Veteran Trees

A guide to good management

What are Veteran Trees and why are they important?

What is a veteran tree?

• The term veteran tree is one that is not capable of precise definition but it encompasses trees defined by three guiding principles:
• trees of interest biologically, aesthetically or culturally because of their age;
• trees in the ancient stage of their life;
• trees that are old relative to others of the same species.
• The girth of a tree is not a reliable criterion because different species and individuals of tree have very different life spans and grow at different rates.
• Veteran trees can be identified by the presence of specific characteristic as listed in the main text.

A veteran tree can be defined as: ‘a tree that is of interest biologically, culturally or aesthetically because of its age, size or condition’. Some trees are instantly recognisable as veterans but many are less obvious.

An alternative approach used by some people is to consider that the veteran, or ancient, stage is the final one in the life of a tree when the cross-sectional areas of successive annual rings in the main stem begin to decrease progressively. (Before this stage, successive rings will have already narrowed, but their areas will have been roughly constant, owing to their increasing girth.)

In turn, the amount of leaf area that can be supported by the reduced annual increment eventually results in dieback of the crown. For this reason veteran trees are rarely tall with large crowns. In theory this definition sounds fine but in reality this growth phase may not be clearly recognisable even though it may be the longest one in the tree’s life. Dryden describing oaks is reputed to have said, ‘three centuries he grows and three he stays, supreme in state, and in three more decays’.

Size alone is a poor characteristic for determining veteran status, although some rules of thumb exist (see box). Different species of tree may grow to very different maximum sizes. The simple comparison of a huge mature oak tree (Figure 1) with a small gnarled veteran hawthorn (Figure 2) illustrates this point. In addition the same species can grow to very different sizes in different situations and conditions.

A rough rule of thumb can be adopted for species, eg oak, in relation to size:

• Trees with a diameter at breast height of more than 1.0m (girth 3.2 m) are potentially interesting.
• Trees with a diameter of more than 1.5 m (girth 4.7m) are valuable in terms of conservation.
• Trees with a diameter of more than 2.0m (girth 6.25m) are truly ancient.

Absolute age is also a poor indicator of ancient status for trees. Different species tend to live for varying numbers of years; thus age can only be used when considered in comparison with other trees of the same species. At 100 years of age a birch would be old and a willow extremely old. At 200 a beech would just be starting to become interesting, an oak just maturing and a yew still beginning. One age-related definition sometimes used is that of an individual older than about half the natural life span for that species (but defining the natural life span is also a challenge!)

The increasing complexity of the tree with age results in a range of features in root, trunk and branch; these features are often good indicators of old age.

Characteristic features found on veteran trees

Listed below are characteristic features of veteran trees (see also Figure 1). The more the tree has, the stronger the indication that it is a veteran:

• Girth large for the tree species concerned
• Major trunk cavities or progressive hollowing
• Naturally forming water pools
• Decay holes
• Physical damage to trunk
• Bark loss
• Large quantity of dead wood in the canopy
• Sap runs
• Crevices in the bark, under branches or on the root plate sheltered from direct rainfall
• Fungal fruiting bodies (e.g. from heart rotting species)
• High number of interdependent wildlife species
• Epiphytic plants
• An ‘old’ look
• High aesthetic interest

Figure 1. Diagram to show the features characteristic of a veteran tree.

In addition the tree may also:

• Have a pollard form or show indications of past management
• Have a cultural/historic value
• Be in a prominent position in the landscape

One of the difficulties of using the above list as an indicator of veteran status is that young trees which have been physically damaged; eg by fire, can show these features, whereas some veterans may exhibit very few.

While a veteran tree is alive, part of its value for wildlife is that it is a self-renewing resource. However, dead veteran trees continue to be valuable for wildlife because of their slow rate of decay. Such trees are often greatly under-valued but they should be treated with almost as much respect as living ancient trees.

It is not surprising that different people or organisations have slightly different ideas about how to recognise veteran trees. (Several surveys have used size as the sole, or major, criterion but this can be misleading, as demonstrated above.) On the whole it is best to err on the side of caution and remember that, even though your tree might not quite be a veteran yet, with care it will become so, helping to ensure the continuity of ancient tree habitats.

How have veteran trees survived in Britain?

A variety of factors have helped some veteran trees to persist in the British countryside (although there have been huge losses in the past):

• Many (if not most) trees were ‘working trees’ (Green 1994), ie their wood and leaves were used, as an essential part of everyday life, for much of the recorded history of Britain. The management methods that predominated may have helped individual trees to survive (eg pollarding and coppicing).
• Very large trees were time consuming to fell and if the tree was rotten inside then the timber value was considerably reduced. This helped the survival of, for example the oaks at Birklands in Nottinghamshire, and Windsor Forest.
• Continuity of ownership on many estates. Changes of ownership may lead to decisions to remove old trees.
• Common land rights. Many veteran pollards were situated on common land and were owned by one person while others managed them (unlike coppice woodlands). This situation helped perpetuate their survival.
• Veteran trees have been incorporated into successive changes in the landscape. This occurred prior to and during the enclosure of land to form parkland and during the creation of design landscape parks by Lancelot (Capability) Brown and Humphry Repton. The retention of veteran trees was considered to give the parks an air of respectable antiquity (Rackham 1991).
• In Britain veteran trees have generally been revered and respected. Some old trees and some species of tree are regarded as sacred, which helped in their survival (eg yew trees in churchyards).

Why are veteran trees important?

..those grey old men of Moccas, those grey, gnarled, low-browed, knock-kneed, bowed, bent, huge, strange, long-armed, deformed, hunchbacked misshapen oak men that stand awaiting and watching century after century biding God’s time with both feet in the grave and yet tiring down and seeing out generation after generation.

The Reverend Francis Kilvert,1876.

The ‘grey old men’ from all over Britain have inspired artists and writers throughout the centuries. They have featured in the paintings of Thomas Hearne and John Peddar while Thomas Gray thought of them as ‘Reverend vegetables .. always dreaming out their old stories to the wind’ (in a letter to Horace Walpole 1737). Notable specimens have been revered in the past and some have become tourist attractions, the Major Oak at Sherwood being a famous example.

Through their individuality, veteran trees have high intrinsic appeal and are strong ‘characters’. A few people have found the distorted shapes of old, repeatedly cut, pollards grotesque but even then they still managed to inspire, as seen in the comments of a journalist writing about Epping Forest. ‘Short,shabby, scrubby, indescribably mean and ugly they were - something like warty railway sleepers with a shock head of twigs’ (journalist in Cole 1894).

All veteran trees are of historic interest; each is a survivor from the past, a relict of a former landscape. In addition to their importance as natural habitats,they are a valuable part of our cultural heritage. This historic interest lies both in the individual trees, each of which is a living document telling us of past management practices and ways of life, and in the tree’s place in the wider countryside.

The distribution of veteran trees in the landscape gives an insight into former land use patterns. Each tree, or group of trees, deserves individual consideration and study, perhaps combined with document-based research in local and national archives to enable us to understand fully its historic context and importance.

Within the existing agricultural landscape, veteran trees are most frequently found as markers along old boundary banks and occur in long established hedgerows. As such they contribute to our knowledge of historic land divisions. Other veterans, particularly pollarded willows, chart the course of rivers, or other water channels such as mill-leats, now often dry, visible on the ground only as archaeological traces.

Veteran trees are closely associated with wooded commons, now almost lost as a form of land management, and are also frequent in churchyards where their existence and location can be of great significance, sometimes pre-dating Christianity.

Some of the highest concentrations of veteran trees are found in current and former parkland. However early in date the origins of a park, all parks were developed from an existing landscape and in most cases features of the pre-park landscape were incorporated into the new enclosure.

Parks as they are today are invariably the result of several changes in ownership and fashion with each phase leaving its mark on the landscape. Successive designs tended to incorporate valuable features that were already present and veteran trees were often considered to add maturity (see Figure 2). Our generation is not the first to treasure their presence.

Figure 2. Wrest Park, Bedfordshire. Early 17th Century sketch by Peter Tilleman showing mature trees incorporated within the immature formal landscape. Courtesy of Bedfordshire and Luton Archive.

Some oaks alive today can be traced back to the medieval period or, in the case of some yew trees, before the start of Christianity. Many more trees predate great architectural structures of the 17th and 18th centuries that we admire and conserve.

Despite surviving centuries, they are now largely at our mercy through the rapid pace of change brought about by modern technology. It only takes a few minutes to condemn a tree that has lived through more changes in its time than we can ever imagine.

In brief, veteran trees are of importance because:

• They have aesthetic appeal and cause inspiration.
• They may have a particular historic link, ie be associated with a specific person or event.
• They often illustrate past land use or cultural landscapes. For example veteran trees are often found on wooded commons, in parkland, as boundary or field markers and in ancient farmland landscapes.

They may be part of a designed landscape or garden. Many formally laid out gardens contain veteran trees, and avenues may be comprised of them.They are also especially abundant in some of the landscapes designed by Lancelot Brown, Humphry Repton and other landscape architects of the 18th and 19th centuries. They are especially important for biological reasons, providing conditions suitable for a wide range of other plants and animals, many of which require the very special environment created in an old tree. They have been likened to a block of flats.

Fungal rotting of the heartwood and dead limbs results in a diversity of micro-habitats suitable for other organisms including a potentially very wide range of invertebrates, dependent on such different micro-habitats, and birds such as woodpeckers which prey on them. Epiphytes such as mosses and lichens may require the old bark characteristic of veteran trees to grow on.

Although some of the organisms are generalists, many are extremely specialist and are confined to veteran trees. Old trees, as a consequence of their rarity, harbour large numbers of rare and threatened species. The biological importance of a tree is greater if it lives long enough to perpetuate the continuity of habitats for future generations.

• They provide an air of stability in an ever changing world.
• Very old trees are more likely than younger trees to be descendants of the trees of the natural wildwood that colonised Britain after the last ice age.This makes them a reserve of important genetic material. (However, some veteran trees have been demonstrated to be of introduced origin.)
• They may be an important gene pool of trees showing particular characteristics, eg disease resistance or good epicormic growth (beneficial for good growth after pollarding but not for good quality commercial timber).
• The annual rings of old trees are historical records in their own right. They illustrate past climate changes or cutting treatments, and the chemical nature of the wood is a potential resource for research into past climates,pollution levels etc. (However, the decay process removes the rings as the tree becomes hollow).
• In addition, Britain has one of the highest populations of veteran trees in Europe (along with Greece and Spain).
• Why populations of veteran trees are more important than isolated trees
• The more trees, the more alternative niches there are.
• Organisms that require precise micro-habitats are more likely to find enough to support viable populations.
• Groups of veteran trees can yield more information about past practice, and their population structure than single trees.
• Groups of veteran trees are less threatened by change than single trees.

Types and locations of veteran trees

Veteran trees found in Britain today can be described and assigned to categories according to their origin and past management. There are three widely found types of veteran tree: maidens, coppice and pollards.

Maiden trees

These are trees that have a trunk extending from the base to the upper crown and have not been cut in any way other than perhaps minor tree surgery. They may be woodland trees that have grown up with other trees close by and thus tend to have a ‘narrow’ profile with a tall stem and small canopy, or they may be open grown with a much wider crown and bigger branches lower down the trunk.

Open grown trees may subsequently be surrounded by younger woodland and a woodland grown tree may be exposed by the felling of surrounding woodland. Trees planted and left to grow without intervention, for example as part of an avenue or designed landscape, are usually maidens.

Coppice stools

A coppiced tree is one cut near ground level, then allowed to produce new shoots from the stool. The shoots from a block of woodland are cut repeatedly in cycles of varying length depending on the size of sticks or poles required. A range of tree species produce coppice growth, some much more readily than others. Although the growth from a coppice stool is usually quite young, the stool itself can be extremely old. These veteran trees can be very different in shape to maidens or pollards.

Generally speaking, the larger the stool width or height, the older the stool (within species). For example, an ash stool 2 m in diameter has been estimated to be over 500 years old and a 16 m diameter lime stool was estimated at 2000 years old (John White pers. comm.). Very old coppice stools may rot out in the centre, leaving a circle of apparently younger stools.

Coppice largely occurs in woodlands managed specifically in this way but is also found on ancient wood or boundary banks, along rivers and in hedges. Some coppice has not been cut for many years and may take on a tree-like appearance.

Pollards

A pollard is a tree cut like a coppice but well above the ground (Figure 3). Usually, the reason for cutting high up was to allow animals to graze among the trees without damaging the next crop of branches by browsing them. Thus the height of the pollard was partly determined by the type of animal (that to deter sheep did not need to be as high as that where cattle were grazed). The products of pollarding were leaves, twigs and bark for animal fodder, bark for tanning and wood for fuel and charcoal.

Pollards were probably first cut when the maiden tree was quite young and small in girth with subsequent cuts made at regular or irregular intervals. In some places it seems unlikely that pollarding was carried out in such a formal and regular cycle as occurred with coppicing. The proportion of branchwood removed at each cut was probably also variable. In the case of willow trees all the growth was removed each time.

For other trees, e.g. beech, it seems likely that some branches were cut while others were left (see also chapter 4). Pollarding is sometimes taken to be the total beheading of the tree, but here a pollard is taken to mean a tree cut back once or more (to a similar point) by removing a substantial number of branches. The presence of a number of pollarded trees in a group is often a good indication that the area was wood-pasture or parkland at some point in the past, though willow pollards are not necessarily associated with grazed systems.

Many, but by no means all, of the veteran trees in Britain today have been pollarded at some stage in their life. However, pollards are not necessarily old trees. The majority of young trees pollarded in recent years can be found in urban situations and on some sites with veteran pollards where owners/managers are now starting to create new pollards.

Figure 3 . A veteran ash pollard in the Lake District.

Where are veteran pollards found?

