Invasive plant species
Alien plant species pose a major threat to South Africa’s native biodiversity. It is estimated that more than 9 000 plant species
Invasive alien plants in the Berg River under siege
The Working for Water programme has a project along the Berg River catchment, where a group of specialized workers known as the Arbor Team are removing invasive alien plants. Invasive plants are, apart from their notable impact on water, forestry and human health, recognized as the second largest global threat to biodiversity.
Liezel Bezuidenhout, the BergBreede area manager, says that the Arbor Team was set up as a pilot project and that extensive training was required due to the risky nature of the job. “The Western Cape region is the first one in the country to have such a team trained to do this job and more often than not the workers are exposed to danger when working under high voltage power lines,” she said. The Arbor Team consists of seven members who are given 2025 days to clear a field of invasive species.
Liezel further explained that the Berg River was chosen as a pilot project for several reasons: the area’s high water yield, its rich biodiversity, the water it provides for irrigation and recreational activities, and its massive infestation by large invasive alien trees.
– Working for Water, July/August 2010
have been introduced so far. Of these, about 198 species are deemed invasive, covering 10 per cent of the country. Since the invasive plant species grow by an estimated 5 per cent a year, their presence has dramatic effects on both native species and ecosystems as well as economic activities in the area. In par- ticular, alien plant species generally consume more water than native species, which poses a major problem to many of the country’s ecosystems, agriculture and local economies. In fact, it is estimated that alien plant species consume as much as 7 per cent of South Africa’s total runoff.1
Examples of problems attributed to invasive aquatic weeds
• Sunlight is unable to penetrate some of the dense mats formed by invasive species causing destruction of the associ ated aquatic biodiversity.
• Deoxygenated water. • Decaying invasive plants affect the smell and the taste of water. • Canals, pumps and turbines are blocked increasing siltation and aggravating floods.
• Invasive plants provide possible breeding grounds for disease vectors such as mosquitoes and snails.
– National Botanical Institute and Invasive Species Programme 2004
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