Hedge
A hedge or hedgerow is a line of closely spaced shrubs and sometimes trees, planted and trained to form a barrier or to mark the boundary of an area, such as between neighbouring properties. Hedges that are used to separate a road from adjoining fields or one field from another, and are of sufficient age to incorporate larger trees, are known as hedgerows. Often they serve as windbreaks to improve conditions for the adjacent crops, as in bocage country. When clipped and maintained, hedges are also a simple form of topiary.
A hedge often operates as, and sometimes is called, a "live fence". This may either consist of individual fence posts connected with wire or other fencing material, or it may be in the form of densely planted hedges without interconnecting wire. This is common in tropical areas where low-income farmers can demarcate properties and reduce maintenance of fence posts that otherwise deteriorate rapidly. Many other benefits can be obtained depending on the species chosen.
History
The development of hedges over the centuries is preserved in their structure. The first hedges enclosed land for cereal crops during the Neolithic Age. The farms were of about, with fields about for hand cultivation. Some hedges date from the Bronze and Iron Ages, 2000–4000 years ago, when traditional patterns of landscape became established. Others were built during the Medieval field rationalisations; more originated in the industrial boom of the 18th and 19th centuries, when heaths and uplands were enclosed.Many hedgerows separating fields from lanes in the United Kingdom, Ireland and the Low Countries are estimated to have been in existence for more than seven hundred years, originating in the medieval period. The root word of 'hedge' is much older: it appears in the Old English language, in German, and Dutch to mean 'enclosure', as in the name of the Dutch city The Hague, or more formally 's Gravenhage, meaning The Count's hedge. Charles the Bald is recorded as complaining in 864, at a time when most official fortifications were constructed of wooden palisades, that some unauthorized men were constructing haies et fertés; tightly interwoven hedges of hawthorns.
In parts of Britain, early hedges were often destroyed to make way for the manorial open-field system. Many were replaced after the inclosure acts, then removed again during modern agricultural intensification, and now some are being replanted for wildlife. As of 2024 in a study using Lidar by the UK Centre for Ecology & Hydrology England alone was found to have a total of 390,000 km of hedgerows, which would span the circumference of the earth 10 times.
Composition
A hedge may consist of a single species or several, typically mixed at random. In many newly planted British hedges, at least 60 per cent of the shrubs are hawthorn, blackthorn, and hazel, alone or in combination. The first two are particularly effective barriers to livestock. In North America, Maclura pomifera was grown to form a barrier to exclude free-range livestock from vegetable gardens and corn fields. Other shrubs and trees used include holly, beech, oak, ash, and willow; the last three can become very tall. Of the hedgerows in the Normandy region of France, Martin Blumenson said,The hedgerow is a fence, half earth, half hedge. The wall at the base is a dirt parapet that varies in thickness from one to four or more feet and in height from three to twelve feet. Growing out of the wall is a hedge of hawthorn, brambles, vines, and trees, in thickness from one to three feet. Originally property demarcations, hedgerows protect crops and cattle from the ocean winds that sweep across the land.
The hedgerows of Normandy became barriers that slowed the advance of Allied troops following the D-Day invasion during World War II. Allied armed forces modified their armored vehicles to facilitate breaking out of their beachheads into the Normandy bocage.
Species
Formal, or modern garden hedges are grown in many varieties, including the following species:- Berberis thunbergii – native to Japan and eastern Asia
- Buxus sempervirens – native to western and southern Europe, northwest Africa, and southwest Asia, from southern England south to northern Morocco, and east through the northern Mediterranean region to Turkey.
- Carpinus betulus – native to Western Asia and central, eastern, and southern Europe, including southern England.
