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South Africa's Invasive Species Guzzle Water and Hurt the Economy


South Africa is losing its battle against biological invaders, according to the government.

The invaders, including forest-munching wasps, and hardy North American bass and trees are attractive to mosquitoes, cost the country about 6.5 billion rand (US $ 450 million) a year and are responsible for about a quarter of its biodiversity loss. That's the conclusion of a pioneering report that the South African National Biodiversity Institute in Pretoria released on 2 November.

Invasive species also guzzle a substantial amount of South Africa's water, a serious problem in a country suffering from prolonged and catastrophic drought that is expected to worsen as the climate changes.

The report, which the institute compiled in response to the 2014 regulations, mandates a review of invasive species every three years, examines the pathways by which these species enter the country and the effectiveness of interventions. It also weighs the toll on the nation's finances and biodiversity.

This achievement constitutes a "significant advance" compared to other countries, says Piero Genovesi, who chairs the invasive species specialist group of the International Union for Conservation of Nature in Rome. He said that other reports have looked at the impact of biological invasions, or at measures to address the problem, but they have not considered all aspects of invasions.

Helen Roy, an ecologist at the Center for Ecology and Hydrology near Oxford, UK, says that this is the first comprehensive synthesis of the state of invasive species by any country. The report provides "an incredible basis" on which to build predictive approaches to invasive species.

Climate change

Across the world, invasive alien species-organisms have been introduced into ecosystems beyond their natural habitats, and they spread over large distances on a major threat to biodiversity, human health and economies. Climate change is expected to further spread in the world, in part by reducing the resilience of the native ecosystems. In 2015, 37 researchers from 14 national organizations, led by the National Biodiversity Institute and the Center for Excellence for Invasion Biology at Stellenbosch University, began compiling the South African report. The researchers collated data from agencies and institutions around the world to measure different aspects of biological invasion.

They report that 7 new species are introduced into South Africa each year, and that about 775 invasive species have been identified so far. This contrasts with the 556 invasive taxa listed in the government's 2014 regulations on invasive species. Most of the species are identified by the latest reports are plants, with the most common. (For comparison, the United Kingdom reports that it has 184 non-native invasive species). The report's authors consider 107 of these invaders to have major impacts on the country's biodiversity or on human well-being.

Invaders of note include trees in the Prosopis genus, such as honey mesquite (P. glandulosa), which was introduced throughout Africa for animal fodder. The shrub damages animal grazing areas, outcompetes local plants and, according to a 2017 study in Mali, seems to encourage the growth of populations of the malaria-carrying Anopheles mosquito, among other things.

Others invasive species include the Sirex wasp (Sirex noctilio), first detected in the country in 1962, which seriously threatens South Africa's 16-billion-rand forestry industry; the ant Linepithema humile, which comes from Argentina and disrupts seed dispersal in indigenous plants; the North American small-mouth bassMicropterus dolomieu), which has outcompeted indigenous fish species; and the water hyacinthEichhornia crassipes), originally from South America, which chokes the country's dams and waterways.

Thirsty invaders

As well as their significant financial toll, the report is invasive species responsible for a quarter of the country's biodiversity losses. The researchers also found that invasive species in South Africa took a shocking toll on the water supply.

This year, Cape Town has become almost the first major city in the world to run out of water. (It was saved at the last minute by stringent water restrictions). In May, researchers have argued that alien plants, which often use more than one hundred million liters of water per day. They warned that water losses due to invasive species could triple by 2050 because trees are black and pines are spreading. The latest report estimates that invasive trees and shrubs, if left unchecked, could threaten up to a third of the water supply to cities such as Cape Town, and consume up to 5% of the country's annual rainfall runoff.

Despite the enacting 2014 regulations and spending at least 1.5 billion rand a year to the invasive species, the country is not keeping up, says the report. Brian van Wilgen, an applied ecologist at Stellenbosch University.

But the authors also note that their confidence is almost all of their estimates are low, because of poor monitoring and evaluation of data-a problem that can be mitigated in future reports through increased research into impacts and monitoring techniques.

Jasper Slingsby, an ecologist with the South African Environmental Observation Network in Cape Town, assists that researchers in South Africa. "We need better funding and concerted research effort in this space as a national priority," he says.

This article is reproduced with permission and was first published on November 2, 2018.

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