FEATURE
Prosopis , a silent but deadly invasion
Ken Coetzee
Conservation Management Services , George , South Africa E-mail Address : consken @ mweb . co . za
Travelling anywhere north and west of Beaufort West reveals an increasingly dominant feature in the landscape , a feature that does not belong , the invasive alien Prosopis or honey mesquite tree ( Prosopis glandulosa var . torreyana ). Previously they could be observed as occasional trees along some of the watercourses , now they completely dominate the drainages , and also well beyond them .
They have benefitted from degraded veld conditions , exacerbated by drought and they are here to stay . Forming dense thickets , to the almost complete exclusion of the local indigenous vegetation , in some areas it is all that can be seen for long distances along the roadsides .
The Prosopis has been classified as a Class 1 invader species due to its aggressive spread and the threat that it represents to natural rangelands and water security in arid areas .
The Prosopis is native to northeastern Mexico and the southwestern United States of America . 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 . It was found to be very useful but by 1912 it had established itself in the wild and by the 1960 ’ s , dense invasions , that were very difficult to control , were already a recognized problem . The invasion had begun .
In South Africa , it was planted for windbreaks and shade in Upington from where it has spread into the Great Karoo and the Kalahari Thornveld . There are approximately 45 species of Prosopis and some species have become a worldwide problem , invading rangelands in the USA , Australia , Namibia , East Africa , India , Hawaii and the Middle East regions . Prosopis juliflora is a rampant alien invasive tree problem in Central and northeast Africa and most particularly in Kenya . Some Prosopis
Figure 1 . A young Prosopis glandulosa shrub , establishing away from ( escaping ) the dense infestation along the watercourse in the background .
species are native to Africa including the djembe ( Prosopis africanus ).
Prosopis is an extremely successful invader . Originating from an arid region , it is well equipped to survive drought and it flourishes under conditions of rangeland overgrazing and extended drought .
Should we be overly concerned ? and should more be done to combat this invasion ? One gets the feeling that nobody seems to be really concerned or to care enough about this problem . Can this be because of ignorance ? or a lack of awareness ? or simply an apathetic attitude to an apparently unsolvable problem ?
I have observed that many landowners who have low density , scattered Prosopis on their properties , fail to recognize the impending threat or to be moved to control these precursors to the invasion that will follow . These low-density Prosopis trees need to be quickly ( and continuously ) removed before they become dense invasions which are costly , and almost impossible to control .
Whatever the reasons behind this apparent lack of concern , it is quite clear that a fresh approach to the Prosopis problem is urgent , an approach that will inspire both the land management authorities and landowners to take action .
Why we need to be concerned
Prosopis has already spread over 1.8 million hectares of South Africa , this represents 1.8 million hectares of grazing rangelands lost . The size of this
21 Grassroots Vol 22 No 2 July 2022