POLLEN ANALYSIS AND WILDWOOD
The dust might have come from anyone’s coat … pollen grains, including those of the sow-thistle, mallow, poppy and valerian.
AUSTIN FREEMAN, THE GREEN CHECK JACKET, c.1925
THE AGE OF EVOLUTION
The world is supposed to be about 4,600 million years old, and has been lived in for about four-fifths of that time, but mainly in the sea. About 500 million years ago land plants appeared, and in the late Devonian, 360 million years ago, there is the first evidence for trees – but trees more like those with which the imagination of C.S. Lewis peopled Venus than the trees of Earth today.1
Palæozoic trees had some familiar properties: clonal growth; annual rings; ability to burn, and adaptation to fire; ability to grow either in a forest or scattered among low vegetation; adoption of fungi to help out the functions of roots; and ability to go hollow when old. Then, as now, not all trees had these qualities. The continents were grouped together, with England roughly where Borneo is now.
Modern-looking trees – the first conifers – appear in the late Carboniferous, some 310 million years ago. Somewhat later came four-footed beasts, especially dinosaurs, which engendered adaptations to resist or recover from browsing.
Flowering plants, including broadleaved trees, emerged in the Cretaceous (150–65 million years ago). By this time the continents had moved some way towards their present latitudes. The Atlantic opened up, first in the middle, leaving North America and Eurasia joined through Greenland (well south of its present position), so that plants could move from America to Japan. Australia, isolated from other land masses, turned into what is virtually a different planet.
During the Tertiary (65–10 million years ago), many present genera, perhaps even species, of trees appeared. Broadleaved forests of oaks, beeches, laurels etc. dominated much of the world. They were predominantly evergreen, indicating a tropical or subtropical wet climate. Such ‘laurisylvan’ forests, which once flourished around London, are now reduced to the warmer parts of Japan, China and the southeast United States.
All this vast time, the environment was very stable. Climate very slowly changed; the earth’s crust rose and fell; continents wandered at less than 2 feet (a half-metre) a century. Animals, rival trees and pathogens became able to devour, shade or kill particular species. But even long-lived trees could apparently adapt by evolutionary change to these slow events. Local disasters came by super-volcano or tsunami, and very rare worldwide catastrophes by the crash of asteroid. These one-off events had a less severe impact on plants than on animals; their effects would probably be indirect, through killing off the browsing animals.
Why do trees coppice?
A legacy of this period is the ability of trees to sprout after felling. Coppice-ability can hardly have evolved in the relatively few generations of trees since people invented axes. Nor is it a universal property of trees. Nor is it related to the history of human contact; it is as common among the trees of North America (Fig. 28) and Japan as among their relatives in Europe; in Australia it is common among eucalypts and near-universal among rainforest trees. Although sometimes a fire adaptation, it is no less prevalent among incombustible trees.
To what influence is coppiceability an adaptation? Catastrophes like ice storms, avalanches and blowdowns (p.19ff) come to mind, but are surely too local to account for so widespread a phenomenon. Presumably it is some factor that no longer operates: was it super-elephants, of which more anon?
Some trees self-coppice. Hazel, if not cut or browsed, sends up new shoots from the base that ultimately replace the old ones. When old, Tilia americana, American lime or basswood, rots at the base and falls down, having sent up a ring of sprouts to form its successors (Fig. 30). So do two Japanese limes, and so, presumably, did T. cordata in Europe. Self-coppicing occurs in a Japanese beech, an American ash, American chestnut, Japanese and American magnolias, and in one of the world’s rarest and most recently discovered trees in an Australian rainforest.2 It is one of the mysterious ways in which trees – long-lived as they already are – further extend their life spans. In effect, they step off the ladder of evolution: ability to hold on to territory supersedes the ability to adapt to environmental changes.
A heroic example is the Californian redwoods, a very ancient tree genus and one of the few conifers that coppice. The huge blackened stump of an 800-yearold tree, felled by loggers a century ago, is surrounded by a ring of its sprouts now 150 feet (50 metres) high, which in turn forms part of a ring of rings. Some of these trees germinated at least half the Holocene ago.3 Is this behaviour a relic of adaptation to browsing by dinosaurs? But what could even the mightiest dinosaur do to these giant trees?
THE AGE OF CLIMATIC CHANGE
Two million years ago, stability vanished: changes went into top gear with the coming of the ice ages. There were about 50 cycles of increasing intensity, during the last half-dozen of which plant life was wiped out at high latitudes; the last but one was probably the most severe so far. Trees moved south, and some of them returned northward when warmer temperatures returned. Glaciations have occupied at least three-quarters of the time; interglacials like the present are relatively brief. Even the Amazon rainforest seems at times to have been reduced to large patches.
In Europe the ice ages were more severe than in America or the Far East, partly because the barriers of the Mediterranean and Sahara left cold-sensitive plants with nowhere to go. Little of the laurisylvan flora survives compared to Carolina or Japan: only one species of holly, one of laurel, four evergreen oaks, no magnolia. In the Mediterranean glacial periods were dry as well as cold.
Evolution was no longer the dominating force in the functioning of trees. That is not to say that it no longer functions. Annual creatures (most animals are, in effect, annual) can keep up with not-too-drastic climatic changes. Perennial plants and trees migrate or sit out the change or go extinct. Trees of remote islands cannot migrate. In Crete three of the four high-altitude trees – cypress, Cretan pine, prickly oak – occur at all levels from the tree-limit at 5,600–6,000 feet (1,700–1,800 metres) down to the coast: they can endure a huge range of temperature. On the mainland prickly oak seldom occurs above 2,000 feet (600 metres). Ability to withstand cold has evidently been forced on insular prickly oak by the glaciations.
Perennial plants and long-lived animals, on the whole, found themselves not so much in environments to which they were adapted, but in those into which accidents of history had thrust them. This may explain why some alien species, like grey squirrel from North America, or Japanese knotweed, or gorse in New Zealand, fare better in environments to which they are manifestly not adapted than in their homelands.