• Wooded commons where commoners had rights to graze animals and cut or collect wood (eg Ashtead Common, Surrey). Village greens are another form of common where veteran pollards may be found.
• Parklands. Private, enclosed, land usually grazed by deer, occasionally cattle (eg Moccas, Herefordshire).
• Wooded Royal Forests. Land governed by special laws where deer owned by the Crown or a wealthy land-owner were kept. Often these forests incorporated existing areas with commoners’ rights (eg Hatfield Forest, Essex)
• As farm trees for a local wood supply, scattered about the farm and sometimes in hedges. Some farmsteads almost had miniature ‘parks’ around them (eg in the Lake District). In places this can produce a pollard landscape (eg parts of the Cotswolds).
• Upland grazed woodlands. Most upland woods were unenclosed and grazed by sheep, cattle or deer especially during the winter months. This practice continues today, although in the 18th and 19th centuries many woods were enclosed. The trees in these woods were sometimes pollarded, especially oak and ash. Some upland woods were summer grazed and may have contained a wider range of pollarded species, including alder, hazel, birch, ash and rowan.
• As boundary markers between, for example, parishes or areas of different ownership (eg East Anglia and Kent). Also as boundaries between different ‘panels’ of woodland, where at least some were grown out from layered hedges (D. Maylam pers. comm.).
• As elements within the designed landscape (eg clumps, avenues and pleasure gardens).
• Churchyards. Although not pollarded, yew trees are associated with churches, other species such as lime were frequently planted and may have been pollarded to keep them manageable. In addition, many churchyards were grazed in the past.
• Beside rivers and in withy beds (for the production of willow branches for baskets, etc.) Often these trees are in grazed meadows but sometimes they are low pollards, cut above ground for the ease of cutting rather than to protect shoots from grazing animals. Black poplars were pollarded in damp meadows close to rivers. Pollards were also used to help stabilise banks along roadsides in areas of wet fen and bog.
• As urban or street trees. Cut regularly to control the size for safety reasons and to reduce the risk of soil shrinkage that might cause subsidence of buildings.

Lapsed pollards

There are considerable numbers of pollards, and coppice, that have not been cut for many years. As the importance of fuel wood and fodder declined and coal became more widely available the need for actively managed wood-pasture decreased. This resulted in lapsed pollards, ie those that have not been cut for many years. The branches have grown for many more years than would have been the case in the past and have become large and heavy (Figure 6). The trunk or bolling of the tree may not be able to support the weight and it becomes vulnerable to wind damage either lifting the root plate or splitting the bolling. This presents one of the most difficult management problems, which will be addressed in chapter 4.

Wood-pasture

Silva pastilis or wood-pasture (Figure 7) is distinguished from silva minuta (underwood) in the Domesday Book. In most wood-pastures the trees were actively managed.

A wood-pasture can be defined as a land use combining trees and grazing animals (either stock or deer) where often (not always):

• The trees are old and at low density.
• The trees are frequently managed by pollarding.
• The grazing tends to be long and sustained,leading to a different structure and species composition than ungrazed woods in similar soils.

Wood-pastures vary between very open and very dense,and three broad types are found:

• Grazed high forest with woodland type flora.
• ‘Parkland’ with a ground flora showing few woodland elements.
• Grazed coppice in which livestock are temporarily excluded until the regrowth is out of reach.

Wood-pastures that are no longer grazed are termed ‘former wood-pastures’.

Why ancient wood-pastures are good for wildlife

• They tend to have a wide range of tree age classes with veterans well represented (even though the veterans are often the result of management).
• They tend to have a mosaic of glades, open and dense woodland.
• The tree boles are often well lit and not heavily shaded by scrub or brambles (unlike ungrazed woodland), a condition favoured by many species.
• There tends to be a high quantity of dead and dying wood on the living trees.

These conditions are better represented in wood-pasture than other modern managed woods. Sites with a combination of wood-pasture and old growth woodland tend to be the most valuable in terms of nature conservation.

Regional variations

Pollard form varies between regions owing to different management. In more northerly countries the importance of the trees for winter fodder (from the leaves and bark) was greater and in many situations the land under the trees was used for making hay (see Bergendorff & Emanuelsson 1996 and Hæggström 1998). In northern areas of Britain this practice of pollarding was sometimes called cropping.

Leaves from pollards may have been used as fodder less frequently when agricultural techniques provided a wider range of winter fodder crops. In recent times hedgerow trees were pollarded in Nottinghamshire as a ‘last resort’ for cattle in bad years (N. Lewis pers. comm.). Holly is also currently cut in the New Forest for winter pony fodder and in Killarney for sheep.

Other types of veteran trees

In addition to the three main categories several other types may be found (see also Figure 4).

Figure 4. Diagram to show some types of veteran trees

Bundles

The term bundle is used to describe a tree, which by design or accident has originated from two or more seedlings or plants grown in close proximity. Bundles are normally, but not always, of the same species. As the young trees grow the individuals become very closely pressed together. Some single boles show natural fluting and convolutions and it is rarely possible in single species groupings to be confident of their origin by visual inspection. Because of the way that they grow, bundles often have many of the characteristics associated with veteran trees. Reasons for planting bundles are not always known but broadly speaking three main types can probably be distinguished:

• a naturally occurring bundle, the result of an accident of seed fall or an animal burying a cache of seeds that then germinate;
• a forester planting trees who slips several in a hole together to finish the task quicker;
• the result of a planned decision to create a bundle or multi-stemmed tree. This can be for several reasons, for example:
• for landscape purposes , often in designed landscapes to create a wide spreading crown more quickly. For example, it was recommended by Evelyn in the 17th century and is a technique known to landscapers;.
• for agricultural purposes. In some wood-pastures a few bundles can be found. This may of course be accidental but it has been suggested that they might have been deliberately managed to confer distinct benefits,eg produce seed (when all the other trees around them were pollarded regularly and did not).

Fused coppice stools.

These are abandoned coppice stools where the stems have grown close enough together to have fused for some distance above the original stool.They can be difficult to distinguish from bundles.

Shredded trees.

A tree where the side branches are cut back repeatedly with a small tuft sometimes retained at the top of the tree. These are now very rare in Britain, though relics occur in the New Forest (N. Sanderson pers. comm.), but they still occur in other countries such as France. Most shreds are probably not particularly old.

Coppards.

Trees coppiced and then later pollarded (or bundle planted trees later pollarded), a feature of parts of Epping Forest (Essex) and Dalkeith Old Park (Mid Lothian).

Singled coppice stools.

A coppice stool where one limb has been retained, when the others were cut, and is left to grow on as a tree (ie is stored).

Layered trees.

Layering is a means by which some tree species naturally regenerate. Old trees may fall over completely and then re-grow or collapse and layer well away from the original base. This is characteristic of lime, willow, alder, black poplar, medlar and bird cherry but can occur in any species. A particularly notable example is the Tortworth Chestnut. The term phoenix regeneration has been applied to trees that have fallen over, or split apart, and successfully continued growing.

Orchard trees.

These trees are pruned to encourage fruit production and for ease of management but the act of pruning will enable the trees to live longer than they otherwise might. Veteran orchard trees have a very distinct invertebrate fauna associated with them.

Naturally damaged trees.

The effect of browsing, wind, fire, grey squirrel or oak scale insect damage can act in a similar way to pollarding. Usually these events shorten the life of the tree but they can create similar conditions to those found in veteran trees. Where the top of a tree has been removed by an agent other than man it is often referred to as a natural pollard or having been self-pollarded.

The categories are differentiated according to management practices and if these have changed or ceased for long periods it becomes difficult, if not impossible, to assign trees confidently to a particular category. For example, a tree pollarded once or twice, then grown on for over 50 years may be indistinguishable from an open grown maiden with a multi-stemmed crown.

Threats to veteran trees

There is a tendency to view old trees as immutable and immort a l . They have demonstrated their resilience to past threats but some of the potential threats of today have no precedents or are on a scale, or are taking place at a rate, that may outstrip the ability of the trees to adapt. Vigilance is needed to identify future threats. Those most frequently encountered today are:

• felling - to obtain the wood and timber, for safety reasons, to increase tidiness, for change in land use (eg development or agriculture) or for landscape reasons;
• competition from surrounding trees both planted and naturally occurring (or sudden release from competing trees);
• neglect (lapsed pollards having heavy branches that the tree is unable to support);
• inappropriate past management (eg filling cavities with concrete, girdling with chains and iron bands);
• unskilled tree surgery (eg cutting into the bolling, uncontrolled major limb removal, damaging retained limbs);
• inappropriate management of surrounding land (eg ploughing close to the trees, use of agricultural sprays and fertilisers or damage to roots by development, trenching and cable installation);
• inappropriate grazing levels (too little results in tree cover that can shade out the old trees, too much does not allow any tree regeneration and can lead to bark stripping, soil compaction, enrichment etc.);
• rapid changes in water table levels or surface water causing drought (eg owing to increased abstraction or naturally induced) or water-logging owing to raised levels;
• fire - externally, eg through fires in the surrounding land, bonfires, or internally owing to vandalism;
• pollution - remote, from industry and traffic, or localised, eg toxic rubbish such as oil and chemicals close to the tree, salt on roadside trees or nitrogen enrichment owing to manure and compost heaps;
• trampling/soil compaction - caused by livestock, people or vehicles (see Figure 9);
• bark damage - caused by people, vehicles or livestock;
• disease - eg Dutch elm, oak dieback;
• lightning strike.
• Often some of these threats are accelerated when land changes ownership.
• Populations of old trees and their as sociate d wildli fe are also threat e ne d , in additional ways by:
• isolation and fragmentation;
• lack of a new generation of old trees;
• removal of standing dead trees and dead wood.

Why manage veteran trees?

Management of veteran trees is often needed to ensure that the threats, identified before, do not cause loss of the trees and the value associated with them. Active management may not involve doing very much for most of the time. The essential point is that the trees and their situation are checked at regular inter vals and management carried out only if it is necessar y. Each situation must be assessed individually.

The broad reasons for managing old trees have changed quite considerably over the years. From Neolithic times until the 18th century the chief reason for the management of woodlands and trees was for their wood, timber, bark, leaves etc. In the 18th and 19th centuries the recreation of the wealthy started to become an influence and people desired places for quiet walking, picnics and exercise.

In the 20th century reasons for management have changed again. As the need for small-scale wood (pollard products) declined many existing trees were just neglected. Others were removed in the process of urbanisation and agricultural intensification. Those that remain have become valued for amenity and biological values. Coupled with this, an interest in repairing landscapes has developed, especially designed ones.

In the last decade the importance of biological value has been further focussed by the Rio Convention on Biological Diversity and so current management aims to provide a continuation of habitat. If no management is carried out habitats associated with veteran trees will be lost.

Dependent specialised species of limited mobility will die out. Management may also take place for landscape, economic, or cultural reasons or a combination of several of these. An opposing pressure has come from a different quarter; as Britain becomes an increasingly litigious society the ‘management’ of trees for safety reasons has also grown substantially.

Reasons for managing old trees:

• to safeguard the genetic resource;
• to provide continuity of habitat for wildlife;
• to keep individual trees alive for as long as possible, enabling a new generation of trees to replace the old ones;
• to maintain traditional practices;
• to perpetuate maturity and continuity within landscapes;
• to perpetuate aesthetic values eg characteristic landscape features;
• to increase the landscape value;
• for historical reasons - association or landmark trees;
• to fulfil safety responsibilities.

Continued management today and into the future depends upon those who have stewardship of veteran trees acknowledging their present value and ideally finding new values.

Further reading: Alexander, Green & Key. (1996), Barwick (1996), Bergendorff & Emanuelsson (1996), Damant (1996), Debois Landscape Survey Group (1997), English Nature (1996), Green (1994, 1995c, 1996a, 1996b), Hæggström (1992, 1994, 1998), Le Sueur (1931), Peterken (1996), Pott (1989), Quelch (1997), Rackham (1986, 1991), Rush (1999), Sanderson (1998a, 1998b), Smout & Watson (1997), Watson (1997).

How a tree grows, becomes old and decays

Tree growth

This section outlines the principles of tree growth that have consequences for management techniques. It is not the intention to give a detailed account of the physiology of trees.

A cross section of a tree (Figure 5) illustrates some of the features important for growth. The bark forms a protective, waterproof layer, and actually consists of several layers, the innermost of which is the phloem , which transports food from the leaves to the rest of the tree. Inside the phloem is the cambium , which is the region of growth, or meristematic, cells. These cells divide, forming phloem to the outside and xylem to the inside.

Figure 5. Diagram of the internal structure of a tree

The xylem is where the water is transported from the roots to the leaves and forms the wood of future years. The outer bark usually remains a relatively thin structure (although it can compose up to 10% of the radius in veteran trees) but the wood builds up so that the overall girth of the trees gets bigger each year as well as the tree, usually, increasing in height. Trees are not perfect cylinders however; they taper towards the top and the higher up a tree a cut is made across it, the fewer the rings that can be counted.

Recently formed xylem (sapwood) consists of conductive pipes surrounded by living parenchyma (packing) cells. In some tree species (eg beech) the living cells progressively die over a period of years and the tissue becomes non-conductive. This older, non-conductive wood is then called ripewood .

In other species (eg oak) the living xylem cells are genetically programmed to die after a certain period of time (approximately 10 years in oak) and after this is termed heartwood . Heartwood may contain substances that increase its resistance to decay. The variation in wood formation and structure between different tree species has consequences for the rotting processes and the organisms associated with rotting and also the longevity of the tree.

Annual growth

Living trees always add annu alincrements of sapwoo d , although their width may vary according to growing conditions and the age of the tree. Trees in Britain hardly grow in the winter months. In the spring they grow very fast; the wood produced has large cells with thin walls and is the earlywood . Later in the year, when the growth is slower, latewood results, with smaller cells and thicker cell walls.

These differences in growth are seen as rings in the wood when a tree is felled. (False rings can occur some years due to lammas (late summer) growth or after a stressful weather e vent such as a drought). The relative widths of the annual rings can give an indication of the growth rate of the tree in a particular ye ar. There may, t houg h, be va ri ation between branches on the same tree eg one side may be growing more quickly than the other, and this can give rise to eccentric rings.

