Exotic plant invasion in the highly degraded upland landscape of Hong Kong, China

Abstract

Plant communities in the continental tropics have suVered less from exotic plant invasions than their oceanic island counterparts. Most studies have focused on nearpristine communities. By contrast, we examine the resistance of semi-natural continental plant communities in Hong Kong, which have been suVering from chronic and massive human impacts. We compiled a list of all naturalized non-native species recorded in Hong Kong and then sampled the plant communities for exotic species along roadsides, a stream through semi-natural vegetation, and in semi-natural vegetation away from both roads and streams on Tai Mo Shan, Hong Kong's highest peak (957 m). Similar surveys were repeated in other areas of Hong Kong. More than 162 naturalized exotic plant species have been recorded in Hong Kong. On Tai Mo Shan, 29 exotic species were recorded in roadside vegetation, with the diversity but not percentage cover declining signiWcantly with altitude. Fifteen exotic species were found along the stream, including two not found along the roadside. Only six exotic species were found away from roads and streams, all in unshaded areas disturbed by feral cattle. In all surveys, no exotics were found in closed woody vegetation or in open areas without feral cattle, except for one species. The shade-tolerant tropical Asian tree Syzygium jambos was found invading along some streamsides without anthropogenic disturbance. Despite centuries of massive human impacts, exotic plant invasions in Hong Kong are still largely conWned to habitats that suVer from chronic human disturbance. Feral cattle promote invasion where people are absent, but this problem still seems potentially reversible. Only Syzygium jambos is of possible current conservation concern.

Primary Succession along an Elevation Gradient 15 Years after the Eruption of Mount Pinatubo, Luzon, Philippines

“…This elevation effect was mediated by greater human activity in the lower elevations. A case study in Hong Kong (Leung et al 2009) lends support for our association of human activity and exotic species diversity in these Pinatubo canyons. They found that after centuries of anthropogenic disturbances, a greater number of exotic plant species was directly related to corridors of greater human impact and less-traveled sites were still relatively free of alien invasions.…”

Minimizing Risks of Invasive Alien Plant Species in Tropical Production Forest Management

“…Some may enter from the surrounding non-forest-most often agricultural-matrix, but the resistance of continental forests to such invasions is well-documented (e.g., [17,18]) ( Table 1). This resistance is usually attributed largely to dense shade [19], but may also reflect the preemption of other resources by a hyperdiverse native flora.…”

“…Land preparation requires careful control, due to the potential influence on seed germination [90]. Clear cutting of mature plantations creates large gaps that favour invasion [18,77]. Moreover, plantations trees may also become invasive (Table 3).…”

Invasive aliens on tropical East Asian islands

“…for Hong Kong-Corlett 1992b;Dudgeon and Corlett 2004;Leven and Corlett 2004;Chung and Corlett 2006;for Singapore-Corlett 1988, 1992aTan et al 2007). In contrast, only single alien plant species, Syzygium jambos in Hong Kong (Leung et al 2009) and Clidemia hirta in Singapore (Teo et al 2003), have signiWcantly invaded native, closed-canopy forests. Additional aliens are established in the margins of some forest areas and along forest paths on both islands.…”