In Britain, the last-but-one ice age covered most of the island in ice. Glaciers scraped up soft rocks from the bed of the North Sea and deposited them as moraines of mud, such as can still be observed around Norwegian glaciers. This formed the boulder-clay that underlies many English woodland soils. The last ice age, though covering less of the country in ice, converted Britain to tundra and probably left not a single tree alive.
THE AGE OF HUMANITY
Half a million years and two interglacials ago, a kind of superman, Homo heidelbergensis, lived at Boxgrove (Sussex), spearing super-horses and avoiding super-elephants. As far as is known, hominids used their stone tools for cutting up super-rhinoceroses, but not for cutting down trees.4
During the present interglacial, the Holocene, changes have gone into overdrive. The present human species enters the stage. By tradition, Upper Palæolithic and Mesolithic people were too few, and too limited in their technology, to have much more influence on the landscape than the beasts on which they preyed, or than Boxgrove Man. They prowled, it was supposed, through boundless forest – trees and trees and trees, with patches of fen and reed-bed – from coast to coast and almost up to the tops of the mountains.
But mankind, even in small numbers, has powers not given to ‘the beasts that perish’: the power to exterminate large animals, to influence sites at a distance, such as by altering the fire frequency, and to introduce plants and animals from region to region.
Pleistocene elephants were not the puny monsters that we rode at the zoo, but dinosaur-sized creatures like the West Runton elephant, from the last-but-one interglacial, displayed at Norwich Castle. All continents had giant mammals in previous interglacials: super-elephants, super-rhinoceroses, super-sloths in South America, even an elephantine marsupial in Australia. They survived many glacial cycles, but died out around the last glaciation, when the super-fierce Homo sapiens expanded. If Upper Palæolithic people exterminated them – and what else could it have been? – the removal of these living bulldozers would have been the most profound effect so far of humanity on the world’s vegetation. The Holocene may be the first period since the Permian without super-herbivores but trees may not yet have adapted to living without them.
There have been forest fires almost as long as there have been forests. People could hardly have set fire to non-fire-adapted vegetation, such as a limewood or elmwood, but in America, Africa and especially Australia, people have influenced whole continents by altering the frequency of fire in combustible vegetation.
Islands
Islands are special. Those near the coast, such as Britain and Japan, get linked up during glaciations when ice on land takes water out of the sea and causes sea level to fall. They tend to have similar plants and animals to the Continent, but with some species missing. Britain never had bison, and some common European plants, such as the yellow thistle Cirsium oleraceum, reach Calais but no further. Some trees, like sycamore and spruce, are supposed not to have crossed the Channel after the last glaciation, but since they are not native in coastal France this cannot be the only factor involved. Others did not reach Ireland.
More distant islands, as in the Mediterranean, lack many Continental species and develop endemic floras peculiar to themselves. Endemic plants, such as those of Crete, have to withstand variations of climate: there is nowhere for them to go during glaciations. On very rare occasions mammals get stranded, to generate bizarre endemic faunas such as the tiny elephants, super-mice and mountaineering mini-hippopotamuses that once roamed Crete. A consistent feature is that they lack adequate carnivores. When people arrive, the surrealist mammals disappear, but the trees and plants – adapted over two million years to overgrazing – withstand cattle, sheep and goats.5
Oceanic islands, like St Helena, have almost entirely endemic plants and land birds, with no mammals except bats. When people and livestock (pigs, rats, goats) arrive, the consequences are disastrous. The entire ecosystem, with no resistance to browsing, collapses; the trees are relegated to cliffs, and universal tropical weeds inherit the land.
POLLEN ANALYSIS
The prime evidence for wildwood and prehistoric woodland comes from pollen. Many trees and other plants produce vast numbers of pollen grains, the shells of which are made of sporopollenin, one of the most indestructible of organic materials. They last millions of years in permanently wet or permanently dry places. To some extent they are identifiable. Any student can recognise pine, oak or lime pollen; to some extent the groups of pine species produce different pollens; hazel, embarrassingly, is easily confused with bog-myrtle; experts can separate the two native species of lime pollen; but so far only one group of experts has claimed to distinguish the two native oaks.6
Palynology, the study of pollen grains, goes back to the 1880s. It can be used to check whether ‘thyme’ honey really comes from thyme, or where a murderer or victim has been, or the provenance of a historic artefact like the Holy Shroud of Turin, or when sufferers from hay fever need to take their medicine. In the archaeology of vegetation it has grown since the 1930s into a science, practised all over the world.
One looks for a lake or peat bog with a stratified deposit: year after year a new layer of mud or peat is added and includes that year’s fallout of pollen. (Sometimes acid soils and archaeological deposits preserve pollen.) A core is extracted with a hollow borer, cut up centimetre by centimetre, taken to the laboratory, and processed to get rid of material other than pollen. A specialist identifies the pollen grains and counts the number of each type from each sample. The result is expressed as a pollen diagram, in which the amount of each type of pollen is plotted against the depth in the profile (Fig. 173). Other samples are sent to a radiocarbon dating laboratory to get a sequence of approximate dates.
Pollen analysis is not straightforward. Pines, oaks and other wind-pollinated trees produce vast quantities of pollen; a yellow film forms on a water surface near pine trees in flower. Lime and blackthorn are mainly insect-pollinated and waste far less pollen, which travels much less far. So a sample containing 20 per cent lime pollen and 80 per cent oak pollen probably means a limewood with a few oak-trees. Poplar pollen has the reputation of being poorly preserved; chestnut is easily overlooked. Herbaceous plants, especially if insect-pollinated, produce less pollen still; the palynologist will be very lucky to meet primrose or bluebell pollen. Grasses are copious pollen producers, but mostly cannot be identified as to species.
Pollen analysis requires a fairly well-equipped laboratory, a good microscope, and a reference set of pollen grains from known species. Preparing the samples uses hydrofluoric acid to dissolve unwanted materials. A century and a half ago hydrofluoric acid was almost a household chemical; artistic young ladies would etch patterns on glass with it; it is now frowned upon because it dissolves most materials except sporopollenin, including the human body in a manner that I shall not describe.