Pollarding has a considerable impact on annual rings and tree growth. After cutting, the crown is reduced in size, so for the first few years the trunk of the tree expands slowly and the rings are narrow. The width of the rings gets gradually wider (varying of course with other local conditions) until either the tree is cut again, or it resumes the growth rate of a maiden uncut tree

Forming new branches

There are two different processes by which a tree can produce new branches from old stems: from dormant buds (also called epicormic growth) and as adventitious growth. In addition the growth of existing small stems may increase, relative to others, following tree surgery or damage.

Epicormic growth from dormant buds (Figure 6)

Dormant buds form from the growing stem or branch of the tree, but do not develop any further at that time. They become embedded in the bark but, by growing a small amount each year they are able to maintain their position and not become completely engulfed by the wood as the tree expands in thickness. Sometimes they can divide to form additional buds that also remain dormant.

Figure 6. Diagram to show how a branch grows

Hormones, such as auxins, from the crown of the tree probably keep the buds in a suppressed condition, but if some change in the root to foliage ratio occurs in the tree this alters the balance of the hormones and the dormant buds may start to grow. The types of change that stimulate growth include ring barking, severe pruning, exposure of the tree to increased light levels and water-logging.

Some species of tree lay down more dormant buds (eg oak, lime, English elm, poplar species,ash) than others (eg beech). Dormant buds can survive in a suppressed condition for many years and then grow when conditions are favourable. However their viability does decline over long periods of time. The longevity of buds is believed to be in the region of 100 years for oak, 60 years for hornbeam and sweet chestnut and less than this for beech and willow.

This is one of the reasons why old trees are less able to respond to cutting than young ones. It is also thought that, as the trunk of the tree has only a fixed number of dormant buds, repeated pollarding will eventually exhaust the supply. Trees cut repeatedly at short intervals, such as street limes and planes have shown a decline in response to cutting over a long period of time, which may be due to the fixed number of dormant buds.

Thus, leaving some young growth on the tree may increase the chance of viable dormant buds being present and hence the chance of regrowth. Dormant buds are not usually distributed evenly over the surface of the tree but form in clusters. Rough bark or burrs may indicate a higher density and trees that have these features may respond better to cutting than smooth barked trees. Some epicormic shoots grow from the buds as soon as they are formed, ie the buds do not have a dormant period.

In many situations epicormic growth is viewed as a detrimental characteristic. Where shoots occur they cause knots in the wood and this reduces the timber value of trees such as oak. They are potentially hazardous in street trees where lots of small branches projecting from the main stem can damage cars and hurt pedestrians. There may also be a genetic component in the production of such growth habits. For the success of pollarding , however , the more dormant buds the better the chance of regrowth and survival.

Perpetuating the genetic stock of trees on sites where pollarding has been carried out in the past may be better than planting commercial stock, which is likely to have been selected because it produces high quality timber with few knots and therefore few dormant buds.

Adventitious growth

Adventitious buds form when a tree is damaged. They result from injury or pruning, developing from the callus tissue that forms at the point of damage. Typically a cluster of small shoots develops but it is unusual for them to persist for many years.

While growth from dormant buds arises from a deep-seated connection to the trunk of the tree, adventitious growth is much more superficial. As a result it is not as strong and is more easily broken. The presence of adventitious growth on old trees is encouraging but often of less value than growth from dormant buds in the long term.

Again, some species of tree are better at producing adventitious growth than others. Oak is generally poor, beech is often cited as being good,but recent experiences at Burnham Beeches and Epping Forest with both old and young trees has not borne this out. Adventitious growth may develop better from natural tears rather than saw cuts, owing to the increased exposure of the cambium.

Growth of existing branches

Crown reduction in old trees may produce a third form of growth as a result of light reaching retained branches that were previously receiving low levels of light. As a consequence, small existing shoots grow rapidly into the light. As the years progress,they become the major branches. This type of growth is characteristic of trees that generally respond poorly to being pollarded (eg conifers and beech), and this is how the classic candelabra-shaped beech pollards arise.

Repeated cutting

Repeated cutting back to the same point may result in swollen areas. This can be seen in old trees and also younger street trees which have been cut many times. This has been attributed to the active growth points attracting a good supply of food, which results in excessive wood production and/or reaction wood, the result of loading from developing branches.

The stages in the life of a tree

Trees do not have a fixed life span; some die before reaching veteran status, others will become veterans at a much earlier age than might be expected. There is considerable variation both between and within different tree species. The life of a tree in natural conditions may pass through three main stages (Figure 7):

1. Formative - This is the stage when most of the energy produced by a tree is used for growth. There is a rapid increase in size as it grows from a seedling to a fully mature tree. Crown size and leaf area increases each year, until the canopy is fully developed. The widths of the annual rings are similar each year but because the whole tree is getting bigger, the cross-sectional area covered by each successive ring is greater.

2. Full to late maturity - This starts when the optimum crown size is reached. The amount of food produced from the leaves remains much the same each year and results in a more or less constant volume of wood being laid down. However, as the tree gets ever larger, this volume is spread increasingly thinly, thus the rings in the stem decline in width.

3. Ancient (Veteran stage) - This is the stage re a ched when the successive increments added to the tree, seen as the rings of wood, have a reducing cross-sectional area, but the tree is still increasing in girth. The crown dies back and branches may be lost, damage and decay also reduces productivity. The result is that as the leaf area declines, less new photosynthetic material is produced each year and the tree is even less able to maintain a complete cover of woody material over the whole stem area.

This process is called retrenchment and is seen most visibly as ‘stag-headed’ trees (Figure 8), typically in oak. This does not mean that the tree is about to die, it is a condition that can persist for many decades or even centuries. Retrenchment is not the only cause of stag-headed trees, it can also occur in younger trees, brought on by drought,disease, insect damage, root disturbance or pollution.

Figure 7. The stages in the life of a tree

STAGES: FORMATIVE	A - B	infancy pre-sexual maturity:	young tree, high vitality growth enhanced by mycorrhizal root associates	ideal natural state: optimum growth germination
	B - C	juvenile to early maturity:	continued fast growth. net increase in annual increment. low volume of dysfunctional tissue.	low habitat contribution	high vitality
FULL TO LATE MATURITY	C - D	full to late maturity:	growth to peak crown size. colonisation by saproxylic (deadwood) invertebrates. maximum pollination and seed capacity. onset of natural limb loss. increase of dysfunctional tissue. accelerated fungal colonisation and activity
ANCIENT	D - E	early ancient stage:	retrenchment of crown: reduction in net annual increment. contraction of live crown increased vegetative vitality in lower crown. increased fungal activity and wood decay. increased colonisation by flora and saproxylic fauna
	E - F	late ancient stage:	advanced retrenchment decline in crown size and annual increment. extensive hollowing crown collapse. declining vitality. advanced heartwood decay and hollowing. advanced activity by fauna and flora	increasing nutrient status of tree for colonisers. increasing habitat.	gradual decline in vitality
	F - G	SENESCENT:	terminal decline : tree death. continuing fungal activity. peak of saproxylic activity. nutrient recycling		death

The response of the tree results in a new balance between the area of woody material and that of the leaves. A tree in the last phase of its life that has retrenched can be very healthy and vigorous despite extensive decay and dieback. This stage may be also be the longest in the life of the tree.

The ancient stage can be further subdivided into three phases.

• Early ancient. When, over a period of years, there is a trend for the amount of dieback to exceed growth.
• Mid-ancient. When the annual rings cannot form all the way round the stem and some discontinuities start.
• Senescent. The terminal decline of the tree, leading to death.

Tree species vary in the proportion of time they spend in each of these phases. Willow and birch tend to have an extremely short ‘mature phase’ whereas others, such as yew can grow in cycles, passing from ancient back to formative growth. All the stages are a continuous process and of variable length. Once a tree has reached the middle ancient stage, nothing should be done to encourage the speeding up of the ageing process and the aim should be to keep it in this phase for as long as possible. When discontinuities in the annual rings develop, the tree is at its most vulnerable stage.

Figure 8 . Sweet chestnut trees at Croft Castle Herefordshire). A standing dead tree is in the foreground and stag headed trees behind. (see colour plate page 84).

Other aspects of the veteran stage

Veteran trees that are retrenching tend to show a diminished growth rate and a drop in reproductive output. They are also slower to occlude wounds if damaged. They tend to develop other features and characteristics to a greater extent than younger trees (eg cavities in the trunk, seepages, dead loose bark, dead wood in the canopy and physical damage). One important point to note is that, as the tree ages it becomes more valuable for a wide range of other organisms and its habitat value increases .

Assessing the age of a tree

Assessing the age of a veteran tree is not an easy task and is usually, at best, an estimate. There are a number of methods that can be used, however.

• Taking a core is one option but many veteran trees are hollow or rotten to a greater or lesser extent. Coring is also detrimental as it can cause damage in an undesirable place (Shigo, 1986a illustrates the possible consequences of taking a core from a tree in terms of the rot induced.) Felling a veteran tree to count the rings should, of course, never be done! Counting the rings on major branches (cut during the course of work or fallen) from veteran trees can sometimes give an indication of age. An allowance of years for the tree to produce the branch should be added to the ring count.
• Age based on tree girth I. Because of the variation in growth rate throughout the different stages in the life of a tree, caused by differing conditions of soil type, nutrient status, rainfall etc and the even greater variation between different species it is difficult to extrapolate age from girth measurements. There are some rules of thumb that can help. Mitchell (1974) states that one inch (25mm) of girth (at breast height, 1.2m from the ground) is equivalent to one year’s growth for a free standing tree and 1/2 inch (13mm) in a tree within a woodland setting. This approximation of age is only helpful for some species of tree (eg: oak) that are in middle age and have not been cut. It is of very limited value with regard to old trees.
• Age based on tree girth II This is a more accurate (and thus more complicated) system also based on tree girth developed by J. White. It has been calibrated using a variety of older trees where the planting date is known and provides the best estimates of age available. (For a description of methods and the relevant tables used for calculation see White, 1998.)
• Age/size ratios within species. Different species of tree grow at very different paces but it is possible to build up a table of girth sizes and estimated age for a particular species, though even within a species there is considerable variation. Yew has been studied with this aspect in mind (Baxter 1992).
• Site-specific information. It is possible to draw up a table for a particular species on a particular site that allows figures for girth to give an estimate of age and which may be able to take into account the effects of historical management such as pollarding (eg Le Sueur 1931). These may not correlate well with data from other sites.

As a general principle it is almost impossible to age pollards, or trees that have undergone natural crown loss, by the methods given above.

Why does pollarding or cutting cause trees to live longer?

A normal tree reaches the veteran stage when the size of the crown is not large enough to produce enough food to maintain the same cross-sectional area for each annual ring. During the process of retrenchment the photosynthetic area is reduced, as is the surface area of the woody branches, so that less food is required by the tree.

Reducing the size of the crown at intervals delays the veteran stage in a tree’s life when the demand for water and nutrients outstrips its ability to increase the root area to absorb them. A reduced crown also reduces the risk of wind throw, owing to the relatively low stature (short ‘lever-arm’) and small ‘sail area’, but a long abandoned pollard with a large sail area may become particularly vulnerable.

In addition, the multiple branches from the top of the bolling produce a larger number of vascular connections into the trunk than in a normal tree. These, in effect, form separate compartments and it is less easy for pathogenic agents, or aggressive decay fungi, to spread through the entire tree.

Severe wounding of a tree is similar to pollarding and has four main effects:

• exposure of cut surfaces to micro-organisms;
• drying out of wood from the cut surfaces;
• reduction in the volume of foliage and sapwood in the tree and thus its existing stores of carbohydrates and the capacity to replace them;
• loss of shoot tips which disrupts hormonal co-ordinating signals and affects growth.

Wounds result in the drying out of an area of wood, causing decay. The larger the amount of wounding (as on an old tree with all branches removed) the more drying out and dieback with the increased chance of infection by micro-organisms. The ability of the tree to compartmentalise will be reduced because of its severely reduced photosynthetic area.

It seems that a few trees are able to cope with this situation although willows can grow new shoots from an old bole. If some branches are retained on the tree, the amount of exposure, drying out, and infection by micro-organisms is decreased. However, these areas will be restricted to strips of xylem and phloem associated with the cut branches.

For this reason (and to keep the sap wood active) it is best to retain good connections of xylem and phloem throughout the tree,thus maintaining ‘channels’ of living tissue between the roots and shoots. In some old trees that have been cut back heavily on one side this connection has been broken and the tree has died back completely thus resulting in a ‘lop-sided’ tree. Leaving branches, at least small ones, all round the bolling is therefore advisable.

The value of pollarding and working trees

When humans started clearing the forest they removed many of the conditions that saproxylic species (or wood decay communities) required such as dead wood on the ground and within trees and standing dead trees. While this must have been detrimental to many populations of saproxylic species the human management of the trees eg pollarding and coppicing, created very similar conditions in a different way. Almost all trees may, at one time, have been used or managed and these can be referred to as ‘working trees’.

The increased life expectancy of working trees and the characteristics they developed enabled the perpetuation of suitable niches for a range of species in the wood decay community despite the change in the landscape that resulted.

The decay process

The process of decay in wood is a complex subject and the details are only just starting to be understood. There are many different agents involved, which make it very difficult to establish the relative importance of each. What is clear however, is that fungi have a fundamental role in the process. The work of A. Rayner, L. Boddy, A. Shigo, F. Schwarze and D. Lonsdale has helped enormously in establishing how fungi behave within living trees and dead wood and how the tree responds. The following sections summarise the crucial points with respect to living trees. Section 7.5 considers the conservation of fungi in relation to veteran trees.

Compartmentalisation

Trees have no wound healing processes, as animals do, but they do have a way of limiting any damage caused. If a tree has been damaged and is then cut some years later it can be seen to have dried out, the dysfunctional area of wood extending back from the wound. This area often has a sharp boundary wall between it and the rest of the tree as shown by a difference in the colour of the wood (Figure 9). This process of boundary setting has been termed compartmentalisation.

