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  • Writer's pictureMartin Ford

Accidental Strangulation!

It seemed innocent enough when this tree was used as a post for a washing line; several years later this picture shows the result. All trees move liquids and nutrients up and down the outer layer of cells just below the bark - each growing season these cells are added to, and last year’s fine tubes are turned into wood. The picture above shows how the tree wanted to expand but instead had to use very limited new growth under the constricting line to keep itself alive. Eventually, this strangulation would have killed the tree. Since removing the line, the tree has responded with new growth as it is able to have natural flow of nutrients and water between roots and foliage, providing a new lease on life.

There are, however, trees which do strangle other trees, such as the Strangler Fig! They do this to gain advantage in dense canopy cover of a forest by being able to use an existing tree’s solid trunk to quickly get their leaves into the sun. They then grow trunks around the existing tree till eventually that host tree dies. The Strangler Fig, however, is also one of the most productive trees in a tropical forest providing fruit for animals.

We used to see very similar strangulation damage on newly planted trees on our city streets. It was standard practice to always stake a tree and put two ties from the stakes around the tree trunk. However, the ties were then left in place since there was no 'follow up' as part of planting standards. Now we plant young trees whose canopies are not too large, and staking is rarely needed. But another benefit of not staking is that the tree’s growth will respond to wind action and by moving in the wind, it will specifically focus root growth to stabilize itself. In addition, its trunk will become thicker. When it was grown in the nursery it was in close proximity to other trees (as when growing in a forest) and so was sheltered from the winds. Now in an open site its canopy is often too large for the trunk’s strength and so it will prioritize its response by laying down new cells to enable the trunk to absorb the energy of the prevailing winds. So, planting younger trees means we only stake and tie where absolutely necessary and then remove these supports after a year, once the tree has grown into its new home, thus avoiding trunk strangulation which killed so many trees in the past.

There is also root strangulation, and this is caused by tree roots growing in circles because they were pot grown. As the trees mature, these roots enlarge but soon there is no room left for the roots to expand and so they constrict each other as they wrap around one another. This results in trees with unnaturally short lives - they will seem healthy but in their 30th to 50th year will go into decline and die gradually over the next 10 years. We often see this in trees along our streets which have sufficient soil available to create a full root system but instead it lives a quarter or less of its anticipated life and remains small. Nowadays, when we take a plant out of its pot after we bring it back from the nursery, we look for circling roots and pull them apart even though it appears to be doing damage to the young plant - and it is! However, when we choose to transplant larger specimens for our city landscapes, it has to be done as the plant can’t redirect these circling roots formed in its youth.

So, plant trees young, but if the need is for immediate presence, then buy the larger tree and also plant young ones to grow alongside as they will form strong, naturally-exploring root systems and thus live much longer and healthier lives. The plant’s health is dependent on always creating new cells and thus expanding. By making this our priority in caring for our new tree, it will be able to give us the presence of a happy tree in our gardens and communities.


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