Non-native species & the pests who ride in with them

By theorkneynews on February 23, 2024 • ( Leave a comment )

Non-native species: after how long a time is it considered appropriate to eliminate them?

Everywhere humans have spread to they brought with them animals, plants, seeds, and even diseases to different parts of the world where they did not exist before. Often this gave the non-native species an advantage over the native and they became a problem invasive species.

In Orkney the most recent example of dealing with an invasive species is the Orkney Native Wildlife Project which seeks to eliminate stoats from the islands in an effort to protect ground nesting birds.

stoat trap — Stoat Trap Image credit Bell

In South Africa the issue is one of oak trees, introduced hundreds of years ago, and which have now become part of the urban landscape.

The oak tree is not native to South Africa it was first introduced as white Europeans began arriving in the region. The earliest written record is in 1656 of Quercus species (Q.robur) in South Africa. As more Europeans arrived so did the oaks:

1795: Planting of historical oak avenue between Company Gardens and Parliament in Cape Town.
1868: First oaks planted in Potchefstroom.
1910: Planting of historical oak avenue in Potchefstroom (declared a national monument in 1977).

The oak-lined streets of historical towns such as Stellenbosch in South Africa (the second oldest town in South Africa after Cape Town) are set to change over the next decade. These centuries old oak trees are particularly susceptible to the onslaught of the Polyphagous shot hole borer. Image credit: Christiaan Gildenhuys

A study has been published of the introduced oaks and the prospect of invasive beetles such as the polyphagous shot hole borer that infect them.

Researcher Christiaan Gildenhuys, a postgraduate student in Stellenbosch University’s Department of Botany and Zoology explained what happened after those first English oaks were planted:

“Dozens of other oak species were introduced to the Cape of Good Hope by early Dutch settlers and the British colonial government. 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.

“Many century-old oaks are at risk, but it also means that infected trees must be removed before the infestation spreads further.”

Christiaan Gildenhuys comments on history of the introduction of oak trees to South Africa by the first settlers in 1656 and their current status.

One solution would be to replace the infected oaks with native species which are less susceptible to the same problems as the oaks.

There is also how South Africans think of these oaks. For some they love the beauty of the treelined streets and their important contribution to breathing spaces. On the other hand they are also a relic of a colonial past and exploitation.

The first record of polyphagous shot hole borer in South Africa was reported from KwaZulu-Natal in 2012.

Oak tree infected by the Polyphagous shot hole borer. Image credit: Christiaan Gildenhuys

Prof. Dave Richardson, an ecologist at the Centre for Invasion Biology says the story of oaks in South Africa is a classic example of how global change is 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.”

Click on this link to access the study, The genus Quercus (Fagaceae) in South Africa: Introduction history, current status, and invasion ecology, published in the South African Journal of Botany.

Fiona Grahame