The Wisdom of Trees

by Max Adams

  ROWAN

  A tree of magic, modesty and rugged endurance, the rowan is a joy at all times of the year with its sinuous intertwining branches, delicate leaves and bouquets of red fruits that presage autumn.

  The wood of the rowan is not renowned for its strength as a timber; it rarely grows to a sufficient size; but it is pliable and will not shatter under tension. It might be used occasionally as a substitute for ash, with which it is sometimes confused—hence its alternative name, the Mountain ash, which is really a misnomer; they are not related. Nevertheless, I recently saw a cluster of rowans growing on the side of Monte d’Oro in Corsica at a height of about six-thousand feet, along with field maple and a few other floral familiars from Britain more than a thousand miles to the north.

  The tree’s folkloric associations run deep. In Irish lore the rowan is protective of houses and beasts; in England it was said to ward off witches; and small crosses were once made of rowan twigs and hung above doorways. In Scotland, necklaces of the berries were a protective charm. It is often associated with natural springs, many of them regarded as holy wells, and it is still regarded as unlucky to cut a rowan down even though it will coppice quite readily. Rowans are much cherished in local country sayings and stories, too.

  The English name derives from the Norse raun, which simply means ‘tree’; in Old English, rowans seem to have been called cwicbeam (cwic meaning ‘alive’, as in ‘quick’) on the few occasions when it was mentioned in charters.

  Easily neglected in favour of louder, brasher trees, the rowan might serve as an exemplar for those simple virtues that can seem increasingly rare: quiet beauty, stoicism and fortitude; modesty perhaps.

  3

  Offspring

  Sex before insects—Spring—Making babies—Pioneers—Massive oak—The human hand—

  TREE TALE: THE APPLE

  Birds do not attend flight schools; rivers do not attend flowing colleges; fishes do not attend swimming conferences; trees do not attend fruit-bearing seminars.

  ISRAELMORE AYIVOR

  Sex before insects

  TREES DO NOT CHOOSE, plan, calculate or devise strategies for their progeny, nor for their evolutionary future. Nature is dispassionate. Animals can, at least, choose their partners in the adventure of sexual reproduction; trees rely completely on chance and the vagaries of wind, weather and animal fancy. But they do have sex—in their case, by pollination—and sex is the driver for adaptation, just as it is in animals. Since trees cannot move they have to engage with potential partners at a distance, which creates complications and obstacles to success in the evolutionary game.

  Trees have been around since before insects, and therefore before most other potential reproductive helpers. The first flying insects evolved around 300 million years ago, and primitive trees were around for at least 80 million years before that in one form or another. So when trees first evolved, it stands to reason that they cannot have relied on other creatures to assist with pollination and the dispersal of their seed. The first trees with pollen—the powdery grains containing the tree’s gametes (sperm)—distributed it by wind and by thermal air currents. It is a tried and tested method, which works well even for trees much younger than the beetles, bees and hoverflies. It seems a rather chancy affair, and so it is: wind-assisted sex has produced great genetic diversity for that reason. But the apparently random, opportunistic nature of the pollination game masks a much more subtle reality.

  To begin with, pollen architecture is enormously diverse, diminishing the chances of hybridization. Those trees that evolved to rely on the wind to move pollen around the forest produce very small, smooth, dry round grains, which are maximized for dispersal on light airs. In fact, anemophilous (wind-borne) pollen is often so light that on release it floats upwards, and it seems that some trees have taken advantage of this fact in distributing their male flowers on lower branches and female flowers higher up, so that pollen from one tree drifts gently upwards until it encounters the flowers of another. This is still rather hit-and-miss, and trees, especially conifers which are nearly all wind-pollinated, must release prodigious quantities of the stuff. In spring, in conifer forests, yellow clouds of it perform an aerial ballet in Brownian motion, very beautiful to watch and a nightmare if you are allergic to it. Even so, one wonders what the chances are of a grain of pollen just drifting into exactly the right spot on a female cone.

  As it happens, the pollen has the odds marginally stacked in its favour because, miraculously, it carries a slight positive charge, while flowers are negatively charged. And more than that, male stamens stand exposed and proud from the flower so that they catch the wind, while the tiny zones of turbulence created by the shapes of female flowers seem to draw pollen in towards the often feathery stigmas, where they are trapped. Almost all gymnosperms are wind-pollinated, and they generally sport their male and female cones on different trees. Many deciduous (angiosperm) trees also use the wind, especially those with unshowy flowers like oaks, beeches, sweet chestnuts and alders. Trees that are gregarious—that is, they favour growing close to others of the same species—gain an advantage if they produce wind-borne pollen: an increased chance of mating. Insect- or bird-pollinated trees are less likely to be gregarious. Their animal partners will happily buzz off to look for another tree of the same species elsewhere in a wood. Clever? Yes. Intelligent? No.

