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Trees not only live much longer than humans and other animals – they also die differently, piece-by-piece, ...
2022-01-13 09:00:00

Trees Die Twice
On the Death of Plant Life

Sławomir Mrożek, Diogenes Verlag AG. Drawing from the archives (no. 843/1961)
Trees Die Twice
Trees Die Twice

Dying does not have to be the same to each and everyone – animals and plants play it out differently, just as differently as they live.

Read in 7 minutes

If you’ve ever wondered if Fangorn Forest or Mirkwood from Tolkein’s The Hobbit actually exist somewhere on this planet, look no further: just visit the Canadian island of Vancouver. Actually, it is not a forest but a construction – an architectural skeleton of trees so huge that they can hardly fit our imagination. A combination of trees living and dead, ones that keep stoically humming to the tune of photosynthetic cycles, and ones that have completely died back, tree corpses. A genuine thousand-year-old forest is obviously alive, consuming billions of sextillions of photons, pumping sticky juices and salty water there and back again. It breathes. The trees throb with biochemistry, they talk to each other, get jealous of one another. It is hard to believe that all this might and stiffness of the forest, tree trunks that sometimes happen to lean on our backs, hard boughs soaring, fractal-like, towards the sky – all of it is a part of the forest because at the right moment it died. It killed itself, purposely mummifying fragments of its tree body and sacrificing them to utilitarianism.

The cambium’s chorus

Let’s start with the wood. Without it, trees could not live in the two worlds – the world of the wet darkness of the soil, and the world of the sunny, windy cold, several dozens of metres above it. Trees have some business in both of these spaces. Underground, they bore micro-tunnels, in search of water and nutritious minerals, they spread out their telephone networks, murmuring in their rooty whisper to other trees, fungi, soil micro-organisms. It is an important area, this is where the bargaining for the spoils of soil takes place. But the realm of light where green leaves undulate – a realm that, when filmed by a drone flying above the tree crowns, looks like rough, celadon sea – is also very important. Thanks to this world, the sun’s photons bore into the leaves and their energy is put into the sugar particles that feed all the machinery, from the tip of every leaf to the ends of the roots’ hair.

Between these two lands, the tree stretches out a column of pipes and wires, stiff microscopic water conduits pushing the solution from the soil up high, to the leaves’ food factories. It turns out that the best way to keep the water conduits in good shape is to kill them, so that all is left from the sticky, living cells are little pipes inlaid with hard substances. As a result, trees keep producing new layers of them, new slices made up of new little canals. The body responsible for the production is a paper thin layer of cells that form a sticky ring around the tree, close to the trunk surface. The wood forming machinery is called cambium.

The painstaking labour of cambium, slowly constructing new conduits of wood, is performed in rhythm with the days and seasons. It is well visible in the cross section of a cut trunk – the tree rings (or growth rings) are evidence of the cambium’s rhythmical, wood-forming chorus. Similar processes take place in the bark. Go ahead, look at the cross section of a tree’s bark; a cut tree would be the best, e.g., from a woodshed. You’ll see a multi-layered waffle, wafer-like structures of stiff cells, stuck together and filled with air. Bark is formed similarly to wood; here, too, we have a cambium-like tissue that pushes outside the new generations of cells it produces. On their way to the surface, they commit group suicide, they kill themselves, emptying their insides of life’s stickiness. Only the hard, cork skeleton is left: this is all the bark needs to be the tree’s corset, a wrapper that insulates the tree. In these cells, life would only be an unnecessary extravagance.

Trees and other lignified plants can afford dying piece by piece, where the dying of certain areas and parts has been carefully planned. It is possible thanks to the fact that a plant – even though it is made up of well-connected cells and interwoven tissues – is still, to a certain degree, a conglomerate of individuals. It may be the result of the slowness of plant existence, a lifestyle that enforces an attachment to a particular place. Therefore, some parts of the plant can die, while the rest will peacefully continue to consume the saltiness of the earth and the sweetness of the sun, as if nothing happened. If you cut off a branch of a willow and plant it in wet soil, not only will the tree not groan at the act of violence, but also the cut branch, after having pondered it for a while, will come back to life, take root, and reorient its physiology to become – suddenly, just like that – an entire, complete tree. It is the modular structure of plants, a certain independence of their parts, that makes them resilient to local deaths and annihilations. Try performing a similar trick on your arm – I don’t need to tell you that there is zero chance of success...

