Putting Pruning in Context Andrew Cowan - ArborEcology - Arbtalk

Every cut made has the potential to change the growth characteristics ofthe tree. Removing living foliage, by pruning, affects the trees physiologyand future productivity. The reduction in leaf area that results frompruning will reduce the tree’s overall photosynthetic capacity, which islikely to affect sustainable growth on the pruned section, or the entiretree. Pruning can therefore have a lasting impact on the viability of thetree and can directly influence its longevity.One of the major limitations of crown pruning is that it has a veryone-sided impact on tree physiology. Before pruning the tree will bemaintaining a natural equilibrium of growth, throughout the crown ofleaves and branches, in balance below ground within a broad spreadingsystem of roots, with their associated mycorrhiza. Raw materials areabsorbed from the soil, moved up through the transport system withinthe trunk and branches to the leaves, where energy is produced throughphotosynthesis. By removing leaves and branches from the crown thearborist disrupts the balance, forcing the tree into a state of turmoil.Avenue of ancient sweetchestnut Castana setiva treesat Croft Castle, Herefordshire,England, UK.The casual observer, of the growth that appears after pruning, could bemistaken for thinking that cutting off branches and reducing the tree’sleaf area is beneficial and encourages new vigour. This may indeedappear to be the case, but it is essential to remember that severelypruned trees will initiate the production and growth of ‘water-sprouts’ or‘sap-risers’, as a response to the need for new foliage to readdress thebalance of photosynthetic capacity and energy requirements. To sustainthis flush of growth the tree must draw on stored energy reserves, whichlimit the resources available to resist infection, disease and decay.For arborists, charged with the responsibility of tree care, the primary pruningconsiderations are those that affect the tree’s physiological condition, itsability to compete with pathogens and its durability within a wider ecologicalcontext. Pruning influences the trees physiological productivity: its ability to resistpathogens, 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 -Putting Pruning in ContextAndrew Cowanwww.ArborEcology.comThis 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 growingin a rear garden of a residential property in WestWickham, Kent. The tree is thought to be in theregion of 600-700 years old. Residential housesnow surround the tree, which has been swallowedby the urban sprawl of London’s 1930’s suburbandevelopment. The houses either side have beengiven planning permission by the local authority tobuild extensions, which have placed more pressureon the tree and the responsibilities of its owners.The neighbours now complainabout the tree, which blockslight from their gardens andbedroom windows.Looking beyond tree care:In most cases the real motivations behind tree pruning are associated with thehuman values of visual aesthetics, amenity and recreation. This may, in part atleast, be due to our need to see trees as being worth something, to have somepurpose or function, which we as humans can use. Whilst the management oftrees using pruning practices such as pollarding have enhanced their longevity,these techniques are now less frequently used as the need for the associatedresource has reduced. These trees may now be seen to have some historicsignificance, but their true value is in their importance as an ecological resourceof co-evolutionary organisms.The primary considerations of pruning specifications are all associated with theimpact 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 treedoes not benefit, with the exception perhaps of formative pruning during theestablishment stages, which may improve the structural form and stability of atree’s trunk and branch growth. However, even this is a human interpretation of‘good’ structural form. Pruning must therefore be considered within the contextof understanding tree physiology over time, while taking into consideration theecological impacts.The point is that although the instigation behind tree pruning is associated andinextricably linked with human values, the implications have a direct impact onthe physiology of the tree and the ecological balance within its environment. Thearborist must, as a person responsible for tree care, work with a knowledge,understanding and respect for the arboreal ecosystem and not just the tree whichhappens to be the subject of the pruning specifications. This is arborecology.Arborecology incorporates an appreciation of the ecological value of trees andan acknowledgement that they might have some intrinsic value, because theysupport a diverse arboreal ecosystem, which is an essential part of the naturalworld to which we all belong. Informed management decisions can enhancetheir longevity with sympathetic pruning, but sometimes to maintain a sustainableecological habitat within populations of trees it becomes necessary to considerdestructive techniques to encourage the process of decay.Putting Pruning in ContextAndrew Cowanwww.ArborEcology.com“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 thatexceeds our own (human) ‘three score years and ten’, yet we offer them verylittle respect for this achievement. In fact, trees figure so low on the day to dayagenda of modern life that the average person will rarely stop to consider theirvalue. However, when someone actually pauses to think of the