  Spring

  Spring is in the air, at last. After the second-coldest March (2013) on record, the northern spring has been agonizingly late. Now everything is coming to life in a rush, or so it seems. But the natural order of things does not change much, even in a particularly harsh winter. Many plants react more to daylight length than to temperature. We will not see an oak or ash leaf for a few weeks yet; even so, if you dumped a woodsman in their element between December and April you would find that they had a pretty good idea of what to look for and what month it was. I always watch out for honeysuckle coming into leaf before anything else. Often in the first weeks of the year it is the only green thing to gladden the eye, a shimmer of jade against the dun backcloth. But, get down on the ground and sweep a few dead leaves away and you will see that woody bulbs are also gathering themselves, their green tips beginning to break cover. Leaf mould is a terrific insulator as well as a mulch and fertilizer. A good covering of snow, too, will act as a semi-translucent blanket, so that when it melts there are the snowdrops, ready to flower.

  Early in February I start taking a good close look at hazels, easy to spot in a winter wood because the hazel is self-coppicing, so that it springs in many shoots from its stump even if it has not been cut by human hand. The shoots are so straight and smooth that the hazel is also known as the walking-stick tree. I cut a hazel stick fifteen years ago for a hundred-mile walk and it still has good flexibility.

  However, what I am looking for, just as the male catkins sprout and open, are the tiny dark-red female stigmas budding on hazel twigs. Pretty much the first flower of the year, for me this sets the spring clock ticking. I will also be checking on new trees that were planted in the autumn murk, waiting impatiently for new growth so I know they have taken.

  Tramping through the woods, once the snow has gone, I will kneel down beside the stump of a birch, hazel, ash or beech that was cut last autumn to see what’s afoot. Once the tree has sensed that its growing tip has been removed (by me, with a chainsaw or billhook), the hormone auxin, which suppresses hundreds of nascent buds from sprouting all the way up the trunk and is especially present in the growing tip, stops sending its message. The reason this benefits the tree is that the growing tip wants to aim for the sky and stay ahead of the competition, so too much side-growth is a waste of energy; but if that tip is damaged by a storm, many other trees are likely to have suffered the same fate, and so the advantage is with those trees that can re-sprout quickly from the stump. Conifers, you may have noticed, do not produce lateral buds in quite the same way when damaged (at least not normally: Christmas trees can be trimmed when young
to make them more bushy by promoting dormant buds). That is why, as a rule, conifers cannot be coppiced. Once cut down, they are finished.

  At the end of March, therefore, I hope to see new buds emerging from stumps. All through the winter the roots have been gearing up to release minerals and water when the time is right, and those buds will be the beneficiaries, growing like crazy with all that infrastructure beneath them kicking into action. I have taken the precaution of covering the stumps with loose pyramids of twigs and brashings, so that the half-starved rabbit and squirrel population, not to mention the deer, don’t get at those juicy morsels. When I first had a wood I used to do the same, but there was a much-used dog-walking path that wound through the woods, and misguided passers-by—convinced that they were doing the right thing—would uncover the stumps with the idea that the tree would grow back.

  By the beginning of April the last of the coppicing is done: neat cords of underwood are stacked against trees for next year’s firewood or charcoal; satisfying piles of brushwood can now be left over the summer to dry. Wood sorrel and wild garlic (ramsons) carpet the woodland floor with green, and the leaves of both make excellent trail snacks. Celandine is out too, the first yellow gem of the season. And every year at this time there is the almost heart-stopping beauty of wood anemone, whose modest white flowers have a special sort of perfection, that of the true artist, perhaps. It is now that I turn my attention to preparing materials for the summer. When I take out long straight spruces (which should have been thinned by a previous owner) I hate to waste them even though they are not much use as firewood and are, frankly, a right pain to cut and process. So I trim all the side branches flush with the trunk, in a process still called by its ancient Anglo-Saxon name, snedding, and then peel the bark with a drawknife. It’s one of my son’s favourite jobs and a great task for this time of year because as the sap begins to rise it lubricates the cells between phloem and cambium, and the outer bark comes off like eggshell, easy as you like. It’s mucky work, mind. The sap gets everywhere; but the resinous reek is a foretaste of woody smells to come. You are left with a twelve- or fifteen-foot pole, which will season in no time and be ready to build with the same year. We contemplate a new woodshed or lean-to shelter, or somewhere to fire up the barby when it’s raining.

  The trees come into leaf in their own good time: hawthorn, birch, whitebeam, rowan, willow, hazel, beech, oak and finally ash. Traditional woodsmen often planted or selected a mix of ash and hazel in a coppice, because the hazel comes into leaf many weeks before the ash and gets a head start before it is shaded out. The two tree species are cut on different cycles—hazel at eight years for hurdles and such, and ash at twelve or fifteen years for poles—so the amount of daylight hitting the woodland floor changes in a series of harmonious cycles, which create wonderful conditions for biodiversity. An unmanaged wood loses life year-on-year, while the ancient partnership between woodsman and trees creates an almost perfectly sustainable use for land. In spring, a healthy wood is bursting with new life: insects come out and test the air; birds mate and nest like there’s no tomorrow. Like Marty South of Hardy’s The Woodlanders, you can almost hear the wood breathing a sigh (and actually, if you put a half-decent stethoscope to a tree trunk you can hear the surge of its sap rising and falling with the day’s rhythms). The woodsman must enjoy it all while it lasts; in no time the canopy will close, it will be summer, and you won’t be able to see the wood for the trees.

