THE CONSTANT SPRING
What Trees and Woods Are and How They Behave
The commercial harvesting of timber, for use or sale, is often considered a prime cause of the disappearance of forests. But it need not be, and under proper management it never is. … the mere cutting of timber need not seriously harm the woods. What does the damage is the prevention of regrowth thereafter …
H.L. EDLIN, TREES, WOODS AND MAN, 1956
In an ideal world, trees would be like an inferior sort of animal or a very inferior sort of person. They would have their origin in the mysteries of sex, would grow up and become ‘mature’; might die when smitten by disease or by the random violence of tempest or fire; would anyway die of ‘old age’ on reaching the equivalent of fourscore years; and would be replaced by new trees arising from seed.
Trees in this world would fit into the affairs of human society. They would grow close together in forests, each tree forming just one straight cylindrical trunk provided by a beneficent Providence for the north European timber trade: genetic modification might even induce them to grow square trunks.fn1 They would die when cut down, and the land they grew on would turn into non-forest. Humanity would plant successor trees to create a new forest even better (by human standards) than the original.
This world sprang from the imagination of the scientists and savants of the Enlightenment in the eighteenth century. It captured the imagination of nineteenth-century governments, who sought to make their trees (and their people) live in that world. Old-fashioned foresters and scientists, and many who write books on trees, still live in such a world. If you believe in a plurality of worlds, there may be, orbiting some far-off star, a world with green men and pink trees behaving thus. But in the real world of Earth, trees are wildlife just as deer or primroses are wildlife. Each species has its own agenda and its own interactions with human activities. If all trees were like the ideal, they would lose most of their significance, all their historic meaning, most of their beauty, and most of their value as a habitat.
SOME FACTS OF LIFE
Coppicing and pollarding
Older readers will have been taught that trees die when felled and woods disappear because people cut them down. The reality is more complex. Many trees, including most conifers, do indeed not survive felling, but most British trees either coppice – they sprout from the stump, like ash – or sucker from the roots, like most elms. Coppicing and suckering, familiar to any gardener, are the basis of nearly all historic management of woodland (Figs 2 & 171). The Bradfield Woods (Suffolk), a typical coppice-wood or copse, have been cut down at least 50 times and show no sign of disappearing: after each felling they constantly produce spring, coppice shoots or suckers (Figs 4,5 & 6).
Trees that are periodically cut tend to live longer. If an ash is felled at 12 years old it will sprout. If repeatedly felled every 12 years it will develop a permanent base, a stool, which will live indefinitely, getting a little bigger at each cycle.
An alternative is pollarding, cutting the tree 6 to 10 feet (2 to 3 metres) above ground to produce a crop of new shoots (Figs 3 & 7). Most trees that coppice will also pollard. The decision whether to pollard or coppice is the woodman’s; the decision whether to sprout, sucker, or die is the tree’s. Pollarding is harder work than coppicing and is normally done for some special reason, such as that it is impossible to exclude browsing animals that would otherwise eat the young shoots.fn2 Pollards, too, have permanent bases that live longer than trees that are not cut.
A suckering tree tends to form an ever-expanding circular patch of genetically identical stems called a clone (Fig. 8). Clonal trees sprout when cut down, but do not form stools.
Timber and wood
The arisings from coppicing and pollarding are called underwood, which has been used for many purposes, but especially for fuel. In most English woods a scatter of bigger trees is left among the stools to grow to a size suitable for beams and planks (Fig. 4). These trees, usually oaks, are called standard or timber trees. Academic writers draw a distinction between the ‘coppice-with-standards system’, including timber trees, and ‘simple coppice’ without them; in practice, however, timber trees come and go, and these are not systematically different forms of management.
Timber is the trunks of big trees. Wood consists of coppice or pollard underwood plus the branches of timber trees: hence we talk of a timber-framed building, but a wood fire. There are similar words in most European languages: bois d’œuvre and bois d’industrie, madera and leña, etc. The distinction is weaker in Scotland than in England or Wales, and is not made in America.
Seed reproduction
Most trees can grow from seed, but not always easily. There is a long and perilous route from a seed to a tree producing more seed. The tree may seldom produce viable seed, like many elms and (until recent hot summers) lime. In oaks there may be a mast year: a huge crop of seed at long intervals. Most bamboos never flower until the last year of their lives, when all the world’s bamboos of a particular species flower simultaneously, produce vast quantities of seed, and die.
