Invasive Plants Causing Despair in Namibia

“Many people are not aware that all cacti come from the Central American states; none are indigenous to the entire continent of Africa”

A depressing situation for our local fauna and flora is the rate at which invasive plants such as cacti are taking hold in Africa. As explained in an article by Luise Hoffmann for Travel News Namibia “In order to save water, and because they have beautiful flowers and are often easily available, one may be tempted to plant cacti in the garden. However, the entire African continent boasts no indigenous cactus species”

Spreading with force these invasive plants cause wild animals to suffer. Travel News Namibia reports that “According to South African weed researcher Dr Helmuth Zimmermann, a world expert on the bio-control of cacti, it is not uncommon to find dead birds, reptiles and small mammals, even small antelope, impaled on the thorns.”

99FM’s MYD Earth sat down with Luise Hoffman to find out more about Invasive cacti and how we as individuals can assist with the solution. Luise is a sworn translator, author and an avid amateur botanist who was involved in collecting data for the Namibia Tree Atlas, she has become well known in botany circles for her research and published information on invasive cacti in Namibia.

99FM’s MYD Earth asked:

How you got into research on cacti?

“In Windhoek in the nineties – as the chairperson of the Namibia Botanical Society at the time – I was contacted by an official of the Windhoek Municipality suggesting that the Society might contribute to fighting the cactus invasion of the area around the Aloe Trail. The Society decided that it was completely beyond their means and manpower to do anything of the kind. Since then I have observed the alarming rate at which various cactus species have multiplied and continue to invade open spaces in that area and in many other parts of town.

During my visits to lodges and guest farms I increasingly find cacti planted for ornamental purposes. When I point out the dangers the answer often is, that these plants have beautiful flowers, are easy to find and grow vigorously with very little water and attention – which is exactly the problem! Many people are not aware that all cacti come from the Central American states; none are indigenous to the entire continent of Africa.”

What about invasive cacti in Namibia upsets you?

“The rate at which cacti spread as is documented by findings of Dr Helmuth Zimmermann of Pretoria, a world expert on the eradication of invasive cacti, who visits Namibia occasionally, and by reports from friends who have been traveling around the country.”

Why is it a concern for Namibia?

“It is a concern for Namibia for the following reasons:

• All cacti are exotic species, well adapted to hot dry conditions
• In Namibia they have no natural enemies – neither insects nor microbes
• They dominate and crowd out the indigenous vegetation – loss of grazing for our animals
• They form impenetrable thickets – bad for humans, animals and tourism
•  The spines of several species have barbs which make them very difficult and painful to remove
• Birds and small mammals become impaled on these spines and die a painful death of thirst and starvation
• In contrast to e.g. acacia thorns many cacti spines dislodge from the plant and work themselves into human or animal flesh
• Parts of the plants easily stick to animals, tyres and footwear and are so dispersed
• Any part of a cactus plant that is left lying on the ground will root and grow
• Baboons, birds and small mammals spread the seeds which germinate readily
• Long distance dispersal of cacti mainly occurs by people taking along cuttings to plant at home
• Although they have beautiful flowers at times, when dry the invasive cacti in the bush look very ugly.”

What can individuals do to be part of a local solution?

“Individuals can do the following:

• Plant no cacti of the invasive species, rather none at all, since cacti are not easy to identify and may only turn invasive after having fully adapted to Namibian circumstances.
• Take photos of any invasive cacti you might find in the bush, or in remote settlements and towns, note the locality and report to Silke Rügheimer at the NBRI,  silker@nbri.org.com or to Coleen Mannheimer manfam@iafrica.com.na
• Remove any cactus plant you might find anywhere, let it rot in a thick plastic bag or let it dry out on a solid surface where it cannot root and then burn it.
• For the eradication of large infestations according to Dr Zimmermann it is best to use bioagents, i.e. certain insects that kill or at least weaken the cactus to such an extent that it can no longer spread. Such insects were already introduced successfully during the previous century for one or two cactus species. However, each cactus species requires its own specific bioagent. To my knowledge no relevant legislation currently exists in Namibia to deal with the many invasive cacti species found now. So if you belong to a tourism or farmers’ association, an environmental organization or any similar grouping that can convince government to pass such legislation, please do so urgently.”

To find out more information you can read Luise’s article for Travel News Namibia here : Battling Invasive Cacti