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This article questions some of the basic principles of arboriculture, tree care and cultivation. It considers pruning, questioning its benefit and the impact it might have on a tree’s physiology and ecology. It also raises some questions about the long term impact of pruning and the need to appreciate the natural life span of trees. However, this article makes no attempt to provide any answers, because the point is we should be questioning our actions, and the motives behind them, constantly striving to care for trees in the true spirit of Arboriculture. Arbor - Arboriculture Arborist - Arboriculturalist or Arboriculturist Arbor – from the Latin for Tree Arboriculture – is interpreted as the cultivation of trees, hence Cultur-al – Cultural-ist or Cultur-ist Arboriculturalist or Arboriculturist - is a person who cultivates trees. Improve, develop, cherish, to care for, are all terms used by the Oxford English Dictionary, to describe Cultivate or Cultivation. This leads us to the current understanding of the words Arboriculturalist or Arboriculturist, as someone who cherishes and cares for trees Arboriculturalist or Arboriculturist which ever you prefer to use, they are words that will always be a mouthful at the best of times, so an abbreviated Arborist, is often used and has been commonly adopted. Arborecology – combines Arboriculture with Ecology in a holistic approach to tree care with consideration to the arboreal ecosystems that trees support and within which they grow. Considering Pruning: The first question, when considering pruning, is whether cutting off and removing living branches will actually benefit the tree? Will the proposed pruning prolong the tree’s useful life expectancy within the context of the surrounding environment and land use? It is important to remember that pruning can quite easily do more harm than good, and in some situations may create more problems than it solves. In fact, does the tree ‘need’ to be pruned at all? Every cut made has the potential to change the growth characteristics of the tree. Removing living foliage, by pruning, affects the trees physiology and future productivity. The reduction in leaf area that results from pruning will reduce the tree’s overall photosynthetic capacity, which is likely to affect sustainable growth on the pruned section, or the entire tree. Pruning can therefore have a lasting impact on the viability of the tree and can directly influence its longevity. One of the major limitations of crown pruning is that it has a very one-sided impact on tree physiology. Before pruning the tree will be maintaining a natural equilibrium of growth, throughout the crown of leaves and branches, in balance below ground within a broad spreading system of roots, with their associated mycorrhiza. Raw materials are absorbed from the soil, moved up through the transport system within the trunk and branches to the leaves, where energy is produced through photosynthesis. By removing leaves and branches from the crown the arborist disrupts the balance, forcing the tree into a state of turmoil. The casual observer, of the growth that appears after pruning, could be mistaken for thinking that cutting off branches and reducing the tree’s leaf area is beneficial and encourages new vigour. This may indeed appear to be the case, but it is essential to remember that severely pruned trees will initiate the production and growth of ‘water-sprouts’ or ‘sap-risers’, as a response to the need for new foliage to readdress the balance of photosynthetic capacity and energy requirements. To sustain this flush of growth the tree must draw on stored energy reserves, which limit the resources available to resist infection, disease and decay. For arborists, charged with the responsibility of tree care, the primary pruning considerations are those that affect the tree’s physiological condition, its ability to compete with pathogens and its durability within a wider ecological context. Pruning influences the trees physiological productivity: its ability to resist pathogens, its successful reproduction and its efficient use of natural resources. So, how often does the advice provided by arborists benefit the tree? Except during the nine months before he draws his first breath, no man manages his affairs as well as a tree does - George Bernard Shaw - This photograph of trees growing through the ruins of an old house, illustrates that ultimately nature will have the last word. This impressive ancient oak pollard, is growing in a rear garden of a residential property in West Wickham, Kent. The tree is thought to be in the region of 600-700 years old. Residential houses now surround the tree, which has been swallowed by the urban sprawl of London’s 1930’s suburban development. The houses either side have been given planning permission by the local authority to build extensions, which have placed more pressure on the tree and the responsibilities of its owners. The neighbours now complain about the tree, which blocks light from their gardens and bedroom windows. Looking beyond tree care: In most cases the real motivations behind tree pruning are associated with the human values of visual aesthetics, amenity and recreation. This may, in part at least, be due to our need to see trees as being worth something, to have some purpose or function, which we as humans can use. Whilst the management of trees using pruning practices such as pollarding have enhanced their longevity, these techniques are now less frequently used as the need for the associated resource has reduced. These trees may now be seen to have some historic significance, but their true value is in their importance as an ecological resource of co-evolutionary organisms. The primary considerations of pruning specifications are all associated with the impact pruning will have on the tree, but if tree care is the drive behind pruning, how does the tree actually benefit? The answer is more often that the tree does not benefit, with the exception perhaps of formative pruning during the establishment stages, which may improve the structural form and stability of a tree’s trunk and branch growth. However, even this is a human interpretation of ‘good’ structural form. Pruning must therefore be considered within the context of understanding tree physiology over time, while taking into consideration the ecological impacts. The point is that although the instigation behind tree pruning is associated and inextricably linked with human values, the implications have a direct impact on the physiology of the tree and the ecological balance within its environment. The arborist must, as a person responsible for tree care, work with a knowledge, understanding and respect for the arboreal ecosystem and not just the tree which happens to be the subject of the pruning specifications. This is arborecology. Arborecology incorporates an appreciation of the ecological value of trees and an acknowledgement that they might have some intrinsic value, because they support a diverse arboreal ecosystem, which is an essential part of the natural world to which we all belong. Informed management decisions can enhance their longevity with sympathetic pruning, but sometimes to maintain a sustainable ecological habitat within populations of trees it becomes necessary to consider destructive techniques to encourage the process of decay. A thing is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends otherwise. - Aldo Leopold - ‘Land Ethic’ 1949 A life time to understand: Trees are one of the few organisms which have an average life expectancy that exceeds our own (human) ‘three score years and ten’, yet we offer them very little respect for this achievement. In fact, trees figure so low on the day to day agenda of modern life that the average person will rarely stop to consider their value. However, when someone actually pauses to think of the contribution trees make to their lives as an individual, or as a member of society, the list can appear endless. There is a growing recognition that trees have a part to play, from the calming influence they have on our everyday lives to their ability to sequester carbon- dioxide, which could influence the sustainability of human survival on the planet. Many of these beneficial attributes are linked to the slow progression of tree growth over their long life spans, which can frequently be measured in centuries. However, many trees are deprived of the opportunity to live out their natural lives, because of a human ignorance that inflicts its will on the world with an arrogance that fails to recognise that everything is intrinsically connected. The technological advancement of human society has created populations of people who have lost track of their cultural connection with an area or community, to the extent that they shuffle around their country and sometimes the world, moving from place to place. Is it any surprise then, that the new owner of a suburban residence has no qualms with felling an oak tree, which may have been planted over 100 years ago during an era he/she feels no connection with? The person who fells the 100 year old oak, fails to appreciate its value and considers that his/her rights, to live in a place without trees, are greater than the accumulative values and benefits of the one oak. However, the same person may only live in the property for no more than a decade, less than a tenth of the trees age. Which of the two has, earned or deserves the greatest right to life? Generations pass while some trees stand, and old families last not three oaks - Sir Thomas Brown - Lingfield Oak The engraving on the south face of the structure under this grand old oak tree, reads; “This cross was built circa 1473 to designate the boundaries of Puttenden and Billeshurst Manor. The Cage for the detention of petty offenders added in 1773 was last used in 1882 to detain poachers.” Was the tree used to mark the boundary before the cross was built? Was it used as a hanging tree? Royal & Sussex Oak These two pictures need no words to explain them, simply to say; where would you rather spend a sunny summers afternoon? Learning the Compromise: In this over populated modern world there have to be compromises to maintain some degree of harmony, and if we are to life in association with trees the compromise is