AIRKNIFE:TREE FRIENDLY EXCAVATION

The Supersonic AirKnife enables the excavation of sensitive areas without fear of damaging roots. This has opened up new opportunities in diagnostic work, soil remediation, and excavation close to trees. The danger of damaging tree roots or even underground utility lines is no longer a concern with this tool.

The AirKnifes we use have been imported from the USA where the tool is manufactured by Easy-Use Air Tools, Inc. The tool's design has been scrutinised for over eighteen years to perfect it in a multitude of real life circumstances, although it has only recently been adopted by a small number of arborists for use in the UK.

New techniques are being discovered and developed that will make these tools the next arboricultural frontier. In the near future, in order to offer ‘complete tree care’, arborist's will need to utilise Supersonic Air Stream technology.

The AirKnife opens a new world of tree care. For the first time we can work with the underground portion of the tree and look closer at the interaction between tree roots and the fungi living with them. It is common for us to think that fungi growing at the base of trees are evidence of decay in the trunk or main root system of the tree, without considering that they may just be living off the dead wood where the oldest tree roots have become dysfunctional.

Using the high pressure air stream to break up and blow away the soil from around the base of trees it is possible to look in more detail at the roots which might be affected by the fungi, while also being able to assess the effectiveness of the reactive growth being produced by the tree. By undertaking such a revealing investigation it becomes possible to make more informed management decisions without employing invasive decay detection equipment.

Working with utilities:
The AirKnife makes excavation around underground utilities much safer for workers and trees. It can be used to locate gas and power lines before digging with mechanical excavators. It can dig a utility line tunnel under a hard surface like pavements or patios as easily as under tree roots.

Where it becomes necessary to excavate a trench close to or under the canopy of a tree, the AirKnife can be used to expose roots that may then be either bent out the way of the trenching work or cut back using target pruning. This reduces the stress caused to trees by preventing roots being ripped out the ground by a mechanical excavator, therefore prolonging the trees life expectancy and enabling the retention of trees that may otherwise have been removed.

However, it is essential that all work to expose tree roots be undertaken by qualified arborists with knowledge of tree physiology and ecology, although, the AirKnife itself is easy to operate and could be used by groundwork contractors during other excavation works. Once exposed the tree roots will need to be treated with care and if left exposed for any length of time they should be sprayed with a hydro-jell to reduced desiccation as a result of water loss, while mulch can also be used to cover exposed roots during excavation work.

Remediating soil compaction:
Soil compaction is widely recognised as one of the most significant stresses associated with trees in urban environments, especially in association with development, while also being an issue in well used parks and gardens. The compacted soils have lost macro pore spaces that normally hold air and water. This has a dramatic influence on respiration and severe compaction can suffocate a tree.

The most effective treatments for compaction have been vertical mulching and radial trenching. Traditionally this has been done with spades, augers, trenchers and backhoes, balancing the increased pore space against root damage caused by these mechanical diggers.

Since the AirKnife does not damage roots, we can now double the treated area without overstressing the tree. Radial trenching to improve root growth is made easy when you can simply blow the dirt away and replace it with improved soil. In addition, vertical mulching with an AirKnife can be four times faster than with a petrol driven auger and with a lot less effort.

How the AirKnife works:
The AirKnife converts compressed air from a portable compressor to a supersonic jet stream by use of its specially engineered nozzle. The finely focused stream of air penetrates the ground to nearly a depth of up to 30 cm and can be aimed to crumble and blast the soil away as fast as the operator moves the tool. Since tree roots, rocks and pipelines are non-porous soil can be excavated quickly with no impact to roots, electrical, and gas lines.

Andrew Cowan
ArborEcology