The Wisdom of Trees

by Max Adams

  In understanding how trees grow in balance with themselves and then cope with changes to the forces operating on them it is worth thinking about one of the great wooden ships of the Age of Sail—HMS Victory, for example. The levers of a ship, not unlike a tree, rely on the integrity of the masts, which act as pendulums with a centre of gravity secured along the long axis of the hull. The ends of the levers (the tip of the royal mast, a ship’s highest point, and the base of the mainmast embedded deep in the keel) in motion describe ellipses—unnerving, believe me, the first time one finds oneself on the high seas clinging on to a mast fifty or sixty feet above the deck. The pivot of this pendulum is somewhere below the deck; it has to be, otherwise, the ship will capsize. The weight of ‘top-hamper’—masts, yards, rigging and sails—which is powered in its pendulum swing by the complex forces of wind and wave, is balanced by the great weight of the ship’s ballast (either cargo or solid lumps of cast iron) and by the force of its keel and hull acting as levers against the mass of water through which it travels.

  At the Battle of Trafalgar in 1805, most of the line-of-battle ships (British against French and Spanish) suffered appalling damage as thousands of great guns let fly at each other. The intention was to cripple the enemy’s vessels by destroying their rigging, sails and rudders. By the time that Victory’s famous admiral was cut down by sniper fire that fateful October afternoon, Victory and most of the other ships on both sides had lost large parts of their masts, and were rendered unable to manoeuvre or therefore to bring their guns to bear, or even to escape. Just as it does in any old clock, the period of a swinging pendulum varies according to its length, like a metronome. Small clocks have shorter pendulums with shorter periods and faster swings. Cut a mast down to deck level and a ship begins to rock to and fro with a short, accelerated motion which is awful to contemplate and worse to experience; she becomes no more than a giant life raft at the mercy of the elements—in the case of Victory the terrible storm that followed the battle.

  A tree is a very stiff, slow-moving pendulum, with even more top-hamper than a ship but also with a keel (its root system), which acts with much greater resistance to the lateral pressure caused by wind working on its leaves and branches. As a ship’s company struggles to fit temporary masts to give a damaged ship back its pendulum length and steerage-way, so a tree must react to wind, and to damage: a tree must repair itself. In fact, trees self-repair constantly. A tree growing on a river bank which needs to lean outwards over the river to compete for light, creates a cantilever effect (like a bridge design) in which the roots and branches on the bank side grow stronger and more massive to support the destabilising mass leaning out over the river: the tree tries at all times to restore its centre of gravity to the vertical line of its trunk. Trees, when damaged, use hormones to create tension and compression wood to support the extra strain placed on their branches, the levers that balance them. A tree half-fallen in a great storm or landslide will force its now unbalanced limbs to bend upwards, to restore its balance and send its new growth skywards. In deciduous species, tension wood forms on the upper sides of branches, where they fork like brackets from the trunk, or from each other, so that broadleaved trees pull themselves into balance. In conifers, compression wood forms on the undersides of branches so that they push themselves back into balance. It is all a question of the length of the vessels or ‘tracheids’ grown in those areas. Tension-wood cells contract as they grow, like a rope being tightened by shortening it; compression-wood cells do the opposite. When a tree fails catastrophically, it is often because the ground to which its roots are anchored has become waterlogged and detaches from the surrounding earth; or, it may be exposed to forces to which it is not inured—the domino effect on the closely planted conifers of a plantation, for example. Britain’s 1987 Great Storm destroyed millions of otherwise perfectly stable trees because, like sailors caught in a sudden tropical squall who cannot reduce sail in time, they were caught with their leaves on in early autumn.

