Coppicing Part 2

The History and Sustainability of Coppicing 

Part 2 of 4: Coppicing 

Definition

Coppicing is the practice of cutting deciduous hardwood poles again and again from the same stool. Generally, the cutting must occur in freezing weather, to be certain that the sap will be below-ground and will keep the roots alive. A tree, managed this way, will learn to heal the cuts quickly and become better at growing the next batch of shoots efficiently.

A good way to remember how coppicing works is this short couplet:
If the roots survive, the tree is alive!

Selecting a tree

The process begins with a mature tree. The root system, below-ground, must be large enough to contain sufficient energy to regrow an above-ground tree after the above-ground section is completely removed. If the tree is too young (say, a 2-yr-old sapling), it may not have enough strength built up to recover from the initial trauma of the cutting.

The tree should also not be too old. When a tree has developed and grown in a certain form for a hundred years or more, it may not tolerate the trauma of suddenly being deprived of its whole above-ground half. The shock of that loss can kill the roots, and thus, the tree. Furthermore, if the stump of the tree is hollow, then rot will kill the roots. Many old trees become hollow over time, and these are unlikely to survive the initial phase of coppicing.

Finally, the tree must be of a species that regenerates from the stump or roots. Not all trees can do this. Generally, deciduous hardwoods make the best coppices. Softwood trees may also rebound from cutting, but their low density may make the stumps more susceptible to rot, and their wood is less desirable. Most evergreen and coniferous trees do not survive felling; their excessive sap bleeding kills the root system. Holly is one exception, as an evergreen that actually coppices well. Maple trees are an exception to the freezing weather rule; maples bleed sap heavily during the freeze-thaw cycle of winter, and prefer to be coppiced if cut in warm, dry conditions (such as late summer).

Standards

A tree can be coppiced anywhere that it grows, but if it stands alone in an open field, the regrowth will be bushy and the poles will tend to branch laterally as much as they can. This comes from the easy availability of sunlight all around the stump. The only competition for that sunlight comes from the tree's own shoots, which consequently try to spread away from one another to maximize their exposure.

If the forester chooses a tree to coppice that stands in an existing woods, however, the stump will regrow in a shaded setting with existing competition. The shoots of the growing coppice will 'reach for the sky,' trying to access the sunlight that mostly reaches them from directly overhead. This encourages the shoots to grow tall and straight, rather than bushy and branchy. Long, straight poles with few branches and knots serve more purposes, when harvested, than irregular, knotted and brushy wood. So, if possible, selecting trees for coppicing that are already in a mature forest will dramatically improve the product harvested from those coppice stools.

There is a point of diminishing returns, in having this existing canopy overhead, if the canopy becomes too thick and will not allow enough sunlight to penetrate to the young shoots below. A tree requires sunlight to photosynthesize energy for growth, or indeed for survival. A shade that is too dark will simply starve the coppice.

Therefore, a forester should manage the coppice grove and mature tree canopy to balance beneficial competition for the coppices without depriving them completely of required sunlight. This balanced silvicultural system is called, “coppicing with standards.” The mature trees whose upper story form the canopy are called “standards,” a term based on medieval heraldic display; a noble's heraldry was carried in battle by a standard-bearer, and the flag itself was called a standard.

These mature trees, or standards, serve another purpose in a managed forestry system. Although coppice poles are useful for most woodworking purposes (fuel, poles, posts, wattle, rafters, closet rods, basketry, pegs and small wood turning) they cannot supply the need for wide wooden planks. A coppice stool must be harvested routinely before it reaches a very wide diameter (even a 25-year or 30-year harvest rotation, as is needed for large oak posts, will not provide planks more than a foot wide). This is for the health of the coppice stool and the continuous training of its root system. Thus, to fill the demand for planks and boards, a forest must also provide some larger-diameter trees that are not coppiced. The forester, therefore, will selectively allow some saplings to grow to maturity, and will selectively cut some standards, in a manner that will preserve that balance of canopy indefinitely. The managed woodlot will therefore mostly generate small-diameter coppice poles, for fuel and other uses, whilst always providing some limited supply of large-diameter wood.

