Whistling in the Bush

Acacia

Talk about having a Defense Department, there is a tree on the East Africa savannah that could teach us some amazing defensive tricks. I was out on a walking safari with Secluded Africa’s Richard Corcoran, who pointed out a small tree called the Whistling Acacia and as we gathered around, he explained that there was more than a symbiotic relationship here – there is true communication between flora and fauna.

The whistling thorn, Vachellia Drepanolobium, is one of the savannah's most fascinating partnerships, an acacia tree that never stands alone. It has 3-inch thorns as protection but interspersed there are swollen round hallow bulbs that a queen ant bores a small hole and enters to lay her larva. These then become a living home, occupied by a fierce cluster of Crematogaster ants. These are one of four different kinds of stinging ant who like this condo relationship. They actually vie for exclusive dominance over a tree. Because the ants compete for exclusive usage of a given tree, some species employ tactics to reduce the chance of a hostile ant invasion. Crematogaster nigriceps ants trim the buds of trees to reduce their lateral growth, thereby reducing chances of contact with a neighboring tree occupied by a rival colony. This does go a step and above. These ants are more than tenants; they are loyal bodyguards. The tree feeds them with sweet nectar, and in return they launch aggressive attacks on any browsing animal that dares to browse (antelope, kudu or giraffe), they swarm sensitive areas like the lips and face until the intruder retreats.

Elephants have learned to steer clear, as when the ants swarm out to painfully bite, they also leave a poison in the wound, compounding the pain. A giraffe on the other hand, can seal off its nostrils and with its very long tongue, can either wipe away the ants or just pull the nitrogen rich leaves away from the limbs. And since a giraffe can consume up to 35 to 50 pounds of leaves, shoots and fruit a day, the acacia has to fight back.

Also, from a giraffe’s long black tongue grabbing and pulling its feathery leaves, this acacia emits an ethylene volatile gas (a colorless, odorless plant hormone) as an airborne warning system to other trees up to 50 yards away that it is under attack. This gas travels downwind where the neighboring acacia “smell” it through their leaf pores. Acting like a signal of attack within 5 to 10 minutes the tree boosts its tannin levels making the leaves bitter and potentially toxic in large quantities. Actually, when consumed in large quantities, these tannins can sicken or even kill the giraffes.  Here again, the giraffe has developed a cleaver behavior to outsmart the botanical warning system. They will typically walk at least a100 yards to trees that are upwind, beyond the reach of the chemical warning gas.

It has been established that some trees communicate through their root system using underground networks, allowing them to share nutrients and send distress signals to one another. But trees communicating through the air, using pheromones and other powerful scent signals to warn each other of danger is one of nature’s most remarkable examples, the wide-crowned umbrella thorn acacia. The magic seems to go even further. The tiny holes carved by the ants into the hollow thorns turn the tree into a natural wind musical instrument. When the wind moves across the plains, it passes through these openings and produces a soft, whistling sound of a flute. It is not just a tree, it is a perfectly tuned alliance of survival, where plant and insect depend on each other to thrive in one of Africa's toughest landscapes. Maybe there is something about “talking trees”.

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