By Ida Rigby, for Let’s Talk Plants! August 2023.
Acacias of Southern Africa - Part 1
Acacias are the iconic trees of the semi-arid savannas throughout Africa. An image of the umbrella thorn, Acacia tortilis now Vachellia tortilis, immediately signifies “Africa.”
The term acacia was derived from the Latin for thorny tree and was first used in the l6th century. The Latin term derives from the Greek for thorny Egyptian tree. They are the “thorn trees of Africa.” Their spikey defenses range from small spines to huge thorns that can puncture heavy duty Land Rover and Landcruiser tires. Giraffes delicately twist their tongues between thorns to pick out delicate acacia leaves.
Elephants chomp down whole branches covered with long spikes, which miraculously pass through their throats and digestive systems intact.
That’s why safari guides avoid driving through elephant dung, which can harbor the prodigious thorns that cause flat tires.
Elephants use the tough soles of their feet to position acacia boughs then deftly use the finger-like ends of their trunks to deliver branches to their mouths where they roll the boughs to peel off the nutritious bark and then swallow the twigs and thorns whole.
Lion's paws are more vulnerable to thorn wounds.
Some acacias grow long, thin branches, which the white-browed sparrow weavers take advantage of for building their nests.
Most weavers position the nests at the end of these thin branches to try to prevent snakes from getting to them.
One of the most commanding sights in the Kalahari and Namib deserts are the sociable weaver condominiums hanging from sturdy camel thorn trees.
A colony can hold over 300 birds and have 50 entrances. The haystack-like structures keep the nesting areas l8 degrees F. cooler in the baking summers and 18 degrees F. warmer in frosty winters.
In this column we’ll focus on the ubiquitous camel thorn acacia, Acacia erioloba now Vachellia erioloba, and in October we’ll look at the other acacias prevalent in southern Africa: The knob thorn acacia, Acacia nigrescens now Vachellia nigrescens, the fever tree, Acacia xanthophloea, now Vachellia xanthophloea, and the candlepod acacia, Acacia hebeclada now Vachellia hebeclada. George Harvey Vachell (1789-1839) was a chaplain for the British East India Company and collected plants in China. Even now that acacias are vachellias, I’ll refer to them all as acacias as that’s what most of us are used to calling this group of shrubs and trees.
The camel thorn acacia has a spreading crown, likes poor soils and easily withstands harsh conditions including sandy soils, frost and drought. The flowers emerge singly from a base of two thorns, each about two and a half inches long. The tree’s bark is deeply furrowed and gray to charcoal colored. The half-moon or ear-shaped pods are woody with velvety hairs.
They fall to the ground, where they can stay for a year or more before breaking open. Elephants savor the seed pods, and, as in these photos from Gomoti Tented Camp in Botswana, often shake the trees to make them fall and then sweep their sensitive trunks over the ground to find them.
Rhinos, gemsbok and eland also enjoy the pods.
Camel thorns can send tap roots down l97 feet, among the deepest of any tree —Juniperus monosperma on the Colorado plateau and eucalyptuses in Australia are deeper, and the deepest, the shepherd’s tree, Boscia albitrunca, in the Kalahari (the subject of a column to come) can have a 223 foot tap root.
In southern Botswana, the camel thorn is known as the Royal Tree. It provides shade for meetings. The tree offers wildlife dense shade in the hot midday sun. Local people view the camel thorn as the tree most likely to be struck by lightning—its rough bark in fact holds water, which evidently makes it more likely than other trees to explode when hit before summer rains fall. The sausage tree . . .
. . . is also associated with lightning and planted in village compounds as a lightning rod. Camel thorn roots are used for flutes, and the San people use the outer layers of straight roots for quivers. The inner bark is used for rope. The tree has indigenous medicinal uses: Powdered pods treat ear infections; pulverized burned bark treats headaches; and the roots are used to treat toothaches and are boiled for treating TB. Roasted seeds are a coffee substitute. The tree’s sweet gum is enjoyed by humans and monkeys. Villagers use camel thorn pods for cattle fodder and firewood.
The dry riverbeds in Namibia, frequented by the desert adapted elephants (who do not need to drink daily) are lined with thriving camel thorns . . .
. . . on which the elephants browse.
They also disperse the seeds. Elephants follow these dry riverbeds, which have permanent underground water accessible to the camel thorn’s long tap roots, to watering sources provided by accommodating local villages.
We followed one herd along a dry riverbed. Alerted by the village elder to the approach of the elephants, children filled the water tank for the elephants’ arrival.
This breeding herd was accompanied by a mammoth, lusty male who infuriated females who trumpeted their displeasure with his clumsy energetic advances. The elephants drank copiously…
… and then took their dust baths in front of the village.
Underground water around the ancient sand dunes at Sossusvlei in Namibia supports camel thorns. A horizontal line marks how high the browsing impala can reach.
At the base of the gigantic dunes camel thorns are being submerged inch by inch, by the advancing sand.
In Dead Vlei five-hundred-year-old skeletons of camel thorn acacias rise out of the remnants of an ancient pan.
Camel thorn wood resists termites and borers so it is useful for construction and fencing. In the past its wood was used for wagon parts and machine bearings and is still used for hoe and axe handles.
In seemingly inhospitable environments, humans find ways to discover the materials, foods and medicinal treatments in their immediate environment. The camel torn supports many aspects of human existence in the dry landscapes of southern African deserts and semi-arid savannas.