Planting models for promoting urban butterfly diversity in Hong Kong

Abstract

Habitat destruction and habitat loss are well-known negative impacts of urbanization which caused decrease in biodiversity. Although the habitats in urban area have been greatly disturbed, urban biodiversity still plays an important role in holistic view in biodiversity. Urban biodiversity conservation is important in creating stepping stones to nonurban habitats or even the wild. Thus the conservation value of urban area cannot be neglected. The Hong Kong Biodiversity Strategy and Action Plan (BSAP) was published in 2017 by the Environmental Bureau. A list of actions for conserving biodiversity in Hong Kong was stated. The promotion of urban biodiversity was action 10 in the BSAP. This action triggered this study of enhancing butterfly biodiversity in urban parks. Butterflies are well known to the public. With attractive look, rich traditional, cultural, and artistic values, and being easy to observe, butterflies become good teaching and educational material for promoting urban biodiversity. As butterflies feed on plants in both adult and larval stages, plants are the most important resources for growth and reproduction for butterflies. Plants play the most important role in butterfly’s lifecycle, making butterflies particularly sensitive to environmental changes. Butterfly has been suggested as an indicator for determining the urbanization impacts on biodiversity in urban environments. Butterfly biodiversity are possible to be enhanced by improving the design of plant composition in urban parks. To obtain information of the current situation of butterfly biodiversity and related plant biodiversity in urban parks for designing planting model to attract butterflies, butterfly surveys, nectar plant surveys and larval food plant surveys had been conducted. In butterfly surveys, 30data sets were collected during 6 months at 5 study sites in 18 survey days. A total of 62 butterfly species from five families and 936 individuals of adult butterflies were recorded. Five data sets of nectar plant survey were collected at 5 study sites in 5 survey days.27 nectar plant species were recorded from 15 families; there are also 5 data sets of larval food plant survey collected at 5 study sites in 5 survey days. Fifty-six larval food plant species in 27 families were recorded. After reviewing of the combinations of plants found in five urban parks, two observations were made. There is a general lack of enough nectar plants for providing nectar resources for butterflies and larval food plants in urban parks are not diverse enough to cover most of the urban butterfly species. The species selection of plants seldom shift to native species which might be miss the advantages of native species such as attractiveness to butterflies and survival rate in the local environment inside the parks. There is a lack of emphasis in choosing native plant species which are attractive to butterflies and increase the survival rate of butterflies in urban parks. To enhance butterfly diversity in urban parks, 100 plant species with benefits to butterfly biodiversity are listed in the planting model to provide different functions in urban parks. Both nectar plants and larval food plants with different growth habits and environmental needs are included in the planting model. Larger proportion of native species are used while lesser exotic species were listed in the model. Besides the planting model, recommendations on urban parks management practices are also provided. The long-term goal of practicing this planting model is to encourage rare species to become residents in urban green areas and compensate the negative effects of habitat isolation and loss due to urbanization.