Invasive pine trees threaten Cape Town, Port Elizabeth water supply

Cape Town and Port Elizabeth could lose up to 36% of their water supply if invasive pine trees are not eradicated from catchment areas.

The warning comes from Stellenbosch University’s Centre for Invasion Biology, which says the war on alien vegetation is being lost and “bold steps” are needed.

It comes as the Western Cape reports dam levels at 42.2%, compared with 62.5% a year earlier.

In the City of Cape Town, dam levels are at 43.5%.

Study leader Brian van Wilgen said the government programme to eradicate invasive species needed to focus resources on priority areas.

“Some areas have a higher priority for invasive alien plant clearing than others. Unless bold steps are taken to improve management, a great deal of money would have been and will continue to be wasted,” said Van Wilgen.

The Stellenbosch research, published in the journal Biological Conservation, focuses on the Cape floristic region. But Van Wilgen said the problem of alien infestation extended nationwide.

His article, co-authored by researchers from South African National Parks, CapeNature, and Nelson Mandela Metropolitan University, says up to R2.6-billion could be needed to keep aliens in the Cape under control.

Van Wilgen said Working for Water should have fewer staff who were better resourced and trained and working in priority areas.

“There are some areas where there have been remarkable progress, particularly if you start where it’s lightly invaded.

“You can actually restore those areas quite nicely; if you don’t let them become heavily invaded for too long then the fynbos will recover,” he said.

“If you look at Table Mountain National Park at Cape Point, that area used to be heavily invaded and it’s by and large been cleared.”

Guy Preston, the director of Working for Water, said while he agreed with Van Wilgens’s assessment of the seriousness of the situation — “if anything, their estimates of the potential damage to long-term water security are conservative” — the use of labour was a key part of the campaign’s success. The invasion of pines into the mountains of the Western and southern Cape is simply unaffordable, in terms of what this will mean for water security.

“It is the single-biggest long-term threat to water security in these areas and beyond,” said Preston, deputy director-general of the Department of Environmental Affairs. "There is no doubt in our minds that without the labour-intensive approach we would not have remotely the resources we have been afforded.”

Preston said the war on invasive species would be helped by increased public support, such as incentives for people to remove pines and use the wood, and biological means to kill target species.

He said that his department’s eco-furniture programme was on the way to becoming self-sufficient in making furniture from invasive species and had already made 400,000 school desks.

“This could be dwarfed by our aligned value-added industries programme, which can utilise all biomass from any plant species to make building materials, including fire-proof walls of structures,” he said.

“There is also potential for our Working for Energy focus on biomass, including bush-encroachment species, for energy needs. Such interventions can fundamentally change the equation for our work.”

Invasive species also increased the threat of wildfires, and Preston said that while a wildfire on Table Mountain in 2000 damaged 85 structures, the removal of invasive plants since then had helped to ensure that only eight structures were damaged during the March 2015 fire.

“When invaded areas burn, the germination of seeds of invasive species is a major consequence. As an example, after the March 2015 fires on the Table Mountain chain, the germination of seedlings has led to a need for urgent follow-up clearing of about R35-million,” said Preston.

Another study showed that Working for Water has managed to reduce alien invasions by 50% in certain areas of the Cape floristic region but that the programme had only reached about 13% of the total invaded area.

But Van Wilgens believes it is too late for a broad approach, and that trees are growing faster than they can be cut down.

“In war situations, you leave the people who are going to die and people who are going to get better anyway,” he said.

“You focus on the ones that 
are going to die unless you do something. In conservation they talk about triage as well, so let’s save the ecosystems that we can save and not try and save everything.”