Naturally, plants can also die in their entirety, completely. Some do it strictly according to a plan: annual plants have death programmed in them the moment they germinate. Everything they do – each twitch of the meristem and every twist of the leaf’s petiole – is headed for the inevitable end. They die without regret, as individual death means little. The plant in question dies having produced hundreds, even thousands, of seeds. Genetically, then, it is still alive.

A much slower death, stretched through several dozens of years, can happen to giants, like those from the Canadian version of Fangorn Forest. It is difficult to pinpoint the precise moment of death. Could it be the collapse of the water pumping wood? When the tree dies, its hydraulic powers diminish. The streamlets locked in microscopic pipes slow down, and eventually they stop climbing up, when the flow in the little canals is broken up by air that filters in the wood. This is the second ‘dying’ of wood. You can hear it: the broken-up trickles of water blow up, making quiet popping sounds. The plant’s modularity stretches the process of dying. For instance, a nearly dead tree can have on its top a clump of green leaves, fed by the last working water conduit, unaware that they are on death row.

The price of living fast

Compared to plants, animals are genuine sprinters of dying. The more complex an animal is, the more sophisticated systems and mechanisms it uses to move and function on an everyday basis, the quicker it is devoured by eventual death. An animal’s body – except for the remote, sticky and rather uncomplicated cases of invertebrates – has very little in the way of plant modularity. It is true that our cells also commit a group hara-kiri; millions of them lay their lives on the altar of the organism’s future, in order to make space for their new, fresh copies. Yet the vertebrae cannot afford the extravagance of plant death. Their bodies are usually powered by a metabolism so fast that each hiccup in the life-giving system’s energy rollercoaster usually ends in death – or, for sure, very severe damage to the animal’s body.

Something that a plant may not even have noticed – a momentary slowing down of water and sap flow, or the cutting off of a small body part – in the case of an animal boasting a sugar-devouring brain, means a severe upsetting of balance. In an instant, the organism of an animal that has been injured – or is otherwise in danger of dying – performs a whole series of biochemical actions that are the equivalent of a yell of panic, aiming to notify every part of the body about the danger. Hormones and messengers released into the blood and lymph desensitize pain receptors, constrict the vessels, minimizing the possible loss of water, and mobilize all reserves of energy. Simultaneously, the nervous system activates entire programmes of reflexes and instinctive behaviours making the animal run away, hide or attack, depending on the situation. As if this wasn’t enough, the racing metabolism of many body parts cannot stop the carousel of life giving energy production, thus poisoning the already endangered body with toxins and the products of a frantic oxidization of various chemical substances.

Getting out of such a physiological catastrophe is not easy, therefore it is no wonder that animal death comes so fast, instead of taking its time like plant death. Of course, evolution hasn’t failed to come up with a response to the deadly pressure – animals are equipped with an array of reactions that help them flee the place of danger, get away from the clutches of death before they manage to inflict real wounds. One should add that a fast death also means the possibility of a fast life – and what more do we, humans, need than a life so fast it can accommodate all our ambitions, plans and dreams?

Should you ever wonder why the apple tree in your garden can enjoy 100 years of slow life, while you must sprint through yours, feeling the breath of death on your back, and barely being able to hit 80, think about the lifestyle plants need to adopt to pay for their slow functioning. It may be that, if you were to live to 100-and-several-dozen years, you would also have to accept a slower dying – so sluggishly slow that it would be horribly unbearable.

 

Translated from the Polish by Adam Zdrodowski

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Szymon Drobniak

is an evolutionary biologist, researcher on colour, ornithologist, illustrator and author. A passionate fan of diagrams, cross-sections and pea soup. In his spare time, he collects roots (not the mathematical kind).