Figure 9.

The sharp boundary results from a response of living cells to the ingress of air and/or micro-organisms and may represent a barrier between healthy and damaged areas. If a tree is badly damaged it spends energy in compartmentalising, leaving less for growth, which can result in a smaller annual ring. The more areas that are ‘sealed off’, the less tissue is available for the tree to distribute food and water to its various parts.

Eventually, when there are too many dysfunctional compartments and the distribution of new sapwood becomes discontinuous, the tree is unable to maintain vital functions and death results. However, the more compartments there are in a tree, the more structural diversity there is and so the larger the number of niches and habitats for other organisms. The exact processes by which compartmentalisation and barrier formation occurs remains unclear.

Fungal colonisation

It seems likely that fungi colonise living trees in two main ways:

• from the outside. In the simplest scenario, physical damage to a tree weakens its physical defences and makes conditions suitable for the fungus to colonise, become established and grow;
• from the inside. The fungus makes use of the tree’s own plumbing system (xylem and phloem) to reach different parts of the tree via the sap stream; this can occur at any stage in the life cycle. The fungi often remain in a latent (inactive) state without any noticeable impact on the tree until conditions within the wood change enough to activate them, eg drought, ageing process.

It is thought that the sapwood of a healthy tree has such a high moisture content that it is unsuitable for the growth of most fungi. However, when the tree is mechanically damaged or is stressed in some way, parts of it may become more suitable for fungal growth. Loss of a branch, for example, allows air in and causes drying out of the wood around the wound and enables fungal growth. Stress brought on by drought or the severing of roots may cause the tree to stop producing food (photosynthesising) from a branch. This branch then dies back and dries out because the flow of sap is no longer as strong as normal. The drier conditions activate some of the latent fungi or fungi entering via the dead or broken wood.

Most of the fungi capable of causing extensive decay depend on wounds or dead branches or roots as entry points. Some of these species grow only in heartwood, while others are confined to sapwood or are able to colonise either. A wide range of factors determine whether or not decay becomes extensive enough to weaken the tree significantly.

Some pathogenic fungal species are able to cause death or dysfunction to parts of the tree even without stress or major injury (eg some honey fungus species or the fungus that causes Dutch elm disease). This relative minority of species are a primary cause of dysfunction in the sapwood or of death of the cambium.

As the fruiting bodies of the fungi are the only parts that are usually noticed they are often misinterpreted. A small number of species (eg some species of honey fungus) can cause the death of a tree but a much larger number produce fruiting bodies only when the tree (or that part of it with fungal fruiting bodies) has died from other causes (ie they are saprophytic). This leads to many misconceptions as to the role of fungi.

The means by which fungi colonise sapwood

• Root colonisers. Species that colonise intact roots and then spread throughout the cambial zone of the tree. They may kill the tree by girdling it or killing too many roots, eg: Armillaria mellea.
• Sapwood colonisers I. Species that enter the tree through a wound or other open entry point on the tree. Most species decay parts of the tree without killing it but sometimes the decay parts of the tree without killing it but sometimes the decay is so extensive that very little functional sapwood is left, eg most Ganoderma species.
• Sapwood colonisers II. These species also enter the tree through wounds but are more aggressive and may kill the host, eg Chondrostereum purpureum.
• Deadwood colonisers. Species that can colonise sapwood only after it has died as they are unable to overcome the active defences of the tree, eg Daedaleopsis confragosa.
• Note that the behaviour of fungi covers a spectrum and that a particular species may fall in between the categories presented here.

Fungi growing within the heartwood

Some fungal species are able to grow in the innermost part of the tree, which consists of dysfunctional wood. It is usually drier than the outer sapwood and so is more suitable for the growth of fungi if they are present. Species that rot the heartwood such as Laetiporus sulphureus (Figure 10) break down only the dead wood. This decays the centre of the tree but leaves the outer, living layers intact. While this may not be desirable from the point of view of a commercial forester, the tree is not harmed and may actually benefit.

Decay and hollowing are part of a nutrient recycling process.The tree can make use of the products of wood decay within the trunk by producing aerial roots from its above ground parts, which grow into the rotting stem. A hollow tube may respond differently from a solid trunk in high winds and is not necessarily more likely to snap provided its walls are not so thin that buckling occurs.

Figure 10. Chicken of the woods Laetiporus sulphureus, on an oak tree.

Types of decay

There is a wide range of variables influencing decay. The result of this is a tremendous range of potential niches available to or ganisms such as invertebrates that mak e use of the rotting process and its products. Premature decay in a tree is not necessarily detrimental, either to the tree or to its wildlife value. Young decaying trees can be very valuable, on sites with veterans, in providing suitable conditions for the saproxylic organisms.

Decay is dependent on many factors:

• age of tree;
• presence of heartwood. (Those species of tree, eg birch and beech lacking durable heartwood tend to decay quicker that those that do, eg oak);
• type of wound or stress agent;
• species of fungi involved and stage of growth within the tree;
• species of invertebrate involved;
• species of vertebrate involved;
• position of wound;
• whether the wound collects water or not;
• whether the wound is enclosed or open to the air;
• whether the wound is permanently covered by water (becoming anaerobic);
• ability of the tree to respond to damage (ie to form reaction zones and to occlude wounds);
• outside factors (eg dung, rotting carcasses, aerial pollution).

There are three main types of rot caused by fungi:

• White rot - When the lignin and cellulose are both broken down. In simultaneous white rot the lignin and cellulose are broken down at approximately the same rate causing loss of both stiffness and strength, which, in the advanced stages of decay produces a thick porridge-like substance.
  
  In selective delignification (or stringy white rot ) the lignin is broken down first and the cellulose degrades more slowly. Initially the result is soft material that is still quite strong, the colour and weight of balsa wood. White rot is more common is broadleaved than coniferous trees, eg rot produced by some Ganoderma species.
• Brown rot - When the cellulose is degraded and the lignin is left intact. The initial results of the decay are brittle but rigid. It does not bend much before breaking but may break into cubes known as cubical brown rot. Eventually a rich, humus like, substance may result (red wood mould) usually after having passed through the guts of many invertebrates. Brown rot is more common in conifers than broadleaved trees. It is produced by, for example Fistulina hepatica and Laetiporus sulphureus in oak trees.
• Soft rot - This is when the cellulose is degraded, as in brown rot, but the fungi invade the cell walls in a very different way. Many white rots and some brown rot fungi can behave like soft rot fungi in living trees, but ‘classic’ soft rots are caused mainly by specialised ascomycetes which grow in the surface layers of dead wood or timber under very wet conditions.

Different invertebrate species and communities are associated with each of these types of rot.

Decay detectors

There is a range of devices available for the detection and assessment of decay. Some of these can help to determine whether there is significant weakening, by providing information on the position and extent of decay. Interpretation of such information is, however, often difficult and should be attempted only by a suitably qualified practitioner who will make a visual inspection in the first instance, and will use the resulting observations to decide which parts of the tree, if any, could be usefully probed, using a particular diagnostic device. The number of probes should be kept to a minimum, as all currently available devices are invasive to a greater or lesser extent.

The value of dead wood

It is important to encourage a variety of types of rot so that suitable conditions are provided for a range of the more specialised invertebrates. The more dead wood a tree contains the more valuable it is. Thus, a living veteran tree is better than a dead one because it will continue to produce more dead wood. Old dead trees left standing are usually better than those in younger growth phases. Damaged young trees may also have valuable areas of rot (natural or even artificially induced).

Trees containing a higher volume of wood have a higher wildlife value, which is why old pollards are generally more valuable than old coppice stools. The latter may have a range of niches, but the sheer volume of wood is considerably less than in most old pollards.

The role of organisms other than fungi

Although fungi have the fundamental role in the decay process in trees, they are not the only active organisms. Many invertebrates assist in the breakdown of wood by boring into it and feeding on the comparatively softer and more nutritious bits. They also enable fungal mycelia to penetrate the wood more easily along the sides of burrows. Some species of insect have nitrogen-fixing bacteria in their guts, which enhance the nutritional value of their faeces which may be re-ingested by other species.

Wood has a very complex chemical structure and is very indigestible. Many of the invertebrates rely on fungi to break the wood down into simpler molecules so that they can take advantage of it. Ambrosia beetles (family Scolytidae) even have fungi associated with them, which they carry between trees to perform this function.

Birds such as woodpeckers may contribute to the process by actively hollowing out areas for nesting, their nests and holes may then be inhabited by other animals. The faeces and dead bodies that build up in the tree holes contribute to the nutrient status of the rotting wood. There are even secondary fungal colonists whose fruiting bodies are found in cavities created by the primary decay fungi.

Further reading: Beckett (1975), Boddy & Rayner, (1983), Coder (1996), Dolwin et. al (1998), Graham (undated), Green (1993, 1994, 1996a), Le Sueur (1931, 1934), Lonsdale (1996, 1999), Mattheck & Breloer (1994), Mitchell, A. (1974), Mitchell, P. (1989), Patch, (1991), Patch Coutts & Evans. (1986), Rackham (1986, 1990, 1991), Shigo (1986a, 1986b), White (1996, 1998),Wignall, Browning & Mackenzies (1987).

Management of land around Veteran Trees

Introduction

Trees do not exist in isolation; the environment around them can be crucial to their welfare and the landscape they are part of can be just as or even more important. The previous section has dealt with the management of veteran trees themselves. In many situations though, it is not the trees that need work done on them as much as the land surrounding them.Conditions in the soil will affect their roots and growth. What is growing on the surrounding land can compete with the tree for water, light and nutrients or present a fire hazard. Outside influences can affect the health of the trees and the organisms found on them.

Ancient trees are part of a landscape, either formal and designed or informal and evolved. It is important to consider what role the trees play within such landscapes as this will have implications for how the land around the trees and the trees themselves are managed.

Open land - Grassland

Grassland management

(for full details see Crofts & Jefferson 1999)

The most sympathetic type of grassland to surround veteran trees (though not commonly found) is unimproved. Unimproved grassland should be managed with great care following the guidelines in Crofts & Jefferson 1999; this management will also be favourable to veteran trees. In general, the ‘improvement’ of grassland through reseeding or the application of fertilisers can be detrimental both to veteran trees and to grassland. For example, fertilisers and herbicides have had an adverse effect on the lichens and fungi at Moccas Park, Herefordshire, and the application of lime can cause problems for the fungal communities.

If the grassland has already been improved and lime must be applied, it is better as coarse-ground limestone than agricultural lime as there is less drift. The ideal management is not to apply any substances although light applications of farmyard manure to improved grassland are acceptable in some situations. No inorganic fertilisers should be applied and no ploughing or reseeding carried out. Note that trees in fertilised pastures may look healthy but in times of stress they may decline quickly.

The ‘improvement’ of pasture leads to a loss in variety and abundance of plants and invertebrates and therefore a loss of food for bats, birds, etc that may depend on the veteran trees for their resting sites. Hay cutting (the traditional management of grassland under pollards in other European countries) can be compatible with veteran trees though it is better if the grassland is not improved.

The control of problem species, such as ragwort, thistles and docks, within grazed systems needs to be considered carefully. There are methods that are sympathetic to ancient trees. For example, cutting of thistles, spot spraying, and use of some modern weed wipes that are relatively specific (see Bacon 1994). There are also suitable mechanical weed pullers available now (Bacon & Overbury 1998).

Effects of grassland improvement on veteran trees themselves

• Inorganic fertilisers disrupt mycorrhizal fungi, and the trees are then more susceptible to stress.
• Lime may reduce the species diversity of fungi (including mycorrhizal species).
• Farmyard manure, slurry, fertilisers and lime may be sprayed onto the trunks of the trees; an excess is toxic to fungi.
• Ploughing damages the roots of the trees and mycorrhizal fungi.
• Rolling compacts the roots.

Grazing

In many situations where veteran trees exist, grazing was an essential part of the management system. There are two quite different types of grazing that can be considered, extensive and intensive.

The benefits of grazing in wood-pasture are that:

• It prevents mass regeneration of trees and shrubs, thereby reducing competition between trees for light and creating more varied growth forms of trees and a greater variety of woodland structures. This results in:
• A greater diversity of habitat structures, allowing other groups of organisms to survive.
• Increased light levels that are beneficial to epiphytic lichens.
• Many insects are sun-lovers as adults and will be lost under shady conditions.
• Densely shaded trunks have cooler interiors and are less good for larval development.
• Many wood-decaying fungi appear to fruit less frequently when the trunk is shaded.
• It is the traditional form of management on many sites and, from an historic point of view, is an essential part of the system.

Extensive grazing

Animals are able to roam over large areas to forage and the stocking density is relatively low. This type of grazing must have existed in the wildwoods, which naturally contained high densities of veteran trees. The grazing would have been by indigenous cattle, deer, bison and boar. Such grazing restricted, but did not stop, tree regeneration and had the effect of creating structural diversity in the ground flora and shrub layer (Figure 11). Today, woodlands with veteran trees benefit from light grazing, which increases the structural diversity and benefits a range of organisms (Mitchell & Kirby, 1990).

Figure 11. Old growth woodland in the New Forest (Hampshire), grazed extensively.

Intensive grazing

This type of grazing involves a higher stocking density and the land under the trees is dominated by plants that are not woodland species (Figure 12). The animals are often given supplementary feed, which is detrimental, to the ground flora and in many cases the grassland has been, or is under pressure to be, improved. Often the areas the animals range over are relatively small. Intensive grazing occurs in some types of wood-pasture (where the old trees were usually pollards), especially in parks where deer (or in some instances cattle) were grazed.

If a wood pasture or parkland has been grazed more or less without a break, it is likely that the most suitable management in both historic and biological terms is to continue with this. Changing the management regime in such circumstances should be carefully thought out before implementing. If there has been a long lapse in grazing, the situation should also be looked at more carefully, especially from a biological point of view, before deciding on what form of management to reinstate. (See also section 5.3 for a discussion of the consequences of opening up woodland from around veteran trees).

