“So even if no further alien species are introduced, the problem will continue to grow due to the species already in the country.”
This is one of the findings of 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 reveals all invasive alien plant species not subjected to biological control have increased their ranges over the past 15 years, some substantially.
“Pompom weed has 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’.”
Seven new species are introduced in South Africa annually.
“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.”
Of the 2034 alien species, 775 are invasive. More than 100 have caused large negative impacts - these include terrestrial or freshwater plants, feral pigs, the small-mouth bass and rainbow trout, the common garden snail, the painted lady and the common myna.
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, Northern Cape and KwaZulu-Natal.
Invasive trees and shrubs reduce surface water resources by between 3% and 5%.
“If no remedial action is taken, reductions in water resources could rise to between 2600 and 3200 million m³ per year; and if fully invaded, catchments in the Western and Eastern Cape will deliver 30% less water to the cities of Cape Town, Mossel Bay, George, Knysna, Plettenberg Bay and Port Elizabeth severely constrains the prospects for economic growth.”
Despite the introduction of the 2014 Alien and Invasive Species Regulations, there are “high levels of non-compliance with some regulations and a shortage of capacity within the Department of Environmental Affairs, and elsewhere in government, to ensure compliance”.