pruning. There is rarely space in our crowded towns, cities and even villages, for the mature size of trees. Some form of pruning has to be considered to readdress the balance, but just because they are perceived to be growing in the ‘wrong’ place, does that mean they have lost their value? A tree may be deemed to require pruning because it is considered to be ‘too big’, a ‘hazard’ or simply growing in a location where it is at odds, or out of context, with the surrounding land use. However, there is no reason to ignore its potential life expectancy, and the ecological values associated with it. Pruning work must be completed with an understanding of the physiological limitations that impact on the tree’s ability to react to the loss of living foliage. Pruning is all about compromise! The reactive capacity of a tree will be compromised to some degree, depending on the pruning techniques employed, and the volume of living wood and foliage which is removed at any one time. When making pruning decisions the arborist must consider the chronological age of the tree, because a tree in its formative years may be able to tolerate the loss of a large limb, but the same tree in full to late maturity might suffer terminally when inflicted similar treatment. An arborist who is responsible for large populations of trees, such as those owned and managed by local authorities or large parks and gardens, must guard against the use of generic pruning specifications which do not take the trees chronological age into consideration. It is also essential that the same arborists keep records of these tree populations, and how they have been managed. This will ensure continuity in the way in which trees are cared for. Generations pass while some trees stand, and old families last not three oaks. - Sir Thomas Brown - The natural balance of tree ecology: It is well established now, through the work of mycological researchers like Lonsdale, Schwarze, Boddy and Raynor that many plant pathogens co-exist for extended periods of time, in harmony with their host. Although the full significance of this has yet to be interpreted from the observational research completed to date. The concept that the organisms we consider to be pathogens (and therefore ‘bad’) offer a positive contribution to the arboreal ecosystem, does not require a ‘leap of faith’ or great foresight. However, it is equally important that we do not jump to conclusions. Thoughtless pruning can interfere with and interrupt the natural balance between symbiotic and parasitic relationships within the tree and associated arboreal ecosystems. The physiological, pathological and ecological impacts of pruning work will not be immediately apparent, because the tree and its associated ecosystem will react through adaptations which occurs over a period of years. Arborists must consider this when assessing a tree by maintaining a cautious approach that is not distracted by the presence or absence of familiar and eye catching fungal fruiting bodies. A greater understanding and appreciation of the long life processes of trees is essential. An arborist responsible for the care of just one tree, can only hope to have an influence for a fraction of its potential life span. However the pruning decisions that the arborist makes, can have a direct impact on the tree and its sustainable life expectancy. A decision made today could have consequences that are experienced decades and possibly centuries in the future. Trees, as long lived organisms, are slow to react to changes in their environment. Our increasingly fast pace of life means that we can inflict change on our surroundings in quick succession. A tree, which may fall victim to this, will suffer stresses that could culminate in premature death after being forced into a spiral of decline. If we represent knowledge as a tree, we know that things that are divided are yet connected. We know that to observe the divisions and ignore the connections is to destroy the tree.” - Wendell Berry - View full article

Fungi are fundamental to the success and health of almost every ecosystem on earth, both terrestrial and aquatic, and essential to the sustainability of biodiversity. In this article Andrew Cowan asks how often do we consider their existence within an ecosystem, let alone how conditions could be improved by active encouragement and management of habitats to enhance fungal diversity? Fungi are perhaps the most unappreciated, under valued and unexplained organisms on earth. When you ask someone to describe a fungus, you will get a variety of descriptions ranging from, mouldy bread and mildew on the bathroom wall, to magic-mushrooms and poisonous toadstools. Some enlightened individuals will tell you that fungi are essential for things like bread making, brewing and medicines. However, these are only some of the more visible supporting roles that fungi play. Rarely considered, even in general scientific circles, is that there are many times more fungi than plants on earth, and that each type plays a crucial role in the processes supporting the functioning of major ecosystems. So much so that it could be argued that we live in a world dominated by fungi and that humans only think they are the superior species on earth. Fungi are present almost everywhere, in a spectacular array of shapes, sizes and colours, and performing a wide variety of different activities. In 1991 David Hawksworth, a mycologist at Kew estimated the world’s fungal diversity at 1.5 million species (equal to the estimated number of all known other living organisms). This was thought at the time to be a radical over estimate, but now other researchers have proposed figures in excess of 13 million. This multitude of different species perform essential roles in every terrestrial, and many aquatic, ecosystems; eg. decomposing dead organic matter to release nutrients, supporting plant life on poor soils by improving the absorption of nutrients when they form mycorrhizal associations with roots, living inside plants as endophytes and forming symbiotic partnerships with algae to form lichens. Any deterioration in fungal populations and diversity can therefore have a considerable impact on ecosystem health, whilst the loss of lichens from an area is often used as an indication of poor air quality. What fungi are and how they live provides some insight into the reasons for their significant role in ecosystems. The basic structures of most fungi are microscopic threads called hyphae, which form the active feeding and growing body of the fungus. The majority of the world’s fungi are microscopic, and they do not usually produce structures that are visible to the naked eye, unless the hyphae form a thick growth (often referred to as ‘moulds’). However, the most familiar species are those which produce spore-bearing fruit bodies, which are clearly visible to the naked eye. These include puffballs, coral fungi, earthstars, truffles and other forms of mushrooms and toadstools, which are the so-called ‘larger fungi’ or ‘macro-fungi’. Some fungi are very adaptable. For example, species of leaf litter decomposers such as the Parasol mushrooms (Macrolepicta species) and Funnel Caps (Critoeybe species) which decompose organic matter indiscriminately regardless of source, while others are far more specific and occupy a very restricted niche, like the Ear Pick fungus (Auriscalpium vulgare) which is only found on pine cones. There are others that are so geographically and biologically restricted they are considered rare and are now included on endangered species lists. Some fungi are known to have rapidly declined due to pollution and loss of habitat. Natural England is lending its weight to a Biodiversity Action Plan which aims to conserver 40 species across England. Oak polypore (Piptoporus quercinus) photographed by Martyn Ainsworth, the fruiting brackets appear in July on exposed oak heartwood of standing living trees in ancient woodland such as Windsor Great Park, which is considered to be the UK stronghold of this rare fungus. The fruiting bodies are reminiscent of the Bich Polypore (Piptoporus betulinus) in both shape and texture. The colour of the upper surface has been described as similar to crème caramel, but darkening with age. They can appear on trees, in July and August, from just above ground level to a height of 12m, on fallen trees, in crevices between root buttresses as well as inside hollow trees. All the fruiting bodies have been found on oak trees, on dead wood of either dead or living trees as individual brackets, in layered tiers or in clusters. Anyone who comes across this rare fungus should contact Carl Borges of Natural England on 01 206 796 666 [email protected], but specimens must not be removed or displaced as they are protected under the Wildlife and Countryside Act 1981 (as amended) Decomposition and nutrient recycling One particularly crucial role of fungi is in the transport, storage, release and recycling of nutrients. Nutrient cycling - the continuous supply, capture, replenishment and distribution of carbon, nitrogen and minerals - is fundamental for the ongoing health and vitality of all ecosystems. In woodland ecology, a substantial proportion of the nutrients stored, or in various states of flux, is in living and dead organisms, both above-ground and in the soil. Fungi, microbes and fauna may account for much of this nutrient resource in soil, and these organisms work together in a soil based food web to recycle the nutrients. They expedite crucial transfers and transformations of nutrients within micro habitats, including transfer from leaf litter, twigs, branches and logs into soil, and from soil into plants. As a result, soil organic matter and nutrient availability to plants is entirely dependent on the activity of soil organisms such as fungi The ability of fungi to decompose major plant components - particularly lignin and cellulose - is the basis of their organic recycling role. Without decomposer fungi, we would soon be buried in litter and debris. They are particularly important in litter decomposition, nutrient cycling and energy flows in woody ecosystems, and are dominant carbon and organic nutrient recyclers of forest debris. Honey Fungus (Armilaria sp.). This infamous group of fungal species are the considered to be the torment of many gardeners who have come to see it as