  Making babies

  Seeds and their germination—a bundle of probabilities, which dictates the success of each new generation of trees—are hailed as an example of so-called game theory, whereby (in its biological context) evolution tests all possibilities to find successful strategies for an optimum number of best-fit species. Trees do not knowingly play games, evaluate decisions or work out strategy; but it is true to say that each species performs a distinct role in the ecological teamwork that keeps life going. There are six dice in this game and they represent seed size, number of seeds, age of first production, method of distribution, method of germination and frequency of production.

  Roughly, the smaller the seed the more the tree produces, from the prodigious quantities of birch seeds—in the millions on a single tree—to the mango or coconut, with perhaps dozens. In the middle are those many species that produce hundreds or thousands. It takes only a moment’s thought to realize that, as in animal species, there is a high risk in putting large amounts of energy into few, large offspring, as mammals do. On the other hand, a tree that produces big seeds containing enough energy to set the seedling on its way—like the oak or chestnut—is stacking the odds in its favour. But an oak needs to be a substantial tree before it can even begin to produce acorns, maybe as old as forty of fifty years, although it can go on producing those acorns for hundreds of years. When an acorn is buried to its own depth in even moderate soil the chances of it germinating are very high: it very quickly sends down a taproot, which can penetrate soil and provide water and nutrients to supplement the energy stored in the acorn. At the other end of the scale, the faster colonizers among native British trees, such as hazel and birch, start to produce seeds from ten years of age onwards. Their seeds are tiny and contain little stored energy; they must land on bare soil and rely on facing little competition. But if you see a bare piece of recently abandoned ground you will notice birch saplings in their hundreds taking advantage before the competition gets going.

  Other trees use inhibitors to delay germination and spread the risk of failure. Ash seeds germinate usually a year or more after falling from the tree; trees of very dry places, like the eucalyptus, which dominates in Australia, delay their seed release by ‘serotiny’, an environmental trigger such as heat or wet. They wait until fire sweeps through the forest, and their seeds survive to monopolize the fresh, mineral-rich soil that results.

  Oaks and beeches do not produce large numbers of seeds every year; their progeny are concentrated in mast years, perhaps every two or three summers. Game theorists reckon that this is what’s called a sating strategy. If the acorn or beechnut production was even through the years, most of the seeds would be devoured by hungry animals, most of the time. If they concentrate production in one great burst it overwhelms the greedy pigs, horses and jays: even they can only eat so many. For oaks, the whole project relies on one of these species, the jay, burying hoards of acorns in little clusters and then failing to remember where they all are.

  The distribution of seeds offers another subtle opportunity to test the market. Acorns and beechnuts fall directly beneath their parents, but acorns benefit from jays carrying them away to a better spot, while beechnuts are shade-tolerant and will grow beneath the parent. But some seeds, especially those of the conifers and colonizing broadleaves, rely on the wind to shift their seed about, just as they do with their pollen. Such seed must inevitably be small and light. The helicopters of the maples and sycamore are a refinement allowing slightly heavier seeds to land further from the parent tree, whose shade is undesirable and where the child might compete with parent for water and nutrients. A more sophisticated strategy involves packaging seeds in an edible bribe: rowan, holly, apple, pear, plum, yew and many others offer (primarily) birds a tasty autumn and winter morsel for taking their seeds just that little bit further from the parent tree. Seeds from these species that merely fall from the parent onto the ground are unlikely to germinate, because they are coated within the fruit with germination-inhibitors. It requires the scarifying effects of the strong acids in birds’ stomachs to strip away the inhibitors.

  In these days when there is no longer any lead in petrol, I’d like to see many more fruit trees growing in cities. I used to get funny looks picking cherries off a tree in my local park; I think it would be great if we all started eating fruit off trees in our towns or cities.

  Pioneers

  If you want to get an idea of how Britain was re-colonized by trees after the last Ice Age melted away, roughly fifteen-thousand years ago, you mus
t consult a palynologist—a student of pollen. Palynologists take cores from peat or from the sediments at the bottom of ancient lakes, and they count the pollen grains—remarkably robust things, considering their size, and extraordinarily beautiful—of all the species of plant nearby. It’s not the simplest task. For one thing, trees don’t produce equal quantities of pollen; for another, they don’t distribute it to equal distances. So if you want to know how many trees there were, and where and when they arrived, you have to know your stuff. (There are far too few lime trees in the record, for example: lime is mean with its pollen.) When you have worked out how to adjust your results for all these variables, you get a good idea of which trees got here first, how quickly they spread, and sometimes whether they were introduced by humans or by some other agency—birds, bees, wind or tide. Pollen diagrams also give a fascinating insight into early hunting, gathering and agriculture: once humans began choosing foods they liked to eat, clearing forests and burning things, they left clues there in the pollen. In that record is crucial evidence that several thousand years ago elm trees suffered a catastrophic decline in Britain, just as they did in the 1970s—and probably for the same reason.