by Max Adams
The other way of grasping how pioneer trees populated the post-glacial landscape is to travel southwards from the top of a mountain in the north of Scotland. You will go from bare rock to mosses, lichens and tundra grasses, from a landscape of no trees (too cold, too windy) to… what first? Post-glacial Britain needed a true pioneer: tough, opportunistic, with seeds that liked bare ground; wind-pollinated and with wind-distributed seeds, because there were no insects or animals before the first trees provided them with something to eat or hitch a ride on. The tree needed to be frost-resistant too. There is only one candidate: the birch, of which three species are native to Britain: Silver, Dwarf and Downy. Birch produces seed in prodigious quantities. You can hold several thousand in the cup of your hand if you rub an autumn catkin between your fingers. As for being frost hardy, the birch is able to recover from the cavitation caused by freezing and thawing (like an air embolism in humans), because it is able to generate positive pressure in its roots, forcing spring sap upwards and clearing any air pockets out—like priming an engine or water pump—and providing the sap for birch wine in the process; maples do the same thing with even sweeter results.
Birch trees made it all the way to Shetland before a wet period around eight-thousand years ago promoted peat bog at the expense of its few native trees. After the birch, which can spread several miles in a year—ask a railway maintenance crew—came the Scots pine (Pinus sylvestris), slow-spreading at first and then, as it began to provide protection for its own seedlings, forming the first great boreal (northern) forest cover. The Scots pine is an ideal tree for the northern latitudes. A conifer, it does not require insects to pollinate it or spread its seeds, it is frost hardy and it can take an Atlantic gale.
Coming down off a mountain in Wester Ross in the terribly cold March of 2013, dressed for the Arctic and longing for a hot cuppa and a dram, I could not have been happier to see the stunted, wind-blasted leafless pale form of a birch tree; then another; and then, in a little sheltered cleft, a copse of them. Another twenty minutes of descent and the famous, majestic Scots-pine woods that clothe the islands and sloping sides of Loch Maree loomed out of the blizzard. Under their clouded green tops, the temperature immediately rose—trees are the earth’s chest hairs: they give you about three degrees of warmth in winter and a commensurate cooling effect in summer. And after all that white and grey, the reddy brown of the pine trunks was damn near as welcome a sight as the reddy brown gemstone fire of a glass of whisky.
One of Britain’s post-glacial pioneers is missing so far: the aspen (Populus tremula), now quite a rarity in Scotland because although, like the birch, it is hardy and able to colonize bare ground poor in nutrients, it prefers dry summers. Often it reproduces by suckering, generating in effect large numbers of clones. Its Latin name reflects the propensity of its leaves to tremble in the slightest breeze. This is an adaptation shared by other poplars, which increases the rate of transpiration and seems to accelerate mineral uptake from thin, wet post-glacial soils; it allows, effectively, increased glucose production against the odds.
CHESTNUT
We owe a debt of thanks to the Roman legions for bringing the sweet chestnut to Britain. The nuts are highly nutritious, and the wood makes excellent, long-lasting fencing.
Coming swiftly on the heels of the birches, aspens and pines are (and were) the willows (Salix: lots of species, often quite hard to tell apart) and then the hazel (Corylus avellana), perhaps the most useful and underrated of our natives—though not underrated by woodsmen. There is much debate about hazel’s arrival, and some suspicion that the human hand was instrumental in its spread, since archaeologists find piles of hazelnuts wherever hunter-gatherers of the Mesolithic period, between the end of the last Ice Age and the beginnings of agriculture, made their camps. Hazelnuts are a valuable source of autumn and winter proteins and minerals, particularly rich in potassium, phosphorus and calcium.
By 8000 BC oak (Quercus) and alder (Alnus) had arrived on Britain’s southern shores. They, like the hazel, droop with male catkins and female flowers in spring, a clue to the fact that (in common with the birch) they are primarily pollinated by the wind—although where there is pollen insects are quick to take advantage, and oak, we know, has its symbiotic relationship with the acorn-spreading jay. Once a population of insects existed, birds were not far behind, and with those two groups of helpmates the trees that require aid to pollinate and distribute their seeds began to flourish: limes (Tilia), hollies (Ilex), rowans (Sorbus), hawthorn (Crataegus) and whitebeams (Sorbus).
Trees, without being able to move physically, have adapted as colonizers by using the elements and a range of partners to lend them a hand; these include humans, who brought such wonders as the sweet chestnut, the apple and the beech to Britain’s shores. The majority of our trees arrived before sea levels rose enough to finally cut Britain off from mainland Europe, around 6000 BC. By contrast, one of the last non-native trees to arrive and become naturalized, so that it spread quite happily under its own steam, was the sycamore (Acer pseudoplatanus). It may have been here for less than half a millennium, and is treated by some slightly snooty woodsmen and conservationists as a pest. Like weeds, trees become pests when some people don’t like them. The sycamore produces excellent firewood and fine veneers; it yields a wonderfully pale white wood which works like a dream when green, and, when turned into a kitchen utensil, does not taint food. The sycamore is generally inoffensive. Leave it be, I say. A well-known London carver, Barn the Spoon, sits in his shop window all day carving—spoons, naturally—and he counts sycamore as one of his favourite woods.