a killer. However, there are several different species of Honey Fungus and only two of them are actually thought to be actively parasitic of woody plants and even then only some of the time. The genus as a whole are associated with the decomposition of wood in arboreal ecosystems, and in their natural habitat are part of a system that is essential to tree survival. Fungi are particularly valuable in acid soils, where the low pH makes it difficult for the survival of other organic decomposers such as bacteria. Bacteria release nitrogen in the form of nitrate which is easily leached from the soil and therefore lost to surface roots. However, the fungi that break down the organic surface litter release nitrogen into the soil in a form of ammonium nitrate which is less mobile. This could be very important to the successful establishment of young trees and to the sustainability of the ecosystem as a whole. Mycorrhiza - ‘fungus-root’ The transformation of nutrients and their transition from soil into plants is an essential component of ecosystem nutrient cycling, which could not be achieved without the fungi. ‘Mycorrhizal associations’ form fungus-root systems, which are far superior to roots alone. By far the majority of the world’s plants are partnered by mycorrhizal fungi, both in natural ecosystems and in agricultural or forestry crops. The fungi have a mutually beneficial relationship with the plants, thanks to a two-way exchange that occurs in modified roots known as mycorrhiza, (literally meaning ‘fungus-roots’). Carbohydrates from the plant are transferred to the fungus, while soil nutrients such as phosphorus are transported from the fungus to the plant. Mycorrhizal fungi are central to the processes of nutrient capture and recycling for most higher plants in low nutrient soils, as they assist in the acquisition of scarce nutrients and improve their absorption by the plant. Networks of fungal hyphae radiate outwards into the soil from mycorrhizal roots, forming a vast mycelial infrastructure capable of absorbing soil nutrients far more efficiently than plant roots alone. The fungi act as an extension of the root system, resulting in improved nutrient uptake for the plant. This is particularly important for soil-immobile nutrients such as phosphorus. In woodland soils, where plants compete for available nutrients that may be in short supply, this association can provide a vital support system to help maintain the stability of the ecosystem. Mycorrhiza are grouped into two main types. Ectomycorrhizae occur predominantly in association with woody plants, including many of the world’s major forest trees. The fungus forms a sheath around the fine roots of plants, penetrating between the outer cells, forming a Hartig Net. Meanwhile a diverse range of fungi form ectomycorrhizae, and most of these produce large fruit bodies. The second type, endomycorrhiza do not have a sheath, but the hyphae penetrate both inside and between the plant root cells. Fewer species of fungus form endomycorrhiza than ectomycorrhizae, and endomycorrhizal fungi do not generally produce large fruit bodies. Fly Agaric (Amanita muscaria) is often found in association with Birch (Betula sp.) trees, and could be responsible for the success of such trees as a pioneer on exposed sites like healthland and industrial wasteland. This photograph was taken on the edge of a sandy ride across Limpsfield Chard on the Kent Surrey border. Among trees, mycorrhizae are a major part of the strategy for capturing, taking up and recycling scarce nutrients, and well over 1000 species of mycorrhizal fungi may be associated with them. Living and dead fungi, microbes and fauna may account for much of the soil nutrient resource in forests and woodlands. Mycorrhizal fungi may also buffer plants against environmental stresses such as disease, for example by protecting plants against pathogens, by increasing host vigour, and by acting as barriers, actively competing against the intruders. Coprinus picaceus, commonly known as the Magpie Fungus, is an impressive mushroom now regularly reported growing on woodchip, but has been listed as a rare species for many years. The increasing use of wood chip as a mulch around amenity flower beds and park trees, has attracted a diverse array of rare and exotic fungi. It appears that this new habitat has resulted in a significant number of new species records for the UK and similar reports are occurring across the world. No one has worked out the source or significant, and this apparent ‘Alien Invasion’ of exotic fungi that has challenged experts, who have had great difficulty even identifying some of the unusual species that have been found. Meanwhile the use of woodchip mulches has also encourage the growth of some of our rarest native species, which have been recorded fruiting for the first time in many decades. So is the identification of new species from the appearance of their fruiting bodies actually an indication of ‘Alien invaders’ or simply due to the fact that these fungi have not produced mushrooms or toadstools in the past. This profusion of unusual fungi could be as a result of the improved growing conditions offering the species the opportunity to produced fruiting bodies. The fungus inside - Endophytes Still unknown and unexplained, the unseen world of fungi living inside plants as an inconspicuous embroidery of threadlike filaments, provides yet another dimension to the fungal support system. Plants are not just single organisms, they are entire symbiotic systems. Virtually every plant species researchers have examined has fungal endophytes including several fossil plants related to club mosses. We have not even begun to understand the complexities of their relationships. Some are thought to help with the storage and distribution of nutrients and carbohydrates around the plant, while some are pathogens waiting for the time to strike when the conditions are right, others may act to defend the plant by producing toxins that make the plant distasteful to herbivores. This fungal world within plant leaves, stems and roots, went largely unappreciated until 1977, when researchers found a grass endophyte to be responsible for many livestock poisonings, in both cattle and horses that eat its host, a tall fescuegrass. Research in Europe has found 40-70 species of endophyte in 11 different trees and a further 400 associated with grasses. Endophytes have been found to play a crucial role in the production of extremely beneficial chemical compounds. For example, the cancer-fighting compound taxol, which was originally derived from the Pacific yew, has been found to be a product of endophytic fungi. A research report published in the New Scientist in April 2000, found not only that multiple endophytes in various yew species produced taxol, but that other fungi in wholly unrelated plants do so too. Since taxol has antifungal properties, particularly against ‘water moulds’ (not true fungi), it may help keep pathogens at bay and strengthen the plant’s defense system. However, a lot more research is needed as taxol may not be the most effective of organic compounds. The potential for finding something far better and even more effective can not and should not be overlooked. Birch Polypore (Piptoporus betulinus) is a fungus exclusively associated with birch trees (Betulus sp.) where it is fundamental to the decomposition of dieing and dead trees. It exists within the tree as an endophyte waiting for the conditions to develop that will enable it to grow as a wood decomposer. It is the ingress of oxygen into the wood of the tree that stimulates the fungal decay process, when the tree is wounded, becomes stressed by drought or simply reaches the end of its life and dies. This is an essential process in the woodland ecosystem, because birch trees are a pioneer species that stabilise exposed sites, providing shelter for longer lives species that colonise the established birch woodlands and benefit from the fast decomposition of the dieing trees decayed by the Birch Polypore. What now? Despite their central role in ecosystems and their applications in biotechnology, knowledge about fungi remains at a low level. For example, it has been estimated that little more than 5% of the World’s fungi have so far been discovered, and for most of these, even less is known about their biology. If we don’t know what they are, how do we know what they do, and what capabilities we could be harnessing? Our lack of knowledge may relate to the inconspicuous nature of many fungi. Most are rarely seen, and those producing conspicuous structures appear fleetingly, at unpredictable and irregular intervals. The masses of fungal hyphae that spread throughout the soil and into the plants themselves are responsible for keeping the entire ecosystem in healthy order. In the deep layers of organic litter found on the surface of woodland soils, the decomposer fungi and those associated with roots as mycorrhizae, form an interlocking web of mycelium, which binds this organic horizon together. Organisms killed by pathogens contribute organic matter for nutrient cycling. Fungal pathogens of trees produce gaps, contributing to natural ecosystem dynamics, creating cavities in trunks and hollow logs, used by animals for shelter and protection, especially when breading. Fungi perform essential ecosystem functions such as accelerating the return of woody organic matter to the soil. Furthermore, some pathogenic fungi are used as biocontrol agents - a good alternative to chemicals for controlling weeds and pests. Fungi need a constant supply of organic matter to survive and thrive. The nutrient cycle relies on the reintroduction of dead material to provide a constant source for the fungi to decompose. In an existing woodland the organic horizon is topped up each year with falling leaves, but in our parks and gardens, or on new planting schemes, this source of nutrients is either non-existent or is removed as over enthusiastic gardeners remove all the autumn leaves. In these situations the application of an organic mulch becomes very important and will improve the quality and productivity of the soil. The recognition of fungi in ecosystem restoration and conservation is long- overdue, and accelerated studies on fungi are now needed, not only so that we may learn to harness more of them in more ways, but also to gain a better understanding of how ecosystems operate. Perhaps most importantly, we need to learn how to lessen human impact on ecosystems and to implement more efficient rehabilitation regimes on degraded land. Ramaria stricta. This is an uncommon fungus normally found on or near stumps of conifers and broad-leaf trees in late summer to winter. Seen here growing on a woodchip mulch spread across a garden flower bed, the dense mass of white mycelium can clearly be seen as a system of cords foraging for resources within the mulch. Such fungi are an integral part of forming the soil organic horizon and the growth of mycelium through wood chip mulches helps hold the surface layers together reducing the deteriorative affects of erosion. View full article

