A wildfire on the Garden Route fuelled by invasive alien trees. File photo
Invasive species, introduced through trade and travel, are spreading rapidly in South Africa, wreaking havoc on its fragile ecosystems and harming biodiversity.
A new report described how the country is a hotspot for invasions. “Preliminary findings indicate 13 plants, five freshwater fishes, and one invertebrate have had ‘major’ or ‘massive’ impacts,” it said. “However, as only a few taxa (36) have been formally assessed, this number is expected to increase.”
South Africa is confronted with a multitude of invasive species that “have taken root in our ecosystems, altering native habitats, outcompeting indigenous species, and disrupting essential ecological processes,” noted Forestry, Fisheries and Environment Minister Barbara Creecy at the report’s launch.
Its findings paint a “sobering picture” with the effects of biological invasions “extending beyond the realm of nature alone” and having far-reaching consequences on the economy, agriculture, water resources and public health.
“Invasive species can devastate agricultural lands, leading to reduced crop yields and increased production costs,” Creecy said. “They can also impair water quality, clog waterways, and impact our ability to access clean drinking water. Additionally, some invasive species pose risks to human health by acting as carriers of diseases or causing allergic reactions.”
She relayed how, in mountain catchments for example, “we are seeing pine trees using up water, increasing the intensity of fires, and crowding out biodiversity. Alien freshwater fishes are invading South Africa and “reducing the diversity of our native fishes and other aquatic organisms”.
In the age of climate change and global warming, invasive species also have the potential to intensify the country’s vulnerability to phenomena such as wildfires and flooding. “For example, some alien plant species such as pine trees are highly flammable, while others clog up our estuaries and watercourses that act as natural mitigation against flooding and cyclones,” Creecy said.
Hefty costs
Most introductions of biological invaders to South Africa are plants introduced for ornamental purposes and horticulture (28%) and for agriculture (10%).
Furthermore many alien organisms (invertebrate pests) have been accidentally introduced along with imported plants, animals or their products. In addition shipping has facilitated many introductions of invasive species through releasing ballast water, biofouling (microorganisms, plants and algae that attach themselves to parts of the ship including on hulls), and when small animals hitchhike a ride on the ship such as the house crow.
Creecy said the government had invested more than R1.5 billion to address biological invasions from 2020 to 2022, targeting priority areas such as strategic water sources, protected areas and biodiversity hotspots. This national-scale management created employment, particularly in rural areas.
But the money spent by the government has declined since 2015.
“NGOs such as the Nature Conservancy and the World Wide Fund for Nature (South Africa) have raised over R180 million from the private sector to fund the control of invasive freshwater fishes and alien plants in the water catchments of Cape Town,” the report said.
A handful of historical studies have made evident the severe effects of invasions on water resources, rangeland productivity and biodiversity. Invasive trees gobble up 3% to 5% of South Africa’s surface water runoff each year; invasive plants reduce the value of livestock production from natural rangelands by R340 million a year; and biological invasions are responsible for 25% of all biodiversity loss, “placing them as the largest impact to biodiversity after cultivation and land degradation”.
The economic cost of the recent introduction of a single invasive alien insect species — the polyphagous shot hole borer — and its fungal symbiont was recently estimated at R350 billion, equivalent to 0.66% of the country’s GDP, said Shonisani Munzhedzi, the chief executive of the South African National Biodiversity Institute.
“This underscores both the severe economic impact that invasive alien species can have, and the imperative to manage them as effectively as possible,” he added.
‘Set to grow’
Biological invasions are a significant drain on South Africa’s sustainable development because they pose a major threat to both the quality of life of future generations and the globally unique flora and fauna in the country, the report said.
The problem is complicated and looks set to grow.
“Invasive species come from many different taxa, invade different habitats, and cause various types of impacts, sometimes in ways which are not yet fully understood but that will have profound effects on the ability of ecosystems to deliver services to people.”
But significant progress has been made in reducing the effects of these invasive species and preventing new invasions.
“Targeted interventions can be highly cost-effective, and so, while interventions can be complicated and costly, by working together as a society we can protect our biodiversity and natural capital from biological invasions,” said the report.
New alien species continue to arrive every year through several pathways, the report said. From 2013 to 2022, 32 new alien species were either illegally or accidentally introduced, a rate of about three introductions a year. This is slightly lower than the numbers seen for 2010 to 2019, where an average of about four new species were introduced a year.
There has been significant progress in collating a list of alien species in the country, with information on their distributions, effects and management, the report said. It includes records of more than 3 500 alien species present outside of captivity or cultivation, at least a third of which are recorded as invasive. But “many alien species are yet to be detected and documented”.
All legal introductions of new alien species require import permits and are issued only if the risks are demonstrated to be sufficiently low. The new National Border Management Authority has committed to improving the prevention of illegal and accidental introductions.
Addressing biological invasions requires integrated governance from international to local levels, the report said. “Of immediate concern, however, is that the number of alien species is increasing, the area invaded is growing, but South Africa’s response has been declining.
Investment into biological control of invasive species has resulted in at least 17 species brought under permanent control and to reductions in many other invasions. Although biocontrol agents have often significantly reduced the negative effects of invasions, “other new alien species are adding to the range, complexity and intensity of the negative impacts caused”.
The report identified a particularly concerning new introduction: the fungus Seiridium neocupressi, which causes the disease cypress canker. It was first recorded in South Africa in 2021 on native trees — the mountain cypress.
“The exact introduction pathway of this fungus is not known, but it was most likely introduced as a contaminant of nursery material and thus there has been an increase in the number of alien taxa introduced through this pathway,” it said.
Countrywide invasions
Invasions are distributed across the country, including in protected areas. Most alien species are found in the Western Cape, Eastern Cape and KwaZulu-Natal and around major urban centres, the report said.
All protected area complexes are invaded to some degree with estimates of relative invasive abundance ranging from minor to extensive.
More than 700 invasive terrestrial and freshwater species (excluding biological control agents) are reported to occur in protected areas managed by South African National Parks and CapeNature, with a few protected areas reporting particularly high numbers of invasive species.
Native species are also being moved and introduced to parts of the country where they are not naturally occurring. At least 77 indigenous species have formed 132 native-alien populations.
“Most of these native-alien populations are ornamental plants and mammals introduced to game farms, but accidental introductions are also occurring, particularly with transported plants and their products.”
For example, samples taken from the shoes of trail runners taking part in races in the Garden Route National Park were found to contain the seeds of 33 plant species, of which 18 were alien to the country, and two were native to the country but alien to the Garden Route National Park.
“Along Sani Pass in the Maloti–Drakensberg Park, alien plant taxa have expanded their distributions from lower to upper elevations, with the pattern of expansion indicating that human-aided long-distance dispersal is playing a role, likely through the adhesion of plant propagules to vehicles and the shoes of hikers moving up the pass.”