Massive oak
Britain’s most massive tree is an oak, a sessile oak (Quercus petraea) growing in Croft Castle Park in Herefordshire. At about 100 feet tall, with a trunk more than 9 feet thick, it is estimated to contain 107.6 cubic metres of wood—that’s over 100 tons. Such splendid snippets of information come from the Tree Register, an annual compendium of Britain’s most special trees. Our trees don’t grow as big as they used to. Some very ancient dead oaks, dragged from peat bogs in Britain and Ireland, show that thousands of years ago much, much bigger trees grew in these islands. The oak log that was hollowed out to make a boat found at Hasholme in East Yorkshire, and which has been dated to the Iron Age, was at least forty-six feet long and eighteen feet around its girth; no oak today would grow a single unbranched stem that length. It belonged to a tree which was more than eight-hundred years old when felled.
The human hand
I used to walk into town through a new housing estate. Outside each house a tree had been planted: mostly whitebeam, which is quite sensible because it’s a decorative tree with pretty leaves and flowers and bright red autumn berries, is pretty resilient and doesn’t grow too big. It is an urban landscaper’s friend. To make the estate look established, the developers used quite big trees, maybe seven or eight years old already. But the whitebeam (Sorbus aria, related to the rowan family) has one fatal flaw: as with other trees, it needs water to grow—a simple fact that urban planners find it hard to accept, because it requires effort in the absence of rain. After about a year of walking through this estate watching, as a tree-lover does, how the whitebeams were getting on and measuring by their progress the passing of the seasons, I felt sadder and sadder and then more and more cross as one by one the trees died. A few had succumbed to the stupidity of careless vandalism. Many, many others had died of dehydration—another sort of vandalism. None of them had been replaced. One sees the same thing whenever urban planting schemes are carried out with no thought for the trees other than how they would look on an architect’s drawing. It is intensely frustrating, partly because if the trees were planted at the right time—for the trees, not for the estate—the autumn and winter would have done the job for them; and partly because, with a little wit, the owners or tenants of the houses could have been asked to keep an eye out and tend them. They might have even felt a little pride at nurturing one of a line of trees in common with thei
r neighbours. Maybe some of them wouldn’t bother to give the tree a bucket of water; but at least they ought to know what they should be doing and know why the tree on their pavement is dying. But I romanticize.
Woodsmen and foresters like to plant trees in autumn, when they are leafless and the air is damp but there is no danger of frost. Trees are at their least active, so moving them around doesn’t stress them too much. You can also be sure that the ground won’t dry out before the following summer. Nevertheless, trees generally need watering before their root systems have matured. Every gardener knows that plants need extra watering when they are first transplanted or during their first growing season. So why bother growing thousands upon thousands of trees in nurseries only to see them planted at the convenience of contractors who fail to follow up planting with the care they need? Why plant at any other time than autumn? I once had the immense pleasure of arranging with a primary school to ‘wild’ their flat, mowed playing fields which were hardly ever used. We collected lots of seeds and saplings and the children spent a couple of days enthusiastically planting them, desperate to see them grow. Immediately, naturally; like me, they were impatient for results. The next spring came, and with it came the council mower-men—that is not what we called them—on their seated grass cutters and mowed our new woodland flat. Heartbreaking.
Planting trees is hard work, especially when you are planting by the hundred or thousand. The basic rule—aside from the obvious one of planting in the autumn—is to avoid letting the roots dry out. Windy days are bad, for a dry breeze can kill bare roots in minutes; but mizzly, dank days are good. Newly planted trees generally survive better with stakes to support them—not because they might blow over, but really to prevent the roots working around and creating air pockets. There have been many theories on staking over the years, but trees do need to move around in a breeze, otherwise they don’t grow strong trunks, and so they should be supported for as short a time as is necessary—maybe only a couple of years, and as low on the tree as possible to anchor the roots but allow the tree to bend to the wind and grow strong.
Tree shelters—plastic tubes that you’ll see young trees poking out of—have been a great advance in tree-planting and care. They may not look all that lovely, but they protect young trees and ‘whips’ (rooted cuttings) from frost, and from squirrels, rabbits and deer; and they provide a gentle greenhouse effect. They were the invention of Graham Tuley, a forester, in the 1970s and have become a familiar sight across Britain and the United States. They biodegrade naturally and there are now several improved designs; personally, I like to cut them off as soon as they have done their job, because trees, once established, need to breathe fresh air like the rest of us (many trees take air in through their bark as well as their leaves: that’s what the thin, scabby lenticels on cherry trees, for example, are doing). The shelters can always be resealed with tape, and used again.
Generally, woodland trees should not be fed; the exceptions are fruit trees, which may need a boost of the essential blood- and bone-type minerals familiar to gardeners. We may not think of orchards as woodland environments, but they are—an extreme form of management, but one that yields not just fruit (for human and animal consumption), but also wood, micro-habitats and pollen for insects. Some woodland species do require special attention to the soil because they thrive best in partnership with fungi and bacteria, especially mycorrhizal fungi.
