Putting Pruning in Context Andrew Cowan - ArborEcology - Arbtalk

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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
Page 4 and 5: A life time to understand:Trees are
Page 6: The natural balance of tree ecology

Putting Pruning in Context Andrew Cowan - ArborEcology - Arbtalk

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