I am a child of Africa. Beautiful, complex, diverse and wild Africa. I spring from the soil of our beloved continent and with that comes my love for the animals that walk on her surface. Elephants, lions, leopard, our endangered rhino, African wild dog, cheetah and the list go on and on and on…
The Beauty Of The Giraffe
But when I think of one animal that is unique to Africa, found nowhere else, not even remotely duplicated in some form or another anywhere in the world, then I think about the giraffe. One of our strangest animals with their long necks, long legs and their graceful walk. The origin of the name “Zerafa” from Arabic means “charming” or “lovely one”. Perfectly evolved and adapted for the niche that no other animal occupies in mother nature, and only in Africa. Being a complete romantic, I always envision a sunset on the plains of Africa with the silhouette of a giraffe and that special tree, the acacia tree. The staple food of the giraffe.
And that brings me to my topic for this blog. The wonderful and mysterious relationship between giraffe, the trees they browse on and the ways these trees evolved in protecting themselves against these browsers. Or do they?
Giraffes And Acacia Trees
At the end of our dry season in Southern Africa, August to September, there is not much vegetation left. Grass is gone and the trees have lost most of their leaves. A trying time for both the grazers and the browsers. This is also a good time to visit these parts of the world as animals tend to congregate around waterholes, vegetation is scarce so you can see quite far and there are not many insects buzzing around. It is this time of the year that our Knobthorn Acacia, acacia nigrescens, start to flower. It is a sight to behold. What is nothing but dry and yellow landscape turns into forests of white flowers all over. Southern Africa’s equivalent of snow I always say. This a welcome relief for the giraffe as there is virtually no food for them on the trees. And now there is a banquet of nutritious nectar and protein for them.
But this leaves a few questions to be answered.
- With hardly any insects around, how are they pollinated?
- With no food around, does the giraffe not destroy the opportunity of optimum seed production if they eat so many of the flowers?
- What defence does the tree use to protect their flowers against the giraffe?
The knobthorn is one of the giraffe staple foods and makes up for about 40% of their diet throughout the year. Like all acacia trees species in Africa the tree produces thorns to protect itself against browser. In the case of the umbrella thorn, acacia tortilis, they have small yellowish flower balls that are protected close to the branches by large sharp thorns and there are swarms of insects around them, as they flower later in the rainy season when there are many bugs about. Hence the fact that they are pollinated by insects, and they try to protect the valuable flowers with their thorns. Not in the case of the knobthorn. They carry their flowers on long stems and are white in colour and are not protected by sharp and long thorns. With not many insects during this time of the year they need something else to pollinate them…
This is where the giraffe comes in. The knobthorn uses the giraffe in an ingenious way. They produce bisexual flowers as well as many sterile flowers on the same tree. With these sterile flowers they pay, or shall I say trick, the giraffe to come and eat them. While doing so the heads and even the necks of the giraffes are covered in the pollen of the fertile flowers. As they move from one tree to another browsing on the nutritious, nectar-filled flowers they will deposit the pollen from one tree to another. Ensuring that the next generation of knobthorn’s “babies” are propagated with a good mix of genes in the pool.
This is a truly remarkable interspecies relationship that has evolved over a long period of time, and which is clearly beneficial to both species.
How Other Trees Protect Themselves
But there are other trees which do not feel the same about browsers and have developed a legion of ways to protect themselves against these animals.
The beautiful umbrella thorn, acacia tortilis, produces very long and sharp thorns to protect their leaves from the marauding hordes. While the thorns protect them, much of their energy is also spent on producing these thorns. As the tree grows bigger the only parts that remain vulnerable to browsers and specifically giraffe is on the outside areas of the tree. Therefore, they only produce long sharp thorns around the outer perimeter of the tree protecting the inner branches and leaves, leaving them virtually free of thorns. This will also be the case in many of the other acacia species.
But what if you are a tree and you do not have thorns, and a giraffe starts eating from you, how will you protect yourself?
Trees use chemical warfare against their enemies. This includes all trees, even the acacias which are armed with thorns.
If you look at a giraffe browsing on a tree you will observe them eating only for a short period of time a one tree. They will suddenly shake the head and move on to the next tree, and most of the time they will feed into the wind. Never downwind. Why, would you ask?
The answer lies in the chemical, tannin. It is a very bitter chemical and lethal if digested in large quantities. Tannin causes a metabolic chain reaction in the browser impeding the digestion system causing death in the end. As a giraffe starts to feed on a tree the tree realizes that it is now in danger and starts to produce more tannin in their leaves within 5 to 10 minutes. This causes the leaves to turn bitter.
While the tree is producing more tannin it also releases a chemical warning in the form of ethylene which is released on the breeze, warning other trees up to 50 meters away, they will in turn start producing more tannin as well. When there is a wind, the giraffe will browse for 10 to 15 minutes on a tree and then stop, move upwind to browse from another one. If there is no wind the giraffe will move about 100 metres in any direction and start feeding there, as if the giraffe knows that the trees are talking to each other and how far this communication is possible.
With giraffe numbers going down and the dreadful possibility that they may go extinct it also leaves me wondering how long mankind will still see the knobthorn acacia flower from August to September, and how many other species are dependant on the giraffe that we do not even know about.
I hope that we will still see these beautiful, bizarre animals for a long time on the plains of Africa and that there will be a myriad of sunsets with the silhouette of the giraffe and the acacia in times to come.
Pula to the knobthorn and their mammalian pollinator the giraffe
Pula to you all from Africa
Kea leboga! Thank you.