Figure 12. Whittlewood Forest (Northamptonshire), a deer park with improved g rassland.

Disadvantages of grazing

There are disadvantages of grazing too, especially where it is intensive or the land is overgrazed:

• Lack of tree regeneration. On sites where grazing has been continuous there is often a generation of old trees with few, if any, younger ones to form the ancient trees of the future. This situation needs addressing to prevent the loss of biological interest on the site and loss of landscape appeal and historic value. There are several ways to overcome this (see chapter 8).
• Activities relating to the grazing of animals that damage the veteran trees. Trees in grazed areas will always develop a browse line, the height of which depends on the animals present. In a healthy mature tree this does not cause too much damage, although the trees are unable to grow branches that reach the ground. This prevents layering and may make the branches more prone to snapping as they cannot be supported from below (Lonsdale 1999a). The grazing of animals may be directly detrimental to the trees in the following ways:
• Animals may chew the bark of the trees. In extreme situations they may ring bark them.
• Animals may use the tree for shelter, causing trampling round it and damage to the roots. Where the animals dung and urinate, the nutrient levels rise and the high nitrogen levels are detrimental to the mycorrhizal fungi.
• Vehicles used to feed and water animals may pass too close to old trees, causing the ground to be churned up.
• Fodder , water ing and mineral lick sites placed too close to the trees attract greater attention.
• Where the animals are fed supplementary feeds the dung enriches the grass land heath and trees. It may also introduce new species and genetic variability via seeds, which may confuse the true distribution and status of species.
• Animals bring other chemicals into the wood-pasture system. Domestic stock are treated, particularly for intestinal worms, using a variety of chemicals. Some of the substances used are not specific to internal parasites and may be long lasting. An example is the widely used wormer with Avermectin as the active ingredient. The action of this has been shown to have an effect on a range of invertebrates including those that break down animal dung.
• Insectivorous species, especially bats and birds, may consequently suffer from lack of prey. The situation is of special concern with regard to cattle because a bolus system is often used which releases the wormer over long periods of time. As a general principle Avermectins should not be used on any site with conservation interest. Other types of wormers may be just as detrimental. For more information see JNCC (undated), Cooke (1997) and English Nature (1994). See also later in this section.
• Overgrazing, especially in the winter months, can cause poaching and this leads to infestations of tall weeds such as thistles, nettles, ragwort and docks.
• Solutions to problems caused by grazing
• There are several solutions to these problems. The best one will depend largely on the situation and the money available for additional management work. They include:
• Reduce the stocking density or alter the grazing regime so that the animals do not bark the trees (but for husbandry reasons avoid single animals in an area). Bark stripping is more prevalent in the winter but can be due to boredom as well as a nutritional need for the bark.
• Experiment with mineral supplements (eg Uniblock produced by Dodson and Horrell) to provide the minerals that horses might otherwise obtain from tree bark; other supplements have been shown to change the diets of animals such as sheep. Be sure to place them well away from the trees.
• Fence off the veteran trees so that the animals do not have access to them. The fence should keep the animals beyond the extent of the canopy. This solution is usually practicable only if there is a small number of trees involved, and it can lead to the growth of competing vegetation.
• Ensure that there is nothing to attract the animals to stand under the trees. Feed and water them in a different place.
• Provide alternative shelter, with watering, etc to attract them preferentially.
• Ensure that vehicles do not use routes under veteran trees. If necessary move gateways.
• Try out other ideas to deter the animals, eg: pile rocks round the bases of the trees to stop them from getting too close or chestnut paling wrapped round the tree (not as a fence). Be sure to check that they work (sheep can climb rocks and continue chewing the bark higher up!) and that they do not create other problems such as compaction or creating a humid day time resting place for slugs that then browse epiphytic lichens at night!

Solutions to the problems caused by wormers

• Don’t use any wormer on site (ideal solution). Worm animals when they are grazing or housed elsewhere. Ensure that they are kept off the site for long enough for all traces of Avermectin, and other products, to have passed through (this will vary with the type of application). Avoid broad spectrum wormers and slow release bolus applications.
• Use wormers that are more specific to internal parasites. English Nature, JNCC and FWAG can provide advice on suitable alternatives.
• Be careful with new products, ensure that they are compatible with any nature conservation interest and seek independent advice.
• Consider carefully the use of other chemicals on the site. This does not mean that the health of the animals should be compromised. However, some chemical treatments for fly strike in sheep, for example, are ‘better’ environmentally than others.
• It may be worthwhile considering the guidelines of the Soil Association with regard to animal husbandry and the use of chemicals and medication, even if the aim is not to produce organic products.

Tree regeneration in grazed areas

In the New Forest, Sanderson (1996a) has shown that even palatable tree species can regenerate in grazed areas and this is also true in Hatfield Forest. Even in periods of heavy grazing thorny bushes, including holly, and dense bracken provide enough cover to allow young trees to become established. Regeneration requires extensive grazing systems that allow a full range of natural processes to occur, including shelter or respite from grazing.

Reintroducing grazing

The reintroduction of grazing on veteran tree sites that have not been grazed for a long period is starting to gain momentum. In these situations a site specific feasibility study is probably the best way forward. The choice of grazing regimes is likely to depend to a large degree on the wildlife interest of the site. In the majority of situations, however, a low density grazing regime is probably the most suitable.

Achieving the right stock type and level at the right time is very difficult and may vary widely according to the type of land and also from year to year. When considering reintroducing grazing to a site it is important to consider the welfare of the animals, the work involved and financial implications. When considering reintroducing grazing to a site with an ancient monument make sure that the fencing and type of animals used are appropriate to the site and acceptable to the archaeologists.

Further reading: Bacon (1994), Crofts & Jefferson (1999), Lewis et al. (1997), Mitchell & Kirby (1990).

Bracken and heathland

The commons and wood pasture on which many veteran trees stand were not normally prime grazing or arable land. One of the contributing factors to the survival of many veteran trees was that the land around them was too poor (eg too low in nutrients, steep or rocky) for growing crops. In some areas heathland developed on the poor soils and where today, through lack of grazing and trampling, they have become dominated by bracken this can cause problems. Bracken has also become dominant in other vegetation types.

The effect of the bracken fronds is very similar to dense summer woodland cover with few other plant species, including tree seedlings, able to get enough light. Bracken is also allelopathic, producing its own substance that inhibits the growth of other plants. The result is areas lacking in other tree species around the veterans.

The dried fronds in bracken-dominated areas build up into a deep litter layer or thatch that early in the year can be a severe fire hazard. Fires can travel under the ground in the leaf litter and when this happens the old hollow trees act as excellent chimneys, fuelling the fire with air, which destroys the trees. For areas of heather-dominated land under veteran trees fire can be a problem too.

On sites with ancient trees and abundant bracken, some form of fire protection should be seriously considered. Ideally fire breaks should be made and kept open so that blocks of woodland are isolated from each other in case of fire and an area round each tree should also be kept bracken free, at least as far out as the canopy.

In order to create such areas effectively, fallen dead wood may need to the moved. However, this is not as easy as it sounds as bracken is a difficult plant to control. Health and safety considerations need be taken into account with some of the following treatments and an added problem is that bracken spores are carcinogenic.

Methods to consider for controlling bracken to create fire breaks or to reduce the fire risk on the site

• Spray or weed wipe with Asulam. When used properly this herbicide is very effective against bracken, but rarely eradicates with one application. Spot treatment of any regrowth is necessary in subsequent years. Prior to spraying, the ground vegetation should be surveyed because Asulam does kill all ferns and some other plants, eg sheep sorrel and some bryophytes.
  
  Surfactants, if added to the spray, may affect invertebrates. On many sites it is preferable not to use chemicals; however, using more modern methods of application the bracken can be targeted with minimal amounts of herbicide reaching other plants. Spraying is the best form of application, weed wiping should be carefully considered before use. The best time of year to spray is when the fronds are fully unfurled but have not begun to die back, usually between mid - July and the end of August.
• Cut. Cutting two to three times per year will reduce bracken cover but this will need to be repeated in subsequent years as bracken re-establishes itself quickly. The first cut should be made when the fronds have just started to unroll (usually late April/early May). The second cut should be made about a month later when the fronds reach a similar height again.
  
  In this way the plant puts maximum energy into growing and loses it all when the fronds are cut. If a third cut is possible this can be done at any time when the fronds are uncurled, but cutting for the first time in a year after July is not worth doing.One drawback of cutting is that the ideal time to cut is also when ground-nesting birds will be most vulnerable. Cut, dried and baled fronds can be used as livestock bedding.
• Bruising. Small rollers that crush the fronds are available. Rolling twice, the second pass at right angles to the first, improves the effect. When rolled in July on a hot day the bracken bleeds, which helps to exhaust it. A special ‘bracken breaker’ has been developed that is especially good at breaking the frond stipes and encouraging ‘bleeding’.
  
  Rolling seems to reduce the vigour of the bracken by at least 50% and it is possible that continued rolling may result in eradication. Since rolling is best carried out later in the year than cutting fewer ground-nesting birds are likely to be affected but the later breeding nightjar may be vulnerable. Rolling may also be detrimental to anthills, reptiles and rare or solitary plants, and can break up any dead wood on the ground.
  
  The rollers designed for bracken may also adversely affect wavy hair-grass but ericaceous species seem to be able to withstand the treatment as long as they are not old or straggly. Heavier rollers may affect plants such as gorse and broom and also trees and shrubs. The compaction of the vegetation produced by rolling can be an advantage in helping to reduce the fire risk and encouraging decomposition, although the small specialist ‘bracken breakers’ cause bruising with negligible compaction.
• Pigs. Pigs in the autumn months dig for and eat bracken rhizomes and this can help to control the growth of the plant. Pigs should not be fed solely on bracken as this causes them to develop thiamine deficiencies. The results of pigs digging can be quite devastating, if not carefully controlled, so this method is most often used on recently cleared land. A low density of pigs can also help in the control of bracken if used in association with cutting, or rolling. Rooting by pigs is beneficial in promoting the germination of some seeds but ‘mob stocking’ can cause similar problems to that of overstocking with other grazing animals (see section 5.2.1.2).
• Removal of bracken litter. If the bracken litter, or thatch, is very deep it can be removed and this may also be desirable if cutting or rolling are being carried out. Removing the build up of thatch can also help weaken the plant allowing possible frost damage but it may also suppress the growth of other plants. Litter can be removed by ‘blowing’ using strong leaf blowers, which causes less root damage to trees than scraping. It may be possible to sell bracken litter to the horticultural industry, as a mulch, and this has been successful in the Netherlands.
• Grazing. Livestock, especially large animals such as ponies or cattle, may trample the young bracken fronds, which can help to keep it in check once major control has been done physically or chemically.
• Woodland. Encouraging closed canopy woodland also helps to reduce bracken cover, though this may not be a desirable option if the veteran trees are unduly shaded by the surrounding woodland.

Bracken control at Ashtead Common

Fires present a significant risk to the veteran oak pollards at Ashtead Common. In 1990 there were over 100 standing charred pollards as a result of a large fire (Figure 13). The risk has been reduced in recent years by creating fire breaks, primarily by chemical control of the bracken. Initially, all dead wood was removed from the fire breaks, into large piles nearby. Although not an ideal situation, it was necessary to allow the safe access of machinery and ensure that the fire breaks would be effective.

Bracken is then sprayed annually with ASULOX by one person on foot, using a high pressure lance with a flood jet and a tractor-mounted spray tank driven by a second person. Small areas are sprayed using a knapsack sprayer. The herbicide provides an effective control rate of around 95% which is enhanced by mixing ASULOX with an oil derived from oil seed rape known as CODACIDE. This ensures that the chemical is water-resistant and improves adhesion to the fronds. Thereafter fire breaks are maintained by an annual mechanical grass cutting programme.

Figure 13 . Veteran trees killed by a bracken fire at Ashtead Common (Surrey).

Disadvantages of controlling bracken

Bracken is an important plant for some organisms. For example, it can provide suitable conditions under the fronds for the growth of violets, which in turn can provide an ideal habitat for some threatened fritillary butterfly species. Other species that may benefit are bluebells, an endemic weevil (beetle) and some fly species.

If there are such species of conservation value on a site with ancient trees then the management should take this into account. Bracken can also provide valuable shade (and frost protection) for piles of dead wood but fire breaks may be needed round these if they are large. In any case, bracken should not be viewed as a species to eradicate, since it is native. It may just need to be kept in check.

Further reading: Burgess & Evans (1989), Butterfly Conservation (1998), Crofts & Jefferson (1999), Forbes & Warnock (1996), Lewis & Shepherd (1996).

Cultivated ground

Ancient trees are also found within land that is cultivated. Many of those in the middle of arable fields have died or been felled but some manage to survive. In addition, those on the boundaries of fields are affected by cultivated land. Much parkland has also been ploughed and converted to arable farmland. Ideally, arable farming should not be carried out in areas with veteran trees. However, where it is unavoidable, steps should be taken to provide the best possible conditions for the trees.

A vital part of the tree, the roots, is out of sight, under the ground. Deep ploughing can be extremely detrimental as it destroys tree roots. Work nearer the surface, especially that leading to compaction can be equally damaging as some trees have abundant roots at quite shallow depths (Figure 14). Even harrowing and rolling can cause problems in compacting the roots and causing mechanical damage, this is especially true of modern power harrows.

Ideally, no work should be done closer to the tree than 5 m outside the extent of the canopy, or a distance from the centre of the tree of 15 times the diameter of the trunk at breast height, whichever is the greater. This establishes a ‘separation distance’ or exclusion zone round the tree and gives it the best chance of long-term survival. It can be quite surprising how far away the roots of some of these trees extend, eg up to 50 m.

Figure 14. Ploughing too close to a veteran tree. The tree has also had its lower branches removed, which is also detrimental.

