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Alien species rapidly expanding in NC

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The report found that seven new species were introduced in South Africa annually

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A THIRD of South Africa’s around 2 000 alien species that have become invasive are now entering a phase of rapid expansion and the Northern Cape has become one of the country’s most invaded provinces in this regard.

Invading alien plants are the “most diverse, widespread and damaging” group of invaders in South Africa with the Western Cape the most invaded province, followed by Mpumalanga, the Northern Cape and KwaZulu-Natal.

This is according to a landmark new report, the National Status of Biological Invasions and their Management 2017, compiled by the SA National Biodiversity Institute and Centre for Invasion Biology at Stellenbosch University. It is the first comprehensive national-scale assessment of the status of biological invasions in South Africa, and the first such global country-level assessment.

Information from the Southern African Plant Invaders Atlas revealed all invasive alien plant species not subjected to biological control have increased their ranges over the past 15 years, some substantially.

The report found that seven new species were introduced in South Africa annually.

“Pompom weed had increased in range by 670% and famine weed, an annual invader of overgrazed rangelands and savannahs, by 493%. Even long-established invasive tree species such as mesquite and river red gum have increased in range by 180% and 61% respectively. These species have large impacts, which grow as the species spread. Thus, even if no further introductions of potentially invasive species takes place, the problems associated with invasive species will increase, a phenomenon known as ‘invasion debt’. The rate at which species are arriving in the country appears to be gradually increasing. Once an alien species is introduced to South Africa it’s very difficult to stop,” the report found.

Of the 2 034 alien species, 775 are invasive. More than 100 have caused large negative impacts..

Findings of the report indicated that invasive trees and shrubs reduced surface water resources by between 3% and 5%.

“If no remedial action is taken, reductions in water resources could rise to between 2 600 and 3 200 million m³ per year; and if fully invaded, catchments in the Western and Eastern Cape would deliver 30% less water to the cities of Cape Town, Mossel Bay, George, Knysna, Plettenberg Bay and Port Elizabeth.