Challenges of the Savanna
By far the greatest challenge facing any life on the savanna is the inconsistent rain patterns.
Depending on the region, the savanna can receive between 20 and 50 inches of rainfall annually. While that seems like plenty, it all takes place in only a six-to-eight-month period. The rest of the year, the grasslands are almost completely dry.
Worse, some regions receive as little as six inches of rainfall, making them little more hospitable than deserts. In Tanzania, there are basically two separate wet seasons, with a gap of about two months between them.
The challenges this irregularity presents go beyond water alternating between abundant and nonexistent. Conditions get so arid during the dry seasons that regular brush fires are just part and parcel for life on the savanna. Plants that live in the savanna need novel adaptions to survive and thrive in these conditions.
Because the soil on the savanna is extremely porous, water will readily drain from the surface, requiring plants to delve deep into the earth to get it. These deep root systems allow plants to store excess water away from the hot summer sun.
They also provide a defense against drought, wildfires, and grazing animals. With the root systems intact, the plant can regrow during the next wet season. For this reason, many grass species simply go dormant as soon as the wet season ends.
More complex plants like trees don’t have the ability to hibernate, however. Many of them instead survive by way of more unique adaptations. Many develop specialized organs like bulbs and corms in which to store water for the dry times.
Other trees have special reservoirs for water between their bark and internal structures. Some even grow special bark that acts as a fire retardant in the event of a brush fire.
And then, of course, there is a prediction by herbivores. Savanna plants provide food for more than 40 species of mammals. With that many grazing animals, plants have to develop defensive strategies to survive.
Many cover themselves with thick spines and barbs to deter potential grazers. Others produce chemicals that make themselves taste terrible. And a few even form symbiotic relationships with ants that come out and attack potential threats.
Among all this plant life, there are a few particular species that stick out.
Notable African Savanna Plants
One of the rare trees to thrive in the savanna, the acacia is one of the most iconic sights in the grasslands. It is also the favored food source of giraffes. It is not uncommon to see a herd of giraffes all gathered around one tree, greedily chowing down.
Their fondness for the acacia has led to something of an evolutionary arms race between the two species. To deter feeding, so species of tree grow thorns as long as 4 inches and as sharp as a knife. To counter this, giraffes evolved an incredibly flexible prehensile tongue that allows them to navigate safely through the brambles.
The trees responded by developing the ability to release tannins in response to injury. The chemicals taste terrible to giraffes and are mildly toxic to them. They even send out chemical signals to nearby trees, warning them to do the same.
This toxic defense forces the giraffes to keep moving upwind, looking for trees that have not yet gotten the memo.
Another iconic sight on the savanna is the baobab tree. It’s often simply called “the upside-down tree”, as it resembles a tree that has been ripped out of the earth and replanted upside-down.
These trees can grow to immense sizes and can live to be thousands of years old. One hollowed-out baobab is so large that up to 40 people can take shelter inside at once.
They’re an incredibly hardy tree. Their trunks are composed of a thick, cork-like substance that allows them to store water for months and is extremely fire resistant. Even if it is somehow burnt or stripped of its bark, the baobab will simply grow all-new bark and carry on like nothing happened.
Another very curious tree found in the savanna is the candelabra tree. It takes its name from the fact all of its branches grow more-or-less straight up out of its trunk, giving it the vague appearance of a candelabra.
Though these 40-foot tall trees are quite something to look at, it is another instance where you will want to keep your distance. These trees secrete several potent toxins. The white sap found inside the tree will cause burning blisters on the skin and will cause blinding if it gets into the eyes.
And instead of growing leaves, it grows cactus-like spines. Its spines are coated in a similarly toxic, latex-like substance. Because of these defensive measures, dwarf versions of the tree are sometimes used as a sort of living fence to deter wild animals.
Growing in the more fertile soils, elephant grass is a common sight near waterways in the savanna. You can’t miss it. It grows in dense clumps that can get up to ten feet tall.
Traditionally cut by farmers to be used as livestock feed, it has recently proven useful in pest management techniques. As it grows readily and is attractive to pests that cause yield loss, it is useful for drawing pest away from valuable crops. The technique is cheaper, easier, and more sustainable than pesticide use.
They also naturally enrich the soil, making them a boon to farmers.
Jackal Berry Tree
The jackal berry tree is most often found growing alongside the termite mounds that dot the savanna.
They maintain a symbiotic relationship with termite colonies. The termites provide the trees with moisture and they aerated soil they need, and the roots of the trees provide shelter for the colony. Though termites tend not to eat living wood anyways, cut jackal berry wood seems to demonstrate a degree of termite resistance.
The trees can grow up to 80 feet tall with a trunk circumference of 16 feet, making them quite easy to spot. The trunks grow straight up, with branches only spreading out a considerable distance off the ground. They have a dense crown with large, deep green leaves.
The fruit is a favorite of many savanna animals, including kukus, nyalas, impalas, warthogs, baboons, parrots, and hornbills. The leaves are eaten by elephants, rhinos, giraffes, buffaloes, and kudus, and emperor butterflies often lay their eyes among the branches.
The fruit can be eaten as-is, dried and ground into flour, or used in the brewing of beer and brandy. And the wood, beyond being nearly termite-proof, is extremely hard and durable. The heartwood is used to make high-quality floors and furnishings, and the trunks are sometimes hollowed-out to build canoes.
A member of the acacia family, the whistling thorn tree is more-or-less unique to Tanzania. Like it’s more common relative, it defends itself from predation with sets of long sharp spines.
These spines are the source of its common name. As the spines grow old, they die and become hollow. When the wind blows, these old spines act almost like flutes, whistling in time to the breeze.
In addition to its musical defense, the whistling thorn has another nasty surprise. The tree produces small, swollen growths that are hollow on the inside. These growths can host up to four different species of stinging ants.
It is thought that the relationship might be symbiotic in nature. Most acacias produce toxic chemicals to ward off insects. But the whistling thorn seems to welcome the colonies.
Ants struggle to nest in the savanna. The earth is too damp and spongy during the rainy season, and it dries out and cracks during the dry season. It seems that in return for shelter, they defend the trees as that home.
When they detect an intruder, the swarm out and attack. Giraffes and other grazers seem to be able to sense the pheromones the ants give off and leave the trees alone.
It’s a fascinating relationship, though probably one better appreciated at a distance.
A Vibrant Tapestry of Life
The savanna’s awe-inspiring nature should land it a place on anyone’s bucket list. With the high degree of specialization in these African savanna plants, every element has a part to play. A cluster of grass is just as important to the ecosystem as the pride of lions.
A Tanzania safari is an opportunity to see the awesome machinery of nature at work. For more information on how to arrange your journey, please contact us.