Few readers will be tempted to do their own palynology, which is a pity because there are plenty of deposits worth looking at, especially in woodland ponds and small wetlands. Many have been destroyed by the fashion for de-silting ponds and moats. In theory the pollen should always be sampled and recorded before doing this, lest a unique document be destroyed unread. Pond-clearers are usually in a hurry; palynologists are few and busy and have their own research interests to pursue, and may not welcome samples randomly thrust upon them by others.
What pollen analysis does not reveal
Palynology records the sequence in which trees returned to Britain after the last glaciation and how wildwood developed. Suitably adjusted, pollen counts give some idea of the composition of wildwood, although this may be biased by trees such as alder that grow round wet places. Especially in drier countries, pollen deposits represent the wettest spots in the landscape and may not be typical.
In Britain, many pollen deposits come from wet hollows that are typically fringed by alder. Extensive deposits, such as from big lakes, tend to catch pollen from a wider area than small woodland ponds. However, dry country, such as chalkland, is difficult to recognise in the pollen record; here snail shells may be a proxy for indicating where woodland was and how long it lasted.7
How much pollen is needed to establish a tree’s presence? Pollen analysts discount odd grains of wind-pollinated species, which could have been blown from a distance. Pine pollen is regularly blown from America to Greenland and from Norway to Shetland. Substantial amounts of pine pollen are needed to prove the presence of the tree, especially if the other contributors to a sample shed little pollen.8
Palynology may not reveal the structure of wildwood or what it looked like. The prickly oak of the Mediterranean, Quercus coccifera, produces the same pollen whether it is a great oak-tree or a shrub 2 feet (60 centimetres) high. However, hazel (as anyone can see who walks round a wood in February) is a prolific producer of pollen provided its leaves are not shaded. Hazel pollen is vastly common in samples of British wildwood, often exceeding all other trees put together. This used to be interpreted as a hazel understorey in ‘mixed oak forest’, which cannot be right, for understorey hazel produces no pollen and is masked. Nor can it mean hazels with a few catkins under a small gap in the canopy. Hazel dominating a pollen sample must mean areas of hazel forming the canopy.
Evidence for the stature of trees exists if the trees themselves are preserved in peat. As modern farming in the Fens dissipates the peat (and helps along global warming), there come to light ‘bog oaks’, occasionally of gigantic size.9 These encouraged scholars to think of wildwood as composed of forest giants, but they grew in a very favourable environment and died a strange death. They were the last generation of trees to grow on the mineral soil before peat began to form. They were killed by water backing up from rising relative sea level, rotted at the roots, crashed down into the developing peat, and were entombed (p.76f).
Pollen analysts have assumed that trees mean forest, and express the degree to which a landscape was forested by the ratio of tree to non-tree pollen (AP/NAP). This is only a rough measure: it depends on whether the tree pollen is lime or pine, and whether the investigator counts hazel as a tree. Pollen records become difficult to interpret in later periods: woodland becomes fragmented, hedges and non-woodland trees appear, and the landscape gives the impression of increasing complexity.
Coppicing greatly alters the ability of a wood to produce pollen. Oak tends to be over-represented because it is a timber tree and produces pollen all the time. Hazel and birch are over-represented because they resume pollen production two or three years after felling. Lime, which usually takes at least ten years to produce pollen, is under-represented; if the felling cycle is shorter than ten years it may be missed altogether.
Palynological criteria are wanted to differentiate between the following:
DEVELOPMENT OF WILDWOOD
About 12,000 years ago, after the last glaciation, trees returned to Britain. The first were birch and then pine, relatively arctic and easily dispersed (Fig. 29). Often a birch-dominated phase was followed by a pine-dominated. Less according to expectation, hazel came from the northwest and spread into England from Scotland; there was a combination of hazel and pine that has no close parallel today. Hazel then became exceedingly abundant, often dominant, over most of Britain and Ireland.
Oak, alder and lime followed, replacing pine and birch. Then came elm and then ash, displacing some of the hazel (or at least preventing it from producing pollen). Holly, beech, and probably maple and hornbeam were the last trees to arrive before a rise in relative sea level cut Britain off from the Continent, about 7,000 years ago.
The return was not always a slow creeping of each species from Kent northwards. Some trees appeared in small quantities – just enough pollen to prove they were here – hundreds or thousands of years before they became abundant. They had to replace existing trees, not merely to occupy vacant ground; they may have had to wait for mycorrhizal fungi to catch up with them.
Changes in climate played their part. There was a setback of re-glaciation in the early Holocene, known as the Allerød Interstadial. The ninth millennium BC saw the rise of lime, which must mean – considering the non-invasive behaviour of lime today – that summers were then hotter even than those of the last 30 years. (Lime probably benefits from unusual heat waves rather than from average summer temperature: today it extends further north in Scandinavia and higher in the Alps than oak.)
Despite some claims to the contrary, beech is native to England and Wales. Its wood and charcoal are known from the Bronze Age. Pre-Neolithic records are of pollen only: was there enough pollen to establish the presence of the tree? As Sir Harry Godwin, greatest of English pollen analysts, showed, beech pollen travels less well than that of some other trees. Even where beech was known to have been present from fossil wood, there was often little pollen in nearby deposits. This, he said, ‘makes it difficult to dismiss as due to distant transport by wind the sites … where beech pollen is present though sparsely’. On this basis beech got into Somerset and Dorset in about 7000 BC, about when Britain became an island. A thousand years later it was locally abundant at Wareham, but not until much later did beech, along with maple and hornbeam, become a main woodland tree.10
Ireland lacked lime. If beech got there – there is one find of its fruits – it did not persist. Maple is supposed to be an introduction in Ireland, but on no very good grounds: its pollen and wood have been found in prehistoric contexts.11
The fully developed wildwood
American ecologists, following F.E. Clements, and Europeans after them, believed that any sort of vegetation, if left long enough, would progress into a stable ecosystem, the climax, determined by climate. Climax theory gave respectability to the tradition of stable, immensely ancient ‘primæval forests’; it was influential for much of the twentieth century, and still influences conservationists.