Tree seeds may need to germinate at once, as with oaks and poplars, or be capable of dormancy: many tree seeds of middle weight (ash, hawthorn, lime) germinate in the second or third year after shedding. The seedling may be light-demanding like oak and ash or shade-bearing like beech and yew; not many British trees can grow up in the shade of trees of the same species. Seedling trees are bitten off by slugs, mice, deer, etc., or attacked by fungus diseases. Some, such as oak and ash, can survive being bitten off at least once, and produce a new shoot.
Seed reproduction enables trees to colonise new ground and create a new wood. Most trees have some dispersal mechanism: light, wind-borne fruits (birch), those transported by animals (jays carrying off acorns and dropping some on the way), those that pass through a bird’s gut and germinate afterwards (hawthorn). (Some eucalypts have walnut-sized seeds that seem to do nothing but drop off the tree.)
Trees such as birch are pioneers: they grow up more readily in the open than in a wood. Oak, which used to grow up easily within woods, mysteriously changed into a pioneer a century ago.
Gregariousness
Hornbeam is a gregarious tree. If a wood is 10 per cent hornbeam, that does not mean that every tenth stool is a hornbeam; more often the wood will consist of 10 acres (4 ha) of pure hornbeam and 90 acres (36 ha) of something else. Clonal trees, such as aspen, are of necessity gregarious, but hornbeam and lime are gregarious for some other, unknown, reason. Ash and maple occur more or less randomly scattered.
Crab-apple, however, is anti-gregarious: it is very unlikely that the next tree to a crab will be another crab. Many trees of tropical rainforest behave thus.
Trees and soil (see also Chapter 10)
Tree books usually claim that trees need soil to grow on, and that they protect the soil; if the trees are felled – it is said – rain washes away the soil and trees cannot return. This can hardly be true of Britain, which has been treeless for most of the last two million years except for interglacial intervals like the present.
In reality many trees grow perfectly well in rock fissures or on derelict buildings. Indeed, in landscapes which are a mosaic of soil and rock, trees often choose the rock, leaving the soil to grassland, heath etc.
Most trees in Britain will grow (though not necessarily well) on almost any soil, but with certain tendencies:
Statistical analysis shows significant but weaker relationships. Maple tends to be on soils with a high clay content, and ash is more tolerant of waterlogging than maple, with hazel intermediate.
Storms
Twenty years ago people thought hurricanes occurred in other continents and killed trees. Learned writers treated ‘storm mortality’ as subtracting old trees from wildwood. Few remembered the ‘Great Storm’ of 26 November 1703 that sank the Fleet and destroyed the Eddystone lighthouse. Fewer remembered 15 January 1362, when (as Piers Plowman put it) ‘pere-trees and plum-trees were poffed to þe erthe … beches and brode okes were blowe to þe grounde’.
Reality intruded with the events of 16 October 1987 and with storms in 1990, 1999 (on the Continent) and 2002. The chief lessons learnt (or not learnt) were:
As in other countries, storms were an unmitigated benefit for wildlife. They broke up areas of monotonous shade and encouraged coppicing plants. They renewed the habitat of ground-nesting birds and (in France) of deer. They call in question the assumption that the ‘normal’ state of a tree is upright.1
While revising this book I was summoned to Slovakia to investigate the ‘calamity’ of 19 November 2004, when a local storm shattered or levelled many square miles of close-packed spruce forest in the Tatra Mountains (Fig. 10). Many of the characteristics of England in 1987 – not least the frantic overreaction of humanity – repeated themselves. Blowdowns probably form part of the normal ecology of spruce, but the overcrowding practices of Central European foresters encourage them.
Other countries and other trees
Table 1 summarises the properties of the commoner native British trees. The first task of anyone investigating an unfamiliar country is to make a similar table for trees there. This may not be simple, for these properties do not run along particular branches of the evolutionary tree. European beech coppices, but the almost identical beech of eastern North America, Fagus grandifolia, suckers (Fig. 11). North America, Europe and Japan each have one or a few species of elm that coppice and grow from seed, and other elms that sucker.
