The broadleaved woods that have attracted most attention from ecologists on Dartmoor are the three upland oak woods at Piles Copse on the River Erme, Wistman’s Wood on the West Dart River, and Black Tor Beare on the West Okement River. They are composed of almost pure stands of pedunculate oak, to which species belong almost all the isolated oaks on the high moor up to 500m, as well as much of the valley oak woodland on the granite. The usual species of oak in the South West is the sessile one. This has led Simmons to argue that sessile oak has replaced pedunculate oak in the South West, but was unable to complete this replacement on the granite. In this sense the upland oak woods of Dartmoor can be considered relicts of Dartmoor’s former forest cover.
It used to be thought that individual trees in these upland oak copses, particularly in Wistman’s Wood, with their fantastic shapes and gnarled appearance, were themselves of extreme age – older than the Norman conquest according to a botanical report quoted by Samuel Rowe in 1848. Some of the trees in Wistman’s Wood may be up to 300 years old but recent work by the ecologist John Barkham on Black Tor Beare (Beare being an old word for wood) has shown on the contrary that none of the trees are much more than 130 years old and that many trees die at under 100 years, giving a remarkably quick turnover for oak which in lowland woods is generally regarded as remaining sound for at least 200 years, often taking another 100 years to decay to the point of falling.
Work on Wistman’s Wood by the ecologists Michael Proctor and Malcolm and Molly Spooner has established, by comparing old photographs with modern ones taken of the same locations, that the wood has increased to nearly twice its former size over the last ninety years. In that time, too, the canopy level has risen, the form of the trees has become less grotesque and more and more normal, and the epiphytic ferns and mosses have lost some of their former profusion. It may be that the contorted trees which have made the wood famous represented pioneers in particular areas whose early struggle was reflected in their subsequent shape, while later trees, protected somewhat by the pioneers from the effects of weather and grazing, were able to grow straighter. At any rate it is clear that both woods are in a constant state of change, and the same is probably true for Piles Copse. According to Molly Spooner, the trees at Piles Copse strongly suggest it was coppiced around 100 years ago, although there is no extant record of this. It too can be shown to have grown up markedly during the last fifty years, when comparison is made with Hansford Worth’s records of measurements taken in the first half of the century.
All three woods are situated on clitter slopes – clitter is the Dartmoor term for scree or sloping field of loose rock – and grow among granite boulders. This suggests how important protection from grazing has been in their survival. But there are plenty of areas of clitter where no trees grow, and other sorts of protection may have been just as important. All three woods are on steep west-facing slopes in deepish river valleys – this might just be coincidence, but a climatic factor cannot be ruled out: for example, with prevailing winds coming from the west, turbulence would be expected to be greater on east-facing slopes. And perhaps we also have the Forest Law, which forbade the taking of green oak, to thank for preserving these high altitude oak copses, especially in view of the temptation they must have presented to the tinners who used wood as well as peat to make charcoal for their smelting furnaces.
Only Wistman’s Wood is actually within the official Forest boundary, but in practice Forest jurisdiction often extended over enclosed land as far as the corn ditches, as is shown by the prosecution of one William Bowden by the Forest Court in 1587 for cutting oaks at ‘Blackerters Beare’. Legal taking of the wood’s products was occasionally endorsed: in 1618 a document refers to payment of 40 shillings for 8 acres of underwood – possibly indicating some form of coppicing. In addition to the Forest Law, vestiges of Celtic respect for the oak as a sacred tree may well have been strong enough to establish a tradition of preserving the woods for spiritual reasons. Dartmoor church roof bosses often depict ‘green men’, faces with oak leaves coming out of their mouths, eyes and nostrils, ancient Celtic symbols of regeneration adapted to encompass Christian resurrection – there are good examples in North Bovey, Widecombe, Chagford and Spreyton to name but a few. Wistman’s Wood has certainly had the power to inspire awe in a number of writers. Tristram Risdon in the 17th century included it as one of three remarkable things about Dartmoor, the other two being Childe’s Tomb and Spinster’s Rock. More recently the novelist John Fowles has written about it.
Barkham has suggested that cycles of degeneration and regeneration have meant that the areas of Black Tor Beare with a closed canopy are constantly shifting. Regeneration can only take place in clearings where trees have died and bracken has moved in to provide additional grazing protection for the young seedlings. Regeneration at the moment is sufficient to ensure survival of the wood, although increased grazing pressure, particularly by cattle which trample down bracken litter, might alter the situation. The spread of Wistman’s Wood and the invasion by trees on the fringes of the Moor can only be good for the soils underneath. Research carried out in the 1980s by the Institute of Terrestrial Ecology has suggested the crucial role that birch may play in the creation of brown earths, and it is interesting to note that in a location where the soils around are peaty gleys, brown earth occurs under parts of Black Tor Beare. The presence of some oak woodland adds immensely to the variety of Dartmoor’s land, as well as supporting more varied animal and plant communities – the luxuriant ferns and mosses of Wistman’s Wood are a dramatic testimony to this.