If ever there was a long enough period of stability in the Holocene for trees and plants to compete and achieve equilibrium in something like a climax forest, it would have been the 2,400 years of the Atlantic Period, ending in 3800 BC. (Whether it was really forest is discussed later; whether it was really ‘virgin forest’, unaffected by humanity, is considered in the next chapter.)
The Atlantic Period began with a sudden rise of alder, which had previously been present throughout Britain and Ireland, and now became one of the dominant trees. This is somewhat of a mystery: it has been attributed to the climate getting wetter and causing ground to become sodden, but alder is a tree of flushed, not waterlogged, ground, and is not very dependent on high rainfall. Moreover, if this were the explanation, the change should have been most marked in drier regions, which it is not.
Oak and lime, and later ash, rose to displace most of the pine, some of the birch, and to displace or mask some of the hazel. Around 4000 BC there were five broad regions of wildwood (Fig. 31):
Each Province included several types and variants of wildwood, some of them related to present woodland types. There were (and still are) outliers of lime in the southern parts of the Oak–Hazel Province. Outliers of pine persisted in special places in all four other Provinces.
Pine declined to extinction except in its stronghold of the Highlands of Scotland. In England and Wales there is no good evidence for it beyond the Roman period; it is last heard of as a fossil in the Fens. In Ireland it lingered late enough to have written records. Birch also declined outside the Birch Province. In the Oak–Hazel Province it persisted in quite large quantities; even in the Lime Province it never quite died out.
LOCAL VARIATION IN WILDWOOD
The south Norfolk meres
In East Anglia there are many depressions, ranging in size from a few acres up to 100 acres (40 ha) or more. They are thought to be karst features, produced by local solution of the underlying chalk, although most are blanketed with Pleistocene deposits of boulder-clay, sand and loess. They include the famous fluctuating meres of the Breckland, which dry out periodically and do not preserve pollen. Others are permanent lakes, whose mud contains pollen, often from late-glacial times to the present.
Thirteen cores have been analysed from eight different meres,fn1 located around the edges of the dry Breckland (Fig. 175). The soils and geology are most complex, with a patchwork of sand, chalk, loess and boulder-clay in different proportions. The region has been farmed since at least the Iron Age. Diss Mere is in the town of Diss, surrounded by a tract of ordered fields, probably Iron Age in date. There is one ancient wood in the region of the meres, Wayland Wood,fn2 which has existed at least since Anglo-Saxon times; it is an ash–maple–hazel wood with oak timber trees, a patch of hornbeam, and (unusually) many stools of bird-cherry (Prunus padus). To the south are Fakenham Wood (hazel) and Burgate Wood (partly hornbeam and partly ash–hazel), both with standard oaks. Further to the east the woods are predominantly of hornbeam; to the northeast is Hockering Wood, a great limewood. There are two small patches of lime (Tilia cordata) within the mere region.
Godwin’s two cores from Hockham Mere were the basis of the classic story of how wildwood developed in England (Table 8). Birch and willows appeared first. Then came the rise of pine, soon overtaken by hazel. Elm came next, followed by oak and by the decline of birch. Alder and lime came together as pine declined. The arrival of ash produced the fully developed wildwood, the end of which is marked by the sudden decline of elm at the beginning of the Neolithic.
What do the 13 cores reveal for the period between the rise of ash and the Elm Decline? This was the late Mesolithic, about 5000 to 3800 BC, when people should have been hunter-gatherers, not having much direct influence on vegetation. I have measured pollen counts off the published pollen diagrams.13 To calculate the contributions of different trees to the canopy I have multiplied elm pollen by two and ash and lime by eight, which (very roughly) allows for them producing less pollen than birch, pine or oak. Hazel is taken to be a good pollen producer as a canopy tree, but to be sterile if shaded.fn3 I have omitted alder and willow as being wetland trees, forming a separate plant community fringing the meres.
Throughout the period, each of the sites had fivemain dry-land trees: lime, hazel, oak, ash and elm. Pine pollen was scarce, and probably blew in from pinewoods in the Fens. Birch was locally present in small quantity. There were insignificant amounts of beech and yew, and only odd grains of hornbeam and maple.
At the beginning of the period most cores are dominated by hazel. The proportion of hazel generally fell, replaced by increasing amounts of lime and then ash. Following Richard Bradshaw, I would interpret this as the working of natural succession. Hazel and pine got in first; hazel then took over, possibly by suppressing the fires which pine needs to maintain itself. Hazel would be stable, being long-lived and densely shading, but later-comers slowly got in and replaced it. Some of the hazel was suppressed and presumably killed by lime. Later, ash began to take over: if modern ecology is a guide, the result would be an ash–hazel wood in which the hazels stayed alive but stopped producing pollen. Oak also increased in places.
This takes us to just before the fateful decline of elm. At most sites, as everywhere this side of the Alps, something caused two-thirds or more of the elm to disappear from the canopy in a few years around 3800 BC. What that Something was is considered in the next chapter.
What took the place of elm? Overwhelmingly hazel: in all but one of the sequences hazel returned to being the commonest tree just after the Elm Decline. The inference is that elms had invaded part of the hazel-wood and converted it to elmwood with an understorey of hazel that ceased producing pollen. On the death of the elms the hazels produced pollen again. Experience in Madingley Wood shows that hazels can survive with little alteration for well over 50 years under elm, but produce no pollen;14 my observation in Hayley Wood shows that when elms die the released hazels flourish and resume producing pollen.fn4
The pollen evidence now reveals, instead of the ‘mixed oak forest’, at least five types of wildwood within the Lime Province of south Norfolk:
This is the minimum number of wildwood types consistent with the evidence. Birch could have been mingled with other trees – it is now one of the few that can (for a while) keep up with the height growth of lime – but more likely occurred as patches on its own. There is no means of telling whether oak was scattered among other trees (a forerunner of its historic position as standard trees among underwood) or formed patches of woodland on its own.
The five to seven woodland types were represented in very different proportions in no systematic way. Hockham core 1 was predominantly hazel-wood throughout. In the same mere, core 2 shows hazel temporarily overtaken by lime just before the Elm Decline. In neither core was any ash recognised at all. In Hockham 3, oak, lime and ash outnumbered hazel throughout, while in Hockham 4 hazel outnumbered lime, oak and ash. In the little depression at Oxborough, lime was dominant at first and mysteriously died out.
