One of the world's best urban forests threatened by a small beetle

Trees border a street in a suburb of Johannesburg, Sunday, August 12, 2018. One of the largest urban forests in the world is threatened by the polyfere borehole which reportedly found its way from Southeast Asia when packing crates or through the movement of plant materials. Many of the estimated 6 to 10 million trees of the city die and no one has found a way to combat the plague. (AP Photo / Denis Farrell)

JOHANNESBURG – One of the largest urban forests in the world is threatened by a small beetle.

The polyphony borehole borehole is believed to have been shipped to Johannesburg from South-East Asia on crates or by the trade in plant materials.

Trudy Paap, a forest pathologist at the University of Pretoria, discovered last year the beetle in the Botanical Gardens of Pietermaritzburg. She published her discovery in the Australasian Plant Pathology journal and called it part of "the increase in the worldwide spread of invasive forest pests" due to globalization.

The beetle has since moved to Johannesburg, 320 kilometers (198 miles) away, and spread across its urban forest, which, according to the initiative of the Massachusetts Institute of Technology, Treepedia, has the sixth largest tree canopy in the world.

Today, many of Johannesburg's 6 to 10 million trees die, a crisis that only by the current winter season. Some of the infected trees have the telltale holes that the 2-millimeter-long beetle makes in their bark.

"This beetle does not really eat the trees," said Paap. Instead, it carries a fungus that blocks the vessels that carry water and nutrients, "which ultimately leads to the death and death of the tree."

Although scientists do not know how many trees have died from the invasion of the beetles, the prospects for Johannesburg are grim: "The city is going to lose many trees."

The trees have no evolved resistance to the polyphagous fibrous borer, unlike in Asia where the beetles occur naturally.

It is the older, more established trees at risk, said tree grower Neil Hill. "So that's going to leave a gap in the landscape, and if we do not start planting immediately with new trees, that gap will become more and more a concern for urban disease, pollution, aesthetic beauty."

Hill has experimented with organic and chemical fungicides and pesticides and will continue in the spring when the trees are no longer in their resting winter phase.

Many residents of the city have expressed their concern, including Markus Scheuermaier, chairman of the Johannesburg Urban Forest Alliance.

"It's a real crisis for the city because the trees provide shade, provide pollution control, provide all kinds of services that disappear when the drinker begins to spread across all the trees in Johannesburg," he said.

Like any other big city, Johannesburg and its population of more than 4 million is a major emitter of carbon dioxide, and its trees provide an important function in storing the carbon.

Tree grower of Adelaide Choko, the plant builder of the city of Johannesburg. e recognizes that it is a big problem to deal effectively with multiple obstacles.

How will inhabitants from poorer suburbs see the city that spends its limited resources on saving trees in the rich predominantly white northern suburbs? And how can the beetles be stopped?

"So far there is no means that has proven to control this vermin," Chokoe said. / muf

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