  Not coincidentally, when shipwrights of old set out looking for wood for a ships’ ‘knees’—the right-angled brackets, which held deck to hull and which gave the ship its essential rigidity, preventing it from over-flexing—they did not search the great woods but the hedgerows, where solitary oak trees, already tested in every kind of weather, produced horizontal branches with precisely the characteristic tension wood that would make for an unbreakable bracket. Masts and spars, in which the straight, true grain required vertical perfection, were not cut from oak but, most often, from slow-grown, dense but flexible and light Scandinavian softwoods. When Norfolk Island, in the Western Pacific, was discovered in the eighteenth century, the Royal Navy thought it had struck gold in the form of a source of immensely large, perfectly straight trees: a natural dockyard storehouse on the far side of the world. Unfortunately, it turned out that Norfolk Island pines (Araucaria heterophylla, a relative of the monkey-puzzle tree) were useless, being brittle and inflexible.

  TREE TALE

  Hawthorn

  Hawthorn (Crataegus monogyna) is a much-neglected small tree, which we are so used to seeing in hedges that it’s easy to ignore. Our ancestors had a higher opinion of it: the hawthorn is the most frequently mentioned tree in ancient charters and boundary surveys, and it is a common element in English place-names. The flowers and leaves, when picked fresh, are known as ‘bread and cheese’ and have long been a wayfarer’s springtime snack. Hawthorn’s creamy white blossoms emerge any time from late-April onwards, and in autumn the unmistakable rich red berries are an equally classic seasonal marker.

  Hawthorn is the tree equivalent of rugged highland sheep or cattle breeds: it is very tough and can withstand the sort of weather that has most of us running for shelter and a warm fire. The wood is hard to work, and because hawthorn, like yew, grows in multiple trunks, it is rarely used for anything other than firewood. It is hard to say when humans first realized that they could cultivate hawthorn as a defensive barrier; but in the period of the Parliamentary enclosure of land, some two-hundred-thousand miles of ‘quickset’ hedges were planted across Britain; hawthorn remains a popular and biologically important hedge species.

  HAWTHORN

  It is easy to neglect the humble hawthorn, to pass it by unnoticed, until it explodes with creamy blossom in May. Historically, it is one of our most important species: for shelter and defence, for wayside sustenance and as a marker for boundaries and travellers.

  One should at this point say something about the art of laying hedges, which is still practised in Britain and Ireland. The principle in this highly skilled… er... offshoot of the woodsman’s art is to thicken and strengthen a hedge, prolonging its life and ensuring that any gaps through which livestock might (and they will) escape are closed. The trick is to half-coppice the shoot of the hawthorn, blackthorn, hazel, beech or hornbeam—they are the most common hedging species. A downwards cut into the side of the stem weakens it so that it can be bent at an angle, in line with the direction of the hedge but above the horizontal. There needs to be enough heartwood, sapwood and bark left for the stem to survive and send up new shoots the next year. Every couple of yards a vertical stake, cut and trimmed from an unwanted shoot, needs to be hammered into the ground within the hedge, and more spare shoots, brashed from the main one, woven between the cut stems and the stakes, creating a hybrid between living hedge and fence. Each region of Britain has its own distinct style. As you might imagine, hawthorn is not the easiest hedge to lay: the woodsman is sure to come away from a session with cuts and thorny splinters all over. But the hedge and its wildlife are beneficiaries for many years to come. I don’t suppose I’m alone in feeling uncomfortable when I see hedges being flayed by tractor-mounted hedge-cutters. (If you are interested in knowing more, there is a National Hedgelaying Society—www.hedgelaying.org.uk. )

  I am planning to plant some new hedges this year, and I reckon that they ought to be productive as well as protective, so I am going to plant a mix of hazel, blackth
orn (sloe-gin supplies), red and black currants, raspberry, gooseberry and hawthorn. That ought to keep the birds happy too, and in spring I reckon it will look sensational with all that blossom buzzing with insects.

  Hawthorn’s blossom, known as May flowers (hence ‘May-day’ and ‘Maypoles’, neither of them named after the month), used to induce a superstitious fear about it being brought into one’s home. It was thought to presage a death in the household. It turns out that there’s a good reason. A fishy chemical called ‘triethylamine’, released as the blossom fades, is the smell of a dead body (and, incidentally, of human sperm). But the flowers also contain a small amount of digitalin, the chemical present in foxgloves, which in high doses is extremely poisonous but which is used as a therapeutic cardiac treatment. During autumn cows browse on the tree’s small bright red berries (‘haws’), and their astringent properties are regarded as a traditional therapy for mastitis.

