ENVIRONMENT: Alien Plant Species Invade Southern Africa

By James Hall Reprint | | Print |

James Hall

MAPUTO, Jun 27 2003 (IPS) - Environmentalists are calling it "the invasion of the invasives." Non-indigenous plant species brought to Southern Africa are alarming conservationists by the way they are taking over the habitats of native plants and, in some cases, causing indigenous species to become endangered.

"It’s the law of the jungle, with plants fighting for dominance," Zelda Montgomery, a British volunteer, who is currently cataloguing Mozambique’s natural flora, told IPS. "Hardier foreign varieties are just taking over from weaker native plants. They grow at a faster rate, reproduce quickly, and sometimes literally consume smaller plants."

Farm land, cattle grazing land, and game parks are all threatened by rapidly growing species of plants that were brought to Africa by colonialists for such benign purposes as garden decoration and wind breakers.

Wattle trees from Australia and mesquite from Mexico are able to sink their roots deeper into the soil than indigenous trees, robbing the native varieties of nourishment.

"This happens with remarkable speed. You can actually see it happen. A single species will crowd out a diversity of plants and trees," says Guy Preston, National Leader of the Working for Water Programme, an initiative of South Africa’s Ministry of Water Affairs and Forestry. Launched in 1996 after thousands of hectares of South Africa had been consumed by invasives, the programme has gained support through its patron, former South African president Nelson Mandela.

"Environmentalists are saying ‘If you don’t get them, the invasives will get you,’" Preston recently told a gathering of conservationists in Swaziland.

Linda Dobson, secretary of the Swaziland National History Society, says that an invasive species called the Demonia weed was blown into Swaziland by a cyclone in 1984. In the years that followed, the weed has rendered useless large areas of formerly productive agricultural land.

In Lake Victoria, water hyacinth, an alien species introduced for decorative purposes, has made fishing from shore impossible. Fishing lines cannot penetrate the mass of shoreline vegetation. Even fishing boats in some places can no longer navigate through the plant. The Hakea shrub from Australia was introduced to South Africa to serve as a hedge, and is now infesting whole forests, displacing native trees and smothering smaller plants.

Explains Dobson, "In their native lands, these species were kept in check by natural pathogens, like bugs. But these plant-eating bugs were left at home when the plants were imported to decorate someone’s garden. They got loose into a new ecosystem, and conquered it."

The resulting loss of biodiversity, which is a combination of an area’s plant and animal life, can be devastating. Environmentalists predict that one-fourth of South Africa’s plants and animals will become extinct if invasive plants continue to proliferate.

"When alien species displace native species, the insects that depend on those plants die. Insect-eating birds and small mammals lose their food supply. They also become extinct. The larger animals that eat the small animals die off," says Dobson.

The national tourism industries of the region are also concerned. "Visitors come to see the scenery as much as the animals. They have their plant guide books, and photograph indigenous species. We have to protect those," Ted Reilly, executive director of Big Game Parks of Swaziland, told IPS.

"The native plants have great cultural importance, and they are what the visitor to Africa wishes to see," said Reilly. The park system is systematically removing foreign plant species, and planting indigenous species in their place.

As they consume ever-greater areas, foreign species of weeds can consume land used for agriculture and grazing, causing economic hardship for farmers and raising the threat of food shortages.

Up to 13 million people require food aid in southern Africa, according to the World Food Programme (WFP).

In winter, alien weeds wither and dry into an easily inflammable mass, and can ignite high intensity veld fires. The invasives burn ten times the heat of indigenous plants, killing the seeds of the latter, while the alien seeds survive to germinate in greater profusion.

Soil degradation follows, and a drop in water resources. In South Africa, alien plant species consume 7 percent of the nation’s available water supply, from rain runoff to underground aquifers, in a country that faces constant water shortages.

"If we can rid ourselves of these plants, which are no good to anyone, we can spare ourselves having to build more and more dams, at considerable cost, that are needed for water security," says Preston.

Even traditional healers are concerned, because their medicines are concocted from indigenous herbs that grow wild in the African forests. As these wilderness areas are threatened, the source of traditional medicine is endangered.

"The problem is here, now, and it will get worse. But we have reason for optimism because containment efforts can turn the tide," says Preston. "It will require a regional effort to counter the invasives, because ecosystems know no national boundaries. The wind carries plant spores for long distances."

Swaziland, Mozambique and Namibia are working on legislation to prohibit the importation of invasive species. South Africa, the first regional country to recognise the danger, is strengthening existing laws.