Travellers in other continents will encounter many of the properties in Table 1. Even Australia – which is, in effect, another planet – has trees that coppice, pollard and sucker, or are gregarious or not. In Mediterranean countries or North America the visitor encounters fire, and learns to distinguish between trees that are flammable and fire-adapted and those that are not. One can seldom look up the answers in a book. What happens after a tree is cut down or set on fire are questions to be answered by going out and looking.
Knowledge of properties changes with time, as the Great Storm showed. The effect of browsing animals on different trees, which has shaped the ecology of the Mediterranean since before human history, is coming to pervade Britain too, as deer get ever more widespread.
WILDWOOD
I use the term wildwood for vegetation before it was affected by settled human activities. In Britain, wildwood ceased to exist in the Neolithic period (or before) and has left no record or memory; it has to be investigated through pollen analysis. Even now it is unsettled what wildwood looked like (Chapter 4).
Over the last two million years there have been cycles of ice ages (glaciations) and interglacial periods with climates somewhat like the present. The current interglacial, called the Holocene, the last 12,000 years, differs from the others in the presence of Homo sapiens, who alters ecosystems in ways not given to his predecessors, Neanderthal or Boxgrove Man. Ecosystems can be affected at a distance by people exterminating animals and manipulating fire. It is debatable whether ‘virgin forest’ or ‘primæval forest’, unaffected by mankind, exists anywhere in the world, or whether it is one of those phantoms, like ‘primitive man’, that haunt the scholarly imagination. (For ‘old-growth’ forest see p.90f.)
TREE-LAND IN CULTURAL LANDSCAPES
In Britain there are three sharply defined traditions of growing wild trees:
Besides wild trees, there are plantations, orchards, gardens, etc., which differ from woodland in that the trees are not wild: someone has put them there (Fig. 13).
Managed woods, wood-pastures and non-woodland trees go back to prehistory; they are already there in the earliest records of landscape, around 800 AD. Plantations, with rare and unimportant exceptions, began around 1600 AD. They became the staple of modern forestry, in contrast to woodmanship, which is the art and science of growing trees in woodland and wood-pasture.
Woodland and wood-pasture are aspects of the world’s great division of tree-lands into forest with a small f (in the sense of trees, trees and trees, with shade-bearing plants beneath them) and savanna (grassland with scattered trees).
WOODLAND
Woodland normally occurs as islands in farmland, seldom more than 300 acres (120ha) in extent, with sharp edges. In England every wood has its own name as if it were a village. Whether this results from fragmentation of what was once a continuum of woodland, or whether insularity is a necessary part of the story of how woods came into being, is discussed.
Woodland structure
In woodland, the trees, as well as other plants, are usually wildlife. They have grown naturally; they will usually have been cut down (often many times) and have grown again by coppicing. (For exceptions see p.264ff.)
On the trees are epiphytes such as mosses and lichens and polypody fern, best developed in damp western regions. Flowering-plant epiphytes (not rooted in the ground) are few in Britain except on pollards. Under the trees there may or may not be layers of understorey trees and shrubs such as dogwood. (Both of these are better represented in Japan than in Britain.)
Britain has five species of woody climbers – honeysuckle, ivy, clematis, dog-rose and woody nightshade. Other continents have many more (America calls them ‘vines’).
Ground vegetation is composed of herbaceous plants, undershrubs such as brambles, and ground-living bryophytes (mosses and liverworts). What distinguishes woodland from wood-pasture is that the ground vegetation consists of plants that evade shade or are adapted to it in one of the following ways:
Underground are the mostly unseen mycorrhizal, litter-decomposing and root-parasitic fungi (p.35f, 369f).
For some of these assemblages of plants the trees provide an environment by casting shade or sucking moisture out of the ground, but for others there is a more intimate relationship.
Sometimes a set of woodland creatures appears to do much the same job, sharing what to the human observer looks like the same ecological niche. These constitute what American ecologists, especially ornithologists, call a guild. Warblers and nightingales that nest together in dense underwood form a guild. So do primrose, bluebell, anemone and violets on the ground of the wood; it seems a matter of chance which occupies any particular square inch. Ash, maple and hazel in a mixed coppice form a guild; so do the five woody climbers; so do the various mycorrhizal fungi that are attached to oak.
