Diario del proyecto NEMBA Alien Species (South Africa)

The genus Quercus (Fagaceae) in South Africa: Introduction history, current status, and invasion ecology,
Christiaan P. Gildenhuys, Luke J. Potgieter, David M. Richardson, 2024. South African Journal of Botany 167: 150-165,
https://doi.org/10.1016/j.sajb.2024.01.066.

Hundreds of species of alien trees have been introduced and widely cultivated in South Africa, and many species have become invasive. Despite their long residence time and widespread cultivation, little is known about the introduction history, current status, and invasion ecology of oaks (genus Quercus) in South Africa.

This study reviews various aspects of the genus Quercus in South Africa. We determine the number of oak species present, assess their introduction status, map their distribution, highlight areas of putative naturalisation, and evaluate the usefulness of the community science platform iNaturalist for assessing these factors. We also conducted a field study to elucidate environmental factors that can mediate invasibility in a riparian zone.

A literature search was conducted to review events associated with the introduction, cultivation and naturalisation of oaks and associated pests and diseases in South Africa. Records of Quercus species in South Africa were collated from herbaria, arboreta, the Southern African Plant Invader Atlas, the Plants of Southern Africa database and iNaturalist. A field study was conducted along the Eerste River in Stellenbosch to elucidate the role of environmental factors in mediating naturalisation.

We found records of 47 Quercus taxa in South Africa which were refined to a list of 22 to 34 species likely present. The earliest record was for Quercus robur in 1656 but first records for most species date from between the late 1800s to the early 1900s. More than 99 % of presence and naturalisation records were of the ten commonly cultivated species. Quercus palustris, Q. robur, and Q. suber were categorised as invasive, and putative naturalisation was documented for Q. acutissima, Q. canariensis, Q. cerris, Q. ilex, and Q. nigra. Most naturalisation occurred at the urban-wildland interface and in riparian vegetation in Cape Town and Stellenbosch. Steepness of the riverbank was found to affect seedling recruitment in riparian areas. iNaturalist records shed new light on the presence, distribution, and introduction status of Quercus species in South Africa. However, taxonomic complexity and data quality complicated attempts to develop a robust inventory of Quercus in South Africa. Molecular studies are needed to achieve better resolution. Nonetheless, this study has greatly improved our understanding of the distribution and status of oaks in South Africa, with implications for their management.

see https://www.inaturalist.org/projects/oaks-in-south-africa

Just for the record. Why did we choose the banner for this project?

The picture shows Fynbos on the hill in front.
In the foreground along the road is Fountain Grass (from N Africa).
In the background we can see a Pine (probably P. pinaster - from plantings in the early 20th Century originally from Portugal, or P. radiata from plantings in the latter 20th Century from California) invading the veld.
On the right, the pines are invading a dense infestation of Silky Needlebush (Hakea sericea) from Australia.
In the distant backgrond the mountain slopes show some peaks invaded with pines, and others relatively clean.
A few gums (Eucalyptus) are visible in the centre. A few people still maintain that they are not invasive, but they need to get out into the veld more often.
Not visible in the valley below are the dense infestations of Black Wattle (Acacia mearnsii).

Of the visible species, we only have biocontrols for the Needlebushes. As you can see in the picture: biocontrol on its own is not really useful: it needs some human intervention in most cases!.

Grasses dont seem to get much attention.

And the sivicultural industry has blocked the release of biocontrols on the pines. Studies have been done and species are available, but final testing in South Africa has not been allowed. Pinus radiata is accumulating pests -which will function as biocontrol - by trade.

And some serious Gum pests have helped (and new ones continue to arrive) keep some species of Gums partly under control.

All our wattles have really effective biocontrols, and hopefully these will be augmented until efficient control is achieved.

If there are any species incorrectly assigned or not on the lists herein, please leave a comment below. We will fix them.
Note that the project "Alien Early Detection & Rapid Response" is adding some potentially new species not on the NEMBA list (but that perhaps should be, or that should be upgraded). Feel free to use it for any species that are suddenly expanding or escaping.

https://www.sanbi.org/resources/infobases/invasive-alien-plant-alert/
http://www.invasives.org.za/
https://www.sanbi.org/documents/nemba-act-no-10-of-2004/
https://www.environment.gov.za/sites/default/files/gazetted_notices/nemba10of2004_alienandinvasive_specieslists2016_0.pdf