The first decision to be made, when considering pruning, is whether cutting off and removing living branches will actually benefit the tree or shrub. Will the proposed pruning prolong its useful life expectancy within the context of the surrounding environment and land use. Andrew Cowan explains how it is important to remember that pruning may do more harm than good, and in some situations may create more problems than it solves. Every cut made has the potential to change the growth of the tree or shrub. Removing living foliage, by pruning, affects the trees physiology and future growth. The reduction in leaf area that results from pruning, will reduce the tree’s overall photosynthetic capacity and may reduce overall growth on the pruned section, or on the entire tree. However, the casual observer of the growth that appears after pruning could be mistaken for thinking that cutting off branches and reducing the trees leaf area, is beneficial and encourages new vigour. This may indeed appear to be the case, but remember that there are often less branches left for the tree to produce new shoots from and severely pruned trees have a tendency to initiate the production and growth of ‘water-sprouts’, as a response to the need for new foliage and increased photosynthetic capacity. It is important that anyone considering pruning work to a tree, has an understanding of the biology of trees and how they respond to pruning in order to optimize their health and structure. Plants are reactive, generating systems, which use basic mineral and organic resources to build new tissues. They do not have the capacity to heal or repair damaged areas, so where week points occur due to injury, all they can do is re-enforce the site by growing, reactively, additional tissues and replace the losses. Trees store energy reserves (starch, sugars, and oils) in branches, stems, trunk and roots. These energy reserves can be preserved by removing, the fewest number of living branches necessary to accomplish the desired objective. Excessive branch removal depletes these reserves and reduces the ability of the tree to photosynthesize and store more energy. It is also important to be aware that if the tree is forced to use vital energy reserves for growth, they will not be available for defense against plant pathogens or wood decay organisms. There should be a good reason to remove more than a quarter, of a trees leaf area, in a single year. It is important to consider pruning over the entire life-span of the tree or trees involved and not as a one-off single operation. Many trees generate adventitious sprouts, in response to over-pruning, as they attempt to replace the stored energy. However live-branch pruning is an essential part of forming good crown structure, and is a necessary procedure in the management of specimen trees within residential parks and gardens. It is essential when considering pruning a tree, of any age, that a thorough evaluation is done to determine the objectives to be achieved, when the work is complete. The decisions can them, be made as to where, how, when and how often to prune the specific tree or trees, to achieve these objectives. This evaluation process is, an essential part of planning the management of any tree or tree population, and should be recorded in a tree management schedule. Each time a tree is pruned, according to the timing regime set out within the management plan, a work specification will need to be drawn up to provide the practical arborist with guidance. The arborist will them be able to make informed decisions, and make appropriate pruning cuts based on an understanding of branch attachment and tree biology, to achieve the pruning objectives. Removing the correct stems, branches or branchlets is as important as making the right pruning cuts. Even with proper pruning cuts, if the wrong branches or too many branches are removed from a trees crown it can defeat the object of the pruning regime. No tree should be pruned without first establishing clearly defined pruning objectives, which may include the following: Improve crown structure and form l Reduce risk of failure Maintain health Prolong useful life expectancy Removal of dead, dying or diseased wood l Influence flowering or fruit production Provide clearance Reduce shade or wind resistance Improve aesthetics or allow a view Maintenance and enhancement of wildlife habitat This list is not exclusive and will vary depending on the tree itself and the surrounding land use that will influence management objectives, but the methods used to achieve them can be selected from the following pruning types; Formative and structural pruning l Crown thinning Crown raising Crown reduction Crown clearing and dead wooding l Restoration pruning Conservation pruning Pollarding Throughout the entire process, from the initial planning stage to the completion of pruning work and removal of arising debris, the following two points should be considered; All pruning created wounds on trees, and can remove significant areas of living tissues. The open wound may allow the entrance of disease organisms and the ingress of oxygen, which could instigate the decay of the exposed woody tissues. Combine this then with the loss of leaf area when a branch is removed leaving that section of the tree with less photosynthetic, energy producing tissue, and one must consider any pruning to be potentially detrimental to the future health and sustainability of the tree. The tree supports a diverse ecosystem of organisms which live around its crown, on its roots and in the soil around it. These organisms may use the living or dead tissues of the tree for food, while others will form symbiotic relationships with the tree itself. So it is important to consider that any removal of dead wood from the crown or the clearance of pruning debris or leaves from the area around the tree could potentially be detrimental to the continued viability of the ecosystem in which the tree lives. Pruning types that could form part of a work specification to achieve a particular objective. Several types of pruning may be used to achieve a particular management objective and work on one occasion could be just part of a pruning regime over several years, and ultimately the entire life-span of the tree. Not all objectives can be successfully achieved after just one prune and others may need to be repeated in order that a desired outcome is maintained. The following pruning types can be used in isolation or in combination, depending on the management requirements and pruning objectives. Formative and structural pruning Structural pruning is most often completed at the establishment stage of tree development, when it is known as formative pruning. The main objective of this type of pruning is to encourage the formation of good stem and branch structure, by improving the orientation, spacing, growth rate, strength of attachment and ultimately size of branches. Well planned, formative pruning during the establishment of a young tree can prolong its useful life expectancy within the context of a particular land use. This type of pruning can reduce the need for large branch removal, and the creation of oversized wounds, when the tree is older. Structural pruning can be completed on semi-mature trees, but should be avoided on mature specimens. The main management objectives of this type of pruning are to help engineer a crown form which need less pruning when mature, and where ever possible limit the development of weak structural features which may fail in latter life. Crown thinning Crown thinning, is the selective removal of small, live branches throughout the entire crown, with the aim of reducing the density of the tree leaf area. There is no external alteration to the trees size or shape because just internal branches are removed. The important aspect to remember here is that the majority of branches should be removed from the outside third of the tree crown. The maintenance of an inner crown leaf area is essential to sustain good branch, stem taper. The excessive removal of branches from the lower two thirds of a branch or stem can lead to ‘lions tailing’ which may have adverse effects on their long term structural integrity, resulting in early failure. It is also important to limit the amount of foliage removed, each time a tree is thinned, to no more that 25% (a quarter) of the leaf area, and ideally between 10-20% where possible within the management objectives. The size of branches to be removed, during thinning operations, should also be limited, and wherever possible within the specification a recommended maximum diameter should be given. In most cases this can be limited to a size between 3cm to 4cm. Crown raising Crown raising, is the selective reduction and removal of branches to create some vertical lift of the tree canopy, allowing space under the tree for light, people, vehicles or buildings. When specifying this pruning type it is essential to consider the importance of maintaining as many low branches as possible to sustain good trunk growth and the formation of even trunk taper. It is important to remember that excessive removal of low branches can lead to the development of poor trunk crown balance, where a tree may become top heavy. It is also essential to be aware that all wounds around the main trunk of a tree could potentially allow the development of decay which may reduce the long term integrity of the trees main supporting structure. Where every possible the number and size of would should be limited and well spaced, so there is less chance of decay pockets