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Written by: Taher Nassrulla on 6 January 2016

Amazing Acacias – a clever species of trees

Acacia tree

While on safari in Tanzania you will not only see animals, but also trees. Tanzania has hundreds of tree species but today I am highlighting one in particular, the acacia family. East Africa has around 62 species of which six are endemic to Tanzania.  Acacias can grow as trees and shrubs, but the most classic acacia trees seen on safari include the umbrella tree, whistling thorn, wait-a-bit acacia and the yellow fever tree.

The umbrella tree has become almost a symbol of the African bush. It is always photographed as the most typical tree in African bush. Ask a person to think about the first tree that comes to mind, when you say ‘the African bush’? They will most probably mention the umbrella tree, envisioning a lone tree in front of a tremendous sunset.

Acacia Tortilis

The Serengeti National Park is a protected area that covers thousands of square kilometers and it is the habitat of several species of acacia trees. These trees are quite formidable and adapt well to their surroundings. Each species has special characteristics, but most of them have one thing in common; their defense mechanism – thorns.

Acacia drepanolobium

Acacias are often referred to as thorn trees. Some have long straight thorns while others have hook-shaped ones. The main reason is that it acts as a deterrent against browsers. Scientists have said that despite the thorns, some herbivores still feed on the trees. Not preventing feeding, but indeed limiting over-grazing.  One interesting fact is that when browsed on by, for example giraffes, some acacia trees release a toxin known as tannin. This makes the leaves inedible and causes the animal to seek ‘greener pastures’. The toxin can be quite dangerous to the animals if ingested and can be lethal.

A zoologist from South Africa, Wouter Van Hoven found that acacia trees also have another chemical defense system, whereby they release a chemical called ethylene.  This chemical can travel up to 45m, ‘warning’ other acacias in the vicinity.  Within 15 minutes all the neighbouring trees increase the tannin levels in their leaves, making the area pretty unappetizing to tree-browsing animals.

In order to ensure enough food, giraffes tend to eat downwind from trees, in the hope that the trees do not alarm each other. They also usually browse only for a short time before moving on to the next tree.

Acacia drepanolobium

Another incredible defense mechanism is that acacia trees have ‘body guards’ in the form of biting ants. The whistling thorn is a good example of this; at the base of the thorns is a hollow bulb. These bulbs provide shelter for the ants and the tree provides plenty to eat in the form of nectar and sap. The ants return the favour by attacking any herbivore that tries to eat the leaves.

Next time you see an acacia tree don’t just think of it as a tree but rather a tree that is actually quite clever.

Author: Taher Nassrulla

Born in East Africa, Taher was intrigued by the natural and geographical diversity of the African bush from a young age. After spending some time in Europe, he returned to Tanzania in 2004 to start a new chapter in his life. Since then he has been spending as much time as possible in the bush, learning. Taher speaks English, Kiswahili and German fluently and is a passionate photographer. Using the skills he has learnt over the years, he now takes tourists out on safari as a German-speaking tour leader and guide.

10 thoughts on “Amazing Acacias – a clever species of trees”

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    • Thank you Mr(s). Mboya, we have just done that. The Headpic is also of the Acacia Tortilis species!

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  • Is any one can help to find acacia raddianna savi seeds, i’ll be great full 🌹

  • I assume the author meant upwind not downwind. The wind blows downwind so any tree downwind would “sense” the ethylene and produce more tannin.

    • No because if they are upwind that means the wind is blowing the pheromone to the next tree. Eating downwind means the wind is blowing away from the next trees you’re visiting. You have your terms mixed up. The wind blows TOWARDS downwind. Thus if you’re eating at a tree that is downwind of your next tree, it’s blowing the pheromones away from it.

  • Incredible knowledge,love it, thanks to whoever gave a bit of summary on these trees. doing a research on these trues hopefully my results will one day be added to site. xox

  • Very exciting info, many thanks. Im a fan of the African acacia tree, which sadly has been ravaged and decimated in my region. I have a small ranch called A Thousand Acacias Ranch where I have tried to conserve and utilize the umbrella acacia, and I’m happy to see that the effort is beginning to increase the appreciation of the tree in my community
    NZUNGI NGWELE – Kitui, Kenya.

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