Coppicing and woodland grassland
Woodland is not wildwood. For centuries people have used and managed natural woods, and ecosystems have organised themselves in response. Woods have been repeatedly felled and browsing animals excluded. Their present ecosystems are easily damaged by too much shade or by letting in sheep or deer, which they are not used to. Many ecologists call these woods ‘semi-natural’; I shall avoid this term because it assumes the existence of a superior category of ‘wholly natural’ woodland, in which humanity is not an ecological factor. It is doubtful whether any actual examples of this category exist (p.91f).
Coppicing plants respond to felling by more vigorous growth or increased flowering. Violets (shade-adaptation category 1), primrose and bluebell (category 2) are visible all the time, but when the wood is felled they are suddenly exposed to nearly full sunlight; they take the opportunity of extra photosynthesis, the proceeds of which are put into extra flowering in the second or third year after felling. Buried-seed plants (category 3) appear from a seed bank laid down the last time the wood was felled. A few, such as dog’s-mercury, appear to be set back by coppicing.
Coppicing plants vary unpredictably even from wood to wood, and are often different from one country to another. The Baltic island of Øland has ash–hazel woods like those in England, but the plants responsive to coppicing include cowslip and a dandelion, which never do this here (Fig. 14). Most countries with coppicing traditions, such as Greece and Japan, have coppicing plants.
Coppicing affects recruitment of trees. By providing temporary open spaces it encourages light-demanding tree seedlings such as birch, and allows others such as ash to progress from a seedling towards a tree. At the same time it prolongs the life of existing stools and gives less opportunity for such turnover. I know of no seed-bank trees in Britain, though North America has one (pin cherry, Prunus pensylvanica).
Open spaces in woods may arise regularly through coppicing, or irregularly and infrequently through death of trees, windblow or (in other countries) fire. There are also permanent open areas, kept in being either artificially or by browsing animals: these are woodland grassland, whose plants differ both from the coppicing assemblage and from grassland away from woods.
Ancient woodland
Thousands of apparently ordinary woods can be traced back to the Middle Ages. There are four ways to do this:
In the 1980s the Nature Conservancy, predecessor of English Nature, produced an Inventory of Ancient Woodland (Provisional), mapping – county by county – the woods that appeared to be ancient, and whether they were still intact or had been grubbed out or replanted since the 1920s. They drew the line between ancient and recent woodland at c.1600. Similar surveys have been done in Wales and Scotland,2 and are proceeding in Ireland.
Most ancient woods have been intensively used; their present state of comparative disuse is not historical. In principle, they could have begun from surviving fragments of wildwood that were demarcated, conserved and periodically felled. Doubtless many of them were, but others show evidence of having been open land in the distant past.
Woods in other countries
In Scotland (and to a lesser extent Wales and Ireland), measuring woods and defining ancient woodland is not straightforward. Woods, especially in the Highlands, lack nice sharp edges; they move around, so that a wood as a whole may have had a continuous existence but only some of its area may always have been woodland. Woods shade off into wood-pasture and moorland; it is a matter of opinion at what point the trees are big enough or close enough together to constitute woodland. The criterion that a wood should have woodland ground vegetation is problematic in a land with a history of grazing animals in woods and a weak distinction between woodland and wood-pasture.
Uncertainties occur in many other countries (Fig. 15). If, as according to official statistics, 31.57 per cent of the area of Ruritania was ‘forest’ in 1931 but only 15.67 per cent in 1991, how much of the difference is because forests have really declined or because the definition of what counts as forest has become more restrictive?
Recent woodland
In most of Britain, land lacks trees because people prevent trees from growing. If they stop ploughing land, mowing grass, keeping cattle and sheep, or maintaining factories or mines, trees invade by their dispersal mechanisms. The easiest way to create a new wood is to do nothing. I remember when railway banks were kept mown to prevent fires, and were beautiful with grassland flowers; since mowing was abandoned they have turned into oakwood. Slippery leaves on the track exhaust trains’ sandboxes and give rise to special slow-running ‘leaf-fall timetables’ every autumn.