combining to form larger cavities. Some of the problematic issues described above can be addressed by the reduction of branches rather than their complete removal. In such cases the size and age range of branches to be remove should be specified, while it may also be possible to reduce the end weight of some drooping branches to bring about some lift, in the overall canopy. Crown reduction Crown reduction or shaping, involves the removal and reduction of branches and stems to decrease the height or spread of a trees crown area. This type of pruning can be completed for a number of reasons to achieve a range of management objectives, from purely aesthetic when used to shape an entire canopy, to the reduction of one limb where excessive end weight may threaten failure. Crown reduction work can be specified to cover every branch within a trees crown or it can be limited to just one. However, one principle should be applied at all times; the desired effect should be accomplished with reduction or removal cuts and not heading cuts. Because biologically the tree has more effective mechanisms for wound decay responses where branches are removed from their point of origin close to the branch collar. The use of heading cuts also spoils good tree architecture and can significantly increase maintenance requirements. An important point to consider in branch reduction is the amount of foliage, or photosynthetic material, which is left to sustain the remaining branch or stem tissues. When a branch of a mature tree is reduced no more than a quarter (25%) of its foliage should be removed, while more can be removed in younger trees to achieve particular management objectives. If insufficient foliage is left, large areas of the main branch wood may become dysfunctional and open to decay fungi, which could lead to branch die-back. A common rule of thumb is that the remaining lateral branch should be at least one-third to one-half the diameter of the removed portion. At such a size, the lateral branch should be able to produce enough energy to keep the parent branch alive, and there should be enough growth regulators present to suppress excessive sprouts. This rule varies with tree species, age and condition, while localised variations in climate will also have an impact. Old, stressed or mature trees could decline or become more stressed if too much foliage is removed. Crown clearing and dead wooding This type of pruning is used where a tree is being maintained as a specimen within the context of an ornamental garden. Here the removal of dead, dying, diseased, detached or broken branches is specified to improve crown appearance and the overall tree aesthetics. The removal of such branches may also be considered desirable where they represent a risk to persons or property. However, it is also important to remember that dead wood is an essential habitat for a large number of organisms in the ecosystem in which the tree lives. The formation of dead wood within the crown of a tree is part of the natural system of tree life and should not be considered to be a negative thing that has to be removed to maintain healthy tree growth. Dead wooding is the removal from the tree of dead, dying or diseased branch wood, broken branches or stubs left from previous tree pruning operations or as a result of storm damage. The work specification should identify one of three categories of dead wooding to be performed: 1 Complete dead wooding The removal of dead, dying or diseased wood, broken branches and stubs left from previous tree pruning operations, provided such material exceeds 10mm in diameter or 100mm in length (smaller material shall be allowed to remain in the tree unless the Employer states to the contrary in the tender documents) 2 Major dead wooding The removal of wood either over 50mm in diameter or over 200mm long, be that wood dead, dying or diseased branch wood, broken branches or stubs left from previous tree pruning operations 3 Stabilisation dead wooding Dead wood to be broken off by hand or by being struck with stick or be partly sawn through and broken off. A throw line may also be used to break off the ends of branches, in order to retain as much aerial dead wood as possible to maintain the habitat value. Restoration pruning Restoration pruning, may be considered necessary where a tree has been damaged, poorly pruned or where a once regular management regime has lapsed, resulting in the formation of poor structural features. The principles behind this type of pruning are similar to those used in structural or formative pruning on establishing trees, but more care is required due to the maturity of the specimens involved. This type of pruning has to be planned over a much longer time frame and only a limited percentage (perhaps only 10%) of a trees leaf area should be removed at any one time. Restoration pruning may involve the training of young epicormic, or water-sprout, shoots to form new branches and allow the reestablishment of new area of crown. It is therefore important to provide a more detailed pruning specification, which may involved the identification of a specific area of the trees crown or even a particular branch. Natural fracture pruning techniques that mimic the natural branch loss that would occur following storm events, small diameter branches may be partially cut through from above and then ripped off, by hand, from within the crown or by rope from ground level, seeking to leave a split or fractured branch end, and exposed heartwood, that may or may not be associated with an existing growing point. Conservation pruning Not all, pruning work is completed to improve tree health or structural form, some management objectives allocate more weight to the creation and management of wildlife habitat. In such cases it may be considered advantageous to create large wounds with the aim of increasing the area of dead and decaying wood in a tree, or to top a limb to encourage a crown of dense re-growth which could provide good nesting opportunities for birds. The retention of dead wood around the crown of a tree may be considered an important aspect of trees managed for their wildlife value. However, there are often conflicts that arise when health and safety issues have to be addressed. In these situations a specification that allows for the sympathetic reduction of dead branches or stems, using cutting techniques like ‘coronet cuts’ to maintain a more natural appearance to the cut ends, may be considered desirable. Destructive pruning techniques may be used to create habitat in trees as part of a conservation project and involve techniques that will result in the creation of decay within the trunks and main branch structure of trees. Veteranisation pruning techniques, could also be used, that are intended to prematurely ‘age’ a tree in a controlled and targeted manner to initiate the creation of habitat or stimulate the formation of a secondary crown Pollarding Pollarding is beheading a maiden tree by removing the main leader or stem and then subsequently cutting on a regular basis (Re-pollarding) back to the same point (Pollard Head). Pollarding is a management system used to control the growth of a tree throughout its life, and is initiated at a young age. When older mature trees are treated in this way as a crude form of size control this can be described as topping, and can seriously damage or even kill the tree. Where pollarding is specified it should be part of a long term management plan for a tree or tree population. If a pollarded tree has lapsed out of regular management, re-pollarding should not be specified. In such cases restoration pruning could be considered to either train the branches to form a normal crown area, or using staged reduction work re-establish a pollard management regime. View full article

The ever increasing pressure on countryside managers to remove potentially dangerous dead trees is one of the reasons for the decline in available standing dead wood. This particular type of habitat forms an essential part of the woodland ecosystem providing wildlife such as woodpeckers a ready supply of soft drillable wood in which to form nest holes , these disused nest holes then provide a whole range of other fauna a safe place to shelter including species such as bats and other nesting birds. Standing dead wood decays slower, lasting for longer than timber stacked on the ground. The dryer conditions are also favoured by different fungi and specialist invertebrates. Finding a safe and sustainable way to retain such standing dead wood in the landscape is the challenge that now faces countryside managers. Dead trees can be made safe by careful reduction work as an alternative to felling. Where there are no dead trees, selectively killing trees by ring barking can be a proactive solution, while the resurrection of large logs should also be considered It may also be feasible in areas where only new planting exists to erect free standing dead timber; this increases the biodiversity of an area of new planting aswell as adding visual interest to the site In this case a limb containing a large cavity has been fixed to the underside of this branch. This allows the feature to continue to be used by wildlife whilst removing the risk of falling deadwood to members of the public using the park Log and Stag Beetle Pile Creation As gardeners, park managers, foresters and arborists we are in some way possessed at maintaining a perfect environment where we strive to remove deadwood, fallen leaves, stumps and anything that we might think could pose a risk or may look unsightly. This attitude to the green areas around us has been around for many hundreds of years having first started with the great gardens of Britain where dead trees were removed leaves gathered up and grass kept impeccably mown, this idea has now manifested itself in the way we manage our small urban gardens, with a greater enfaces being placed on those all too important words Health & Safety. This apparently well maintained and safe environment that we have created for ourselves has with out doubt drastically affected the flora and fauna that relies so heavily on the very things we deem to be unsightly or unsafe. We utilise a unimog mounted crane to assist with lifting the larger logs into place which allows each log to be held in place until it can be made secure. In an attempt to turn back time there are many things that we can do to boost an areas bio-diversity, at ArborEcology we are now offering a service to install both vertical and horizontal log piles to cater for stag beetles aswell as a whole host of other species which will take advantage of the shelter and food source associated with these habitat improvements. These stag beetle piles formed part of the mitigation measures for the loss in habitat created by a nearby development. This style of habitat replacement is designed to mimic the habitat provided by dead tree stumps and is specifically aimed at providing a habitat for stag beetles although other wildlife will become associated with it in time. View full article

