10 August 2017

Namibia: Why Are Cacti So Damaging?

CACTI came to Namibia without the pests and diseases that keep them under control in their countries of origin namely the Americas.

Finding ideal growing conditions here, they tend to spread very fast and in doing so crowd out our indigenous vegetation. Due to their sharp spines, cacti in general are not eaten by livestock and game, therefore the encroachment by cati reduces the fodder available for our animals.

However, in times of drought animals in desperation may eat the pads and stock losses due to infections of the gut caused by the spines they swallowed have been reported from the Outjo area during the past drought.

Cacti, due to their sharp spines, prevent movement of people and animals in the areas they overgrow. Our local acacias also have thorns but our wild animals and our livestock have evolved with these plants and know how to avoid them.

Acacias, some of which are also regarded as damaging to the environment, at least fix nitrogen from the air in the soil and in doing so fertilise the soil. Animals can eat their nutritious leaves, flowers and pods.

In contrast, the sharp and often barbed spines of cacti easily come off the plant and stay stuck in the skin of animals. This of course also happens to people coming into close contact with these spines, which often can only be removed by surgery as the spines - due to the barbs - work themselves deeper into the flesh when the person or the animal moves. Wild animals of course have to suffer without such help.

Segments of the so-called jointed cacti ["lietjieskaktus"] as the various cylindroputia cacti are commonly called, easily break off the plant and attach themselves to the wool or hair of livestock and small antelope.

Cases of sheep dying of starvation as a result of cacti sections becoming entangled around their mouths, preventing them from feeding or drinking have been reported from South Africa and Australia.

Similarly such cacti sticking to the wool or hair of animals around their reproductive organs may interfere with reproduction. Hares and small antelope get immobilised when entering cacti thickets and die of thirst and starvation. As shown on the photo, birds and small reptiles become impaled upon the barbed spines and die.

Tourism is the second largest earner of revenue in Namibia. It is a rapidly growing industry and can be sustainable if we handle it correctly. The world is getting more and more crowded every day and tourists come here to enjoy our open spaces and our relatively unspoilt nature.

Of course they admire the beauty of a cactus plant in flower but usually they are not aware of the potential danger that the invasive cacti species pose. Recently, when I warned someone about an invasive plant in his garden, he replied: "I do not want to take it out because tourists admire it".

For the sake of biodiversity and the safety of our own people and animals, we need to protect our natural surroundings from damaging foreign invasive species. During the dry season, and without flowers, cacti are not a pretty sight at all! So please, on no account plant cacti to please tourists! Plant indigenous aloes, succulents, shrubs and trees instead.

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