Felling

As already mentioned, the initial cutting of a tree to form a coppice should normally occur in freezing weather. This is to ensure that the majority of the sap, the energy reserves and lifeblood of the tree, will be stored below-ground in the root system. However, cutting may also work if simply done in late fall, after the tree drops its leaves; some of the sap, at least, will be stored below-ground at that point in its cycle. Not all climates provide a long period of freezing weather, so a forester must work with the existing conditions.

After selecting the appropriate species of tree, of the right age, hopefully in a good location for coppicing, and waiting for the right time of year, the forester should fell the tree. This can be done by axe or by saw, or modernly by chainsaw. This must NOT be done by girdling the tree (stripping the bark off the trunk in a ring), since that gradual method of felling will kill the tree and roots alike.

After safely felling the tree, the forester should clean the stump. This means cutting it close to the ground (a hand's breadth or two, at most) and with a clean slope to drain water. If rainwater collects on top of the stump, then rot is likely to set in and kill the roots. 

Growth

The new shoots should emerge from the cut stump in early spring. The forester must already have in place some method for protecting these tender, vulnerable buds. Without protection, the sugary new shoots are likely to fall prey to any grazer passing through the forest; deer, elk, boar, goats, sheep and even bears may devour the buds, leaves or stalks before they have a chance to grow above browsing height, and to toughen their bark to resist injury.

Medieval coppices in Europe were often protected by mounded earth banks and ditches, which came to be known as “deer-leaps” or “ha-has.” Building a ha-ha became popular in the seventeenth to nineteenth centuries as an aesthetic form in landscaping, but their original purpose was to separate out protected areas from the main grazing areas. Essentially, if starting with level ground, the dirt is removed to create a sloping ditch, and built up to form a wall on one side, rising up abruptly from the bottom of the slope. The top of the wall is level with the original ground, or just barely mounded up, and thus does not interfere much with drainage or create stagnant pools. Deer and livestock cannot, however, climb up the berm—and the slope leading up to the wall discourages them from jumping, which a simple trench would not, even if the distance is constant. 

A ha-ha, consisting of a slope leading down a earth wall. The slope distorts the perceived height of the wall, discouraging grazers and browsers from jumping.

New coppice growth can also be protected by dead brush. This is particularly convenient to place when the tree is newly felled, since the upper branches of the tree, too spindly to be useful for other purposes, can be piled up in a dead, bushy barrier around the stump. This debris barrier will keep all but the most determined of browsers from accessing the new shoots in spring. Even goats rarely push far through a pile of dead branches, since the pointy ends poke their eyes and scratch their faces as they force their way through. The pile of debris will deteriorate over time, rotting down to add its fertility to the soil around the roots; the forester can replace it with new brush, if needed, but the coppice growth may already be tall enough to survive a little browsing by the point that the brush pile no longer protects it. Also, the forester can pull the brush aside in order to access the shoots once a year, for trimming and maintenance.

Finally, a fence around the individual stump, or around a grove of newly cut stumps, can keep livestock and deer out of the enclosure. However, fences are expensive to build or install, and the larger the area enclosed, the taller the fence must be to keep deer from jumping in. A deer can easily leap over a 6' fence, if it has adequate incentive. A tiny fence enclosing an individual stump does not offer much incentive, or does it look spacious enough inside for the deer to land safely, so it is unlikely to attempt to jump in. Building a fence around every coppice stool is very labor-intensive, however, and the fence itself must be kept far enough back to keep goats from leaning over it to reach the new growth, but still be small enough to prevent deer jumping, and accessible enough for the forester to be able to tend to the coppice over the years.

