Aliens shock department

2010-07-27 15:02

Invasive alien plants now infest 20 million hectares of South

Africa – an area twice as large as previously estimated.

The shock finding comes from an Agricultural Research Council (ARC)

report commissioned by the Department of Water Affairs.

The department’s natural resource management programme operations

head, Christo Marais, said: “The previous figure was 10 million hectares.


knew this was an under-estimate, but we didn’t think it was this big. It’s come

as quite a shock.”

The ARC had briefed the department on the new estimate at a working

for water (WFW) implementation meeting earlier this month.

Marais said it had long been obvious there was an under-estimation

of the scale of the problem, particularly in the Eastern Cape and


Invasive alien vegetation, including various species of wattle,

pine, poplar, weeping willow, gum trees, hakea and prickly pear, among others,

pose a serious threat to South Africa’s water supply, as well as the country’s

agricultural potential and biodiversity.

If the 20 million hectares of alien invasive vegetation across the

country could be condensed into a single area, it would form a dense,

impenetrable thicket about twice the size of the Kruger National Park.

Marais said that 15 years ago, government had established WFW to

tackle the problem of invasive aliens, while at the same time provide skills

training and employment for thousands of poor, jobless citizens, particularly in

rural areas.

In the current financial year, the project had been allocated “a

more than R635 million budget,” he said

Asked how long it would take to clear 20 million hectares of alien

vegetation, and what this would cost, Marais said a “conservative” estimate was

R34 billion over the next 25 years.

Left untouched, the alien vegetation would spread at an average

rate of 1% a year, threatening water and food security.

Marais said: “This is actually one bit of good news. We initially

estimated it was spreading at five percent a year, but the figure now appears to

be 1%.”

According to the ARC report, over 600 000 hectares (condensed area)

of the Eastern Cape are infested with black, green and silver wattles, as are

more than 300 000 hectares in KwaZulu-Natal.

The Eastern Cape has also lost over 200 000 hectares to prickly

pear, and the same area again to invasive Australian gums.

A further 250 000 hectares of KwaZulu-Natal have also been taken

over by the North American invader, Chromolaena odorata, more commonly referred

to as “paraffin” bush because of the fire hazard it poses.

Poplars infest more than 150 000 hectares in the Free State, while

prosopsis, better known as mesquite, takes up 350 000 hectares of the Northern


On a national scale, black, green and silver wattles have taken

over more than 1.6 million hectares of South Africa, gums occupy 1.4 million

hectares, and a million hectares are under invasive pines and poplars (500 000

hectares each).

Other significant alien invasives listed in the report include

lantana, syringa, queen of the night cactus, agave, guava, Spanish reed and


Marais said the department was looking at ways of off-setting the

cost of clearing invasive plants, including biological control.

He said: “Biological control could reduce the clearing costs by

between 10 and 20 percent, assuming such control can reduce the plants’ seed set

and expansion.

“Another possibility is utilising dense stands of alien vegetation

for bulk fibre production, or as an energy source. This could further offset


Land owners also needed to take responsibility for invasive plants

on their properties.

Marais said: “According to current environment legislation, the

land user is primarily responsible for management of their land, therefore land

managers must take responsibility.

The cost burden cannot be placed on

government alone. Land managers must come to the party.”

Marais said the department was also examining the cost benefits of

clearing land, particularly water catchments.

Surveys showed that clearing invasive alien plants from a watershed

could increase the water yield significantly.

This extra water could then be

sold and the money used to offset the clearing costs.

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