Re-vitalising the health of our Heritage Trees

9 August 2017

City of Trees has been using the unusual technique known as Air-spading to help bring new life into Greater Manchester’s heritage trees.

Working alongside arborist Fraser Green, of Greentreehealthcare, City of Trees identified a number of mature trees as part of their Heritage Trees project which would benefit from the works.

The four heritage trees, between them approximately 1,000 years old, which have benefitted from this unique method are; the Yew at Dam House in Astley, the Red Oak at Longford Park in Stretford (main picture) and two Elms in Buile Hill Park in Salford.

What is air spading?

Air-spading equipment looks very similar to a high pressure water hose used at roadside car washing businesses, although instead of water, high pressured air continually shoots out of the hose. Unlike using tools to break up the soil, air-spading loosens up the compacted soil and reaches the whole area evenly and crucially it causes far less damage than any other method.

As Fraser explains “Air-spading is not the arborist’s equivalent to air-guitar, as fun as that sounds! The basic principle is to loosen hard or compacted soils that lack of nutrients by replacing the air that has been lost in the soil. Air can be squeezed out of the soil gradually over time and by rainfall”.

WATCH: Air spading the red oak at Longford Park, Stretford.

Why is it important?

Airspading, with the incorporation of wood mulches, helps to promote increased soil microbial activity (beneficial worms, insects and funghi that help condition the soil), improve nutrient uptake, protects roots from frosts and maintain soil moisture during periods of hot weather/ drought. Crucially, the tree roots also benefit from the slow release of nutrients from the mulch as it breaks down. 

In a woodland environment the organic matter, such as fallen leaves, would help replenish nutrients in the soil. Bigger and older trees that many of us admire have much of this organic matter swept away, or have large areas of grass over the tree roots.

The depth of beneficial tree roots i.e fibrous mycelium roots that absorb water and nutrients, are generally in a shallow zone of soil just 8 - 10 inches deep, potentially putting them into direct competition with grass roots.

Fraser points out; “Trees cannot move themselves to another area when the soil deteriorates." He adds; “That’s where we can help; while the soil is being air-spaded, woodchip or mulch is added. This changes the consistency and feel of the soil from a solid concrete to a fluffy duvet. The mulch also adds organic matter to the soil and increases microbial activity”.

In addition the air spading works attracts invertebrates which continue to move around within the top layers of soil keeping it aerated.

If air is not present it can lead to the roots being under a lot of stress and root failure where the tree can’t absorb the nutrients needed, reducing their lifespan.

In mature trees this has big consequences not only for the tree, but also for the creatures that rely on the tree for food or shelter.

Andy Long, City of Trees comments; “We have grown to admire and cherish mature trees in our parks and gardens and they cannot be easily replaced. We hope these innovative works will ensure these amazing trees’ longevity and reap the benefits they bring”.

For more information about our Heritage Trees projects visit www.heritagetrees.org.uk.