Ivy is a plant that attracts strong opinions, especially when arborists are asked to consider its impact on trees and their ecology. Andrew Cowan considers some of the common arguments for and against ivy, while also looking at the influence of climate change on the natural balance of arboreal ecosystems. When I first tackled this issue it was with the objective of expressing some form of balance to the frequent heated discussions and arguments about whether ivy should be considered good or bad and subsequently something to be removed from trees. To some, it is a pernicious weed that smothers the natural form of trees and on which constant war must be waged. To others, it is an integral part of the arboreal ecosystem offering an essential wildlife habitat, providing shelter and food for a diverse range of different organisms. #jscode# In reality, it will all depend on where and under what circumstances the tree is growing. Context is the key word here, and what might be fine in the middle of woodland may not be so desirable in formal parkland or a residential front garden. However, there are numerous variations and considerations needs to be given to such things as tree species, age, maturity and vigour, but ultimately it is the management objectives associated with the trees location that should have the most influence on the decision. Meanwhile, there is now more to think about, because with the climate progressively changing and creating longer growing seasons, especially for evergreen plants, the ‘natural’ balance of plant growth is changing too. There is an increasing argument that ivy may be gaining advantages from our warming climate that is extending its growing season and enhances its growth rate to the extent that it can actively compete with even healthy trees. This is an issue that requires serious consideration because it could affect the way we manage the balance between the longevity of the tree and the value of wildlife habitat created by the ivy. Ivy is very well adapted to living in woodland, which represents its natural habitat. The growth characteristics of ivy enable it to survive where light levels are low, on the ground and up trunks of trees whose dense foliage shade the woodland floor. Ivy’s attributes of shade tolerance and evergreen foliage have proved invaluable in our gardens, where it has been used for attractive evergreen coverings for north facing walls and to provide ground cover in dark corners. Although the common ivy Hedera helix appears the most frequent, a variety of cultivars and other species are available for horticultural use. Hedera helix, is the only evergreen climbing shrub that is native British. It has a habit known as dimorphism, whereby two forms occur within the same plant. The juvenile growth, with its characteristic lobed ‘ivy shaped’ leaves, is adapted to living in low light conditions and is found creeping along the ground or climbing up walls and tree; while as the plant matures, it can throw out bushy branches and flowering shoots with very different, elliptical leaves (lanceilate to ovate). This adult form will only develop where the light conditions allow, and it is mostly found on the climbing section of the plant, only rarely on the ground. The mature oak tree, pictured here, is in decline and the ivy is beginning to smother it. This process is a natural part of the woodland ecology, but with the tree adjacent to a public path there are clearly some concerns with regard to health and safety. However, this prominent location also makes the tree of particular value for bats that could make regular use of the dense ivy for roosting while foraging along the ride and woodland edge. Meanwhile the tree would live for longer, if it did not have to compete with the ivy, and it could undergo the process of retrenchment to a lower canopy, although the removal of the ivy to prioritise tree survival will incur considerable cost and effort while potentially inflicting the tree to thermal exposure that could result in extensive bark death. Ivy has a very bad reputation and it is commonly thought that it kills trees. Contrary to popular belief, ivy is not parasitic and does not directly affect the health of the trees it climbs. Unlike true parasitic plants, (such as mistletoe, whose roots tap directly into the resources of the host plant) ivy has its feeding roots anchored in the ground and simply uses the tree as a support to get to where it wants to go. The masses of tiny, hair-like roots sprouting from the under surface of the stems, are designed to provide support and allow the plant to climb. Although these roots provide almost immovable adhesion to the rough surfaces of tree trunks and walls, they are not used for feeding, and at worst only penetrate the outermost layer of bark on host trees. It is primarily in terms of competition for natural resources that ivy affects the health of trees, particularly where light is concerned. If ivy has become established on a tree, it is more likely to be a sign of stress than a cause of it. A heavy infestation of ivy, particularly in the upper crown, is usually an indication that the tree is in a natural state of decline; most healthy crowns will let insufficient light through for the ivy to grow vigorously. Ash, Fraxinus excelsior, is an exception as the crown tends to be thin and open. This allows major infestations to occur, thereby restricting photosynthesis, but it is still considered unlikely that the life of a healthy tree will be shortened. In the case of a diseased or dying tree, where its growth rate and vigour may be slow or in decline, the ivy’s more vigorous growth allow it to smother the tree. The bushy adult growth will then have a tendency to make the tree top heavy, making it more likely to fall, particularly during adverse weather conditions. On ancient trees the presence of a dense ivy coverage over the trunk and main branches can reduce the ability of the tree to generate a lower crown canopy during retrenchment, so it could be important to control ivy growth on such trees. However, it is also important to consider thermal impact on the tree when dense ivy growth is removed, because a sudden exposure to the heat of increased sunlight on the bark can kill it and be counterproductive to the original objective of ivy removal. One of the most important aspects when contemplating the removal of ivy, from a mature tree, is its enormous wildlife value. The dense mass of foliage and intertwining stems around the trunks of trees, provide shelter for birds to build their nests, and dark nooks and crannies where bats can roost through the day. In Autumn, ivy flowers are an important source of pollen and nectar for wasps, butterflies, bees and a host of fly species. Over winter, ivy protects woodland soils from full snow cover and frost. This enables ground foraging birds such as blackbirds, robins, dunnocks and thrushes to continue feeding, while a sheltered habitat is also provided for small mammals and insects. The berries, which ripen in March / April, have a high fat content and, although poisonous in large quantities, they provide both native and migrant birds with an invaluable early energy resource. Woodpigeons, starlings, resident and migrant thrushes and newly arrived summer migrants such as blackcaps feed on them. Some species of invertebrate are known to feed on the foliage of ivy, and several species of beetle bore the mature stems, while spiders spin their webs to catch others that fly in to shelter. It should rarely be considered necessary or appropriate to remove ivy from trees within a woodland setting, where it is an integral part of the native arboreal ecosystem. On the other hand, in parks and gardens where conditions have allowed it to grow unchecked, it can become quite a problem; choking the crowns of ornamental trees, swamping less vigorous shrubs and smothering walls and rockeries. Although rarely a problem to the tree, a dense covering of ivy over the trunk and throughout the crown of a mature specimen can inhibit essential safety checks, by limiting a visual inspection of the trunk and main branches. Where mature trees are growing in residential gardens often close to dwellings or public open space, it is important to be able to complete regular hazard assessments and monitor the decay of old wounds. In such circumstances it may be necessary to remove the ivy. From a practical viewpoint, the most effective way of removing ivy is to cut it near to the base of the tree. When doing this, it is necessary to remove a section of all the stems around the entire circumference of the tree’s trunk. Once cut from its roots the ivy growth, up the trunk and branches, can be left to die on the tree, and when sufficiently dry and brittle it can be removed. The best time to consider this work is over the winter when the host tree is likely to be bare of leaves and visibility while completing the task is much improved. However, it is important to be aware that dense ivy is frequently used by bats for roosting. To avoid unnecessary disturbance of hibernating bats it is best to cut the stems of ivy in the late summer or autumn, so the foliage dies before the winter months. The removal of ivy during the summer should be avoided where possible, because of its likely use by nesting birds and roosting bats. It is an offence under the Wildlife and Countryside Act 1981 (as amended), to intentionally damage or destroy a wild bird’s nest, whether in use or under construction. The use of the ivy by bats for shelter and roosting must also be considered. A bats roost is protected both under the Wildlife and Countryside Act 1981 (as amended), and The Conservation (Natural Habitats &c.) Regulations 1994 (as amended), which make it an offence to damage or destroy a breeding site or resting place of any bat, and it does not require the offence to be intentional or deliberate. Furthermore, under an amendment made within the Countryside and Rights of Way Act 2000, it became an offence to recklessly damage or destroy a bat roost, and it could be reckless not to consider possible use of ivy for roosting. However, considering the habitat implications of removing ivy from individual trees or felling a tree with ivy on it, there can be reasonable argument to support decision because although it offers good roosting and nesting opportunities, they are frequently commonly found in other trees locally. As such the loss of roosting opportunities in one or two ivy covered trees in an area with a number of other similar trees is not likely to have a negative impact on the conservation status of the local bat population. To summarise the decision process to remove or manage the growth of ivy up trees is a matter of considering the context in which the tree is growing and the management priorities associated with the surrounding area. Personal prejudices should be avoided because they hinder informed and balanced decisions. View full article

