Pine guzzlers great risk to Cape’s water

CAPE Town and Port Elizabeth could lose as much as 36 percent of their water supply in the next few decades, if the government’s celebrated Working for Water programme does not improve its management of invasive pine trees in protected areas of the Cape Floral Region.

In a new assessment, researchers from several of the country’s major conservation outfits warn unless “bold steps” are taken to improve the management of invasive pine trees in protected areas of the Cape Floral Region, a biodiversity hot spot of global significance, “Cape Town and other coastal towns and cities along the Garden Route stand to lose more than a third of their current water supply over the next 30 to 50 years”.

In the article, “Historical Costs and Projected Future Scenarios for the Management of Invasive Alien Plants in Protected Areas in the Cape Floristic Region”, researchers from the DST-NRF Centre for Invasion Biology at Stellenbosch University, SANParks, CapeNature and Nelson Mandela Metropolitan University reveal the findings of their assessment of the historical costs, and extent of efforts to control invasive plants in the CFR since 1995.

The study’s lead author, ecologist Professor Brian van Wilgen of the Centre for Invasion Biology, said if bold steps were not taken to improve management, “a great deal of money would have been, and will continue to be wasted”.

The problem “is simply going to run away from us, growing faster than we can contain it”, he warned. “Cape Town and all other coastal towns and cities up to Port Elizabeth stand to lose up to 36 percent of their water supply, putting a serious damper on economic growth and future employment opportunities for tens of thousands of people.”

The study, published in the journal Biological Conservation last month, estimated R564 million had been spent to date on attempts to control alien plants in 25 of the CFR’s protected areas. But while the focus had been on the eradica- tion of acacias, invading pine trees posed a much greater threat in the long term, as they created shade which halts the growth of native groundcover plants.

The article notes how, over the past three years, the Working for Water programme, “praised worldwide as a unique conservation initiative” to clear invasive plants while providing social services and rural employment, has offered jobs to an average of more than 20 000 people a year.

Yet, after 20 years, it had reached only a small proportion – up to 13 percent – of the total invaded area in the Cape Floral Region, where more than 1 000 indigenous plant species had been identified as being threatened by invasive alien species.

“If invasions were to reach the full extent of their potential distribution, overall biodiversity in the region could be slashed by as much as 40 percent,” the article noted.

The Biological Conservation study says R170 m will be needed to bring remaining invasions in the CFR under control, where only pines and hakeas are controlled, and a staggering 2 608km² where all species are controlled.

Van Wilgen said the essential element of an improved management approach would be to practise “conservation triage”, focusing effort only on priority areas and species, and accepting tradeoffs between conserving biodiversity and reducing invasions.