  The hawthorn, like a grumpy old teacher, reminds us that a prickly personality may hide unexpected virtues.

  9

  The Charcoal Age

  Material gain—Making charcoal—T he sword in the stone—Seahenge—Riddley Walker—Colemen and Colliers—

  TREE TALE: THE HOLLY

  Clevverness is gone now but littl by littl itwl come back. The iron wil come back agen 1 day and when the iron comes back they wil bern chard coal in the hart of the wood.

  RUSSELL HOBAN, Riddley Walker

  Material gain

  CHARCOAL is a material with magical properties. It is produced by a process called the ‘destructive distillation of wood’. In making it, the collier burns off something like four-fifths of the volume and mass of a pile of wood. And yet, what remains is far more valuable than the original material: a pure form of carbon, capable of producing great heat when burned; and tar, which is useful as a water-proofer, preservative and glue.

  Charcoal is the natural by-product of a fire in which complete combustion has been inhibited by a lack of oxygen. Even the smallest camp fire will tend to produce a few charred sticks at the bottom—and, wonderfully, these are often the sticks that were used to kindle the fire in the first place. Charcoal is no invention of humans, but in realizing its potential some eight- or nine-thousand years ago the human race first harnessed, then unleashed, an unimaginable power. The Greek Titan Prometheus was said to have stolen the secret of fire from Zeus and given it to humankind so that they might liberate themselves and rise above the animals. Prometheus is punished by being chained to a rock forever. This, surely, is a folk-memory of the discovery that charcoal produces a fire so hot that it will melt liquid metal out of rock: the crucial technical breakthrough in humanity’s technological and cultural evolution.

  Charcoal is not just useful for prising metals from the earth. Its lightness means that it is a fuel for the traveller, and good-quality charcoal makes a superb firelighter. A stick of it produces a very dense black stain, which has been used since time out of mind to draw pictures on the walls of caves, on wood and on paper. It has important filtration properties too, since its structure produces a very large internal surface area: if laid out flat, the cell walls of one gram of charcoal may have a surface area equivalent to a staggering five-hundred square metres. Gas masks and water filters have traditionally used crushed charcoal; and often the charcoal can be re-activated, once spent, by heating it again. One reason it burns so hot is that all those exposed carbon atoms suck oxygen in with a rabid appetite—as it does with air-borne and water-borne pollutants like bacteria and toxic gases. In East Africa, a new generation of entrepreneurial inventors has developed a refrigerator in which charcoal, soaked in water, evaporates in the very dry heat, thus cooling delicate crops (such as beans and squash) and preventing them from wilting before they are taken to market. When it burns, charcoal produces a gas that can be used as an industrial fuel—thousands of lorries ran on so-called wood gas in Britain during the Second World War.

  There is much talk at the moment of a substance known as ‘biochar’. It is really no more than charred organic matter, effectively the charcoal of the compost heap. What gets the Green movement so excited is that biochar was being used in the Amazon Basin over a thousand years ago to fertilize poor soils by improving their moisture retention, nutrient content and microfaunal activity (more grubs and earthworms). The native villagers may not have known they were producing it, because it is a by-product of kitchen and garden management. But the results are impressive. Even more significant is that these improved soils stay improved—permanently. Such enhanced soils were noticed by early European settlers in the region, who called it terra preta. Archaeologists working on the defunct towns of the Roman Empire have noticed a similar ‘dark earth’ deposit covering the ruins of former urban spaces. Experimentation is ongoing, but some scientists believe that we should pay very special attention to this technique for enhancing our soils—not just to help fertilize them, but to lock away large amounts of carbon that would otherwise be released into the atmosphere.

  Making charcoal

  For such a marvellous material, charcoal is dead easy to make. You can start with an old coffee tin or a traditional earth clamp kiln (a mound of carefully stacked wood covered with soil and turf) and work up through modified oil drums to an eight-foot double-ring steel kiln or even to an industrial retort: the process is always the same. To scale it up, you use more wood and it takes longer, but the chemistry and physics don’t change much.

