Although trees perform many valuable ecological services, not every tree is a “good tree.” Some can be downright problematic, especially when they are invasive, crowding out native species and hogging resources like water and growing space.
This is especially true in South Africa, where invasive plants like imported eucalyptus trees cover about 10% (19-million hectares) of the country, and the invaders are spreading — like weeds — at an exponential rate. But forest managers are fighting back.
A recent report points out the multiple benefits of a longstanding invasive species eradication program, established in 1995 to address “what was then perceived to be the single biggest threat to the country’s biological biodiversity and water security, which intensify the effect of fires and floods and increase soil erosion, while also diverting water from more productive uses, and impeding industries, such as agriculture, fisheries, transport, recreation and water supply, causing billions of rands of damage to South Africa’s economy every year.”
The country’s eradication program has cleared more than two million hectares of invasive plants, while providing jobs for more than 25,000 people a year, many of them hailing from marginalized parts of society, and 54% of them women.
The South African government now spends well over a billion dollars a year dealing with invasive plants, but the recent report suggests that’s not nearly enough.
Christo Marais, natural resource management programs head of operations for the Department of Water Affairs’ Working for Water program, told Engineering News, “The estimated costs of controlling invasive plants, restoring degraded land, implementing an integrated veld and forest fire management program and restoring and maintaining degraded wetlands and riparian zones are orders of magnitude (about R57-billion) more than what government is currently investing, and this is a challenge that might hamper growth in industry.”
Scientists estimate that 9,000 plants have been introduced into South Africa, with about 198 currently classified as being invasive. Among the most notorious are several species of eucalyptus trees, especially E. camaldulensis, E. cladocalyx, E. diversicolor, E. grandis, and E. lehmannii.
Eucalyptus trees are mostly native to Australia and neighboring islands, though they have been imported to many parts of the world for use as timber and as ornamental plants. In many places they have become invasive, since they grow rapidly and often suck up large amounts of water, harming freshwater ecosystems.
A 2011 paper in Biological Invasions by Willem de Lange and Brian van Wilgen suggested that the water lost to invasive plants every year was worth R6.5-billion in South Africa. Without government control efforts, that could have been R41.7-billion, said Marais.
South African officials are now investigating ways to turn invasive eucalyptus trees into biofuels. One pilot program at Farleigh is already turning eucalyptus wood into “eco-furniture,” including school desks.
When people plant trees they typically have the best intentions, but sometimes nonnative species can cause more harm to freshwater ecosystems than good. This can lead resource managers to seek creative solutions.
Brian Clark Howard is a writer and editor with NationalGeographic.com. He was formerly an editor at The Daily Green and E/The Environmental Magazine and has contributed to many publications, including TheAtlantic.com, FastCompany.com, MailOnline.com, PopularMechanics.com, Yahoo!, MSN and elsewhere. His latest book, with Kevin Shea, is Build Your Own Small Wind Power System.