Intense cultivation brings more potential problems. Spraying can be very damaging to the tree and its fauna and flora. Fertilisers have a detrimental effect on the tree, the lichens and the mycorrhizal fungi. Fungicides also affect the vital mycorrhizal species that the tree needs in order to survive and they also affect the lichen flora. Insecticides may kill the specialist dead wood species and are most damaging when used between May and July in the vicinity of the tree or on any plants in flower. These chemicals should not be used anywhere near old trees to avoid drift affecting them; the minimum distance is 15 times the diameter of the tree (as for cultivation). Ideally there should be an island of uncultiv ated land

surrounding the tree but it is important that this is of sufficient size and is not ‘eroded’each year. Ploughing and spraying right up to the trunk is extremely harmful. Veteran trees on the edges of fields are vulnerable to cultivation too. Remember that the roots will extend into the field, even if the trunk is in a hedge.

Amenity land

Veteran trees are also found in amenity areas. These range from private golf courses to school playgrounds and public parks. The same principles apply here as in other grassland or cultivated areas. Grassland tends to be very intensely managed in some of these situations, but the use of chemicals should be avoided close to the trees. An additional threat is the regular mowing and strimming, which if not carefully done round the bases of veteran trees can easily cause damage to the bark, exposing vital tissue. Wherever possible, try to create a ‘nature area’ of rough grass around the trees to alleviate these problems.

Trees in prominent positions are frequently used as locations for notice boards and signs. It is far better to use purpose-made posts but if trees must be used in this way, tie notices on, do not nail them. Make sure that they are removed before the tree grows into them. Old, neglected fences that are attached to trees cause a similar problem. Attaching fences to veteran trees should be avoided.

A frequent threat to veteran trees in amenity areas is compaction. Car parks, picnic sites and building development may reduce the amount of water a tree can obtain and lead to its rapid decline and eventual death. If a veteran tree is a valuable source of shade, consider providing alternative facilities nearby and relocate car parks, picnic benches, etc. Wherever people or property are in close proximity to a veteran tree the tree becomes a potential threat so the situation is best avoided.

Surrounding woodland

Veteran trees in woodland

There are three broad types of woodland which are found surrounding veteran trees:

• high forest woodland that has developed naturally (usually ancient woodland) which contains old trees, eg a particularly old specimen of an oak within oak woodland;
• n aturally regenerated woodland (usually broadleaved) which has developed around veteran trees, for example on commons or wood pasture, in which the ancient trees are found;
• planted woodland (usually coniferous) where a commercial crop has been grown, the ancient trees being left at the time of planting.

The first of these three categories is the nearest to a wildwood but since British woodlands have been so actively managed in the past, all three situations potentially create problems for veteran trees. In the second and third categories especially, if the young trees start to grow over the top of the veteran, not enough light will reach the veteran tree. The natural ageing process and effects of any tree surgery are likely to reduce the crown of the veteran such that shading by younger trees has an even greater impact. Understorey bushes, such as holly or rhododendron, may compete with the veteran trees for water and nutrients (though in terms of competition for water, woodland may be less of a problem than grassland or bracken).

Removal of competing woody vegetation

As a consequence of these factors, on sites where previously open grown trees are now surrounded by others, some opening up may be necessary (releasing the trees). However, even this is not as straight forward as it might appear. The sudden exposure of a tree that has been shaded for many years can cause problems, for example:

• The leaves may be vulnerable to sun scorch.
• The tree itself may suffer increased transpiration rates and, with a root system that developed in a woodland situation, it becomes more susceptible to drought.
• Desiccation of the bark may stress the tree and cause cracking of hollow trunks through drying out in different places.
• General drying out of tree and increased exposure may be detrimental to the organisms associated with it, eg mosses and invertebrates.

These problems are inherent in any veteran tree canopy reduction but are considerably more pronounced when surrounding woodland is cleared away. The sudden opening up of old trees may also be more of a problem where conifers are involved because they cast dense year-round shade and create a cooler moister microclimate.

If you do need to open up around veteran trees, make sure that the species of interest associated with the site (and old trees) are known, and assess the impact that opening up of the woodland will have on them.

Some points to take account of are:

• Clear around the trees a year (or more) before doing any remedial cutting on the veteran trees (but be careful that the veteran tree is not exposed to greater winds).
• Clear round the trees in stages over a period of years. These stages may take five years or even ten. Be particularly careful if the veterans are in commercial forests in case all the surrounding trees are felled in one go.
• Consider clearing from the ‘outside’ in, ie: leave trees closest to the veterans until last.

Clearing conifers from around veteran trees

Birklands is a woodland within Sherwood Forest (Nottinghamshire) containing some 500 veteran oak trees. The woodland has been planted up with commercial pines since 1935. In recent years work has started to restore 50 ha to oak woodland. Clear - felling of the plantation pines has been carried out on half of this area and crown thinning of the conifers on the other. Seven years or more later the result indicated that more veteran trees survived in the crown thinned area than the clear-fell and some of them showed stronger crown regeneration than in the felled area. The clear- felling was considered to involve a greater risk of desiccation to the trees and the dead wood (Barwick 1996).

Similar conifer clearance work is being carried out atWindsor Forest (Berkshire) (Searle 1996), Castle Hill (Yorkshire), Croft Castle (Herefordshire) and Ethy Park (Cornwall). As at Birklands, the indications are that thinning of woodland surrounding the veterans is more successful than clear-felling (Figure 15).

Figure 15. Gradually opening up around a veteran oak surrounded by conifers, Ethy (Cornwall).

• Selectively fell, leaving some shade trees, especially if species such as birch, which cast a dappled shade, are present.
• Leave shade trees on the south (or most exposed) side.
• Pollard surrounding trees (if appropriate) to bring down the height of the surrounding canopy.
• Consider ring barking (or other equivalent methods) on surrounding trees to decrease the shade over a period. Note that some species take a long time to die when ring barked.
• Be careful not to expose the trees to other problems such as spray drift and air pollution.
• Avoid substantial clearance work in drought periods.
• When selecting which trees to fell and which to leave, remember that damaged ones (in terms of commercial silviculture) are more valuable for nature conservation.
• Fortunately, this means that the higher value trees commercially can be removed.
• Obtaining the correct balance of light and shade round old trees is a challenge.Achieving it will depend largely on the species of tree and site concerned.

Rhododendron and holly

These evergreen species can be detrimental to veteran trees when the bushes become large enough. Being shade tolerant they can grow very close to the trunk of the veteran and compete for water in dry years. They are also serious competitors for light when tall. As they cast a deep shade all year round, be careful that their sudden removal does not cause excess desiccation of the trunk.

Some additional points apply to veteran trees in commercial forests:

• According to the UK Forestry Standard (Forestry Authority 1998) individuals or groups of over mature, veteran or pollarded trees should be retained in both broadleaved and coniferous forests where it is reasonably safe to do so. Also, some (number unspecified) dead or dying trees should be retained in regeneration areas.
• The risk of pests damaging trees or timber when ancient broadleaf trees or dead wood is retained in commercial plantations is extremely small.
• Standard forestry practices carried out on commercial conifer crops in areas of ancient trees may have a detrimental impact on the saproxylic fauna. Under conifers there is a cool climate and restricted light levels. The nectar sources are reduced and dispersal may be inhibited.
• Selective felling should also aim to leave an uneven age structure of retained trees and some trees to form veterans of the future (especially in deciduous forests).

The management of land surrounding veteran pine trees in, for example, Scotland is not considered here.

Retaining trees within harvested forests to become veterans of the future

Ideally:

• Aim for 5 - 10 trees per hectare.
• Keep trees that will not be in the way or become hazards to the public in the future, will not become overtopped by crop trees and are close to areas with conservation interest, eg plentiful dead wood, glades.
• Encourage them to develop a full crown.
• Consider making pollards, if a full crown is not appropriate, but remember that they will need to be managed in the future.
• Select native, longer-lived species such as oak, ash and beech. Keep some others such as, willow, wild service and other fruit trees, which are valuable as nectar sources or have a distinct invertebrate fauna.

Bear in mind that the harvesting of the crop trees will have a large impact on retained trees, especially if the crop is coniferous.

Further reading: Alexander, Green & Key (1996), Barwick (1996), Crofts & Jefferson (1999), English Nature (1994), Forestry Authority (1998), Forestry Commission (1990), FWAG (1997), JNCC (undated), Key & Ball (1993), P. Kirby (1992), Lonsdale (1999), Sanderson (in prep.), Searle (1996), Wall (1996),Winter (1993).

Storm damage

Storm-damaged woodlands can contain large amounts of dead wood. In the short term this provides potentially good conditions for saproxylic species but over-zealous tidying up can result in a significant loss of dead wood habitat. A code for dealing with such woodland is given in English Nature (1994). After a storm event in a woodland, follow the guidance in section 5.4 together with the following additional points:

• Living but broken trees should be kept if possible. If necessary (ie in public areas) reduce any hazard without felling the tree completely. Try to retain a mixture of age groups.
• Trees where the crown has been blown off but the bole remains should be left if possible. Some species may regenerate and continue to live;others may not but will provide a valuable dead wood habitat while they decay. Reduce any potential hazards if necessary.
• Broken branches and stumps should be left and not sawn flush.
• Fallen mature timber should be left in situ as far as possible. Especially, try to retain pieces that are badly damaged or show signs of decay. If some has to be removed to a different position use the same criteria as in 5.4. Reduce pieces in size as little as possible and keep the branches as intact as possible.
• Leave some fallen trees with upturned root plates; these are beneficial for insects such as solitary bees and wasps.
• Do not leave the wood for some years and then come in to clear and destroy it; many organisms will be destroyed with it.
• Do not remove, treat or burn stumps.
• Leave the wood to regenerate naturally if possible. If planting is necessary then use a species composition appropriate to the area.
• Leave some of the open spaces/glades created by the storm.
• Attempting to stand up wind-thrown veteran trees is usually unlikely to succeed, though reducing the ‘sail area’ helps increase the chance of survival. Some species may continue growing horizontally, and some may naturally layer, in which case they should continue to be looked after as other veterans.

Management of dead wood

The management of dead wood is an important aspect of the management of ancient trees. While the survival of the trees themselves is not usually affected by what happens to their branches when on the ground, many of the organisms associated with veteran trees can be found in fallen dead wood. If all fallen branches and slightly decayed trees are removed from a woodland, it may be impoverished by the loss of more than 20% of its species.

All types of dead wood are valuable but some are more so than others, with each type (depending on its species, state of decay, size, etc) supporting its own assemblage of invertebrates. The decay rates of logs on the ground are very variable depending on the species and situation but as an example large oak logs in the USA are predicted to take over 170 years to disappear.

The conservation value of dead wood has received much greater attention in recent years but there is still plenty of room for improvement in terms of our management of it. The following principles of managing dead wood can be applied to almost any site, particularly woodlands.They are especially important on sites with large numbers of old trees and/or large numbers of saproxylic species.

Figure 16. Diagram of an ‘ideal’piece of dead wood.

Dead wood on the ground

• Size and shape. Size matters and the bigger the better! The more the internal temperature and humidity of the dead wood is buffered from drying out and very high temperatures the greater the number of organisms it will support. The smaller the piece of timber the higher the surface area to volume ratio is, which causes greater temperature fluctuation and desiccation.
  
  Large diameter branches and tree trunks should be cut up as little as possible, preferably not at all - they should certainly not be cut into rings as these dry out quickly and in public areas are subject to disturbance. A range of ‘natural’ sizes is useful. They also look more natural if they have broken rather than having sawn ends.
• Position. Ideally it should be left where it falls. If this is not possible, the ideal place to move it to is somewhere with dappled shade but:
• Some organisms prefer wood in open conditions, eg jewel beetles, solitary bees and wasps re-using beetle holes and dead wood lichens.
• Dead wood fallen into water should be left if possible. A different range of organisms live in it.
• Dead wood in a range of different conditions is ideal.
• Removal of wood. Do not remove dead wood as firewood. If you have to remove it do not leave it on site to mature first. Make sure that any felled/cut is removed before the end of April or left permanently. If it has to be left and stored on site cover it with a polythene sheet. This speeds up the seasoning process and prevents invertebrates from laying eggs in it.
• Habitat piles. Tying small diameter twigs into tight bundles that retain moisture better can increase the value of them. They may then attract some specialised species.

Shade can also be encouraged, eg brambles/bracken can be left when they grow up. Freshly fallen dead wood is best in more open conditions and more decayed wood is better in shade. If felling a tree with the intention of leaving it as dead wood it can be felled into an open situation if it is likely to be shaded in the future by regeneration.

If it is possible to leave dead wood on only part of the site, choose that part with the highest potential value for saproxylic species (ie with dead wood of good quality and quantity and with good nectar sources).

• When moving wood:
• Move as short a distance as possible.
• Keep wood as intact as possible.
• Move as soon after cutting/falling as possible.
• Move into partial shade/sun.
• Leave on the ground, not on top of other wood.
• Move near nectar sources (beneficial for many dead wood insects).
• Move adjacent to dead wood in a more advanced state of decay (to provide continuity of habitat).

Species of tree.

The wood from native species of tree especially those naturally occurring on the site is best. Introduced species can be valuable (eg sweet chestnut rots in a similar way to oak). Longer lived tree species tend to support a wider range of invertebrates. Broadleaves are more valuable than conifers except in Scotland (and perhaps a few other areas such as the Breckland).

Wood with decay.

Dead wood showing any sign of decay should always be left. It is more valuable for wood to decay from the inside out than from the outside in - decay derived from internal heartrot is likely to be far more valuable than that initiated from the bark or from the cut ends of sawn timber (Figure 17).

Figure 17. The base of a large beech tree, fallen apart and left to decay naturally, Windsor Forest (Berkshire

Burning is a major source of damage to dead wood. Bonfires to burn brash (small branches cut from trees), or timber, kill living organisms, damage the soil structure and can physically damage living trees if they are lit too close. However, some organisms live in burnt wood. If a bonfire has been lit, do not start the next one with the charred wood of the previous one.