CHERRY
I wish that we planted more fruit trees in our towns and cities. I get some very funny looks when I go into town with my carrier bag and strip a cherry tree of its purple or black treasure.
I am happy to relate that I recently went back to that housing estate—the first time for a few years—to check the survivors of the whitebeams, which are now a good fifteen feet tall. I was delighted to see that the dead trees had been replaced and that the new ones are thriving. Is the message getting through?
TREE TALE
The Apple
Apples: not as simple as they look. Apple trees possess more than fifty-thousand genes, the most complex plant so far known. All domestic apples are descendants of a single species, Malus sieversii: these grow wild on the slopes of the Tien Shan mountains of Kazakhstan, whose capital Almaty, originally Alma Ata, is the Kazakh word for ‘apple city’. Their seeds were first spread by grazing animals, and it seems likely that those animals—horses (which originate in the same area), pigs, deer and cattle—over thousands of years selected the varieties that were sweetest. Some of these wild apples hybridized with the crab-apple more common in Europe. ‘Domesticated’ apples seem to have been introduced to the West by the armies of Alexander the Great: apples are marching food—sustaining, full of vitamin C and keeping well when dried. And the Greeks understood the art of grafting, so they could propagate their favourite varieties.
Nowhere has the apple been so cherished and celebrated as in Britain, where something like six-thousand varieties have been grown over the last couple of thousand years. They are one of the great glories of our landscape and heritage, each with a subtly distinct flavour, texture and colour; each adapted more or less to the landscape, soil and climate where it was first discovered.
And I mean discovered: try crossing apples, like sheep or cows, and you will generally come unstuck. Why not just plant a pip from a favoured apple tree to replicate it? The awkward truth is that apples are heterozygous, which means their genes are not passed on like those of most animals. Our children generally look like us and share, for good or ill, our accumulated genes, from both parents. In apples, which for the most part need a different variety to pollinate them as well as an insect partner like the red mason bee (Osmia rufa), genes are randomly mapped onto the chromosomes of a new generation. So, although the parent genes are inherited, the progeny of an apple tree will not produce fruits that look (or taste) like those of the parents. So most apple trees are grown instead by the grafting of a favoured variety onto a hardy root stock, such as the crab-apple. When you plant a pip from a Cox’s Orange Pippin you might produce a tree with apples that taste horrible; you might equally produce one unknown to humanity, with the sweetest-tasting apples ever. That’s why, in the precious apple groves of the Tien Shan, there are thousands of varieties of apples still waiting to be tried.
Apples, like other fruit trees and all those plants that boast flashy, fragrant flowers, are pollinated by insects and sometimes by birds. Some flowers have very specific pollinating partners; many are generalists, so that a variety of insects will do. Generally, the tree offers nectar—and pollen, which is food for some—in return for the vicarious sexual gratification that the insects offer by transporting pollen (on their backs, bellies, wings or tails) to the stigmas of others of the same species. Many trees produce male and female flowers at slightly different times to reduce the chances of self-pollination. Others, like the horse chestnut, change the colour of their flowers to something less attractive after they have been pollinated. Some species of tree have evolved elaborate, sometimes seemingly over-elaborate, flower architecture to load the odds of success in their favour. None more so than the six-hundred varieties of fig, each of which has a flower inside its developing fruit body (the fig) and each of which has just one specific fig-wasp partner, co-evolved to pollinate it. The female wasp must enter the flower through a tiny tunnel, rifled like a gun-barrel, during which process she loses her wings and dooms herself. She lays eggs inside the figs, pollinating some of the flowers. The resulting male wasps emerge first and mate with the unborn females; after that their only job is to drill holes through the fruit to the open air for the young females to escape and begin the whole, bizarre sadomasochistic process again.
The shiny coating on an apple pip contains cyanide, which keeps the seed dormant until it has been scarified or stripped away, generally by the acid inside the stomach of the bird that has consumed it. This makes it likely that a new apple will grow some distance away from its parent, increasing the probability of its survival. Less likel
y was the invocation of an apple pip in a sensational defence at a famous murder trial in 1845. Coincidentally, this was also the first case in which the electric telegraph was used to catch the suspect, who was trying to escape on a train between Slough and Paddington. John Tawell enjoyed a mixed career: he started out as an assistant to a Quaker chemist, married and had two sons, survived a capital conviction for forgery, was transported to Australia, but was later pardoned and started a successful business, returning to England before his wife and sons died. His mistress, the murder victim Sarah Hart, had been his wife’s last nurse. Tawell’s lawyer, Sir Fitzroy Kelly, argued that his client’s mistress had eaten several apples and that the cyanide in their pips had killed her. He argued in vain. Tawell was hanged for murder by the administration of Prussic acid, with which he had laced a bottle of his lover’s beer.
Apple wood is one of the very sweetest when burned on a fire. It also produces lovely grained veneers and furniture, and the teeth of gear cogs on mill wheels used often to be made of applewood because it is hard and contains lubricating oils.
