Projections by hydrologists working for the Greater Cape Town Water Fund – a consortium of government, businesses and conservation groups – show that getting rid of foreign tree species could produce an additional two months' worth of water for Cape Town at a much lower cost than other solutions such as desalination. .
So far, crews brandishing chain saws and hand saws have cleared 120 square miles over the past three years, with a similar area yet to be bulldozed.
This month, The Nature Conservancy, which is leading the project, released the Water Fund's first statistics, which are based on 4.5 years of preliminary data measuring water flow in six watershed areas. They showed that a watershed area covered by native fynbos plants averaged 34 percent higher annual flow than an adjacent pine-invaded watershed.
This data was collected by South Africa's science director, Richard Bogan, who climbs the mountains every two months to download information from sensors that record streamflow and rainfall. He and a team of experts also wade through streams to observe insects, fish and amphibians. His equipment has been burned by bushfires and swept away by floods – and he was almost left with snakes and baboons when the winds became too strong for a helicopter to fly – but he says the results are dramatic.
These findings are consistent with independent research conducted by Alana J. Rebelo, a senior researcher in the Water Sciences Unit of the South African Agricultural Research Council, and other scientists. Their paper found that removing mature trees of exotic trees, such as pine, from areas that might otherwise be treeless increased available water by 15 to 30 percent.
Many other countries – including the United States, Canada and Australia – have used similar methods to manage their water, said Aida Barges-Tobila, a tree and soil expert at the Swedish University of Agricultural Sciences. Although in many cases trees improve soil quality, Tobila said Cape Town was a special case because the land had not degraded and the trees were a water-hungry invasive.
Harvesting trees to manage water for reservoirs or hydroelectric dams is “a very well-established science,” said Rhett Harrison, a Zambia-based landscape ecologist at the Center for International Forestry and Global Agroforestry Research, whose practitioners include the U.S. Forest Service.
The additional water provides a lifeline for Cape Town. Five years ago, the city was weeks away from “Day Zero,” when authorities warned they would shut off household taps and force residents to line up for water at distribution points. Civil engineer Linda Siengo heads up the city's water resources and infrastructure planning, and his team has been leading the effort to try to conserve the last drops before the water turns into sludge. “It was like trying to extract water from a rock,” he recalls. “We reduced the pressure in the pipes until it was minimal.”
The drought was so bad that it usually only occurs once every 400 years. Not anymore. Scientists from Stanford University and the US National Oceanic and Atmospheric Administration (NOAA) published research in 2020 showing that climate change has made drought in Cape Town five to six times more likely, and that future droughts are likely to be longer and more severe.
It's not just Cape Town. This month marked a full year in which the world was an average of 1.52°C (2.74°F) hotter than in the pre-industrial era. Globally, extreme weather events are on the rise – with more intense hurricanes as warmer air retains more water, longer droughts in other regions, and more wildfires as heat dries up plants.
Fires are not always bad. Many of the Cape's most popular species – conebush, protea and Erica shrubs – need fire to reproduce because fire causes the flowers to release their seeds. But the pine burns 10 times hotter than the fynbos shrub, burning seeds and scorching the ground so native species cannot recover.
Now the water trust wants to set fire to trees in the hard-to-reach valleys starting in July, confident that mice and ants will carry the seeds again. For the past three years, the Fund has sent workers by helicopter to rappel down slopes and cut down trees. . But this is slow and expensive. Fires are quick, cheap and can be controlled if done correctly, said Kirsten Watson, director of the Water Trust. Fires are already ravaging the Cape, and the trees don't provide a long-term store of carbon because they'll soon burn out one way or another, she said.
“We can burn it safely — or it can turn into a wildfire,” she said, pointing to a steep ravine of pine trees during a recent trip to a clearing. “This may happen when the winds are strong and helicopters cannot fly and cannot be managed.”
Watson, a former civil servant who studied botany, stops along the hills to coo at the flowers as if they were old friends — the silvery brunia, under pressure from the Asian flower market, and the sunset-colored clusters of Erica that decorate the hillsides. . She fears that rare species will slide into extinction without anyone noticing.
Karen Eisler, distinguished professor of conservation at Stellenbosch University, said more than two-thirds of South Africa's 20,400 plant species are found nowhere else in the world. The invaders have already caused the extinction of at least seven plant species on the Cape, and 14 percent of them are at immediate risk of extinction, she said, adding that if native species are lost, local ecosystems will be further disrupted by climate change.
Former firefighter Ayabunga Philem now heads a team of loggers fighting to save the fynbos. In the Hottentots Holland mountain range this month, the echoes of their chain saws echoed down the escarpment.
The workers are a mix: some former firefighters, a civil engineering intern, recent graduate job seekers, and former government employees. Many say it's hard to be away from family for weeks on end, but they find camaraderie in the mountains. Sometimes they find love: Children born to workers they met on the mountain are given the names Carabiner, Chainsaw, and Pine. “I want to be called Spark,” said Willem, smiling.
Although South Africa has cleared invasive species For decades, previous government efforts paid low wages and sometimes suffered general budget cuts, so the clearing campaign was sometimes erratic or fragmented. Workers mostly headed toward where they could hike, leaving large areas of invasive species undisturbed at the top.