Note that livestock can never be kept permanently in the coppice grove; goats and sheep will strip the bark from the young poles, even if the leaves are out of reach. Pigs will dig at the roots and scrape the bark. When the coppice growth is old enough to be moderately resistant to injury, it is possible to rotate sheep and pigs through the area briefly—but the herder must monitor for evidence of bark stripping. Goats love to strip bark and should be kept out at all times, unless there are weeds available that they enjoy more than bark (certain vines and undergrowth), and they have plenty of mineral, and a dedicated herder who moves them the moment they decide to try the bark.

Maintenance & harvest

The first winter after cutting a coppice stool, the shoots that grew from the stump should be thinned, according to the intended size of the harvested poles. Side-branches and leaf-buds below the top branches should be trimmed or scraped off, to encourage the shoots to grow straight and without knots.

In other words, if the goal is to have large, heavy poles that require 25 years to grow, the forester should thin the stool so that each shoot is separated by more than a hand from its closest neighbors. This ensures that the annual fall of leaves can blow away or be swept out easily, and not collect on top of the stump; it also helps the tree concentrate its energy on growing the few poles left to it.

If, on the other hand, the intended harvest should be thin, whippy wands for basketry, then these withes may be ready to cut in the first year. The same goes for livestock feed (stick hay), medicinal bark harvests, wood pulp for pellets, and biochar production (the latter two are modern uses). All of the shoots should be cut simultaneously, to help train the tree to heal quickly and regrow like that every year.

If the goal for the coppice is to generate living stakes for creating hedge-rows or living fences, fedges, the cutting should occur at the end of winter as buds form. These should ideally be cut during the last of the cold weather, for the sake of the roots system, and while the buds remain dormant, but not too far in advance of warm weather, when they should be planted. NB: Spare cuttings from willow stakes can be cut into small pieces, or mashed, in a bucket of water. These contain a concentrated form of rooting hormone that can help other living stakes to set roots. Soaking the cut stakes in this bucket for a few days prior to planting increases the likelihood that they will take.

If the goal for the coppice is wattle, the ideal species is hazel. The horizontal weaving rods for wattle are typically harvested between 2-6cm in diameter at the base, on average about 4cm, which takes about 7 years. Willow rods for wattle grow to this size faster but are more fragile, while birch and ash take longer. The upright stakes for wattle are normally around 4-5cm in diameter, but are typically harvested around 14 years old, and are more durable and less dramatically tapered. In other words, the shoots grow tall quickly, and reach about 4cm in diameter in a handful of years, but then they slow down, thicken, become denser and more even; poles, not withes. These sturdier poles take twice the time that the flexible, lighter withes require (1).

If the goal for the coppice is fuelwood for charcoal production or a woodstove, the ideal diameter is about 10-13cm (roughly 4”) and the ideal species is oak, followed by birch and holly. Depending on species and location, this may take between 7 to 25 years.

Harvesting can be done with an axe, or a billhook, or loppers, or a saw. The small size of the poles increases the safety of felling; it is easier to control their fall, and felling them does not typically kill or crush other trees in the way of their fall. If accidents do occur, still the falling tree rarely does much damage to the person or structure struck. Furthermore, the poles grow denser sooner than regularly grown saplings, meaning that woodworking and turning require less removal of sap wood. Finally, growing fuelwood to the proper diameter for use saves the intense labor involved in splitting firewood, meaning that the fuel can simply be cut to the length required (around 20” for most woodstoves) and stacked to dry. The young bark rarely creates a mess the way that older bark does, when bringing firewood indoors, and shelters fewer beetles or other pests. Also, cutting in freezing weather means less sap is present in the wood, which speeds the drying process for fuel.

Apart from thinning in the first year, a coppiced stool should always be cut or harvested all at once. Cutting one pole one year and another pole another year trains the tree to redirect its energies into the remaining trunks, rather than training it to tolerate the sudden loss of all its above-ground growth, with rapid healing and regrowth. It is a good idea to train your trees to a single purpose; either pollard it, or coppice it, but do not try to make it accept both.

