Learn about treating soil compaction near trees in this Blog post. The trunk, branches and leaves of a tree are only telling half the story. A healthy tree is a result of the balance between the roots below the surface and the canopy above the ground. One is directly dependant on the other. Without the trunk, branches and leaves there is no structure to create the demand for water flow, and no system for converting sunlight into food. Without the roots there is nothing to keep the tree from falling over, and there is no means of absorbing water and minerals from the ground. The root system also has an important function in storing food (or energy) created during photosynthesis until it is needed.
The root system below the ground, however, is easy to forget.
It is easier to be mindful of the above ground portions of a tree as they are highly visible and are often brightly coloured at different times of the year. Often much care and attention is given to the canopy of the tree ensuring it has the right conditions to grow in. Applying the same amount of care to the root system and its environment can significantly improve the health of the tree, and can often be the most beneficial action you can take to support a tree.
In the forest, tree roots have plenty of space with rich, light soil full of decomposing material, air, and earthworms making for ideal growing conditions. In the urban environment things are often rather different. Because leaves and branches are often removed from the ground surrounding the tree there is no decomposing material. The area the roots have to grow is often limited by buildings, roads and other structures. And the ground is often compacted.
Compaction can have a variety of causes from parking or driving over roots plates.
Construction vehicle traffic, or even merely walking over the root plate (for example in a park where a path may cross it and there is a lot of foot traffic). Compaction acts to denature the soil by closing any small cavities of air that may exist between soil particles. Although trees do not need the air in the soil themselves, many of the beneficial organisms that keep the soil healthy and alive do. Compacted soil is not able to carry water very well meaning less is available for the tree, and making it harder for the tree to draw the nutrients it needs.
One of the best measures to avoid these issues is to prevent compaction in the first place.
Where possible, vehicle traffic should be kept away from the root plate. If vehicles must pass beneath the tree there are a range of products that can be used to spread the load of the vehicle more equally across the surface. Car parks should also be sited away from the root plate of trees. Root zones should also be protected during construction projects and is often a requirement of planning law. To help aid the natural processes of the soil, aged wood mulch can be applied around the root plate. As it decomposes nutrients are released into the soil at a rate that is more suitable for the tree and microorganisms. Mulch can also help protect against the impact of foot traffic if pathways are not able to be re-routed.
If the soil around your tree is already compacted, there are tools that can be used to break the soil up and get air back into it without damaging the tree roots. One of these is an air-spade. This treating soil compaction near trees tool uses compressed air to undo the effects of compaction. Once the soil has been aerated mulch can be applied to help restore the natural processes in the soil.
An interesting article about treating soil compaction near trees is this de-compaction case study at Kew Gardens in England:
If you think you have compacted soil and would like a solution please give us a call to discuss your options.
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This highlights the importance of knowing who is working on your trees and what knowledge and experience they have. Make sure that anyone working on your trees has a long-term management plan in mind and is not just out to make a quick buck. A bad pruning job may only take a few hours but its effects may last for years to come.
The New Zealand Arboriculture associations guide to pruning can be found at the following link: