated or severely restricted green space and threatens habitats
habitat suitability index (HSI) curves' findings suggested that achieving a nectar plant area of more than 25 m2 and not less than 10 nectar plant species would greatly benefit butterfly number; the age of green roof was higher than 38 months, butterfly number is expected to increase rapidly
Few less common species were observed on green roof, which support a lower abundance of bees than nearby urban park (Brenneisen, 2006; Gedge & Kadas, 2005; Kadas, 2006; Snep et al, 2011)
Summary
The increase of human populations in city centers and urban sprawl has eliminated or severely restricted green space and threatens habitats. Since large amounts of land area are covered by various kinds of buildings makes the urban green space area at ground level is limited, many countries have begun to consider the green roof as an important habitat for wildlife in the city (Oberndorfer et al, 2007). Green roofs in large cities have high potential as habitat for species negatively impacted by land-use changes (Brenneisen, 2006). Blair & Launer (1997) asserted that some butterfly species can survive in urban areas that have suitable habitats. Butterfly diversity in urban areas can be preserved by constructing suitable habitats in these areas (Chikamatsu, Natuhara, Mizutani, & Nakamura,2002; Collier, Mackay, Benkendorff, Austin, & Carthew, 2006; Smallidge & Leopold, 1997; Wood & Pullin, 2002)
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