Environmental benefits

To start with, coppicing preserves soils and subsoil ecology in a way that normal timber harvest can never achieve. Because the tree roots remain in place and healthy, cooperating with their symbiotic microorganisms in the soil and stabilizing the structure of the dirt around them, harvesting coppiced trees does not result in erosion or soil loss. The swamps created by deforestation in Roman times do not occur where coppicing replaces clear-cutting. Furthermore, leaving the dead brush in protective screens around the coppiced stools helps to return nutrients to the soil—while the trees themselves, trained to store their surplus energy underground, build a healthier soil over time.

In addition to keeping the tree roots in place, coppicing also keeps the tree roots alive for a longer period—sometimes centuries or even millennia longer than the normal lifespan of the tree! For instance, one stand of coppiced linden/basswood still being cultivated today in England is over 1,000 years old—over four times the average lifespan of a linden tree!

This is because coppicing keeps the vulnerable, above-ground part of a tree in a state of perpetual youth and health. A mature tree, whose bark and sap wood grow and live while the old, inner wood is generally dead, has a definite life expectancy that cannot much exceed a certain diameter (determined by the species of tree). At some point, the inner wood will begin to rot, or insects will invade, or the living bark will cease to be capable of sustaining all of the upper growth of the tree. When this giant tree dies, it often falls (damaging its neighbors) and levers its dead roots up out of the ground. There it slowly decomposes, leaving a muddy hole and many injured or toppled trees around it. With coppicing, however, the inner dead wood is not allowed to accumulate, nor to rot and kill the roots, nor to become so tall and heavy that it risks falling over. By continually removing the above-ground growth, the forester essentially makes the tree immortal (so long as generations of human foresters continue to care for the tree).

Blights almost never attack a coppiced tree, because most blights attack mature bark and heartwood. Likewise, most bark-boring pests attack their host species only when the bark reaches a certain age. With coppicing, the above-ground trunk remains below that target age range, thus providing no habitat for the blight or parasite. American chestnuts, for instance, can be kept alive if coppiced—whereas their standard counterparts rarely survive.

Coppiced groves, furthermore, grow cyclically in the middle story of a forest. The upper canopy, provided by standards, and the middle canopy, provided by the coppice, only begin to keep sunlight from reaching the forest floor at about the age when the coppice is ready to be cut. Thus the undergrowth of low-lying plant species on the forest floor are only cut off from sunlight by dense shade for a brief period on a cyclic basis. When the coppice lot is cut back, every 7 or 10 or 20 years (however many years are normal for the species & purpose), sunlight floods the forest floor, spurring a heavy growth of diverse ground cover. This continuous cycle of regrowth at the ground level promotes a healthy diversity of forest species, which feed upon or live among these low plants. A multitude of nesting bird species then make their homes in the branches of the young coppice growth.

Certain species of ground-cover plants, and species of understory birds, have evolved to be dependent upon this cyclical habitat. For example, the nightingale requires a diverse environment of upper canopy, healthy mid-story trees and abundant lower-story plants to survive and breed. The abandonment of many coppice groves during the industrial revolution has led to a severe decline in nightingale populations. Areas that had active coppice woodlands for almost 6,000 years, or perhaps more, are suddenly being allowed to grow into dense, single-canopy mature forests—this starves the under-stories of sunlight and may even result in the eventual extinction of the species that relied upon coppicing. Fortunately, coppices are now seeing a resurgence of interest, thanks to modern emphasis upon renewable energy, local economies and sustainability.

To continue reading about other methods of coppicing, see the next post, Coppicing Part 3. To return to the previous post about deforestation, see Coppicing Part 1.

Sources: 

1) Lynn, C. J. and McDowell, J.A. Deer Park Farms; The Excavation of a Raised Rath in the Glenarm Valley, Co. Antrim. Northern Ireland Environmental Agency, W.G. Baird, 2011. p. 448-468