Species selection in Britain’s hedgerow heritage

THE historical reasoning behind the establishment of hedgerows as living fences was that they would serve as boundaries to establish the ownership of land, but also restrict the movements of livestock.

Of particular interest to me is how hedgerows have evolved through invasion and selection (natural or otherwise).

The four groups of woody-plant species and herbaceous plants which comprise the hedgerow in its entirety are:

• the classic shrub forming species like hawthorn and blackthorn which respond well to cutting and trimming and therefore form the fabric of the hedge;
• those species which, left alone, develop into substantial dedicated trees, traditionally encouraged as ‘hedgerow trees’ at intermittent locations along the hedgerow;
• woody species such as ivy, traveller’s joy and dog rose, essentially clingers and climbers which rely on the fabric of the hedge for support; and
• the multitude of herbaceous plants, both grasses and broad-leaved plants, which grow and seed on the narrow verge of land traditionally left along the hedge.

A large proportion of the hedgerow tree stock is old and in decline, or even dead as a doornail, like this English oak.

These divisions are not always cut and dried. Hawthorn and holly, though traditionally regarded as shrubby species, will grow into substantial trees if left uncut. By the same token, oak and ash – the most common hedgerow trees – are frequently found in the fabric of the hedge, having been trimmed annually instead of left to develop into hedgerow trees. And ivy, though requiring the hedge for support, will eventually form an important part of the fabric of many old hedgerows.

Common lime is infrequent as a hedgerow tree but, where planted, wastes no time in helping to form the very fabric of the hedge, due to a propensity for epicormic growth low down on the trunk and therefore at hedgerow height.

Most intriguing in this respect is English elm, which pre 1970 was the most frequently occurring hedgerow tree in many areas of England. English elm was subsequently lost as a mature hedgerow tree due to Dutch elm disease, but the species continued to sucker and now forms the fabric of many hedgerows.

A large proportion of the hedgerow tree stock is old and in decline, or even dead as a doornail, like this English oak.

HISTORY OF HEDGEROWS

The roots of the English hedgerow go back thousands of years to the Neolithic period, and Bronze and Iron Ages, but have experienced an up-and-down history since then. Hedgerows were greatly added to during the field rationalisations of medieval times when many of the hedges that now separate fields were first established, and later, during the 18th and 19th centuries, when heathlands and uplands were enclosed.

Many of the oldest hedges were destroyed to make way for the manorial open-field system and replaced after the Enclosure Acts, only to be removed again during post-World War II agricultural intensification. Some, but only a tiny fraction of those most recently lost, are being replanted in the cause of wildlife and biodiversity.

Common ash is frequently found in the fabric of the hedge which may well provide a springboard for Chalara spores to infect the lower branches and leaves of hedgerow ash trees.

SPECIES SELECTION

The selection of species for hedgerow planting was dictated by a range of considerations including availability of planting material, ability to thrive in local soils and longevity, capacity for planting as cuttings or regeneration from seed, response to trimming and ability to form a livestock-proof hedge.

Taking all these factors together, hawthorn appears to have been the number-one choice. Hawthorn is essentially unfussed over soil type, being widely spread and available throughout most of the British Isles. It is a long-lived plant that can be propagated from cuttings and grown from seed of which there is invariably a ready supply. And significantly, hawthorn responds well to trimming to produce a dense and thorny barrier. Indeed, along with blackthorn, hawthorn is the only native deciduous broadleaf species capable of establishing a livestock-proof hedge. Hawthorn and blackthorn together still account for 60 per cent of the species used for hedgerow planting.

British hedgerows clearly contain a lot more species, but working out whether they were deliberately planted or the result of natural invasion is another matter. Contemporary hedgerow planting increasingly features mixtures of species with an emphasis on native plants and the interests of wider biodiversity.

As such, a typical hedgerow mix based on native species and with hawthorn as the main component may also contain blackthorn, bird cherry, rowan (mountain ash), field maple, dog rose and hazel. More specialised are hedgerow mixes designed for coastal environments and in which sea buckthorn, wild privet and elder may be prominent.

A relatively young hedgerow oak tree established in a hedgerow and no more than 30 to 40 years old. Such examples of young, healthy hedgerow trees are becoming increasingly scarce in our hedgerows.

Wild privet is generally regarded as poisonous to livestock if ingested, while elder, though one of the easiest native tree species to strike from cuttings, does not have the dense framework of hawthorn and will not respond in the same positive way to cutting. This makes elder a very open hedgerow completely unsuited to the containment of livestock. By the same token, wayfaring tree is an obvious selection for chalky soils, but not holly, which prefers a slightly acid soil regime.

Britain has never been blessed with native evergreen shrubs and trees, broadleaf or conifer. Only holly fulfilled all the universal hedgerow requirements. Yew has long been a popular choice for hedges in landscape situations. Yew mazes, including the oldest commissioned by William III in 1700 at Hampton Court, are testimony to the density of yew hedge, but it is never used on farmland, presumably due to its poisonous nature.

Holly also became a popular choice for amenity situations. However, in my neck of the woods (South Hertfordshire) holly is most likely encountered as a very old hedgerow tree and frequently in the form of a pollard. The archives suggest holly foliage was traditionally cut and fed to livestock. And, given the longstanding belief that holly trees were a bulwark against evil spirits, communities were loath to cut them down.

English elm was the most frequent hedgerow tree across much of England until trees were virtually wiped out by Dutch elm disease in the 1970s and 1980s. English elms in the hedgerows around a field of oats near Hitchin in North Hertfordshire as it appeared in the 1920s (picture courtesy of Tom Williams, owner and managing director of Maydencroft).

HEDGEROW TREES

Mature trees have always been an important feature of Britain’s hedgerows, but are increasingly under threat for a variety of reasons. English elm, English oak and common ash in that order (all light-demanding trees), traditionally made up the majority of hedgerow trees. English elm was abruptly removed from this position by Dutch elm disease, and Chalara ash dieback looks set to deliver a similar blow, albeit not so quick or complete, to common ash.

According to recent research from France, isolated common ash trees are less at risk than woodland common ash from Chalara. However, hedgerows will often contain common ash as a shrub component originating from saplings that were cut instead of being left to grow into hedgerow trees. As such, hedgerow ash may well provide a stepping stone for Chalara spores to reach the lower branches of mature ash trees in the hedgerow.

Hedgerow trees are in general decline. There are a range of reasons, but increased farm mechanisation and the need for larger fields is at the fore. Hedgerows are now cut mechanically, which lessens chances for saplings to escape the blade and grow into maturity.

Hedgerow trees were generally removed along with the hedge itself. However, there are some instances where the English oaks left in situ now stand out starkly in a straight line across a very large field as a grim reminder of what was lost.

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