Loose ‘habitat piles’ may be of value for vertebrates and a different range of invertebrates. Habitat piles made from larger diameter logs are better but the logs are always more valuable if on the ground (ie not on top of other logs). Piles of smaller logs are usually more valuable if lashed together or made into a ‘Waterhouse’log pile (see Figure 18).

• Root plates and stumps . Leave the root plates of fallen trees as they fell unless they constitute a safety hazard. They can be good for nesting bees, wasps and birds and the holes left in the ground provide valuable damp patches/pools.
• Leave tree stumps in the ground. Consider cutting high stumps if this does not interfere with other management techniques.
• Brash on grazed sites . The retention of brash on heavily grazed sites can have a useful function in protecting tree regeneration. Stock can be prevented from getting caught in the dead branches by arranging them in such a way as to block access.

Figure 18 The design of a 'Waterhouse' log pile

Standing and canopy dead wood.

Dead wood in the canopy of trees is different from that lying on the ground. Together with standing dead trees it forms an extremely valuable habitat (Figure 13). A variety of saproxylic species need timber to be still standing, either to maintain the moisture regime or aspect or because the ‘search images’ of the prospecting colonisers are geared only to habitats on standing trees.

Broadleaved trees when they have died standing lose their twigs first, then small branches and bark. They tend to lose larger branches from the top downwards. As they offer little wind resistance they often remain standing for a long time and may take decades to decay. They do need periodic checking for stability. If necessary remove the branches and leave the trunk standing (creating a ‘monolith’).

Fallen trees can also be fixed in a vertical position, by strapping to living trees, to perpetuate this habitat type. Small dead elms should also be retained if possible.

Creating standing dead wood by ring barking live trees

Ring barking is the removal of the bark and cambial layers all the way round a tree. This prevents the distribution of water and the products of photosynthesis and, over a period of time,kills the tree. It can happen accidentally, for example by grazing animals or grey squirrels, or intentionally. Ring barking can help create standing dead trees but they often decay from the outside, which is not quite as valuable as a natural decay column in the middle of a tree.

When considering ring barking a tree, make sure that it is not in a position where it will constitute a hazard in future years. The ring of bark removed needs to be both wide and deep to be effective.

Dead wood in living trees

The dead wood that is found in living trees is especially valuable for saproxylic organisms. The following guidelines should be followed in order to maximise the quantities of this rare habitat.

• Leave decayed wood inside hollow trees; be careful when carrying out remedial work.
• Leave dead limbs on trees.
• Be careful not to cut into cavities or damage them in any way.
• Leave dead bark.
• Keep commercially poor trees (they are usually the best for dead wood species).
• Try to retain trees that are due to be felled because they contain defects (they usually have interesting features), or at least retain the wood.
• Ensure that there is a continuous supply of dead wood on the site. Use short lived or fast growing species such as horse chestnut or birch to close up the generation gap if necessary and/or consider inducing rot in some trees.
• If branch removal is necessary, cut back only the weaker ends of the branches or cut part way through and knock them off to leave a natural shattered branch stub.

The quantity of dead wood

It is difficult to put a figure on the amount of dead wood required for saproxylic species. Broadly speaking the more the better and, ideally, all should be left. It has been estimated that one hectare of undisturbed woodland produces six tonnes of dead wood annually, equivalent to half the annual leaf fall, and that in the wildwood three to eight trees per hundred were standing dead.

A suggested aim is for over 40 m³ of dead wood over 5cm diameter per hectare and more than 50 standing dead trees, some over 40 cm in diameter. This is considered a good site by Kirby et al. (1998). Quality is better than quantity and the aim

should be for a good representation of all successive stages in decay on the site.

There are various methods of estimating the amount of dead wood, both standing and fallen. That most widely used is outlined in Kirby et al. (1998). A simpler method is being developed by the Woodland Trust.

Summary of how to manage surrounding land for veteran trees

The key to managing the land around veteran trees is to remember that anything that is carried out to the land will also affect the trees. Aim for as little disturbance and input of substances as possible, especially close to the trees themselves. Extensive grazing is compatible with veteran tree management but intensive grazing and cultivation are not. Try to avoid any sudden changes of regime especially where these greatly alter light levels or affect the root systems. Wherever possible reduce chemicals or additives used on the land or livestock. Finally, avoid physical damage to the tree (especially the roots) either intentional or accidental.

Further reading: Alexander, Green & Key (1996),English Nature (1994), Ferris-Kaan et al. (1993), Fry & Lonsdale (1991), Fuller (1995), Green (1996c, 1997), Harding et al. (1988), Hodge & Peterken (1998), Key & Ball (1993), Kirby (1992), MacMillan (1988), Peterken (1996), Speight (1989), Spencer & Feest (1994), Watkins (1990),Winter (1993).

Managing Veteran Trees of landscape and cultural interest

The land surrounding veteran trees may be very important for their survival, and appropriate management can enhance the conservation value of the tree or the site. The situation of the tree is also important for its contribution to the landscape itself.

Veteran trees in the wider landscape

Introduction

The over-riding importance of veteran trees in landscape terms lies in the trees themselves. While replacement is no substitute for the conservation of the veterans, detailed survey and careful re-planting programmes are needed to perpetuate their pattern within the landscape. The choice of species, source of stock, siting, planting and subsequent management are all vital, in order to provide continuity.

In different parts of Britain the ‘Countryside’ has a very different feel to it and the ancient trees often reflect this. For example, the flat landscape of the Vale of Aylesbury with its black poplars is very different from the undulating Lake District with field boundary pollards (Figure 19). This in turn has a very different character from the wooded nature of the Chilterns. It is important that this local distinctiveness is maintained and that cutting practices in terms of tree types and shapes continue the local traditions as far as possible.

Figure 19 . A landscape with veteran trees,Watenlath,Lake District.

Following the devastation of the elm population through Dutch elm disease many of the large trees remaining within hedgerows or along the edges of fields and roads are oak or ash trees as maidens or pollards.These are now especially vulnerable because of management for safety reasons along highways. Recent emphasis on planting and managing hedges should take into account the importance of leaving some trees to grow on. In the meantime, existing old trees need to be treated sympathetically to ensure their survival and that of the general aspect of the area they are found in.

Certain older landscape features also have historical associations with trees, many of which are now veterans, for example earth banks delimiting areas of former ownership or management. It is equally important that these features are retained and managed.

The management of veteran trees (and future veterans) in the landscape

Studying the characteristics of veteran trees in the local area can be valuable in perpetuating the character of the landscape. The following are some ideas to consider:

• Pollard (especially young trees) if there is a history of pollarding on the site or in the local area. If there is no historical reason for pollarding check that the historical value of the site is not compromised by doing so.
• Cuts on trees. In an area where trees were actively managed, flat and even cuts can look quite in keeping. If the overall atmosphere is to ‘look natural’ flat cuts can be quite intrusive. In this case try methods such as pulling or winching to make more natural looking breaks or roughen up the cuts after they have been made. This can be done simply by making coronet cuts, or V shapes, with a chainsaw in the cut surface (Figure 20).

Figure 20. ‘Coronet’cuts on a veteran oak tree, Ashtead Common (Surrey).

Be careful when planting new trees or encouraging regeneration. Make sure that they are in the most appropriate position, for example don t destroy vistas and do not create competition for existing veterans.

When replacing trees (either by natural regeneration or planting) try to use the same species of local provenance and, if possible, trees that have very similar characteristics. Species that have been lost from the site can also be used. The planting of exotic species, for other than timber production, is not necessarily a problem for nature conservation and may be desirable from the landscape point of view - to maintain traditional or planned planting patterns. Exotics should usually remain in the minority on sites with high nature conservation interests.

Veteran trees on ancient monuments

Where veteran trees are sited on an ancient monument their management must be carefully considered (Figure 21). While it is likely that disturbance by the trees root structure has already occurred, further physical damage to the monument through collapse of the upper parts of the tree or lifting of the root plate (and underlying archaeological features) continues to be a potential threat.

In these cases it is important to limit the damage that may occur to the monument. Regular inspection is necessary and, where possible,reduction of the height/weight of the tree. If it is of suitable shape, encouragement of growth lower down, prior to cutting, may help to keep the tree alive without damaging the monument.

An additional factor to be considered in the management of veteran trees on ancient monuments is the depth and structure of the substrate. On ancient monuments this is frequently compacted, encouraging a shallower rooting pattern than is encountered elsewhere in the area.

Advice can be sought from the inspector of the appropriate heritage authority. If works are likely to affect an ancient monument, Schedule Monument consent may be necessary.

Figure 21. Veteran tree on an ancient monument, at Hailes Abbey.

Veteran trees in designed landscapes

When considering the future management of historic parks or gardens the starting principle should be to conserve, and where necessary repair, the surviving historic fabric. Veteran trees are as much a part of that historic fabric as the structures - from the main house or hunting lodge, to the park wall or park pale - which lie within the park. They should be valued equally as individual features and for their contribution to the wider parkland landscape. In general there should be a strong presumption in favour of keeping them and ensuring their future survival.

For those sites with public access, matters of health and safety can arise and must be given serious consideration. Similarly, in more formal areas such as gardens, half dead trees and fallen timber might detract from the design or be viewed as evidence of neglect by the visiting public. In these cases a balance should be struck and where removal is considered necessary the timber should be re-located to a less formal area for creation of a habitat. Better still, in some situations this problem can be solved through education and explanation.

At a limited number of sites, the veteran trees will themselves form the basis of an overall landscape design. Usually this happens where the trees have been planted, or incorporated, as part of a late 17th or early 18th century layout that has not undergone the more usual reworking as a result of changing fashions. At such sites there might well be a debate about how to best manage the landscape for the benefit of present and, more particularly, future generations. This becomes more pertinent as the design loses its integrity and becomes gappy.

For example, avenues planted on new lines may result in the loss of much of the historic interest. Felling sections causes a temporary loss of historic fabric, as well as natural habitat, but provides continuity of historic design and new generations of trees.

As the above suggests, good management of veteran trees within a designed landscape needs to be considered in detail in order to maximise understanding and appreciation. Using site-based and documentary research, a comprehensive site plan can be drawn up against which the value of the landscape as a whole, and its individual parts (including veteran trees) can be assessed. Only by working through such a process can an informed decision be made about priorities for protecting veteran trees, the historic interest and valuable habitats.

Further Reading: English Heritage (1998),Phibbs (1991),Rackham (1986, 1988, 1989, 1990).

Veteran trees in a modern world

Veteran trees are often features in their own right, for example outside houses,pubs (Figure 33) or churches, on village greens and in prominent places. When managing trees in these situations the views of local residents and visitors must be considered. These types of tree are often unlikely to be felled because many people appreciate them. They are, however, vulnerable to concerns about their safety.

Veteran trees also occur in urban or suburban surroundings. It is unusual to find populations of ancient trees in such places (though they do occur) but individuals can be found in the most unusual situations. Sometimes it seems as if the threats are so great and the space the tree is in so confined that encouraging the attributes of old trees in such places is a foolhardy occupation. However, one of the chief management techniques used on old trees is quite applicable to urban situations and can help create veterans of the future: pollarding.

Some street trees such as plane, lime and sycamore respond very well to pollarding or heavy pruning. Although urban trees may be pollarded, this is not done for the same reasons as trees in rural settings. The aim is to keep the tree to a manageable size and any technique that achieves this can be used. In addition, regularly cut, responsive trees develop unusual appearances, which can add character to the neighbourhood (seen more regularly, for example, in France than Britain). If the work is done for practical or aesthetic reasons the result can be a tree with ancient features. There is no reason why characterful trees should not be found on city streets as well as in the countryside. Although street trees have been understudied in this respect, they may still offer valuable sites to wildlife.

An urban habitat can be a hostile environment for veteran trees, which can suffer from:

• excessive safety work, trimming and ‘tidiness’;
• severing of roots caused by the digging of trenches for cables etc. Excavation work should not be carried out within a separation distance, extending away from the tree for 15 times the diameter of the trunk at breast height (ie 30 m for a tree of diameter 2 m). This should be regarded as a minimum;
• run off from roads polluted with salt and trace elements from worn tyres;
• tarmac, concrete or other unnatural substances right up to the trunk of the tree causing drought conditions;
• excessive compaction round the roots;
• vandalism and damage;
• high nutrient levels from dog excreta.

It is important to realise that pollarding trees in this, as in any setting, needs to be done carefully by tree surgeons who show proven experience of working with veteran trees. Lopping the top off a tree that is too big for its setting is not the same as planned and careful pollarding. Poorly cut trees may be regarded as eyesores, incur the wrath of local residents and at worst be felled. In towns the future management of the trees is particularly important. Pollarding a tree once is not an appropriate method of dealing with it.

A freshly made pollard needs to be cut at fairly frequent intervals (which can be as short as one to two years for street trees) so that the branches do not grow too big. If a gap in the cutting regime occurs, the task of dealing with the tree becomes substantially more difficult in the future. Today there are lapsed pollards on the streets of our towns that are in need of attention but are more likely to be felled and replaced. Pollarding some of these old trees might still be worth trying, otherwise the numbers of old plane trees, for example, will decrease dramatically in forthcoming years.

With planes and limes there is plenty of scope to create artistic ‘patterns’ through pollarding by cutting at higher points than previous cuts. Aesthetic proportions have even been suggested using ‘golden mean proportions’ where the stem of the tree should comprise 62% of the total height and the branches 38%. These dimensions produce an outline that is thought to be pleasing to the eye (Figure 22).

Figure 22 An illustration of 'golden mean proportions'

Further reading: Coder (1996), Mayhew (1993).

Educational opportunities

Veteran trees provide ideal educational opportunities for people to learn about their local environment and traditions. Collecting seeds and growing them on to plant out is a good starting point and enables local communities to ‘connect’ with their local ancient trees; this is the main focus of the Trees of Time and Place campaign. Activities promoted by organisations such as Common Ground also help to provide a focus and structure for such work and distributing information.