The wildwood of southwest Norfolk thus comprised a patchwork of tree communities, probably related in part to soil differences, from which the various lake catchments received more or less random samples of pollen. The mosaic was on a small enough scale for more than one type to contribute to the catchment of any one mere. In general terms it resembles the patchwork of tree communities still extant. Limewood, hazel-wood, ash(–hazel)-wood, alder-wood and birchwood are familiar in ancient woods in south Norfolk today; elm–hazel-wood and oakwood are extant elsewhere in East Anglia.
There is little pollen evidence for woodland containing maple (insect pollinated) and hornbeam. Is this because those trees became major components only after the wildwood period? Or is it a sampling effect – the meres sampled different parts of the landscape from surviving ancient woods? On present evidence we cannot be sure, although these pollen cores fail to document any subsequent rise in hornbeam or maple.
Regional differences
Other parts of eastern England tend to be more strongly dominated by lime, notably in the Norfolk Broads and the Epping Forest area, but have little or no ash. A core from Mar Dyke, south Essex, however, has oak, hazel, elm, lime and ash in much the same proportions as some of the Norfolk cores.15 Cores from the Fens show a strong dominance of lime, and also considerable quantities of pine. The buried ‘bog oaks’ in the Fens, however, are indeed mostly oak, with pine, yew and even birch (preserved as bark), but bog trees of lime and hazel are not reported. This must be an effect of taphonomy: the more rot-resistant trees were engulfed by the peat and preserved, but limes and hazels rotted before they could be entombed.
Pollen from wildwood lime is found in Lowland peat, usually in abundance, almost exactly as far north (to the Lake District and County Durham) as lime still exists, but within Lowland England it bears no relation to whether or not lime is still extant.
The Oak–Hazel Province
The most extensive researches are those of Dr Judith Turner and colleagues at 52 sites in County Durham and the northern Pennines, covering the Boreal Period of about 8700–6200 BC. The principal trees (other than wetland alder and sallow) were hazel, birch, pine, oak and elm, this being outside the range of lime.16
There was local variation much as in East Anglia. Allowing for differences in pollen production, hazel was usually the commonest tree, sometimes very strongly dominant. Pockets of pine and birch occurred here and there. Elm was very prevalent, especially in the wildwood that then covered the highest fells of the Pennines.
This is an earlier and transitional period, preceding the fully developed wildwood of the Atlantic Period. The decline of birch and pine, and to a lesser extent of hazel, had not yet occurred. However, two peculiarities of the high dales, especially Swaledale, can be traced back to wildwood times: abundance of elm (in historic times often the commonest tree) and scarcity of oak (now absent from Swaledale except the lowest few miles).
WHAT DID WILDWOOD LOOK LIKE?
In a region absolutely covered with trees, human life could not long be sustained … The depths of the forest seldom furnish either bulb or fruit suited to the nourishment of man; and the fowls and beasts on which he feeds are scarcely seen except upon the margin of the wood, for here only grow the shrubs and grasses, and here only are found the seeds and insects, which form the sustenance of the non-carnivorous birds and quadrupeds.
GEORGE PERKINS MARSH, NORTH AMERICAN ECOLOGIST, 1864
Wildwood as forest
Hitherto, for simplicity, I have treated wildwood as forest; but the story now becomes controversial. Scientists and foresters traditionally assert that the ‘natural’ place for trees is close together in dense forests. The Enlightenment ideal seemed to be confirmed by climax theory. (Would palynology have developed differently if it had come before, rather than after, the development of modern forestry?) The discoveries of palynology were taken to reconfirm that ‘mature’ wildwood consisted of trees, trees, trees and trees, from coast to coast and from the Fens to Cross Fell. This was the ‘Tansley’ theory, in which only details still called for explanation: How big were the trees? How long did they live? How did they renew themselves? In what combinations did they grow: was there a monotonous ‘mixed oak forest’, or were there patches of different trees and mixtures of trees? How did Mesolithic people manage to squeeze between the great trunks and earn a living?
In the 1980s, I became dissatisfied. Pollen deposits have a continuous record of plants that do not flower in shade. Some of these are now plants of meadow or pasture; others are associated either with coppicing (wild strawberry, ragged robin) or with permanent open areas (betony Stachys officinalis, devil’s-bit scabious). Their pollen was not abundant, but since such insect-pollinated plants waste little pollen even a few grains must be taken seriously. Wildwood therefore contained persistent open areas, the predecessors of the present woodland grassland of rides and glades.17 These plants have a somewhat greater pollen record in previous interglacials.
Wildwood as savanna
A fable: Once upon a time there was a grassy plain interspersed with groves of trees. Deer, bison, wild horses and wild oxen grazed on it. They devoured most of the young trees that were forever springing up in the plain, but occasionally a few hawthorns or blackthorns would escape and form thickets. One such thicket gradually expanded into the fringe of coarse grass that surrounded it. Passing rooks and jays dropped acorns and hazelnuts; these germinated and grew up, protected by the thorns, to establish a grove of oak and hazel.
Folk in those days prowled around the edges of such groves, snaring the deer and eating the horses and carrying bags of hazelnuts to their camp on the edge of a nearby fen. Occasionally they speared a great bull – bigger than a rhinoceros and faster than a racehorse – and celebrated their valour with a feast, drinking out of its horns.18
Our grove slowly spread into the surrounding grassland as new thorns and then oaks sprang up in its edge; it grew into a roughly circular wood half a mile across. In the interior there were no new oaks or hazels, which need light, but there came a new generation of shade-tolerant limes and beeches. For the purpose of this story, trees have finite life spans, and after a few hundred years the grove would have broken up: as the trees in its interior died, a new area of grassland would have arisen to complete the cycle.
All this happened several times over 5,000 years, but there came a time when the cycle was not to be completed, because new technology intervened. People had acquired cattle and sheep and tame horses, which pastured in the grassland and stopped the grove from expanding. These people exterminated the terrible wild oxen and the deer; they dug up part of the plain and grew corn.
