The secret social lives of plants

Contrary to the long held idea that plants are un-communicative, recent research has made it clear that they do in fact conduct informative exchanges between themselves. Film fans might be reminded of the 2009 blockbuster Avatar. On the moon where the movie takes place, all the organisms are connected. They can communicate and collectively manage resources, thanks to “electrochemical communication between the roots of trees."

Tree of souls....Avatar

Although the general theory of plant communication is not new – plant scientists discovered it in the 1980’s – more accurate experimentation is now helping us understand more about how and why they communicate. And it is certainly more then mere gossip, but an important means of spreading news about danger.

The ability to no only react to danger but to warn others of it has been a controversial finding, suggesting that a brainless tree can not only send and receive messages, but interpret them as well. Despite the growing evidence that plants are capable of communication, many plant scientists still question whether this cross talk is biologically meaningful. No experiment has yet demonstrated that the signalling between neighbouring plants can benefit the emitting plant, prompting some researchers to suggest that “eavesdropping” is a more accurate description of what has been observed than “intentional” communication.

This diagram displays how plants communicate. It is not only hungry animals they have to be aware of, but insects too! Source: Logan Parsons, The Science Magazine

Back on on earth, scientists have revealed that plants communicate through the air, by releasing odorous chemicals called volatile organic chemicals (VOCs), and through the soil, by secreting soluble chemicals and transporting them along thread-like networks formed by soil fungi. It turns out almost every green plant that has been studied releases its own cocktail of these chemicals, and many species pick up and respond to the various messages. As an example, the smell of cut grass — a blend of alcohols, aldehydes, ketones and esters — may be pleasant to us but to other plants signals that danger is on the way. 

Wouter Van Hoven, a zoologist from Pretoria University found that when Acacias were nibbled on by antelope, they produce leaf tannin quantities that are lethal to the browsers, forcing them to move on, and in addition the acacias emit ethylene into the air, which warns other trees of the impending danger. Trees up to 50 yards away then react to this message and step up their own production of leaf tannin within just five to ten minutes. You don’t need to be a scientist to see this in action…next time you are watching giraffe, notice how they tend to feed in the opposite direction of the wind, avoiding the bitter leaves from trees that have been pre-warned and already upped their tannin levels! The defensive compound that gets emitted from the leaves is called Jasmonic acid, providing the name “Jasmonation” to the process of the tree’s talking to each other.

Life and death in the African Savannah

I hear murmurs of excitement as we round a bend and standing in the road in front of us is a dazzle of Zebras, including a very young foal. We watch them grazing for a while, happy to see them content now with the heat of the afternoon having passed and recent rain providing new shoots of grass on which they feed. Quite suddenly, sharp eyed tracker Phanuel, exclaims he’s spotted a Cheetah, lying underneath some bushes just 100 meters away. We drive off into the veld and indeed; a male cheetah lies there full bellied and snoozing under a bush.

It is always so special to see a cheetah, as so few exist in the wild today. We sat captivated, observing his beautiful spots, delicate whiskers and distinct red-orange eyes that look straight through you. Surprise and joy of the cheetah aside however, the crowd pleaser of the afternoon remained the zebras, who were still grazing near the road a short way off, and in particular the young zebra foal, who after hopping around in play started nuzzling its mother and began to nurse. The collective “aww” was soon interrupted however, when we realized that the cheetah too was watching the youngster suckling. The cheetah’s body language changed in an instant and suddenly he was on his haunches, directly facing the dazzle of zebras. We sat in anguish for the following minutes that passed as, completely oblivious, the zebras grazed ever closer to the predator lying in waiting. We had previously semi-discounted the cheetah from hunting due to his full bellied, panting nature, but what a turn of events this was to be. It goes to show how opportunistic these rare animals are however, because without warning, he leapt up and shot off, scattering zebras every which way, his eyes on one individual only…the foal. Over in just seconds, the dust settled to present the cheetah and foal lying in a tangle on the ground, the cheetah’s mouth clamped firmly onto the foals neck, suffocating it to death.

What happened out next was truly heart rendering as the rest of the zebras re-grouped, recognised their missing foal, and came back in search for it, calling out their desperate, shrilly whine, loudest of all it’s mother. They soon found their quarry, lifeless at the feet of a cheetah, and apart from snorting alarms and calling out, they recognised that the situation was helpless, and left the area, heads down, whining in sadness.

Action over, the cheetah panted hard in recovery and then eventually pulled the foal by its tail, beneath a small bush to feed. As if convinced that a nearby predator or scavenger must have heard the zebra alarm calls, he nervously looked all around, in anticipation of an approaching predator coming to steal his kill. None arrived however, but we left before it got too gory, my guests heartbroken at the loss of the young animal they had grown so fond of that afternoon. Such is life and death in the African savannah. 

Lucky to survive...the rest of the zebras look on at the cheetah suffocating the foal

Checking for approaching danger