- Crataegus monogyna – native to Europe, northwestern Africa, and West Asia
- Fagus sylvatica – native from northern Europe, in Sweden, Denmark, Norway, Germany, Poland, Switzerland, Bulgaria, eastern parts of Russia, Romania, through central Europe to France, southern England, northern Portugal, central Spain, and east to northwest Turkey where it intergrades with the oriental beech
- Fagus sylvatica 'Purpurea' – a variant of the above
- Ilex aquifolium – native to western and southern Europe, northwest Africa, and southwest Asia
- Ligustrum ovalifolium – native to Japan and Korea
- Ligustrum × ibolium – native to Japan and Korea
- Photinia × fraseri – a hybrid between Photinia glabra and Photinia serratifolia, native to Japan, China, Taiwan, the Philippines, Indonesia, and India, respectively
- Prunus laurocerasus – native to regions bordering the Black Sea in southwestern Asia and southeastern Europe, from Albania and Bulgaria east through Turkey to the Caucasus Mountains and northern Iran
- Prunus lusitanica – native to southwestern France, Spain, Portugal, Morocco, and Macaronesia
- Quercus ilex – native to the Mediterranean region
- Taxus baccata – native to Western Europe, Central Europe and Southern Europe, Northwest Africa, northern Iran, and Southwest Asia
- Thuja occidentalis – native to eastern Canada and much of the north-central and northeastern United States
- Thuja plicata – native to the Pacific Northwest of North America
Hedgerow trees
The most common species are English oak and ash, though in the past field elm would also have been common. Around 20 million elm trees, most of them hedgerow trees, were felled or died through Dutch elm disease in the late 1960s. Many other species are used, notably including common beech and various nut and fruit trees.
The age structure of British hedgerow trees is old because the number of new trees is not sufficient to replace the number of trees that are lost through age or disease.
New trees can be established by planting but it is generally more successful to leave standard trees behind when laying hedges. Trees should be left at no closer than apart and the distances should vary so as to create a more natural landscape. The distance allows the young trees to develop full crowns without competing or producing too much shade.
It is suggested that hedgerow trees cause gaps in hedges but it has been found that cutting some lower branches off lets sufficient light through to the hedge below to allow it to grow.
Importance of hedgerows
Hedges are recognised as part of a cultural heritage and historical record and for their great value to wildlife and the landscape. Increasingly, they are valued too for the major role they have to play in preventing soil loss and reducing pollution, and for their potential to regulate water supply and to reduce flooding. There is increased earthworm diversity in the soils under hedgerows which also help to store organic carbon and support distinct communities of arbuscular mycorrhizal fungi.In addition to maintaining the health of the environment, hedgerows also play a huge role in providing shelter for smaller animals like birds and insects. A recent study by Emma Coulthard mentioned the possibility that hedgerows may act as guides for moths, like Acronicta rumicis, when flying from one location to another. As moths are nocturnal, it is highly unlikely that they use visual aids as guides, but rather are following sensory or olfactory markers on the hedgerows. Larkin et al. 2013 find 100% of northwest European farms have hedges, providing 43% of the wildlife habitat there.
Historically, hedges were used as a source of firewood, and for providing shelter from wind, rain and sun for crops, farm animals and people. Today, mature hedges' uses include screening unsightly developments.
In England and Wales agricultural hedgerow removal is controlled by the Hedgerows Regulations 1997, administered by the local planning authority.
Dating
Hedges that have existed for hundreds of years are colonised by additional species. This may be useful as a means of determining the age of the hedge. Hooper's rule is based on ecological data obtained from hedges of known age, and suggests that the age of a hedge can be roughly estimated by counting the number of woody species in a thirty-yard section and multiplying by 110 years.Max Hooper published his original formula in the book Hedges in 1974. This method is only a rule of thumb, and can be off by a couple of centuries; it should always be backed up by documentary evidence, if possible, and take into account other factors. Caveats include the fact that planted hedgerows, hedgerows with elm, and hedgerows in the north of England tend not to follow the rule as closely. The formula also does not work on hedges more than a thousand years old.
Hooper's scheme is important not least for its potential use in determining what an important hedgerow is, given their protection in The Hedgerows Regulations of the Department of the Environment, based on age and other factors.