General Impact
Invasive plants present a major problem to conservationists because of their tendency to replace diverse natural vegetation with exotic monocultures (Cronk and Fuller 1995, Rejmánek 1996, in Peters 2001). Plant invasion poses a serious threat to forests because of its potential to reduce biodiversity and lead to the extinction of native flora and fauna (Usher 1991, in Peters 2001). Invasions may precipitate species extinction through either the direct displacement of native species by aliens or through the indirect effects of alien species on the ecosystem (Phillips 1997, in Peters 2001).
C. hirta may be present in a location without causing observable changes in an ecosystem for up to 30 years. For example, in both Hawaii and Fiji, ca 30 years elapsed between the first sighting of the species and the time that it was recognised as a conservation problem (Wester and Wood 1977, in Peters 2001). In Hawaiian communities, C. hirta may be replacing endemic species that formerly predominated, threatening their extinction (Wester and Wood 1977, in Peters 2001). The impact of this weed on native species and ecosystems is devastating and the rate at which it spread throughout the islands is alarming (Smith Undated). Its invasion into Hawaiian forests is apparently aided by a release from these herbivores and pathogens (DeWalt Denslow and Ickes 2004). It is a highly invasive shrub in the montane rain forests and cloud forests of Samoa, Fiji, Wallis and Futuna, and the Hawaiian Islands (Meyer 2000, in Binggeli Hall and Healey Undated). While C. hirta has not yet had the far-reaching ecological consequences at the Pasoh Forest Reserve (on the Malaysian peninsula) that have been documented in Fiji and Hawaii, some modification of the natural ecosystem seems likely, especially if the recent increase in disturbance continues. The results of at least one study have implied that by competing with native species in gaps, the C. hirta invasion in the Pasoh Forest Reserve, a previously undisturbed continental tropical forest, has the potential to alter forest regeneration. A survey on the status of invasive woody plant species in the western Indian Ocean found that the major environmental impact of invasive species in the region is the reduction of the native regeneration through competition by exotic species (Mauremootoo 2003). This becomes most apparent with thicket-forming species such as C. hirta (and also including Chrysobalanus icaco, Lantana camara, Psidium cattleianum, Ravenala madagascariensis, Rubus alceifolius and Syzygium jambos) (Mauremootoo 2003). The survey also rated C. hirta as one of the most problematic invasive species in the Comoros Archipelago and Réunion and as one of the main invasive species on Mauritius and the Seychelles (Mauremootoo 2003).
No Impact information recorded for Clidemia hirta
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