A planning strategy to augment the diversity and biomass of roadside trees in urban Hong Kong

Abstract

Hong Kong's urban environment has an extremely high development density pervasively filled by buildings and roads. Little ground-level space is left for amenity planting within and without town lots, resulting in a cramped city matrix with inadequate green cover. The community desires for more and better trees for cityscape enhancement and environmental amelioration. A city-wide roadside-tree census was conducted recently together with a survey of potential planting sites (PPS) with a view to augmenting tree biomass and diversity in the long run. Sites with a suitable plantable corridor were evaluated in detail in the field to glean data on growing-space geometry (configuration and dimensions) and qualitative attributes (adjacent land use, building setback, unpaved soil, and air quality). Some 1094 PPS with a total capacity for 12063 trees had been studied. Most PPS are spatially scattered and small, each with <14 trees capacity. A suite of 111 species had been selected for suitable dimensional and amenity attributes to fit the harsh and tight roadside sites, and to avoid the currently rampant discordance between trees and habitats. Environmental conditions within and in the vicinity of individual PPS, with an emphasis on plantable-space geometry, were matched with species characters. A strategy was adopted to maximize final biomass, floristic variety and ornamental functions especially attractive flowers and seasonal changes. A 5 year master planting plan was designed with site-specific species recommendations and a schedule giving priority to tree-deficient and readily-available localities. The landscape in 398 more streets will be improved with congruous trees. A similar green-planning strategy could be applied to other cities with a congested urban morphology.