In a written reply to a parliamentary question, tabled on Friday, Water and Environmental Affairs Minister Buyelwa Sonjica said recent studies showed some Acacia species could respond to warmer conditions by developing stronger, deeper root systems, which sucked up more water.
"The research on the impacts of climate change on the ability of invasive alien plants species to out-compete indigenous vegetation is being led by the SA National Biodiversity Institute.
"So far, one of the most significant findings was that the root and shoot systems of some Acacia species could become stronger, which means that they will be able to access water deeper below the soil surface.
"This could make them more aggressive and increase the potential for invasions, leading to an even bigger threat to our natural resources and biodiversity."
Very expensive
Research on this was ongoing, but "very expensive" and dependent on the availability of funding, Sonjica said.
Earlier this year, an Agricultural Research Council (ARC) report, commissioned by the department of water affairs, found invasive alien plants now infest 20-million hectares of South Africa – an area twice as large as previously estimated.
Among the ARC's findings were that invasive black, green and silver wattles alone have taken over more than 1.6-million hectares of the country.
The two most badly affected provinces in this regard are the Eastern Cape and KwaZulu-Natal, where an estimated 600 000 and 300 000 hectares (condensed areas) respectively have been overrun by alien wattles.
In her written reply, Sonjica said recent research – by the Water Research Commission – in KwaZulu-Natal showed stream flow increased by 75 000 cubic metres a year after 65.4 hectares of invasive black wattles were cleared from one study area.
She said the research had also shown that reduction in stream run-off per hectare was twice as great in wattle-infested areas adjacent to streams compared to water losses in infested areas further away from them.
Earlier this year, a senior water affairs official told Sapa that a "conservative" estimate of what it would cost to rid South Africa of invasive alien plants was R34bn, spent over the next 25 years.
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