Acquiring trees is the first and easiest stage in creating a wood. The trees will be pioneer species, often hawthorn, oak, ash or birch, depending on which are available in the nearest existing wood or hedge. Hornbeam may come in the next generation of trees, but lime, an ancient-woodland plant, seldom comes at all. Herbaceous plants are less easy to establish. New woods often have little ground vegetation, except remains of the grassland or moorland that was there before, or farmland weeds like nettles (Chapter 12).
Many woods date from the 1930s or earlier periods of agricultural depression. The term secondary woodland includes all woods – including some ancient woodland – that show signs of once having been open land.
Secondary woodland is worldwide. Alongside the well-publicised destruction of forests, large areas of farmland turned into forest in the twentieth century. Mechanisation of agriculture put farmers out of business whose difficult land or lack of capital prevented them from mechanising; their land ‘tumbled down to woodland’. This can be seen on a huge scale in most countries of southern Europe, in North America, and even in densely populated Japan (Fig. 16).
WOOD-PASTURE OR SAVANNA
Wood-pasture (Table 2) combines trees and livestock, either domestic or wild beasts such as deer, antelopes, American wood buffalo or kangaroos. There is a tension between these: the shade of the trees is bad for the pasture, and the livestock eat the regrowth of the trees. In woodland most of the edible matter is far above ground, where only sloths, monkeys, koala bears and tree-kangaroos can climb for it. Shade-bearing herbaceous plants make meagre sustenance, and many, such as lords-and-ladies, are distasteful or poisonous.
Cattle and deer love tree leaves and prefer them to grass, but soon eat all the foliage within reach, creating a browse-line; they eat the edible herbs, then the brambles, and then starve unless they can get out of the wood and find substantial grasses. If Nature had intended cattle and deer to be woodland beasts, evolution would have given them long necks; but the giraffe is an odd side-branch of ungulate evolution.
Most wood-pastures consist of trees scattered among grassland or heath, with a history of grazing by cattle, sheep or deer. These are so characteristic of modern English deer-parks that similar-looking ecosystems in other countries are called ‘parkland’. They also occur in places like the New Forest and Epping Forest; rarely in East Anglia and Wales trees are scattered in farmers’ fields. Usually the trees are wildlife: they got started either at times when grazing was in decline, or in the protection of thorny thickets that held off the animals.
Backward in time and outward in space, examples of tree’d grasslands multiply. A thousand years ago they cannot have occupied much less than one-tenth of the whole of England. They cover about one-sixth of Portugal and one-eighth of Spain. They are widespread in the Balkans, Greece and Turkey, formerly as far north as Sweden,3 and even in Japan. In lower latitudes they merge into the savannas of Asia, North America, Africa and supremely Australia (Fig. 17).
Wood-pasture lacks shade-adapted plants. Savanna is grassland (or heather, etc.) with trees, and is similar to grassland or heather without trees.
Wood-pasture now attracts attention because of revived interest in ‘veteran’ trees. Other than coppice stools, trees seldom grow old in woodland: if woodmen do not cut them down, competition from neighbouring trees forbids them to live through a long period of decline. Ancient upstanding trees are a strong indication that a site is not an ancient wood.
Wood-pastures result where various factors – drought, grazing animals, fire – create conditions for trees to grow, but not forests. In historic England the predominant factor has been people keeping plenty of livestock. In Africa it may be drought. However, recent researches show the importance of human activities even in tropical savannas:4 the distribution of tree’d grasslands would be very different if people had never existed.
Branches of wood-pasture
There are three forms of wood-pasture:
Forest (with a capital F) must not be confused with forest in the woodland or plantation sense. A medieval Forest was a place of deer, not of trees. About half the English Forests were wooded, in the limited sense of having more woodland per square mile than the surrounding landscape. Only a small part of the woodland and wood-pasture of England was actively involved in Forests.
In the uncompartmented type of wood-pasture, livestock had access to the entire site every year, and the trees were normally pollards. Compartmented wood-pastures were demarcated into coppices, one of which would be felled each year and then fenced to keep out the beasts until the wood had grown up sufficiently not to need protection. Many wooded Forests, such as Hatfield and Blackmoor (Chapter 20), were compartmented, many parks, and a few wooded commons.
