An oak tree (left) infected with invasive shothole borer eventually dies.
The history of oaks in South Africa spans nearly four centuries, but the oak tree's era may soon fall victim to a small invasive species, the polyphagous shothole borer.
According to a research team at Stellenbosch University, this could permanently change the tree landscape of towns and cities such as Cape Town, George, Paarl, Stellenbosch and Swellendam.
In a research paper published in the South African Journal of Botany, ecologists from the University's Climatology Department's Center for Invasion Biology traced the history and circumstances of the introduction of the oak genus Quercus to South Africa. and the factors that are changing its distribution across the national landscape.
They found records of 47 Quercus taxa, which they narrowed down to a list of 22 to 34 species that are probably present.
The first written record of English oak (Quercus serrata) Its origins date back to 1656, when it was introduced under the authority of Jan van Riebeck, said Christian Gildenhuis, a graduate student in the university's Department of Botany and Zoology and lead author of the paper. .
“Dozens of other oak species were brought to the Cape of Good Hope by early Dutch settlers and the British colonial government,” he said.
“Many oaks have since become widely cultivated throughout the country and today are one of the most widespread and recognized genera of trees in South Africa.”
Gildenhuis found that three species of oak – English oak, pin oak and cork oak – have become benign invaders along riverbanks and urban-wildland boundaries in Stellenbosch and Cape Town. . These orcs haven't caused any major problems so far, but they could in the future.
At the same time, many species, including the most widespread species, the English oak, are highly susceptible to disease and invasive beetles such as the polyphagous shothole borer.
“This not only means that many 100-year-old oaks are at risk, but also means infected trees must be removed before the infection spreads further,” Gildenhuis said. said.
“We don't think they think so.” [the oaks] something serious will happen [invasive] The impact could be felt in the near term, especially given that they are highly vulnerable to polyphagous shot hole borers. ”
Once shothole borer infects an oak tree, it will inevitably die as there is no treatment. “And it stretches from Somerset West to Cape Town, Stellenbosch and Johannesburg.”
Mr Gildenhuis told how he recently walked down Dorp Street in Stellenbosch and noticed that half of the oak trees were already infected. “So things don't look good for the Stellenbosch oaks at the moment. We predict that five years from now they will be dead or dying. That’s a bigger problem that needs to be addressed now…it’s quickly becoming a problem.”
The story of the South African oak is a classic example of how global change is rapidly changing the role and perspective of species in urban areas, says Dr. E., an ecologist at the Center for Invasion Biology and author of the article.
“We must accept that the potential impact of the polyphagous shothole borer is a game changer. As a result of this invasion, the treescapes of many South African towns will change quite radically. It will be.
“Landowners and authorities who may decide to replace infected Q-robar trees with less susceptible tree species should also consider the potential negative impacts these species may have.”
Infected trees should be replaced with native species that are less susceptible to diseases and pests, such as the polyphagous shothole borer. But people's attachment to the oak boulevards could hamper replanting efforts and cause conflicts between management and stakeholders, Richardson said.
Guy Midgley, interim director of the School of Climate Research, said trees make a vital contribution to mitigating the effects of climate change by reducing heat stress in urban areas. But how we dispose of thousands of diseased trees can have a big impact on our carbon footprint.
Gildenhuis added that an important tool for research and continued research is the citizen science platform iNaturalist.
“It's a downloadable app that allows users to upload photos of plants and animals, and researchers like me can use it for all kinds of projects,” he said.
“This gives the public the opportunity to contribute to science and interact more closely with the researchers working on these projects.”
Next, there is a discussion about the cultural value of oak. The research paper describes how oaks are a distinctive sight in many South African landscapes, particularly in the Western Cape.
Stellenbosch, South Africa's second-oldest settlement, is known as 'Eikestad' or 'Oak City' because of the oaks planted along its streets, gardens and parks, researchers said. He pointed out the presence of orcs in many towns and cities. Outside the Western Cape.
“For example, the town of Potchefstroom has the famous Q Robber Street. [in North West]. Oak trees adorn the streets of large cities such as Pretoria, as well as the streets of many small towns in South Africa's Highveld, where they are prized for their aesthetic appeal. They are also associated with several edible mushroom species,” the authors noted.
Oaks were first planted in Potchefstroom in 1868. The town's historic oak avenue was planted in 1910 and designated a national monument in 1977.
Many oak species became culturally important after their introduction. Several individuals of multiple Quercus species are listed as “champion trees,” which are considered culturally significant and have been granted special protection status under the National Forest Act.
The authors said the importance of Q Robber in South African literature, art and architecture is well documented.
“Oak symbols such as acorns and leaves are used in the logos of many local organizations and schools,” Gildenhuis says. “However, the use of the oak symbol has recently sparked debate. The oak (particularly the Q robur, one of the first widely planted tree species in Europe) is a symbol of South Africa's painful colonial past. Some argue that it is.”
He said the topic had come up in discussions leading to the replacement of the oak leaf as Stellenbosch University's logo in 2022.
According to Gildenhuis, oak trees have many benefits. “I like to look at them objectively in a way, as if they add a lot of value aesthetically and in terms of services like shading and cooling.
“There are so many great things about oak trees and trees in general, but the sad thing is that we have the polyphagous shothole borer. When these trees become infected, they have to be removed and the impact can be devastating. You also have to consider the downside of “the associated costs.” ”
Mr Gildenhuis said he had read a recent scientific paper estimating that the cumulative cost of removing diseased oak trees across South Africa over the next 10 years would amount to about 0.6% of South Africa's GDP.
“All we can do is hope.” [the polyphagous shot hole borer] We will do our best to prevent the infection from spreading further and contain it.”
