The Honey Mesquite tree (or Prosopis glandulosa var. torreyana) is an invasive alien plant (IAP) species that is taking over large tracts of overgrazed rangelands in South Africa’s more arid regions. Prosopis is a highly 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. Its similarity in appearance to our native Acacia species makes it challenging to identify. So much so that most people hardly pay them any mind. However, these trees are out of place in the landscape they have started to dominate and are an increasing threat to biodiversity and resources.
The Dangers of Invasive Plants.
There are many threats that invasive alien plants can pose regarding biodiversity. Habitat loss, the displacement of native plant species, biological pollution and the creation of monocultures can all be caused by invasive plant species.
To prevent the adverse effects caused by invasive plant species, strategies must be put in place to combat the spread of these species. These efforts often require the cooperation of landowners, organisations, and individuals who work together to identify and eradicate harmful invaders.
What Is The Problem With The Honey Mesquite Tree?
The Honey Mesquite Tree has taken advantage of degraded veld in drought-stricken areas. The dense thickets they create will outcompete and exclude the indigenous vegetation that once thrived there. The Prosopis is now seen as a Class one invader species due to its aggressive spread and threat to natural rangelands and water security.
This invader was first introduced into Southern Africa in 1897 in what is now known as Namibia, where German settlers planted it to use as shade and livestock feed. By the 1960s, this plant was well established in the wild. By this time, the invasion was already out of control. This isn’t the only species of Prosopis to have gained invasive status, as several of the 45 species of Prosopis have invaded worldwide.
This plant can survive droughts and can flourish under challenging conditions. This allows them to grow and invade in conditions where other species might already be struggling to survive. This is just one of the many reasons that this plant can be a cause for concern. Some other contributing factors are:
- The Prosopis has an aggressive, rapid spread.
- Prosopis can withstand a wide range of rainfall patterns, from 100mm to 1500mm per year on average.
- Prosopis can adapt to a wide range of soil types, including stony substrates, terrace gravels, alluvial dune sand, clay soils, lime-rich soils, and saline soils.
- It can live for 100 years or more and can grow at a rate of up to 30 to 60 cm per year.
- There is a worrying lack of concern, most likely due to insufficient awareness.
- Prosopis along watercourses can hinder livestock and game from accessing the water or pasture and shade provided.
- Since the spread has already taken over such a large area, it will be very difficult to eradicate before spreading even further.
To find a solution for this invasion, enough concern must be present to encourage individuals to help with the eradication of this harmful invader.
The Long Term Effects of The Prosopis Invasion.
Prosopis has already spread across a large area of the country, causing a significant loss of grazing rangelands. The invasion is said to have already distributed over approximately 1.8 million hectares of land in South Africa. Since the size of this invasion is estimated to double every 5- 8 years, that is only the beginning.
Prosopis doesn’t live in harmony with the indigenous species; it replaces them, reduces them and ultimately eradicates them. This is because the indigenous plants must compete with the Prosopis for water, but the Prosopis can use water more efficiently and lowers the water table far beyond the reach of local plants.
The Prosopis tree is also allelopathic, meaning that it contaminates (poisons) the soil that it grows on to prevent the germination and growth of other native plant species. As this species uses a lot of water, it is seen as a water waster. Still, it spreads best in overgrazed, eroded and drought-stricken areas. This means that as climate change escalates, there will be an even more significant amount of favourable regions for the Prosopis invasion.
There is also a threat to infrastructure as deeply rooted Prosopis can damage borehole pipes, block springs and pipes, and damage natural hydrology. These plants can cause erosion as dense infestations and water-carried plant debris can create barriers that divert the normal water flow into surrounding habitats.
All of the harm brought forth by this plant species has made it abundantly clear how important it is to keep up with eradication efforts.
Article adapted by Boudine Kruger from Ken Coetzee’s “Prosopis, a Deadly Green Cancer”