Terms
I use wood and woodland in the original English meaning of the words. A wood is an island of woodland – what an American calls a wood-lot. Woodland has been used in distant countries to mean other things, such as savanna. In Australia woodland means savanna (at least the denser forms of it); tropical forest is called bush.
NON-WOODLAND TREES
Freestanding trees grow in hedges and fields and around settlements. Some are planted: there is a much stronger tradition of planting trees in hedges than in woods. Others have grown up out of bushes and underwood forming the hedge itself.
Hedges in Britain go back beyond the beginning of records, with archaeological evidence from the Iron Age and beyond.5 They are not merely linear woods: they tend to be less shady, less stable and more fertile. A test of whether a plant is an ancient-woodland indicator (Chapter 12) is that it shall not grow in ancient hedges. A few hedges are ghosts of woodland, the edges of woods that have been destroyed: they retain woodland plants but do not acquire new ones.
Non-woodland trees have historically been an appreciable part of the total tree cover, especially in areas that also had woodland. Many hedges were regularly coppiced for fuel. However, even such a woodless place as medieval Bassingbourn (Cambridgeshire) had non-woodland trees: the parish derived a small income from the ‘loppe’ of ‘Asshewel Strete tree’, ‘the asshes in the Marketsted’, and other pollards growing on public land.6
PLANTATIONS
In plantations the trees have been put there, as an alternative to sugar beet or ryegrass; they have no relation to the natural vegetation. Usually they were transplanted from a nursery. They are meant to be cut down for timber when quite young (40 years for most conifers, 100 years for oak) and not to grow again: the stumps should die and the land be put to some other use.
Modern forestry, as concerned with planted trees, has two branches. The commercial branch mass-produces trees in even-aged plantations and fells them all at once; it was what the Forestry Commission did for most of the twentieth century. The estate branch operates in more complex and varied ways, felling small groups or single trees and even using natural regeneration by self-sown seedlings.
Plantation trees do not pretend to be wildlife. The ground vegetation, if any, is a remnant of what was on the site before. However, plantations if neglected begin to take on the character of woodland as the planted trees die and unwanted wild trees come in. They may begin to acquire a woodland flora as plants invade from nearby woodland. This depends on how near the plantation is to existing woodland, and whether the soil is too fertile (Chapter 12).
Some plantations are on the site of natural woods that have been replanted (or ‘restocked’) by killing the wild trees and planting trees instead. They retain something of the previous ground vegetation, and often also of the previous trees that resisted the killing. Such survivals result from neglect rather than intention: estate as well as commercial forestry drains out the distinctive features of ancient woods, leaving nothing (other than woodbanks) older than one generation of timber trees. ‘Unreplanting’ or ‘deconiferisation’ is now an important branch of woodland conservation (p.378f).
The plantation tradition is earlier and stronger in Scotland than in England. Scots travellers introduced exotica, several of which, such as Douglas fir and Sitka spruce, became fashionable foresters’ trees. Scotland played the leading part in introducing modern forestry – based on the German model via British India – to Britain. The Forestry Commission was largely a Scottish invention.
EVOLUTION
Animals and plants, in theory, have become adapted to their environment by evolution and natural selection. Evolution acts through sexual reproduction, which for plants takes the form of seed. Animals, most of which are short-lived, keep up with changing environments through genetic change in successive generations. The textbook example used to be melanistic moths, which had changed their camouflage patterns in response to acid rain exterminating the lichens on tree trunks.
Most creatures evolve, but some evolve more than others. If an oak takes 50 years to produce its first acorns, evolution acts 200-fold more slowly than on mice. Longevity and vegetative reproduction delay its operation still further. A clonal oak can produce acorns a thousand years after it germinated. Many trees seem to have dispensed with sex as a means of reproduction: I have never seen a seedling English elm or black poplar, and in many years of exploring Greece I have only two or three times seen a seedling prickly oak, one of the commonest Greek plants.
With very long-lived plants, evolutionary adaptation is somewhat a relic of distant prehistory. It came to terms with the slow environmental changes of the Tertiary geological period, but has not caught up with the violent climatic fluctuations of the last two million years, still less with disruption by humanity in the last 7,000 years (but see p.436f). These events have thrust trees into environments to which they are not yet adapted; they may retain adaptations to environmental factors no longer operating, such as European elephants.