Their successors went on doing this until all the plain and some of the groves had been grubbed out and made into farmland. Our grove, however, survived. They cut it down from time to time; they made a bank, ditch and hedge round it to protect the regrowth, and it became a permanent island among farmland. They called the plain Cambridgeshire, and the grove they called Hayley Wood. A thousand years ago it passed into the hands of the Abbots of Ely, and in 1962 to the Cambridgeshire Wildlife Trust. It still keeps the roughly circular shape of its expansive origin. It is still full of oaks, but deprived of horses and oxen it has no younger generation of oak. (And the students of my college still celebrate their examination valour by drinking out of a super-bull’s horn.19)
The Vera model: My story illustrates (or parodies) the alternative model of wildwood expounded by the Dutchman, Francis Vera, in his book Grazing Ecology and Forest History. His thesis is that wildwood was not all trees, but contained large areas of grassland, maintained by the grazing of wild beasts. It was not a stable climax, but was in a state of gradual flux. Wooded areas (‘groves’) would extend at their edges, invading the grassland, and decay at their centres, giving rise to open areas which would turn into new grassland. This went on, so he claims, from the end of the last ice age until the spread of farming and forestry put an end to the dynamics – although some of the groves survived into medieval and even modern times as woods with a characteristic compact, rounded shape.
For want of a better term, I shall call this the ‘savanna’ model of wildwood. Most savannas in the world today consist of single trees in grassland, which is not (in the main) what Vera had in mind, although one can imagine that some of the ‘groves’ might never have got further than a patch of thorns with one or two oak-trees. A closer modern parallel might be the mott savannas of Texas (Fig. 32), with clonal patches of oaks and elms in grassland, some of them two or three acres (0.8–1.2 ha) in extent, having woodland shrubs and woody climbers as well as trees. A model of a Vera-type landscape (although the dynamics are different) is the New Forest or Hatfield Forest, with areas of trees, some of them many acres in extent, in a matrix of grassland or heath (Fig. 33).
Vera claims that browsing animals affected the composition of woodland. In particular, ‘without horse and ox oak will not survive’: oak and hazel, trees from the middle of the successional sequence, do not now grow from seed within existing woods, and need browsing animals to create fresh habitat.
Vera’s thesis explains how there came to be large numbers of big game, and provides a role for them in maintaining the structure of the landscape. A savanna-like structure (rather than continuous forest) gives more scope for ancient trees. It allowed the first farmers to find pasture for domestic animals and open areas to grow crops without having to dig up trees.
Most large herbivores, like deer and wild oxen, find it difficult to make a living in continuous forest. They eat off the low tree leaves and brambles, creating a browse-line. There is not enough edible biomass within reach to sustain a reasonable density of beasts, especially of herd animals.
Deer today may live in woods, but earn a livelihood by feeding on fields outside. Elk (like moose, their North American brethren) are best at home among low trees or perhaps reed-beds. Red deer are mixed feeders, at home in moorland, but needing trees for shelter. Roe are the most wood-adapted of deer, but even they are not reliant on woodland. (It should be possible to tell whether fossil animals fed on woody or grassy vegetation by examining the microscopic wear of their teeth.20) Wild swine, feeding underground, can live in some types of dense forest, although in Spain they extend far into steppe.21
All this applies to large herbivores that no longer have natural predators. Île Royale is a big island in Lake Superior; it has never been much inhabited by people and is now a National Park. Originally it was densely forested and had few, if any, large ungulates. After logging and mining it developed clonal thickets of aspen and became suitable for moose, which swam across around 1910. They multiplied into thousands, helped by a great fire in 1936 that renewed their habitat, and by the 1940s were eating themselves out of a home: ‘another of those big game ranges, degraded by overpopulation, where the animals hang on at the limit of numbers permitted by their food supply, to be decimated periodically by hard winters.’ While the National Park authorities were searching their hearts about the propriety of introducing wolves, the problem solved itself. When the lake froze more extensively than usual, a wolf pack trotted across from Canada and began eating the moose. The interaction between moose, wolves, trees and weather will take many years to elucidate fully. Predation affects not only numbers of herbivores but also their behaviour: they avoid places where they cannot see who is coming to eat them.22
Mankind is often thought of as a savanna animal. Forest is an inhospitable environment because most of the action takes place in inaccessible tree canopies. Many authors point out that forests provide things like nuts, toadstools, ‘roots’ etc., but it is hard work living on them: many are seasonal, and some (especially berries) are not produced in shade. Anyone who tries to live off the tubers of an English wood is in for an unpleasant surprise on encountering lords-and-ladies. Forest peoples, like desert peoples, are specialised and few in numbers.
Discriminating between Vera and Tansley models:23 An objection is that Vera’s theory is too general (Table 9). His book is mainly about the Netherlands and Germany, but he draws on other countries, especially England, because of the abundance of historical records. Instead of going through all the evidence country by country, he combines evidence from half Europe: fieldwork from Germany can be used to interpret records from England.
The herbivores diminished westward. In Britain, reindeer, Irish elk, bison and wild horse did not survive into the Holocene. There were elk (down to the Mesolithic); aurochs (down to the Bronze Age), although historical records of aurochs associate it with fens; red and roe deer; wild swine; and beaver. In Ireland, Irish elk barely survived into the Holocene, and only wild pig was abundant: red deer, if present at all in pre-Neolithic Ireland, were rare, perhaps because there was too much forest. There should, therefore, have been a gradient from a Vera-type landscape in eastern Europe to a Tansley-type in Ireland.
The trees were different. Ireland lacked beech and lime, the principal trees of the last stage of the Vera cycle. In Britain, although beech has a historic association with wood-pasture, it was largely in the southeast. Lime in Britain avoids places with a browsing history; it is reluctant to spread to newly available ground, and seems to require a less dynamic landscape than Vera proposes.
