Mesquite: a silent but deadly invasion

Ken Coetzee, founder of Conservation Management Services, says that the spread of the invasive alien Prosopis in South Africa is a serious threat to livestock and indigenous plants, and needs urgent attention from farmers and landowners.

- Ken Coetzee

Travelling anywhere north or west of Beaufort West in the Western Cape reveals an increasingly dominant feature on the landscape: the Prosopis or honey mesquite tree (Prosopis glandulosa var. torreyana). This invasive alien species (IAS) has benefited from degraded veld conditions, exacerbated by drought. The Prosopis has been classified as a Class 1 IAS due to its aggressive spread and the threat it represents to natural rangelands and water security in arid areas.

The Prosopis is native to north-eastern Mexico and the south-western US. It was first introduced into Southern Africa in 1897 in South West Africa (now Namibia), where German settlers planted it for shade and livestock feed. In South Africa, it was planted for windbreaks and shade near Upington, from where it spread into the Great Karoo and the Kalahari Thornveld. There are approximately 45 species of Prosopis, and some have become a worldwide problem. Prosopis juliflora is a rampant IAS tree problem in Central and north-east Africa, particularly in Kenya.

Prosopis is an extremely successful invader. Originating from an arid region, it is well equipped to survive drought, and flourishes under conditions of rangeland overgrazing and extended drought. I have observed that many landowners who have scattered, low-density Prosopis on their properties fail to recognise the impending threat or take the trouble to control these precursors in order to prevent the invasion that will follow. These low-density Prosopis trees need to be quickly (and continually) removed before they become dense invasions that are costly and almost impossible to control.