The bad biodiversity: alien plant species in Hong Kong

Abstract

The flora of Hong Kong has been well-surveyed since the mid nineteenth century and has had a long history of alien plant invasions. To the present day, more than 2130 wild plant species have been recorded, including 238 species that are probably naturalized alien species. Among them, Mikania micrantha, Ipomoea cairica, Eupatorium catarium, and Panicum maximum are most abundant. Naturalized alien plants are most prominent in human-disturbed habitats, such as abandoned farmland, wasteland and roadsides, and are rarely important in relatively undisturbed forest habitats, or in fire-maintained impoverished shrubland and grassland. Impacts of naturalized alien plants on local ecosystems are so far limited to lowland habitats, including wetlands and forest margins, where they form monospecific thickets, out-compete native plant species, and reduce local habitat and animal diversity. The biggest impact on the local flora by an alien species, however, was caused by the Pinewood Nematode introduced in the 1970s. Introduction of alien vertebrates may also have an impact on Hong Kong' s vegetation. As the biggest port on the southern coast of China, Hong Kong has probably been an important entry point for alien species to China. Among Hong Kong' s naturalized alien plants, some have only recently been noticed, and have few or no records from the mainland. The potential for these species to invade the mainland should not be neglected. Appropriate measures to control spread of these plants, both locally and regionally, are essential.