Making children aware of the importance of trees, especially veterans, is a great investment for the future but adults should not be forgotten. The use of voluntary parish tree wardens helps to involve people and inform them about the importance of ancient trees and promotes tree recording as a contribution to the knowledge of trees in Britain.

Management of Veteran Trees for other organisms

Introduction

One of the reasons that veteran trees are so important is because of the range of other organisms that live on them or are associated with them. Indeed, many sites with populations of veteran trees have one or more statutory nature conservation designations for the species they support. For this reason it is essential to manage with other organisms in mind, not just the trees themselves.

Many of these other species are important to the survival of the trees too, so they should be viewed as an integral part of the system. A number of the species associated with veteran trees are protected in their own right, via the Wildlife & Countryside Act, and many are listed in the Red Data Books or in the UK Biodiversity Action Plan and are therefore considered vulnerable or threatened.

Ideally, the site or tree should be surveyed to find out which species are present and management can then be targeted. In reality detailed surveys are rarely achieved in the short term, but try to involve various experts early on if possible.

Indices of Ecological Continuity have been drawn up for lichens and beetles based on the species that are more or less confined to old pasture-woodland and pollards. Similar indices may be developed for some other groups of organisms, but may not be possible for others, such as mosses, as there are too few species that can be used.

Managing for a range of organisms

Despite the variety of groups that species associated with veteran trees belong to, many benefit from very similar management practices. These practices are beneficial to the veteran trees themselves too and should be considered together with chapters 4 (management of the veteran tree) and 5 (land surrounding the veteran tree).

Management of the tree itself (Figure 23)

The majority of species will benefit from the following:

• Try to keep individual trees alive for as long as possible; live trees continually produce dead wood as well as leaves, and branches.
• Do the minimum amount of surgery necessary on a tree.
• Ensure that there is plenty of standing dead wood (including whole dead trees) and dead branches on old trees. Try not to remove the lower branches of trees, eg to allow vehicular access. If they are dying, due to shading from above, they might be used by some specialist insects.
• Never cut into cavities or holes, or drain them. To avoid this, test the depth of the cavity by using, eg a piece of flexible hose, inserted into the hole, and ensure that any cutting necessary does not go into it.
• Try to avoid damage to the lower parts of the tree trunk, including damage by grazing animals (rubbing or chewing etc). As well as harming the tree itself, such damage may be detrimental to other wildlife, for this is where lichens grow and there may also be cavities at ground level, which can be good for invertebrates.
• Don’t tidy up (ie flush cut) rough ends to branches,the broken ends form egg-laying niches.
• Leave any dead wood in the canopy.
• Don’t treat stumps or cut/damaged branches with sealant,fungicide or insecticide.
• Do not remove fungal fruiting bodies; it can be harmful for the fungus and also for any organisms living in it.
• Do not plough close to veteran trees,this damages the mycorrhizal fungi as well as the tree.

Figure 23. An ‘ideal’ veteran tree for wildlife.

Land surrounding a veteran tree (Figure 24)

• Ensure that there are plenty of holes, cracks and crevices, in other trees in the surrounding area eg for bats, birds and invertebrates.
• Leave abundant dead wood on the ground in a variety of sizes, shapes, positions and states of decay. Leave fallen dead trees as intact as possible.
• Poor or damaged trees are often those removed by foresters. Try to retain them if possible; they are often the best wildlife trees.
• Avoid using chemicals (herbicides, insecticides or fungicides) on the surrounding land (or the tree), keep the use of veterinary chemicals, especially wormers, on livestock to a minimum.
• If fertilisers have to be used, farmyard manure or pelleted versions are best. They should be applied on still days and kept at least 15 times the diameter of the trunk at breast height away from the trees and not allowed to splash onto the trunks.
• Encourage natural regeneration to ensure long-term continuity of trees. Try to encourage native trees and shrubs with a good population and age structure. This provides continuity of trees and suitable habitats for mycorrhizal fungi that require different age classes of each species of tree. The regeneration and planting of conspecific saplings near isolated veterans is important for this reason. On parkland sites with good lichen floras some younger exotic trees are worth encouraging if veteran specimens of the same species occur.
• If dead wood is in short supply, or will be in the future,(ie there is a generation gap) consider artificially creating suitable cavities and decay in younger trees .
• If there is no new generation of the same species of tree consider using other, more quickly growing, species to try to help close the gap as well as planting conspecifics.

Birch is quick growing and can provide the conditions required for some species, Sweet chestnut may provide a suitable alternative to oak. Horse chestnut may have good sap runs.

• Create and maintain glades and rides.
• Ensure that there is continuity of linear landscape features such as lines of veteran trees and hedgerows. Bats and some invertebrates use such features as flight paths. (A gap of as little as 10 m in a line of trees can be enough to dissuade some bat species from flying along it as they travel between their roosts and their feeding areas.)
• Encourage flowers as nectar sources for invertebrates, eg hawthorn, composites, umbellifers and flowering ivy. A healthy invertebrate population will also support a healthy bat and bird population.
• Create and/or maintain associated habitats such as ponds and wetlands.

Figure 24. An 'ideal' veteran tree site for wildlife

Creating cavities and decay in younger trees

If there is a lack of holes, crevices and decay it may be desirable to initiate some. This can be done in a variety of ways that are all best tried on younger trees, rather than veterans. Different groups of organisms have different requirements:

• Bats prefer deep narrow crevices.
• Birds mostly prefer holes rather than crevices,a variety of sizes will suit a range of species.
• Invertebrates use an almost infinite variety of decay, holes, crevices, etc. Consider drilling holes of various sizes into trees as well as making larger holes with saws or breaking off branches.
  

There is considerable scope for creating holes and initiating decay in trees (Figure 25). Customised ‘boxes’ can be made or more general cavities; experiment with what you have available.

Figure 25. Suggestions for the design of artificial cavities.

Bat and bird boxes can be made or purchased. They should only be necessary if hollow trees are exceptionally sparce or specific boxes are needed for particular species, eg spotted fly-catcher or tawny owl. Nest boxes should be viewed as a ‘stop gap’ until suitable, natural, places are available. Take care when putting up boxes that you do not put them on part of a tree next to that used by rare invertebrates; the bats or birds may make a meal out of the threatened species.

In addition to the general requirements listed above, most groups have some very specific needs, which are dealt with below.

Epiphytes

Introduction

Various species of epiphytic plants are associated with old trees. The groups of greatest interest in this habitat are the mosses, liverworts and lichens but some vascular plants, such as ferns, can be epiphytic too. Among the bryophytes there is considerable regional variation in the numbers of rare and total species found. Epiphytic mosses and lichens can mostly be found throughout the year and are relatively easy to record and monitor although they require specialist identification skills.

Characteristics of moss growth on veteran trees

• In more highly polluted areas epiphytic mosses are found more on old trees than on young trees. They occur mostly low down on the trees and in sheltered positions (where they may be more susceptible to agricultural contamination).
• Veteran trees (and pollards) provide a variety of microhabitats, eg rain tracks, crevices, bark sheltered by protruding parts of the tree and exposed roots, where different species are able to survive.
• The underside of horizontal branches and leaning trees keeps the plants dry and provides shelter from acid rain. Horizontal branches also have higher nitrogen inputs (eg as bird droppings) on the top and are good for certain species. Rot holes are good too when the rainwater persists and leaves accumulate. Mosses at the lip of the hole act as a wick so that it empties very slowly creating a rain track down the trunk for several days. A cavity with a small hole lower down may allow water to run out slowly for several weeks. Trees with such features are rare and support rare bryophytes.
• Oak, ash, field maple and beech are the most important old trees for mosses, followed by hornbeam, sycamore, and hawthorn. Elm is also very good but few veteran elms survive except in the Scottish Highlands and Islands.
• Grazed wood-pasture allows light to the boles of the trees but the humidity is still relatively high. Dense woodland is often not so good for mosses despite the increased humidity that is liked by some species.
• Older trees have also had more time than younger trees for bryophyte growth to accumulate.

The characteristics of lichen growth on veteran trees

Two distinct lichen floras are associated with veteran trees. These are: old growth woodland species and those thriving in more open, drier, parkland type situations. Lichens are more sensitive to undergrazing and less to overgrazing than most groups of organisms.

Lichens and pollution

Lichens are very susceptible to sulphur dioxide and nitrous oxides and the location of the tree in relation to major sources of these substances is very important. Trees close to pollution sources tend to be species poor. Those in deep valleys are often better as the air passes over the top without penetrating (except when local pollution is trapped in a temperature inversion forming ‘valley smog’).

The tops of hills tend to be more polluted. The reduced levels of sulphur dioxide in southern England has enabled some of the more mobile species of lichen to recolonise but others, especially those typical of veteran trees, have very poor dispersal mechanisms.

The lichens of old growth woodland and veteran trees

• Rich woodland lichen floras depend on old growth woodland (ie stands older than 200 years) with veteran trees.
• Communities rich in important species take many years to colonise.
• The ideal conditions for woodland lichens are those with adequate light and shelter from drying winds.
• Ideal sites are those with a mosaic of dense and open areas; different species of lichen have different tolerances to exposure and light levels.
• Woodland lichens are adapted to low nitrogen levels so high nitrogen (ammonia) pollution from intensive farming is a serious threat.
• Slow growing species are found on virtually all types of bark, including acid bark but base rich bark is usually the richest habitat. Exotic tree species are rarely as valuable as natives, especially acid barked trees.
• Exposed heartwood areas may have special and rare floras.
• Ancient coppices are rarely good for lichens as they are more like young growth woodlands.
• In areas with a few old growth woods, local rarities can occur on occasional old trees within young growth woodland.
• Large populations of veteran trees are required for rich lichen floras to develop, as many species have very narrow and rare niches even in near-natural woods.
• REMOVE A WEDGE FROM.THE TOP OF THE STUMP
• A distance of as little as 2.5km can prevent many species recolonising.
• Recovery time from clear-felling for most lichen communities is 200 - 300 years if there is nearby old growth. Communities of dry craggy oak bark take over 400 years.

Lichens of wayside and parkland veteran trees

• These communities are best developed on full lit trees with moderate enrichment from dung or dust. Well developed communities are absent from extensively grazed wood-pasture as the grazing levels are not high enough. Hence these communities are largely associated with human activity in Britain.
• The rarer species include slow growing ones and southern species at the edge of their range. Post mature and veteran trees are the richest.
• Unimproved grassland is the ideal habitat surrounding the veteran trees for these types of lichens.
• Base rich and mesic bark are the main habitats of interest but, unlike woodland lichen communities, acid bark is rarely of any interest. Exotic base rich barked trees such as Norway maple (a good elm substitute), walnut and tulip tree can be important. Sycamore can be rich but is not nearly as good as Norway maple. A few local specialists can occasionally be found on conifers.
• Landscape parks are now a major resource for this type of lichen flora but it was once common in agricultural areas with frequent old trees. The lichen communities have declined at least as much as those of the unimproved neutral grassland.

Management recommendations

The ideal management for lichens depends on the type of community present. Old growth woodland communities require light grazing and a mosaic of habitat structure. Parkland communities need more open conditions and can benefit from some exotic tree species being present.

Mosses and liverworts

• Don't drain or divert existing streams or damp hollows away from old trees as they may contribute to the overall humidity of the area (unless failing drainage threatens the tree.
• Do not block past drainage ditches in an attempt to increase humidity; if long established water levels are raised this can kill veteran trees.

Woodland lichens (Figure 26)

• Maintenance of old growth woodland containing veteran trees is crucial . Management of woodlands for commercial forestry is not very compatible with the conservation of woodland lichens. Traditional management such as grazing and pollarding can be compatible.
• Light grazing is beneficial in preventing uniformly shaded conditions. Deer alone may achieve this but the reintroduction of other grazers may be necessary. Where grazing has either ceased or declined dense shrub layers of, for example, holly or rhododendron can cause problems. Holly may be pollarded as it supports rare lichen species when not too shaded.This has been done in the New Forest as it also creates enough light to benefit lichens on old trees nearby. In addition, it perpetuates historic management on the site.
• Ivy, and other evergreens such as holly, can cause problems. Especially in ungrazed woods they can smother epiphytic growth. Ivy in the early stages of colonisation should be prevented from establishing on trees with high epiphytic value but old plants should be left. Ivy is beneficial to other forms of wildlife as it is a useful nectar source and provides cover. However, consideration might be given to its removal from trees in sites of high value for epiphytic plants, but low value for other groups of wildlife. Browsing of ivy on the lower trunks of the trees is the best and most natural method of ivy control.
• Be careful of suddenly opening up around relic lichen floras as lichens are very sensitive to light and humidity levels. Thus, clear small areas at a time and work on small groups of veteran trees at any one time to minimise local climate change. Also, the subsequent growth of the undergrowth (eg bramble) and tree seedlings in these areas may shade out lichens on trunks unless grazing levels are sufficiently high.
• Do not fell large,post mature exotic trees without checking for rare lichen species first.
• Some lichen rich communities are found on rocks (especially in upland areas) so these should be left if on site. (Other habitats can also support rich lichen communities e.g. the park pale or fence.)

Figure 26. Site characteristics and management for old growth lichens.

Wayside and parkland lichens

• The maintenance of low intensity farming is the most important factor in conserving these lichen floras. In relict sites that are intensively farmed, ideally low intensity farming on permanent pasture should be restored.
• The application of farmyard manure or pelleted fertiliser is acceptable as long as it is not plastered on to the trees.
• Exotic trees with a base rich bark can be important and are much more acceptable in this habitat than in native woodland. Norway maple and walnut are especially good. New tree plantings should include all existing species of value on a site.
• When planting new trees, plant close enough to the existing veteran to maximise colonisation but not so close as to shade them out. As an example, plant three or four trees of the same species, or the same potential lichen flora as the veteran, in a semi-circle round the existing old one, avoiding the south side. A good guideline distance is 15m.
• Parkland lichen floras are often able to respond relatively quickly if individual plants, showing signs of regression due to reduced light, are opened up sympathetically by trimming the canopy of the veteran tree or cutting surrounding trees.