Thursday, March 23, 2023

Killer plant ‘colonizes’ South west Botswana

Botswana is home to a whopping 2500 species of plants and trees. Of these, one has raised alarm and is seemingly a threat to the environment. In our backyard there is a fascinating plant that apparently originates from South America and has found home in and “colonized” the Kgalagadi, Gantsi and Central districts in Botswana. Commonly referred to as sexanana, the prosopis mesquite is proving to be a nuisance plant.

The mesquite is from the prosopis genus invasive plant species. It is said to originally originate in South America (areas like Mexico, Kansas, Texas, Carlifornia, Sonoran desert, and Colorado Desert). The plant tree is shrubbery, has long thin multi-branches and the leaves are “forever green” regardless of the season or climate. Since it is invasive by nature, the prosposis covers grassland pastures and areas previously covered by native plants. It reportedly destroys and dominates these native plants.

The seed root down to deep sub-surface water and deny this water to woody and non-woody parts, and that’s why it’s always green. Obviously, to stay this green, the plant requires a lot of water and since it rapidly delves to sub-surface areas to retrieve the water, it poses a threat to water supplies in the area. It is also suggested that it clogs boreholes with its extensive roots and lowered fresh-water aquifers ÔÇô which degrades rangeland and reduces biodiversity.

Government now wants measures put in place to control or eradicate this plant, almost three decades later. At a function in Gaborone over a month ago, the Ministry of Environment, Wildlife and Tourism deputy permanent secretary Rapelang Mojaphoko stated that prosposis poses a potential threat to biodiversity and ecosystem which has prompted her department to take measures to control, eradicate and prevent the further spread of the plant.

This action plan has been named the National Mesquite Management strategy. The prosopis mesquite is said to have been introduced into the country in the 1980s to address issues of desertification and growing sand dunes in the arid regions of South west Botswana. However, it has seemingly over-appreciated its welcome and is causing unanticipated damage. The plant spreads at an abnormally fast rate and covers all areas it occupies. Although there are no official measurements, estimates recorded in 2009 indicate that the plant covers about 5110 hectares (or more) in that area.

Rankae Motshwegwa, a senior officer at the Department of Forestry and Range Resources (DFRR) in Tsabong says this plant tree has advantages and disadvantages. According to him the tree is a source of fodder for locals’ livestock if consumed at an appropriate rate. It can also be used to make poles (traditional not commercial) “It is also a good windbreaker. Wind erosion is a problem in this area but the sexanana holds onto dust sand, therefore in that instance it is good for the environment.” He also said that during consultation sessions with locals, it came to light that although there are niggling complaints about the tree, many locals still don’t want to get rid of it. “We unearthed some interesting revelations like that the thorn of the tree is possibly poisonous. Locals explained to us that when the thorn pierces someone, it becomes extremely painful and the affected skin area itches and quickly swells.

There have been reports of people’s legs or fingers swelling to abnormal sizes after they came into contact with the thorns. However, some locals don’t perceive this as reason enough to get rid of it despite its rapid growth and that it covers unintended domestic areas.” Motshegwa pointed out that some locals benefit from the plant. “They graze their livestock from it and even use it for firewood. There have been rumours of its medicinal properties but they have not been confirmed. We often encourage locals to cut down the trees that give them problems but they seem reluctant to do so…”

Research on the plant alludes that the plant can also be used for enhanced honey production, charcoal and firewood.

The Bokspits, Rappelspan, Vaalhoek and Struizandam (BORAVAST) Community Trust seem to also be against cutting down the tree. The committee has however confirmed plans to undertake a project aimed at developing a management strategy for this plant.

In some instances however, it seems its cons outweigh its pros. This plant worsens water shortage in an area already plagued by strained water supply. It also affects people’s livelihood (shortage of water) and environment (it kills other plants) making it a cause of distress. If left to spread, it could as well occupy vast areas of the area, putting it under siege.

If managed, it can be exploited and apart from the uses stated above and can be a source of timber for commercial purposes. Enquiries into how the plant found a home in Botswana hit a snag. Motshegwa however noted that this plant can be unintentionally moved from one area to another. “The plant seed can stick onto clothes or find its way into luggage. It claws easily and grows almost anywhere.” Bringing a plant into the country requires that permission be authorized by the Chief Agricultural Research officer.

This plant also exists in South Africa, Namibia and has also been identified in the East African country of Kenya. Neighbouring South Africa has legal obligations. Legislation regarding noxious weeds is not new to that country. As early as 1860, spiny cocklebur (xanthium spinosum noxious weed) was found in the Cape Peninsula, which was way before the Noxious Weeds Act No 42 of 1937. Current legislation which was amended in 2001 forms part of the Conservation of Agriculture Act which deals with the eradication of problem plants. Invasive plants are specified and control measures stated for them.

These changes were accelerated by the deterioration of the country’s natural resources due to invasion by alien plants, as well as increased public awareness on environmental matters. The proposis is categorized under plants non indigenous to South Africa.

While it would be interesting to know who initially authorized for this plant to be brought into the country, it remains to be seen if managing and controlling this killer plant will be a success because at this moment, it’s “hard at work” spreading to other areas!


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