NATIVE, NATURALISED AND EXOTIC SPECIES
Native plants and animals are species which reached this country by natural means, usually while Britain was still joined to Europe before some 7,000 years ago: for example ash and badger. Alien species were brought by people, deliberately or accidentally, and behave in one of two ways:
Naturalised species are divided into archaeophytes, historic (but not native) members of the British flora like sweet-chestnut, and neophytes, modern introductions like Norway maple; by convention the dividing line is set at 1500 AD.7 Casuals are plants like borage that do not persist without reintroduction.
In principle (and in this book) these are matters of fact, to be resolved by scientific and historical investigation. Either maple was brought to Ireland on a ship, or it got there by natural means. At present sycamore counts as a neophyte, but if someone finds good evidence of its presence in the Middle Ages it will become an archaeophyte. But of late years the issue has become contaminated by value judgements and political correctness. The question of whether sycamore is native has become muddled with whether conservationists should approve of sycamore. The addition of species to the British flora has become confused with people’s attitudes to human ‘aliens’ in the Customs & Immigration sense of the word.
Plants need not be native or alien everywhere. Scots pine was native in the early Holocene throughout the British Isles. It died out by Roman times from England and Wales, and probably rather later in Ireland. It was reintroduced in or about the seventeenth century and became naturalised, spreading on to heathland, but not into native woodland unless put there. Pine is thus native in parts of Scotland and naturalised (a neophyte) in the rest of Britain.
A recently prominent matter is introductions of ‘native’ species from foreign sources. Some writers refer to native species as ‘true natives’, the implication being that there are also false natives. Indeed there are (Chapter 13). Much of the introduction of ‘Scots pine’ was from Continental sources and is visibly different from the native pine of Scotland.
OAKS AND ELMS
There are two native oaks in Britain (Table 3): most other countries have more. To most readers the common oak will be Quercus robur, ‘pedunculate oak’; Q. petræa, ‘sessile oak’, is the oak of oakwoods and of the north and west. They are very different ecologically, although they often overlap and hybridise.8 Until 200 years ago only botanists recognised the differences: they thus have no common names, the English names being translations of earlier botanical Latin names.
Many alien oaks have been planted, of which Turkey oakfn4 and the evergreen holm-oak have become naturalised. Besides the different species, it is possible to distinguish wild from planted-type oaks (Table 17) and indigenous oak timber from Baltic oak.
There are arguably more kinds of elm in England than of all other native trees together. Wych-elm (Ulmus glabra) is a ‘normal’ species; it is not clonal, grows from seed, and coppices. It is the common elm of the north and west and Ireland, getting rarer towards the south and east. Clonal elms generate a host of ‘microspecies’, rather as brambles and dandelions do.9 These fall into three main groups:
There are many intermediates and possible hybrids. It has been claimed that some, if not all, the non-procera elms are ancient introductions from Europe, but so far this lacks confirmation.10 Elms of the minor group occur throughout southern Europe and as far away as Crete. I have never seen any recognisable procera outside the British Isles. Sarniensis (as its name implies) occurs in the Channel Islands (Fig. 172).
SEVEN QUESTIONS TO ASK ON VISITING AN UNFAMILIAR COUNTRY
Footnotes
fn1 Californian redwood often grows trunks that are squarish in section. Japanese cultivators grow square bamboos by confining the young stems in square tubes.
fn2 Some coppicing trees form a massive solid base called a lignotuber, from which new shoots arise every time the tree is felled or burnt. In Australia the seedlings of many eucalypts form a kind of fireproof wooden radish that persists throughout the life of the tree and can grow to 20 feet (6 metres) in diameter. Some American oaks and ashes form lignotubers that resist fire or drought. Californian redwood, that mysteriously huge tree that is even longer-lived through coppicing, forms lignotubers called burls, prized for their beautiful contorted grain. In Britain lignotubers are exceptional, though the massive bases of old coppiced ashes and the ‘elephant’s-foot’ bases of some oaks would count as such.
fn3 I shall avoid the term ‘pasture-woodland’ because it suggests that wood-pastures are a derivative of woodland, which most are not: they can equally be thought of as tree’d grassland.
fn4 The European tree (Quercus cerris), not the American turkey-oak (Q. lævis).