Tuesday, January 14, 2014

Pollarding: Is it Sensible Management for Street Trees or Just Plain Tree Abuse?

Lucerne, Switzerland

Gary Westlake, Peterborough

I have always thought that topping a tree was a bad thing to do but this might be just my North American bias. Where we grow most trees, we have the luxury of space to allow them to do their own thing, but this is not always the case in Europe and elsewhere.

Carrying on the centuries old practice of pollarding has permitted trees to be used in urban locations where they would quickly outgrow the available space if left to their own devices. Pollarding was originally used to provide the fast-growing whips used for baskets, wattles and forage for livestock. It was also brought into city streets to control the size of street trees.

Pollarding is the straight forward but scary and expensive practice of allowing a young tree to reach the height you would like to keep it at, then cutting off all its main branches including the leader and then yearly pruning it to maintain this height for the life of the tree. There is a great deal of skill and experience required to keep the tree from becoming weak or diseased. Pruning is normally done in spring before the leaves come out, causing the tree to respond by sprouting vigorously from dormant buds. Each year the whips are removed so that the tree forms a gnarly knuckle of scar tissue. Unfortunately, if you stop maintaining these trees for a few years, they can become very weak and dangerous at the knuckles. Many trees will not respond well to pollarding but some that work include oak, catalpa, maple, linden, mulberry, redbud, willow, hornbeam, and black locust.

These trees, while they look very little like the species growing in nature, have a certain architectural quality to them and they provide shade and a bit of greenery to places where it would otherwise be impossible. If you have ever walked along the lake in Lucerne, you would find it hard to judge the practice as barbaric.

Contrast that with the common practice in our cities of planting trees in “tree coffins” and replacing them when they get too big or die a slow death; or our practice  of planting a large tree under power lines, then abusing it later as it tries to grow. I would not want to see a pollarded tree in our garden but perhaps it should be kept as an option for urban environments.