Why lay hedges?
Hedge laying developed as a way of making a stockproof barrier out of readily available material, that is, living woodland plants. Until the invention of wire, hedges were the only practical and cost-effective way for a farmer to enclose his stock in areas where walling stone was not to hand.
Hedge laying involves partially cutting through the living stems near ground level, and bending them over as ‘pleachers’. They should lie close, like plates in a rack. Depending on the style of laying, the pleachers are anchored by stakes and binding to form a type of living fence. This ‘fence’ has several purposes.
- It forms an immediate barrier to stock or people.
- Depending on the style, it provides protection from browsing animals for the young shoots, which grow up from the base.
- It improves the micro-climate by slowing the wind and raising the air humidity, so helping the growth of the young shoots.
- Even in the period immediately following laying, hedge laying retains sufficient of the pleachers to maintain some habitat for other organisms, including birds, small mammals and invertebrates.
- Some new shoots also sprout along the pleachers, thickening the hedge for the first few years after laying, until most of the pleachers eventually die. By this time the new shoots from the base have grown up to form a thick hedge.
In the past, the hedge laying cycle would have been similar to the coppicing cycle in woodland, although developed in response to a different need, namely that of maintaining the hedgerow as a thick, stockproof barrier. Coppicing keeps woodland trees small and manageable with hand tools, so they can be easily cropped. Laying keeps the trees of the hedgerow small and manageable. The importance of hedgerow maintenance and the economic value of the crops produced during the laying cycle are clearly recorded in Medieval documents. Laying every 10 to 20 years not only rejuvenated the hedge, but would have produced a crop of poles, firewood, faggots and kindling. The years between laying would have provided crops of blackberries, sloes, nuts and other hedgerow fruits. Like coppicing, hedge laying provided a way of managing trees with the hand tool technology available to all.
Laying is not the only way to manage a hedge. Hedges can be managed by coppicing, where the temporary loss of the barrier and shelter of the hedge is not a problem. Coppicing can be used to rejuvenate neglected hedges, or as the regular method of hedge management. The rejuvenation effect, of new shoots sprouting from the base, is effectively the same, although new coppice shoots may be more vulnerable to browsing by stock and wild animals. However, most newly laid hedges are fenced against stock where necessary. Some species can also be maintained almost indefinitely by trimming.
Why the pleachers live
The stem of a tree has several rings of different types of growth, which can be seen in cross section.
The bark protects the tree from fire, frost, predators and disease. The bast is a thin layer formed of tiny channels which carry sugar sap downward from the leaves into the roots. The cambium is also very thin, and is the part of the stem which actually undergoes cell division and growth, forming sapwood inwards, and bast outwards, as shown. The sapwood supports the tree and carries the ascending sap with its inorganic nutrients from the roots to the leaves.
In older trees of most species, the inner sapwood dies to form heartwood as the tree grows bigger.
All broadleaved hedgerow species will coppice, that is resprout from the base even when completely severed, as long as the tree is actively growing and not too aged. In fact, growth of new shoots at the base is likely to be better if all the old growth is removed, as effort is then concentrated into the new basal growth, rather than the plant trying at the same time to maintain sap movement up old stems. If the plant is not vigorous enough to regrow from the base, it will not be vigorous enough to maintain growth along a pleacher, and is likely to struggle along for years before eventually dying. Where hedges are neglected, and are effectively a line of trees, coppicing is the best way of rejuvenating them.
The laid pleachers should survive as long as the necessary nutrient flow can still take place from roots to tip. Bark, bast, cambium and at least a little sapwood must be left, joined in a thin strip of stem from which the upper portions can draw nourishment. This is what hedgers mean when they say you ‘have to leave the bark and a bit more’ when cutting through the tree, and when laying it, ‘if you break the bark at the back, or if it kinks up, then the stick will die’. The cut must be neatly made and trimmed off, to ensure that water cannot collect and encourage rot.
Pleachers are normally laid at an angle of 35-45˚ from the horizontal. The further the stem is bent over, the greater the chance that sap will stop flowing due to the cambium being kinked or it peeling away from the bark. This is the reason behind the advice ‘never to lay a pleacher downslope, because sap won’t flow downhill’. In fact sap will move downwards, as shown by trees with pendulous branches, but a pleacher laid through more than 90 degrees from the vertical will usually fail due to damage to the cambium.
