Author: Barbara Curtis
At least 217 alien species have become naturalised, which means that they can propagate themselves without assistance from people (Klaassen & Kwembeya, 2013).
These trees should not be planted, and where they occur, they should be eradicated.
However, although they can withstand drought, they are very thirsty plants. They soon left the farm homesteads and kraals where they were planted and invaded ephemeral river systems, particularly those flowing southwards, such as the Fish, both Nossobs and the Aub.
While there are cactus species that are not invasive, it is far better not to plant cacti at all.
There are many indigenous species that do not require much water. Namib Trees is a nursery in Windhoek that specialises in indigenous plants (not just trees).The best method for eradicating cactus is bio-control, where a host-specific insect is released onto the plants.
Please help me with this task by sending in records of places that you have seen aliens, and by spreading the word as widely as possible.
It would be best if you can upload the information directly onto the Alien database (www.the-eis. com).