contributiontrees make to their lives as an individual, or as a member of society, the list canappear endless.There is a growing recognition that trees have a part to play, from the calminginfluence they have on our everyday lives to their ability to sequester carbondioxide,which could influence the sustainability of human survival on the planet.Many of these beneficial attributes are linked to the slow progression of treegrowth over their long life spans, which can frequently be measured in centuries.However, many trees are deprived of the opportunity to live out their naturallives, because of a human ignorance that inflicts its will on the world with anarrogance that fails to recognise that everything is intrinsically connected.The technological advancement of human society has created populationsof people who have lost track of their cultural connection with an area orcommunity, to the extent that they shuffle around their country and sometimes theworld, moving from place to place. Is it any surprise then, that the new owner ofa suburban residence has no qualms with felling an oak tree, which may havebeen 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 andconsiders that his/her rights, to live in a place without trees, are greater than theaccumulative values and benefits of the one oak. However, the same personmay only live in the property for no more than a decade, less than a tenth of thetrees 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 Theengraving on the southface of the structureunder this grand oldoak tree, reads;“This cross was builtcirca 1473 to designatethe boundariesof Puttenden andBilleshurst Manor. TheCage for the detentionof petty offendersadded in 1773 was lastused in 1882 to detainpoachers.”Was the tree used tomark the boundarybefore the cross wasbuilt? Was it used as ahanging tree?Putting Pruning in ContextAndrew Cowanwww.ArborEcology.com

Royal & Sussex Oak These two pictures need no words to explain them, simplyto 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 maintainsome degree of harmony, and if we are to life in association with trees thecompromise is pruning. There is rarely space in our crowded towns, cities andeven villages, for the mature size of trees. Some form of pruning has to beconsidered to readdress the balance, but just because they are perceived to begrowing 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 potentiallife expectancy, and the ecological values associated with it. Pruning work mustbe completed with an understanding of the physiological limitations that impacton the tree’s ability to react to the loss of living foliage. Pruning is all aboutcompromise!The reactive capacity of a tree will be compromised to some degree, dependingon the pruning techniques employed, and the volume of living wood and foliagewhich is removed at any one time. When making pruning decisions the arboristmust consider the chronological age of the tree, because a tree in its formativeyears may be able to tolerate the loss of a large limb, but the same tree in full tolate maturity might suffer terminally when inflicted similar treatment.An arborist who is responsible for large populations of trees, such as thoseowned and managed by local authorities or large parks and gardens, mustguard against the use of generic pruning specifications which do not take thetrees chronological age into consideration. It is also essential that the samearborists keep records of these tree populations, and how they have beenmanaged. This will ensure continuity in the way in which trees are cared for.Putting Pruning in ContextAndrew Cowanwww.ArborEcology.com“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 likeLonsdale, Schwarze, Boddy and Raynor that many plant pathogens co-existfor extended periods of time, in harmony with their host. Although the fullsignificance of this has yet to be interpreted from the observational researchcompleted to date. The concept that the organisms we consider to be pathogens(and therefore ‘bad’) offer a positive contribution to the arboreal ecosystem, doesnot require a ‘leap of faith’ or great foresight. However, it is equally importantthat we do not jump to conclusions.Thoughtless pruning can interfere with and interrupt the natural balance betweensymbiotic and parasitic relationships within the tree and associated arborealecosystems. The physiological, pathological and ecological impacts of pruningwork will not be immediately apparent, because the tree and its associatedecosystem will react through adaptations which occurs over a period of years.Arborists must consider this when assessing a tree by maintaining a cautiousapproach that is not distracted by the presence or absence of familiar and eyecatching fungal fruiting bodies.A greater understanding and appreciation of the long life processes of trees isessential. An arborist responsible for the care of just one tree, can only hope tohave an influence for a fraction of its potential life span. However the pruningdecisions that the arborist makes, can have a direct impact on the tree and itssustainable life expectancy. A decision made today could have consequencesthat 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 oursurroundings in quick succession. A tree, which may fall victim to this, will sufferstresses that could culminate in premature death after being forced into a spiralof 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 andignore the connections is to destroy the tree.”- Wendell Berry -ArborEcology Ltdwww.ArborEcology.com0845 658 1400