不受欢迎的生物多样性:香港的外来植物物种

The bad biodiversity: alien plant species in Hong Kong

香港早在 19世纪中叶开始就有外来植物入侵的记录。迄今为止 ,已发现多达 2 38种已归化的外来或怀疑为外来的植物 ,其中又以薇甘菊 (Mikaniamicrantha)、五爪金龙 (Ipomoeacairica)、假臭草 (Eupatoriumcatarium )、大黍 (Panicummaximum)等最常见。外来植物最常见于受人为干扰的生境 ,例如荒废农田及路旁等 ,而较少在天然林地生境及贫瘠的灌草丛中发现。外来植物对本地生态系统的影响主要局限于低地生境。它们常形成单优种群 ,减少了生境及动植物的多样性。外来动物对香港原生植物影响最大的是于 2 0世纪 70年代入侵的松树线虫(Bursaphelenchusxylophilus)。外来的脊椎动物也有可能对香港的植被演替产生影响。目前香港的外来植物当中 ,有些在大陆较少分布或没有记录。作为华南最大的港口 ,香港对外来物种的引入扮演着重要的角色。因此制定控制外来种在香港及华南地区的引入及传播的政策及措施非常重要。

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, outcompete 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.