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Conserving Trees on your development site

Recently a Subcontractor of the US communications company Verizon were fined by New York City after damaging and not conserving Trees correctly.

A development plan that aims to preserve existing trees is a great idea. However,  no matter how delicate your plan, it will not be sufficient if the right, equally tree-friendly techniques aren’t used.

Damage can come in the shape of lack of the elements needed for the tree to survive or like in this particular case direct damage to the tree itself.

Often it takes time for symptoms from damage to show on a tree, this sometimes makes cause and effect a little unclear.

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Soil compaction

One of the most common indirect causes of tree damage is soil compaction or root losses.

How much soil?

The amount of soil needed as well as the area you need to protect and avoid working on is calculated using the Tree Protection Zone radius or TPZ radius for short. For your average tree this is can be calculated at 12 inches (30.5cm) for every inch (2.5cm) of  trunk diameter as measured at 1.5m or about 4.8 feet from the ground.

Diameter measured at 1.5m above ground level

On a slope measure for the highest ground level

For trees with low forks, measure at the lowest point below it

How to protect your TPZ

Even if your plans are going to be low-impact to the existing trees, the work done in building will certainly require more space than the final footprint of the structure. Excavation tailings need to go somewhere, and equipment and supplies must be staged nearby. If trees are located in the middle of the project, their TPZs are going to see some action. How can we utilize the space efficiently while building is going on and still protect soil and roots? Some typical strategies recommended by arborists are listed below.

Materials and excess soil and rock from excavation need to go somewhere, and equipment and other supplies must be kept close. In particular trees in the middle of the site are going to see a lot of actively though their TPZs.

The question is then; how can we utilize the space efficiently while building is going on and still protect trees soil and roots? Some of the most commonly used strategies are listed below.

Image courtesy of: Alex Cheek

Fencing

One of the most obvious things you can do to protect a tree’s TPZ is fencing it off.

Before any work commences trees and shrubs to be retained should be fenced off from the working area ideally with relatively high, strong fencing. These fences should be retained for the whole of the construction period and any damage to them should be repaired immediately.

Trunk protection

If you can’t use fencing because you need to use the space either for work to take place then it’s a suitable defense is wrapping the trunk. A recommended configuration for doing this is 4 layers of plastic snow fencing, then a layer of 2×4 planks set on end, edge-to-edge and wrapped with another 4 additional layers of plastic snow fencing.

A recommended configuration for doing this is 4 layers of plastic snow fencing, then a layer of 2×4 planks set on end, edge-to-edge and wrapped with another 4 additional layers of plastic snow fencing.

Others have built a plywood box around street trees to protect both the trunk and soil.

Image courtesy of: Apostoloff

How to keep trees safe throughout the project.

The reality of the situation is space is at a premium and trees are just one of many things competing for it. the real word is far cry from the tree huggers’ paradise where all trees can be kept with a comfortable safety buffer. Builders, contractors, and other workers are most likely not going to appreciate the importance of preserving trees and are not going to put in the amount of care and attention needed to keep them safe. For these reasons it’s essential to have some sort of site supervisor to monitor the trees and space around them.

Site supervision

Ideally, tree officers would supervise each site and ensure that planning conditions are observed.  The vigilance will pay off as workers learn to take your wishes seriously.

It’s also a good idea to take photos at every stage of construction. If any infraction of your specifications does occur, it will be important to prove liability.  Remember building works can easily damage trees, especially the roots, and trees may then die back and become unsafe, you don’t want to be held liable.

Whatever project you’re working on, we hope that you come to us for all your arboricultural equipment needs.

Thank you for reading this article and we hope your project goes to plan.

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