Clidemia hirta Invasion at the Pasoh Forest Reserve: An Unexpected Plant Invasion in an Undisturbed Tropical Forest1

Abstract

CIi&mia hirta is a highly invasive shrub in tropical forests throughout the world, but has had little success invading mainland sites and undisturbed forests. In the early 199Os, this plant was found to have invaded an unexpected site, an undisturbed continental tropical forest at Pasoh, Peninsular Malaysia. In 1997, a study was conducted of the C. hirta population at the Pasoh Forest Reserve. A demographic survey of the 50-ha long-term research plot at Pasoh located 1002 C. hirta individuals, 69 of which were reproductive at the time of the study. All but 8 individuals were located in high light gaps or gap edges. Relative growth rates were significantly higher in gaps and gap edges than in the understory, and no reproductive individuals were found in the understory. Mean plant size and dry biomass density increased steadily over the course of the study, while the observed mortality rate was 0 percent over two months. The biomass density of Clidemia at Pasoh was <500 g/ha at the conclusion of this study, but because the population is confined almost exclusively to high light environments, its density in these sites is much higher. The location of C. hirta plants in gaps was significantly correlated with past disturbance by wild pigs, suggesting that soil disturbance and light availability are essential for their establishment. The implication of this study is that by competing with native species in gaps, C. hirta invasion has the potential to alter forest regeneration at Pasoh. Changing land use practices near the reserve have increased the number of wild pigs, and thus the level of disturbance, which may explain the recent success of C. hirta at Pasoh.

Spread of invasive plants along trails in two national parks in West Java, Indonesia

“…If conservation measures are applied to open land for several decades, these invasive species will decline. Only C. hirta is a relatively shade-tolerant small woody shrub (DeWalt et al 2004) that invades gaps of natural forests, such as in Pasoh, Malaysia (Peters 2001), and in Singapore (Teo et al 2003). This species often inhabits the forest floor of natural forests in Java and Kalimantan, although it does not dominate.…”

A invasão de um fragmento florestal em São Paulo (SP) pela palmeira australiana Archontophoenix cunninghamiana H. Wendl. & Drude

“…Existem plantas invasoras de todas as principais formas de vida, de ervas a árvores, ocorrendo nos mais diversos tipos de ecossistemas (Cronk & Fuller 1995). Florestas tropicais pouco perturbadas parecem ser raramente invadidas (Laurance & Bierregaard 1997), embora haja exceções a esta regra (Cronk & Fuller 1995, Peters 2001. Ainda em florestas tropicais pouco perturbadas, lianas e trepadeiras exóticas podem ter efeito importante nas bordas, sendo também freqüente a ocorrência de plantas exóticas colonizando clareiras.…”

Human-Altered Mesoherbivore Densities and Cascading Effects on Plant and Animal Communities in Fragmented Tropical Forests

“…Yet, tree species have differential ability to regenerate following snapping; the dominant dipterocarps have particularly poor regrowth rates (Ickes et al, 2003). The wild pigs are also implicated in Pasoh's recent invasion by Clidemia hirta (Melastomataceae), an invasive shrub colonizing recent treefall gaps and pig-disturbed soil (Peters, 2001). Thus, the ecological release of feral pigs in Pasoh, due to a combination of artificial food inputs (i.e., oil palm) and lost native predators (Ickes, 2001;Ickes & Williamson, 2000), is having and will continue to have dramatic cascading effects on forest structure and tree community composition.…”