Pollarding
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Pollarding is a pruning system in which the tree is headed back (tree stem or minor branches removed) every year.[1] This pruning encourages lateral branches and is normally done two or three metres above ground level. The tree is allowed to regrow after the initial cutting, but once begun, pollarding requires regular maintenance by pruning. This will eventually result in a somewhat expanded (or swollen) top to the tree trunk with multiple new side and top shoots growing from it.
A tree that has been pollarded is known as a pollard. Pollarding older trees may result in the death of the tree, especially if there are no branches below the cut, or the tree is of an inappropriate species. Pollarding is sometimes abused in attempts to curb the growth of older or taller trees, but when performed properly it is useful in the practice of arboriculture for tree management.
Pollard trees may attain a greater age than normal, because they are maintained in a partially juvenile state, and they do not have the weight and windage of the top part of the tree. Older pollards often become hollow, and so can be difficult to age accurately. Pollards tend to grow slowly, with narrower growth rings in the years immediately after cutting.
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[edit] Practice
As in coppicing, the tradition of pollarding is to encourage the tree to produce new growth on a regular basis in order to maintain a supply of new wood for various purposes (particularly firewood), and in some areas for tree hay – dried leafy branches stored as winter fodder for stock. Depending upon the use of the cut material, the length of time between cutting will vary from one year for tree hay or withies, to five years or more for larger timber. Sometimes only some of the regrown stems may be cut in a season – this is thought to reduce the chances of death of the tree when re-cutting long-neglected pollards.
Pollarding was preferred over coppicing in wood-pastures and other grazed areas, because animals would browse the regrowth from coppice stools.
An incidental effect of pollarding in woodland is the encouragement of underbrush growth due to increased levels of light reaching the woodland floor. This can increase species diversity. However, in woodland where pollarding was once common but has now ceased, the opposite effect occurs as the side and top shoots develop into trunk-sized branches. An example of this occurs in Epping Forest in London/Essex, UK, the majority of which was pollarded until the late 19th century. Here, light levels on the woodland floor are extremely low owing to the thick growth of the pollarded trees.
Pollards cut at only about a metre or so above the ground are called stubs (or stubbs). These were often used as markers in coppice or other woodland. Stubs cannot be used where the trees are browsed by animals, as the regrowing shoots are below the browse line.
[edit] Species
As with coppicing, only species with vigorous epicormic growth may be made into pollards. In these species, which include many broadleaved trees but few conifers, removal of the main apical stems releases the growth of many dormant buds under the bark on the lower part of the tree. Trees without this growth will, of course, die without their leaves and branches. Some smaller tree species do not readily form pollards, as cutting the main stem stimulates growth from the base, effectively forming a coppice stool instead. Examples of trees that do well as pollards include broadleaves such as beeches (Fagus), oaks (Quercus), maples (Acer), black locust or false acacia (Robinia pseudoacacia), hornbeams (Carpinus), lindens or limes (Tilia), planes (Platanus), horse chestnuts (Aesculus), mulberries (Morus), Redbud (Cercis canadensis), Tree of Heaven (Ailanthus altissima) and willows (Salix); also a few conifers, such as yews (Taxus).
The technique is also used in Africa for Moringa trees, to bring the nutritious leaves into easier reach for harvesting. Pollarding is also used in urban forestry in certain areas for reasons such as tree size management, safety and health concerns. It removes rotting or diseased branches for the overall health of the tree, living and dead branches that could harm property and people, as well as expanded foliage in spring for aesthetic, shade and pollution concerns. Trees may be "rejuvenated" by pollarding – for example Bradford pear (Pyrus calleryana "Bradford"), a beautiful flowering species when young, but brittle and top-heavy when older.
Oaks, when very old, can form new trunks from the growth of pollard branches - i.e. surviving branches which have split away from the main branch naturally.
[edit] Origin and usage of term
To poll was originally a verb meaning to crop the hair, this being extended to similar treatment of the branches of trees and the horns of animals. A pollard simply meant someone or something that had been polled (similarly to the formation of "drunkard" and "sluggard"). For example, a hornless ox would be referred to as a pollard. Later the noun pollard became used as its own verb: "pollarding" from a neologism developed from the noun as happens frequently in speech. "Pollarding" has now largely replaced "polling" as the verb in the forestry sense. Pollard can also be used as an adjective: "pollard tree". [2]
[edit] See also
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Look up pollarding in Wiktionary, the free dictionary. |
[edit] References
[edit] External links
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