  Britons get through sixty-thousand tons of charcoal a year, yet only five per cent of it comes from British woodlands. Dave Hutchinson, who runs the Yorkshire Charcoal Company, is an evangelical champion of charcoal, who would like to see Britain self-sufficient in the stuff. British hardwood charcoal is much, much better than the mangrove-wood charcoal or charcoal-dust briquettes that most people burn in their summer barbies. It burns hotter for longer and is always guaranteed to come from a sustainable source. Dave has designed several new industrial kilns; he even had an idea to run his charcoal delivery wagons off charcoal gas (using modified fire-extinguisher shells to store the gas and feed it straight into the engine’s carburettor). When I lived in my first wood Dave came to teach a group the basics of charcoal production. He brought his own kiln with him, loaded on a trailer, and we supplied the wood—oak and beech, if I remember right.

  The basic process works as follows. Seasoned wood that contains perhaps twenty per-cent water, lots of cellulose and a few impurities such as sulphur is heated to the point at which the water is driven off as steam. It takes a lot of heat, so the first thing to do is light a fire that will get your wood hot. All that heat is being drawn into the wood to vaporize the water—you are doing what a kettle does. Heating the wood is what’s called an ‘endothermic process’—the same as when you put a fresh log on the fire and the fire cools off for a bit. At a critical point the fire becomes exothermic, that is, it’s producing more heat than is required to burn off the volatiles. Now the wood starts to combust—if you let it continue you will be left with a pile of ash and not much else—and the collier can tell when this stage has been reached because the dense white pall of steam pouring skywards from the kiln begins to become a thinner, hazy blue/brown smoke. The burn now reaches its mature phase, when controlling the air intake becomes absolutely critical.

  Now you must rein in the fire’s voracious appetite for oxygen. You must close down the air inlets of your kiln and almost close the outlet (the lid). So long as the steam that emerges from the top is white, you are still driving off water and other volatiles without combusting the wood; so the process has to be watched almost constantly, and inlets and outlets trimmed accordingly. Colliers do not abandon their burns, although there are plenty of other pleasant jobs that can be done at the same time: sharpening tools, tidying stacks of wood, fixing things and drinking the odd beer. Make charcoal in a coffee tin (stick some willow twigs in a tin, make a small hole in the lid and put it on a bonfire) and you might have charcoal in forty minutes; an oil
drum burn will take four hours; in a steel kiln it is an overnight job, and in the traditional clamp kiln it can take two or three days or even more to get a complete burn. When the collier believes the burn to have been as complete as possible, the kiln must be shut with absolute certainty: no air intake at all or it will combust completely. It must cool from the point of perfect charring. Opening a kiln to find it empty except for a heap of white ash on the floor is about as dispiriting as a woodsman’s life gets.

  It has to be said that as an industrial process, charcoal-burning comes top for satisfaction, aesthetic pleasure and philosophical contemplation. There is the excitement of lighting and waiting for the stack to take; the wonderful, intoxicating chocolatey smell of the wood charring and the enveloping fug of steam. There are periods of hard physical effort in stacking the wood (wood which you cut the previous year) and building the kiln; there are times when watching for stray signs of trouble—such as too much bluey-grey smoke or a tell-tale smell of burning—merges unconsciously with contemplative reverie; and at the end, as with opening a Christmas present, the lid comes off and you find out if your burn has been good. A properly charred log, weighing a fifth of its cut original, snaps easily in the hand with the sound of tinkling glass.

  Grading and bagging the end-product and selling it is the only wholesale/retail experience I have ever actually enjoyed; ours was called Edenhill Charcoal, after the name of the wood. Today there are about a hundred professional colliers working in Britain and many more who own kilns and work them seasonally. I would like to see more. Much of the poor-quality charcoal we burn on our summer barbecues comes from the unsustainable felling of precious mangrove trees or the thinnings from illegal logging. We should not be importing ninety-five per cent of our charcoal when the material from which it is made grows on trees.