It is hard to believe that after 70 years of intensive study of pollen deposits there should be any difficulty in discriminating between forest and savanna, but when I wrote this, few pollen analysts had responded to Vera. F.J.G. Mitchell applied three tests:
Oak and hazel seem not to be maintained by browsing. Both got on very well in pre-Neolithic Ireland. In England there is not much correlation between browsing and oak regeneration. Oak certainly perpetuated itself without browsing in woods such as Hayley down to the time of the Oak Change, c.1900, as tens of thousands of oak timbers in buildings bear witness (Chapter 11); recent browsing by deer has not brought it back. It might perpetuate itself today had oak mildew not been introduced from America. Non-reproduction of hazel is likewise partly due to the introduced grey squirrel. How much turnover of hazel there had previously been is unrecorded; my impression is that hazel stools are very long-lived and do not need much seed establishment.
Vera’s model could operate without the oak and hazel story, but central to his thesis are hawthorn and blackthorn. These were present and were a favourite firewood; their charcoal is found in Mesolithic archaeological sites. They are insect pollinated; their pollens are not very distinctive and are probably often overlooked.25 But they produce considerable quantities of pollen, especially when growing at the boundary between woodland and grassland, and had they been abundant this ought to have been recognised. In pre-Neolithic deposits their pollens are far rarer than lime.
Another difficulty concerns grasses, the predominant ‘non-tree pollen’ in most samples. Why is there so little grass pollen in pre-Neolithic wildwood? Vera’s answer is that grasses were there, but the herbivores ate their flowering tops. But this calls for such intensive grazing that the thorns could not spread and the dynamics would come to a halt, as happens now in Hatfield Forest.
Tree-to-non-tree pollen ratio is a blunt instrument. Both sides of the ratio add up prolific and sparse pollen producers indiscriminately. If there were only oak, hazel and grasses – good producers – this might not matter too much, but if the trees were lime and maple the ratio would necessarily be low, and if the non-trees included plenty of pretty flowers and not much grass (like an alpine meadow) even scattered or distant trees would appear to be dominant.
Fire might be another way for open areas to form. However, pine, the only fire-promoting tree, was local by the mid-Holocene; it plays no significant part in Vera’s scheme, much of which deals with such very incombustible trees as lime, beech and elm. Grassland might just burn, but the amount of grazing that prevented the grasses from flowering would prevent dead grass from accumulating as fuel. Wildwood tree trunks buried in peat, even pine, are seldom scarred by fire; however, heather charcoal has often been identified, showing that moorland fires go back to Mesolithic times.26 If fire did occur its consequences should appear in the form of peaks of heather pollen or bracken spores. A study of charcoal in the Norfolk meres found no more evidence of fire than could be accounted for by Mesolithic campfires.27
A specifically savanna plant that has a pollen record is mistletoe. Palynologists regard it as an indicator of warmth, but it also indicates a habitat. In my experience the British subspecies is exclusively on orchard and freestanding trees, hardly ever in a wood. It is most familiar on domesticated apple, lime and poplar; its commonest wild host is hawthorn. In Hatfield Forest, its chief stronghold on wild trees, it occurs on old hawthorns and old maples, but only in the plains and not in the woods. Its pollen would thus indicate freestanding trees, old trees, and especially old hawthorns. It is abundant in the last-but-one interglacial; in the Holocene it is uncommon before the Neolithic. (Many Australian mistletoes, too, grow on savanna eucalypts.)
Grassland plants that might show up in a Vera-type ecosystem are buttercups. These, though insect pollinated, are relatively prolific pollen producers, and are so distasteful that they flower even under severe grazing. Buttercup achenes and pollen are particularly numerous in the last interglacial, and occur in the pre-Neolithic Holocene, although they much increase in the Neolithic and after.28
Diss Mere (Fig. 175) is one of the best pollen deposits published in Europe. The pre-Neolithic portion indicates tree-land divided between oak, lime, ash and hazel. Among Vera-type indicators, there is a small amount of mistletoe, which disappears after the Neolithic, and the odd grain of hawthorn. There are a few plants that do not flower in shade, such as heather, sorrel (woodland grassland), Angelica-type and cow-wheat (now a coppicing plant), together with appreciable amounts of bracken, but no buttercup. Such plants greatly increase with the expansion of farmland in the Bronze Age and after. There can be little doubt that the landscape round the mere was predominantly woodland, with only small permanent open areas.29
Fossil evidence also comes from remains of insects. Although these are called ‘old-forest insects’, their modern ecology associates them with ancient trees, which are more likely in a savanna context. Many of them require flowers as well as trees, and some call for sunny situations.30
Outside palynology, some aspects of Vera’s timescale are unpersuasive. Several thousand years elapsed between wildwood times and the earliest historic records – especially in England, which has been densely populated since the Iron Age. Vera could be right in claiming that in Germany and Poland, as late as the Middle Ages, cultural landscapes were still being carved out of primæval wildwood, although such assumptions tend to be based merely on lack of archaeological survey of earlier human activity. In England, however, all the unwritten centuries of late prehistory and the Roman period, with retreats and advances of woodland, lay between the times of elk and aurochs and the earliest written records. By Anglo-Saxon times every inch of England had an owner.
Other countries: Mediterranean islands had unbalanced faunas with elephants, hippopotamuses and deer – often in dwarf forms – but no effective carnivore until Man appeared, usually well into the Holocene. Here, if anywhere, the aboriginal landscape should have been savanna, especially as the dry climate would hinder regrowth of trees after browsing.
Of islands having a pollen record, Corsica apparently had forest and maquis in the early Holocene much as it has now, with some differences in the species. Native herbivores seem to have been scarce, the forest being too dense for them, or already extinct. On Mljet in Dalmatia, the indications also imply forest, including such palatable trees as elm, so herbivores too played little part.
In Crete, which is drier, the indications are definitely against forest. The pollen record includes non-shade-bearing plants such as asphodel, as well as trees. The diverse landscapes of Crete already existed; trees took the form of savanna or maquis rather than forest. The arrival of people is not very clearly marked. This is surprising, since on present knowledge the earliest evidence of human presence is around 7000 BC and the beasts had died out much earlier. The climate alone may have been dry enough to create savanna, independent of browsing animals.31
Provisional inferences
Pollen evidence is against the Vera model, especially in Britain and Ireland. However, it cannot be simply dismissed, for there are ragged robins and devil’s bits to be explained, as well as a place to be found for the beasts and the Mesolithic people who lived on them.