There are no coniferous trees which today are regarded as native to Dartmoor, though the pollen record as analysed by Ian Simmons suggests that some pine existed until the time of the chambered tomb builders, around 3,000 B.C. On the other hand, some species of broadleaved tree and shrub which are present today are also not native, in the sense that they have been introduced within recorded history. This is true of sycamore and rhododendron which have spread extensively, and of sweet chestnut, which is more or less confined to plantations and gardens. Some regard beech as an introduced species on Dartmoor and in Devon generally, though it is native to much of southern England. It is true that the majority of beech in upland situations on the Moor gives the impression of having been planted; it has been a favourite tree for shelter belts. But when it comes to valley woods, a case can be made for supposing that some beech at least has been there for a very long time. Simmons’s pollen analysis shows a continuous thread of beech from about 3,000 B.C. to the start of the medieval period. At this point it disappears from the pollen record, not to reemerge until the last two hundred or so years.
It was during the medieval period that oak began to be valued and managed both for timber and as a coppice tree to produce bark for tanning – green oak being one of the two items expressly forbidden the commoners of the Forest, who otherwise enjoyed extensive rights. But oak will not regenerate well under its own canopy, and is therefore vulnerable to invasion and replacement by other species. The ecologist Sue Goodfellow has found evidence that suggests small-leaved lime may have been deliberately managed out of oak woodland in the valleys, and the same may be true for beech which regenerates well in shade, thus posing a threat to the more valued oak. Today, beech has to be carefully controlled to ensure that the threat does not materialise, but this should not necessarily be seen as a simple case of a native species under attack from an exotic invader.
The continuous closed canopy formed by even-aged trees which is characteristic of Dartmoor’s fringe valley woods, is itself artificial – the result of management as coppice as recently as the beginning of this century in some cases. Oak would be much more likely to hold its own if the canopy was patchy and there were many clearings in which oak’s ability as a pioneer, or coloniser of open ground, would help it to regenerate. The even age and close spacing of many of these former coppice trees also means that they tend to fall at the same time, causing widespread devastation such as occurred in the East Okement valley during a gale in 1981
The two most extensive tracts of this semi-natural oak woodland are in the Teign and Dart gorges, largely on soils derived from metamorphic rock, but along the Dart the woodland continues up onto granite for some way, the species changing from sessile to pedunculate via a hybrid. Other valley oak woodland on granite, again mostly pedunculate, occurs in the valleys of the Becka Brook near Manaton, below Vixen Tor on the Walkham, along the Webburn valleys and in scattered stretches elsewhere, particularly where rivers pass through farmland. In places, especially on the surrounding metamorphic aureole, ash is co-dominant with oak, while in the wetter valley bottoms of the smaller streams, alder (if left to its own devices) develops a world of its own, sometimes in company with willow species.
Alder carr, as it is called, is the nearest thing on Dartmoor to a jungle environment, with its impassable swampy floor and its hanging tangle of honeysuckle, ivy and half-fallen trunks. Gravelly hummocks left behind by the tinners provide sites sufficiently well-drained for the occasional oak and holly, while light-demanding birch grows along the fringes. Although admittedly occurring in patches of minimal extent, this type of woodland is just as interesting as the coppice derived oak woodland, and deserves to be more highly valued as a wildlife habitat. Distributed as it is over almost every farm in the areas around the high Moor, it constitutes a major reservoir for birds and mammals which need more privacy than hedges can provide, while on its floor wild daffodils, primroses, kingcups, water crowsfoot, introduced pink purslane, marsh violets, flag irises and opposite-leaved golden saxifrage flourish.
A particular type of habitat is produced where stock are allowed to graze underneath the broadleaved valley woodlands and keep down the undergrowth. Though not ideal for regeneration, this may benefit ferns, mosses, liverworts and lichens, which do not have to compete with brambles and other shrubs for light. It also seems to suit some species of woodland birds. The ornithologist Mark Robbins suggests that pied flycatchers and wood warblers thrive as they do in some valley woods around Dartmoor because many of these are kept clear by grazing. Other bird species, however, may be deterred by the lack of a well-developed understorey.
Buzzards are common nesters in any kind of broadleaved valley woodland, though they are most often seen wheeling high over open country, scanning the ground for small rodents. Kestrels likewise, often woodland nesters, are usually seen riding the wind on open slopes, every muscle in action to keep them motionless.
The broad-leaved valley woodlands are also home to some of Dartmoor’s finest-looking butterflies. The white admiral occurs in oak woods on the fringe, while further into the Moor woodland glades harbour strong-flying fritillaries, especially the pearl-bordered and silver-washed species. The speckled wood and ringlet, too, are common Dartmoor woodland butterflies. Down by the rivers in the wooded gorges, big wood ants can be encountered crossing paths with their trails. I have heard a forester suggest that the reason deer (mainly sika and roe) do not damage seedlings in the oak woods under Holne is that the ants act as a deterrent. Occasionally red deer are seen in the valley woods, or even rarely on the open moor, possibly having moved across from Exmoor, but more probably part of a small but increasing resident population.
MARK BEESON – 1986
How should we treat an alien? A film set in Dartmoor’s woodland looks at attitudes.