Dead wood may well have recently died, and no longer part of the living tree or even attached to it, but we should not be calling it DEAD, because it’s DECAYING. You may think this is just another word for the same thing, but unlike Monty Python’s dead parrot sketch, the point is that dead wood is anything but dead. The description dead wood implies a static state, without the consideration for the process of decay, and the diversity of life forms involved. It is the process of decay which is the focus here, the progression of use by different organisms. Some like their wood served up fresh with the sap still ebbing from its vessels, while there are those that prefer it when others have had their fill and all that is left is a mass of soft cellulose or brittle lignin. The diverse array of organisms that are involved in the breakdown of dead woody tissues is truly amazing. So much so that decaying wood can be considered a specialist habitat in its own right. #jscode# There is a growing emphasis on biodiversity and protected species, which is influencing a change in management strategies and a shift in long term objectives. However, now there appears to be a revolution afoot, with more and more people, and organisations, recognising the need to focus on a broader picture. In conservation the world over, the time and money has been invested in ‘fire fighting’, to protect and preserve endangered populations of particular species. The solution is one that manages the system, rather than concentrating on its component parts, if we can maintain healthy ecosystems the biodiversity should take care of itself. However, we cannot and should not try to force long-term change, if we are to be successful in sustainable conservation our role needs to be one of encouragement and persuasion with a respectful appreciation for the diversity or organisms involved. Historically, woodland managers have removed dead wood on the basis of hygiene, to protect the timber resource from what have traditionally been perceived as pests, like insects and fungi. This is also true of many, parkland and garden sites managed by arborists, where dead wood in trees is seen as a liability, and is removed for fear it may fall and injure someone. The result is that there is simply not enough decaying wood habitat to sustain populations of many key species of conservation importance and an integral part of the arboreal ecosystem. Dead and dying trees play a vital role in the functioning and productivity of arboreal ecosystems through effects on biodiversity, carbon storage, soil nutrients cycling, energy flows, hydrological processes and natural regeneration of trees. This is a point now generally recognised by most of us, but this has not always been the case. The generations of managers that have religiously felled and removed dead and dying trees, has left us with a huge shortage, which is likely to take decades to replace. The generation gap is aptly demonstrated when we look at the rare species, which are associated with our ancient and veteran trees. Many of these are only found on sites where there has been a continuity of decaying wood habitat for hundreds of years. However, ancient trees may appear plentiful today, but for how much longer? Next time you visit a site containing ancient trees, look around at the rest of the wood or parkland, and consider where the next generation will come from. The organisms that rely on decaying wood habitat are becoming increasingly isolated, in time and place. This is made worse by their lack of mobility, which means that the creation of an intermediary ‘bridge habitats’, is essential if these species are to survive. This is a fundamental part of our involvement in the sustainability of arboreal ecosystems and the maintenance of biodiversity. Veteran or Ancient? The terms ‘veteran tree’ and ‘ancient tree’ have been used interchangeably for some years now, but recently an effort has been made to clarify the distinction between the two terms. Veteran: The term veteran is used to describe the growth characteristics of a tree, and has no relation to age, other than the fact that old trees are more likely to be described as veteran. Trees grow reactively, by producing additional ‘wound’ wood or reactive tissue where an injury or associated decay has weakened the residual strength of a stem or branch. The physical signs or symptoms of injury are known as a tree’s veteran characteristics, and a veteran tree is one that has suffered to such an extent that its whole growth form has been permanently altered. The tree has become a veteran. Ancient: The term ancient is used to describe a tree’s age class. An ancient tree is considered to be one that has reached an above average age for its species. Such a tree may also be a veteran, due simply to the number and extent of veteran characteristics it has accumulated over a long life. Ancient English oak (Quercus rubor) pollard, Windsor Great Park, Berkshire, Endland UK Decaying Habitats There are two distinct types of decaying wood habitat, the first is associated with standing dead trunks, limbs or branches left around the outside of the tree, while the second is found within the trunks and branches themselves, where the decay forms cavities. It is important to be aware of this distinction because the habitats that are created are quite different and require specific techniques to recreate them. Standing dead wood, whether as whole trunks or branches within the crown of otherwise healthy trees, is relatively easy to replace by the creative use of destructive pruning, ring barking trunks and branches or by the re-erection of logs. This type of decaying wood habitat breaks down from the outside in, providing a large surface area for occupation by invertebrates, fungi, lichens and mosses. However, when it comes to the creation of the decaying wood habitat found within the trunks and branches of trees, the techniques involved are not quite so simple. The decaying wood inside living trees decomposes from the inside out, creates cavities, rot holes and hollow trunks, which are created by invertebrates and fungi, but go on to provide shelter for a diversity of birds, small mammals and reptiles. Destructive Pruning: May be used to create habitat in trees as part of a conservation project and involve techniques that will result in the creation of decay within the trunks and main branch structure of trees. Veteranisation: Pruning techniques intended to prematurely ‘age’ a tree in a controlled and targeted manner to initiate the creation of habitat or stimulate the formation of a secondary crown Natural Fracture Pruning: Pruning techniques that mimic the natural branch loss that would occur following storm events, small diameter branches may be partially cut through from above and then ripped off, by hand, from within the crown or by rope from ground level, seeking to leave a split or fractured branch end, and exposed heartwood, that may or may not be associated with an existing growing point. Ancient English oak (Quercus rubor) collapsed pollard Richmond Park, London, England, UK. Creating the Habitat Training as a practical arborist has progressed over the years, from the days of old when tree surgery work involved carting a hand axe and cross cut saw around the tree, through the era of flush cutting and cavity excavation, to the enlightenment of target pruning and an understanding of CoDiT (Compartmentalisation of Decay in Trees). However, modern pruning techniques may prolong the safe useful life of the trees in our parks and gardens, but they are threatening the sustainability of arboreal ecosystems, and potentially the life expectancy of the tree themselves. There is a tendency to use pruning techniques, like reduction or thinning, to maintain trees in a particular form or shape. Our use of terminology is prone to describing a particular state, like dead wood for instance, rather than considering the process of decay, hence decaying wood. When we look at managing a process, the emphasis shifts, because this involves an understanding of how things change as they adapt and evolve within a natural system. To create the bridge habitat so desperately needed by some of our rarest flora and fauna, we are going to have to adopt destructive pruning techniques, which will contradict much of our formal training as ‘tree care professionals’. However, our knowledge of tree biology is going to be essential, because if these methods are going to succeed we need to mimic the natural processes of tree decline, which is a slow progressional balance. The term veteranisation is being used to describe destructive pruning methods, which accelerate the ageing process of trees, by inducing controlled stress. We do not have the knowledge or understanding to duplicate nature, because natural tree decline starts below ground, when the root system becomes exhausted and can no longer support a full crown of leaves. The transportation paths then start to break up and the tree progresses into a stage of retrenchment, like an army in