Some hedges are very ancient; many date from the Enclosures; some are less than a century old. Is it possible to look at an individual hedge and assign its age? Hedgerow dating is a subject of more than academic interest for two reasons:
- Hedges of great antiquity have a historical value which makes them particularly worth protecting. Ancient hedges may be a genetic reservoir linking directly back to the ancient wildwood from which they were formed. It has also been suggested (Morgan Evans, in Watt and Buckley, 1994), that as ‘man-made’ features they can be treated as artefacts and worthy of study by archaeologists. Historical value can only be recognised if the hedge can be dated by means of historical source material, field evidence or some inherent indicator of age.
- Old hedges tend to have greater wildlife value due to their diversity of component species.
Historical records and field evidence
Written references to field boundaries in Britain can be traced back over a thousand years. County boundaries are among the earliest for which there is precise data, many of them dating from the middle of the 9th century. Anglo-Saxon land charters sometimes go into great topographical detail particularly where borders were disputed. Parish boundaries, which may date anywhere from the 7th or 8th to the 12th centuries, and later divisions within parishes, can be sought in old ecclesiastical records. Minor place names can give clues: ‘Olditch’ on the edge of Dartmoor was known as an ‘old ditch’ as long ago as 1263. Domesday Book (1086) is reliably detailed for certain parts of the country, allowing identification of important home farm boundaries as they then existed. Ordinary farmsteads are more difficult to trace. By the medieval period park boundaries were becoming important. Cartularies (monastic and estate charters) often indicate new boundaries made to settle disputes.
By now we are starting into the Enclosure Era, with quantities of Parliamentary and legal records worth investigating. Towards the end of this period, in the 1840s, the Tithe Surveys produced some of the finest and in many cases the earliest maps on record for most parishes. They showed every farm, every field and every hedge, and are a basis from which modern changes can be measured.
Changes in field boundaries between those shown on a tithe map and those on a post-Second World War aerial photography or modern Ordnance Survey map can be accurately plotted without physical correlation. But the only way in which the true ‘Olditch’, for example, can be picked out from all its neighbours is by actually trying to walk it based on the historical topographical description related to such field evidence as now exists.
Pollard, Hooper and Moore (1974) give a number of examples of the uses and possible abuses of field evidence. On occasion it can be extremely suggestive of historically interesting hedged fields which might otherwise go unnoticed. Take the problem of hedgerow length. Scrutiny of the 1:25,000 Ordnance Survey maps reveals a remarkable correlation between the lengths of hedged field boundaries, and multiples of a chain (22 yards, or about 20m). The most common length is 220 yards, or one furlong, i.e. one ‘furrow long’. Twelve and eight chain multiples are next most common, although other multiples may predominate in certain regions. All indications are that the chain has been the basic unit of hedgerow length for many centuries. In parts of north Norfolk, however, the most common field length is 410 yards. The area is rich in Roman roads and other remains, and this field length approximates two stadia, a Roman unit of measurement. The hedges themselves are probably not Roman, but the field boundaries may well be.
Field evidence can be misleading, however, unless backed up by other sources. For example, it is known that medieval fields developed a gentle ‘reversed S’ form because it was the most efficient shape to work using teams of four pairs of oxen pulling heavy fixed mouldboard ploughs. For this reason curved field strips are thought invariably to pre-date 1400, and visible evidence of them today is a sure sign of medieval farming. At Crimscote, Warwickshire, there is a hedge which follows the boundary of one of these field strips, conforming to its reversed S shape. From this one might conclude that it was 600 years old. In fact, it dates from the post-First World War agricultural depression, when this area which had long been grazed was allowed to grow up in hawthorn scrub. When the land was cleared again for grazing, a line of scrub along one furrow was managed to form a new hedge.
M D Hooper noticed that it was difficult to account for the number of shrub species in a hedge simply through reference to its management, soil type or any other obvious factor. He suggested that the only correlation which did hold true for a wide sample of hedges was one which related the number of shrub species to the age of the hedge. The hypothesis is that the number of woody species in a 30 yard length of hedge equals the age of the hedge in centuries (Pollard, Hooper and Moore, 1974). This hypothesis aroused considerable interest amongst local historians. It is generally accepted now as a useful rule of thumb, to be applied with some caution, and taking other factors into account.
The assumption is that species diversity will increase over time, as bird-ferried or windblown seeds take root in the shelter of the hedgerow. Regular trimming will help new species establish, by controlling existing species. The formula may also work because ancient hedges are more likely to be remnants of mixed woodland, or because hedges before about 1700 tended to be planted of mixed species.
The formula becomes difficult to apply the further back one goes, and cannot be applied to hedges earlier than about 1000 AD. It cannot distinguish Anglo-Saxon hedges from earlier Roman hedges. going further back, a late Bronze Age hedge from 1000 BC would need to show 30 species in 30 yards, to fit the formula. It can be used to differentiate between medieval, Tudor or Stuart, and Enclosure-Act hedges, but there are exceptions. Elm hedges may have too few species for their age, because of the suckering habit of elm. Elm may even invade a mixed hedge, suppress the existing species, and turn it into an elm hedge. Some pre- Roman field systems of south-east Essex have mainly pure elm hedges. Anew hedge planted close to an ancient hedge may acquire species more rapidly than if it were isolated (Rackham, Oliver, 1994). The formula should be applied with caution north of Derbyshire, or on extreme types of soil, where the number of possible species is limited.
Other hedges may have been planted as mixed hedges. Mabey (1996) describes hedges which were planted around smallholdings in Shropshire in the 18th and 19th century that are full of fruiting shrubs such as damson, gooseberry, blackthorn and apples, giving 30 yard counts of over 20 species. Some of the mixed ‘wildlife’ hedges currently being planted may mislead future observers.
However, the formula has been tested widely enough to give a reasonable degree of confidence that, used carefully, it can assist in dating hedges back to the Anglo-Saxon period.