Pollards are trees that have numerous branches arising from the same height on the trunk. Pollarding is commenced when a tree is young generally after it has become established and has a stem diameter of between 25 and 50mm at the desired height. Usually 2 to 3 metres depending on the situation.
Pollarding trees is a method of maintaining trees at a certain height often in formal situations. Historically pollards were used to mark boundaries and culturally they were a method of feeding cattle. Fresh leafy growth was allowed to grow out of reach of the grazing animals and then cut and let fall to providing fresh animal feed as required.
Depending on the species and the knowledge of how well they will respond to this treatment it may be that pollarding can be initiated up to a stem diameter of 200mm. If this is the case or if the species is particularly prone to dieback after heavy pruning, then lower branches should be retained and these can then undergo phased removal.
Once pollards are initiated there ongoing management will always be to re-pollard. The reason for this is that the stems that re-grow will always have relatively weak unions with the trunk. While they are small and young there is little problem, but if allowed to grow they will eventually become more prone to splitting out. Some species are stronger than others.