On Vera’s model it is easier to find room for ancient trees and their specific invertebrate animals and lichens. Ancient trees fare better in savanna where they escape the competition of younger neighbours and can more easily resist wind-blow.
Vera’s model needs to be developed in relation to the palatability, longevity and gregariousness of different trees. What part did elm clones play? Did they slowly expand as fixed objects in an otherwise dynamic landscape? Or were the suckers sought out by aurochsen and ruthlessly devoured?
The Vera model of wildwood would have been much more favourable to Mesolithic hunter-gatherers than the Tansley model. Whether people already at this stage were manipulating vegetation in favour of edible animals is still uncertain. Mesolithic people took advantage of the abundance of hazel: they were hazelnut-eaters rather as north Italians used to live on chestnuts.
How can Vera’s and Tansley’s models be reconciled with the continued existence of woodland herbs, many of which do not survive grazing? Was there some form of compartmentation analogous to that in medieval parks and Forests? It is difficult to imagine a physical barrier, but were the depths of the groves no-go areas for deer and wild cattle, either because there was not much to eat or because of danger from carnivores?
Further work is needed on specific aspects of the pollen record chosen to differentiate between forest and savanna. Fossil insects too might help. It is too much to hope for a differential pollen record of primrose (forest) versus cowslip (savanna), but pollen data should be searched for other plants that do not flower in shade, preferably unpalatable species like buttercup. Published pollen diagrams do not always contain the information. A full pollen record is an unwieldy piece of paper, and authors too often leave out what they consider to be unimportant or irrelevant pollen types. Many diagnostic species leave little pollen and so are particularly liable to be omitted.
Could a few wildwood groves still be there in the shape of medieval woods with near-circular outlines? Hayley Wood is not a good candidate, for the faint earthworks that underlie some of it (Fig. 193) point to prehistoric activity. Nor are the coppices in Hatfield Forest. However, there are many others, especially in Lincolnshire, that would be worth searching.
Comparison with previous interglacials
Whatever may be said for the Holocene, Vera’s model works better for previous interglacials. Non-shade-bearing herbs are then more strongly represented, as are blackthorn, hawthorn, mistletoe and buttercup. Oak, however, was not notably more prevalent than in the Holocene.
The landscape of Boxgrove Man, two glacial cycles ago, apparently included wide expanses of grassland. The trees were much the same, but the big game was bigger and more savanna-like: super-elephants, rhinoceroses, hippopotamuses, lions, hyænas, bison and super-deer.32
The Holocene stands out for the abundance of hazel throughout Britain and Ireland. Hazel as a dominant tree had been approached only late in the last interglacial. Spruce and fir (Abies) had been native in previous interglacials, but in this interglacial they never returned. This was probably not just an accident of rising sea level. Neither is native across the English Channel today; they probably had Atlantic ecotypes that were wiped out by the vagaries of glaciation.fn5 Other unusual features of this interglacial are the abundance of alder and lime and the persistence of birch.
Is there a link between the peculiarities of this interglacial – lack of elephants and rhinoceroses, abundant hazel, sparse evidence of non-shade-bearing herbs – and the presence of that new and terrible monster Homo sapiens?
WILDWOOD VERSUS ANCIENT WOODLAND NOW
It is a theme of this book that ancient woodland is not the same as wildwood. Conservationists do no service to woodland if they try to remake it in the image of what they imagine wildwood was like, whether on the Vera or the Tansley model. Woodland comes of processes of development and management, discussed in the next chapter. Nevertheless, there is some continuity from wildwood. How far are the differences in tree composition due to actual changes on the ground and how far to pollen sites and surviving woods representing different samples of the prehistoric landscape?
The Lime, Oak–Hazel, Pine and Birch Provinces still mark major differences in woodland distribution; only the Hazel–Elm Province is barely recognisable, largely because little ancient woodland survives.
In the Lime Province, lime still occupies its whole range in wildwood times, but in vastly less quantity. The decline, however, is curiously uneven: there are regions, such as around Sudbury (Suffolk), where lime is still the commonest tree in ancient woodland, and others, such as northeast Suffolk, where it is entirely absent. Elm suffered the Elm Decline in the early Neolithic and never fully recovered; doubtless farmers grubbed it out first because it grew on the most fertile soils. Hazel is still abundant in the Lime Province. There is now much more ash and birch, but this is partly a twentieth-century increase. Oak shows an apparent increase, partly because of long-standing and increasing encouragement from woodmen, and partly because it would have grown on the less fertile soils.
In the Oak–Hazel Province, hazel is now much rarer as a woodland tree (though common in hedges). Probably it grew on fertile soils and has been grubbed out, leaving oak on less rewarding soils.
The prehistoric scarcity of hawthorn is an argument against the Vera model. Maple (also insect pollinated) and hornbeam (wind pollinated) are also rare. Were they indeed less common than now? Or do no pollen sites sample maple-or hornbeam-dominated parts of the ancient landscape? If there has been a real increase, it is difficult to explain in terms of processes now operating. Hawthorn is encouraged by hedge planting and intermittent grazing, but what human activity can have encouraged hornbeam and maple?
Beech also has a poor pollen record in Britain. There was apparently a real increase in the 2,000 years before the tree-planting period, probably at the expense of lime, but even the good historical records of beech fail to explain why.
Footnotes
fn1 The smallest, the Oxborough site, is a hollow only 15 feet (5 metres) across and is apparently a pingo.
fn2 The Babes-in-the-Wood wood; it belongs to Norfolk Wildlife Trust.
fn3 Some investigators did not distinguish hazel from bog-myrtle pollen. Although small quantities of bog-myrtle are known to have been present, I have taken all ‘coryloid’ to be hazel.
fn4 Is the excessive dominance of hazel after the Elm Decline due to insufficient allowance having been made for its high pollen production?
fn5 The word spruce is short for ‘spruce fir’, meaning fir of Pruce, that is Prussia. ‘Norway spruce’ is a curious misnomer.