retreat, resources are moved to a more central location. The selective use of destructive pruning methods that involve natural fracture techniques and coronet cuts, encourages premature retrenchment, by reducing the crown area, while providing niche habitat for decaying wood organisms. This veteranisation of healthy trees is an essential part of the management of arboreal ecosystems, particularly in association with ancient decaying wood habitats where the generation gap is greatest. It can also be used instead of natural target pruning when managing hazardous trees, by reducing the potential for a lever arm to fail, while also retaining more structure within the trees crown. Coronet Cuts: The cut end of a reduced branch or a large stub that may be creatively cut into the form of a ‘coronet’ which is a man-made wound so-called because it resembles the appearance of a coronet, whilst it approximates to the appearance of a naturally fractured broken end. The siting of the cut is generally around a distance of five times the diameter of the branch from the branch union. Retrenchment Pruning This involves a combination of pruning techniques that are utilised to mimic the natural processes of aging whilst extending tree viability and retaining habitat features. The techniques seek to reduce the potential for a tree to collapse under its own weight due to excessive end weight on long or weakly attached limbs over a long period of time. Reduction in height, and weight, encourages the development of adventitious growth and the formation of a lower or secondary crown form equivalent to natural canopy retrenchment. Ancient English oak (Quercus rubor) pollards following retrenchment pruning, Elan Valley nature reserve, Mid Wales, UK Sustainable Conservation The creation of bridge habitats is a lengthy process, so consideration has to be given to the sustainability of the existing decaying wood, within our ancient arboreal habitats. As we are all aware the slow process of decay can significantly reduce the integral strength of trees, compromising their structural stability, ultimately leading to partial then total collapse. This is a natural progression and would not normally be a problem, but our obsession with the removal of, what has been perceived as, dead wood now means that for many organisms, there may be no where else to go. Research into the sustainable management of ancient and veteran trees has been the focus of the Ancient Tree Forum (www.ancient-tree-forum.org.uk) in the UK, for over fifteen years now. A pruning method known as restoration pruning became a recognised system of trying to reinstate lapsed pollards, which had become unstable due to neglect. This involved the selective reduction work necessary to restore a more uniform and sustainable lower crown form. There are some, who would express reservations about the use of the term restoration pruning. This is because it is in principle, a descriptive term for, a method of restoring, reinstating and imposing a physical state on the tree, which we perceive to be desirable with consideration to the management objectives of tree longevity and safety. However, ideas have evolved and a new term has been adopted, which was suggested by Paul Muir, of Treework Environmental Consultancy, that of ‘retrenchment pruning’, where the idea is to mimic the natural processes, encouraging a progression to a more sustainable structural form which considers the tree’s physiological systems. Nectar Sources A large proportion of the decay process is performed by juvenile invertebrates (grubs), which survive in the shelter of the decomposing wood, which provides them with all the nutrients they need to develop. However, when they leave the decaying wood as adults, they need a source of nectar to provide them with sufficient energy to fly, mate and disperse the population to the next available decaying wood habitat. Nectar provides an energy-rich food, which can rapidly be assimilated and used to fuel flight, and pollen is a protein- rich food, which aids egg production. Flowering trees and shrubs are by far the most important sources, although other plants can also be very popular. It is therefore important to consider retaining and planting suitable species in association with decaying wood habitats that are part of an integrated conservation project. Noble Chafer (Gnorimus nobilis) beetles on elder flowers How much Decaying Wood and Where An alliterative phrase adopted and promoted by Ted Green, is ‘sustainable, successional, structural, supply of decaying wood’, which sums it up neatly, although the implications may not be immediately obvious. However, it is clear that, an arboreal ecosystem needs just that, if it is to support a diversity of organisms, and maintain ecological integrity. It is a description of the level that needs to be achieved if our creation, management and maintenance of decaying wood habitat are going to be anywhere near natural. It is however, difficult to accomplish something even near a natural state, when we have no real idea what that might be like, since it infers the absence of human manipulation. We therefore face a challenge where the ultimate goal is unobtainable, so it is important that our aims are based on viable benchmarks. This is exactly what Jill Butler, Fred Currie and Keith Kirby have attempted to do with a paper called ‘There’s life in that dead wood – so leave some in your woodland’ published in the Quarterly Journal of Forestry April 2002 (Vol.96 No.2 131-137). The arboreal ecosystem relies on a sustainable supply of decaying wood, because the process provides a range of habitat types, thats are utilised by a large number of different organisms, which are in turn responsible for a particular stage of decomposition. It is therefore an absolute necessity that there is enough decaying wood around to provide the range of conditions needed to support these organisms. To achieve a sustainable supply of decaying wood, without the necessity to keep importing new material to a site, we have to encourage a successional ecosystem. It is fundamental part of managing decaying wood habitat, that there is the diversity of niches, available at any one time, to support the full range of organisms associated with decaying wood. Finally, we have to appreciate that arboreal ecosystems have multiple levels, and the creation, management or maintenance of this habitat needs to work in a structural way. It is not sufficient to have a sustainable, successional, supply of decaying wood on the ground, in piles of logs or brash wood. There needs to be decaying wood in all of the following places: dead limbs on living trees; decay columns in trunks and main branches; rot holes in standing trees; sap runs from decaying cavities or recent wounds; dead bark on standing trees; standing dead trees; fallen trunks and large branches; fallen small branches and twigs; dead tree stumps and old coppice stools; exposed root plates of wind blown trees; decaying wood in water causes; and it is important to have all of the above in a diversity of locations, and conditions, in full sun, dense shade and various stages in between. Therefore our management goal is a Sustainable, Successional, Structural, Supply of Decaying Wood Summary The recognition that decaying wood habitat is a dynamic system of processes, which are a constantly evolving part of the arboreal ecosystem, is an important step towards its successful and sustainable management. It is also a demonstration of how the terms we use can influence our perception of the management objectives. Our role as arboricultural managers is one of careful guidance, to encourage and support natural processes, not to impose a physical form or state, to fit our ideas of what is right. We must strengthen our recognition for the fact that trees live within a different time frame to us mere humans. Their living processes are almost the ultimate in sustainability, to a point where, in the right circumstances, they have the capability to attain immortality. We therefore have a responsibility to consider the management impacts of tree life spans measured in hundreds of years, and in some cases millennia. The implications of this are that the component parts of arboreal ecosystems can undergo cyclic fluctuations, which are measured in centuries. The knowledge we use to develop tree management strategies, must have a depth of understanding that considers the tree’s interrelationship with its environment and other organisms, included within a broad arboreal ecosystem. It is also essential to have an appreciation of the ageing process of trees and be aware that different management methods are needed, which are sustainable in the context of tree longevity. Conclusion If sustainable conservation is to work we need to move away from management strategies that concentrate on individual species, and embrace an ecosystem based approach. This is needed, not least, because it would help define some common objectives for the various wildlife conservation organisations. As we are now, each group has it’s own goals and it is common knowledge that these conflict and are in many cases counterproductive, often canceling one another out. These are not new ideas, and there is an evolution towards ecosystem based management, with the concepts of ecosystem health and sustainability becoming strategic goals. However, it has taken us decades to get to this stage. In conclusion it is clear that we need to think more carefully about the far- reaching effects and repercussions of our management decisions. However, this is hardly a new concept. Aldo Leopold proposed the following metaphor in an essay he wrote in 1949, called ‘The Land-Health Concept and Conservation’, which was published for the first time in a book called ‘For the Health of the Land’ in 1999. The biotic clock may continue ticking if we. 1 - Cease throwing away the parts. 2 - Handle it gently. 3 - Recognise that its importance transcends economics. 4 - Don’t let too many people tinker with it. Andrew Cowan View full article

As you suggest two engine rebuilds might seem a little much, but again as you say, running all day does tot up the hours ..... Have parts been easy enough to get hold of? Yes, I did wonder about the pull off power when loaded. Not helped if you fit large tires either. Have you done much towing with it?