The ever-changing story of oak trees in SA

Stellenbosch University (SU) researchers recently published their study on the nearly 400-year-old history of oaks in South Africa. They said that the story of oaks in the country may, however, be coming to an end, forever changing the treescape of towns and cities such as Cape Town, George, Paarl, Stellenbosch and Swellendam.

In a paper published in the South

African Journal of Botany, ecologists from the Centre for Invasion Biology (CIB) at SU’s School for Climate Studies said the team traced the history of the introduction of the genus Quercus into South Africa, as well as its current status and the factors that are changing its distribution across our landscapes.

Postgraduate student from the Department of Botany and Zoology at the university and first author on the paper Christiaan Gildenhuys said that the first written record of English oak dated to 1656, reportedly introduced under the authority of Jan van Riebeeck himself. He said following this, other species of oak had been introduced by Dutch and British settlers. “Many oaks were subsequently widely cultivated across the country and have since become one of the most widespread and recognised tree genera in South Africa today,” said Gildenhuys.

According to the study the species may now have arrived at a crossroads. Gildenhuys found that three oak species – English oak, pin oak, and cork oak – had become invasive along riverbanks and the urban-wildland interface in Stellenbosch and Cape Town. They did not cause major problems as invaders now but might do so in the future. The other concern was some of the species were highly susceptible to diseases.

Prof Dave Richardson, an ecologist at CIB and co-author, said the story of oaks in South Africa was a classic example of how global change was rapidly changing the roles and perspectives of species in urban areas.

“We must accept that the potential impact of the polyphagous shot-hole borer is a game changer. As a result of this invasion, the treescapes of many towns in South Africa are going to change rather radically. Landowners and authorities who may decide to replace infected Q. robur trees with less susceptible tree species must also consider the potential negative impacts of these species.”

Prof Guy Midgley, interim director of the School for Climate Studies, said trees made a vital contribution to lessening the impact of climate change by reducing heat stress in urban areas. On the other hand, the way thousands of diseased trees were disposed of might significantly impact carbon emissions.

The authors warned that further study on the invasiveness of oak species was necessary.