Mapping the roots of an ancient oak

mapping the root system

Using pioneering technology, we are using "Tree Radar" to map the extent of root growth of one of our cherished ancient oaks. The results will provide a 3D map of the root system so we can see how far out it extends and whether there are any gaps in its health.

The root system of an ancient oak

We are working with Sharon Hosegood Associates to investigate the root system of an ancient oak tree.

We are using as a test case an ancient oak which sits by the side of the Decoy Lake.  Known affectionately as the "Eiffel" oak, due to its hollow base and wide ‘buttresses’ which hold it up, it is estimated that this important tree is over 400 years old.  

The mighty buttresses of the "Eiffel" oak
Base of the
The mighty buttresses of the "Eiffel" oak

Originally this area was a coppice but was cleared when the Decoy Lake was created as part of a plan proposed by the landscape designer Lancelot Capability Brown in 1757.  The oak would have been a coppice ‘standard’ or straight-grown timber tree, and was left as a specimen, to enhance the visual appeal of the lake side.

It is estimated that the substantive root system would extend to about 26 m from the tree trunk, way beyond the present drip line.  Close to the trunk, the roots are thicker, and thin out as the distance increases.  The bigger roots absord moisture and nutrient from the soil, to help feed the tree, and provide stability, to hold the tree in place. These are assisted by myriad of fine hair-like feeder roots which not only pick up water and nutrients but also help the tree to breath.  The roots are in turn surround by root friendly mycorrhizal fungi.  In a symbiotic relationship, the fungi provide protection against pathogenic ("bad") fungi, in exchange for some carbohydrates from the tree root system.   

The investigation will provide a detailed picture of what is going on below the surface, without having to do any potentially destructive digging, only heavy duty data crunching.

Our survey was carried out by Ian Leigh, from Sharon Hosegood Associates, the work being carried out on a "not-for-profit" basis. 

Tree Radar

This is a special form of ground penetrating radar (GPR) which can detect roots down to about 20 mm in thickness (about thumb size), up to a depth of 2.5 m .  The radar detects water in the root system and can distinguish this water from water in the surrounding soil.  

The technique is non-invasive, to allow assessment of the root system, without the need for any digging, thus avoiding harm to the roots, in particular the fine roots.

The radar is housed in a red box, and carried in a low cradle mounted in a tricycle, so it is close to the surface.  It is pushed by the operator slowly moving in concentric circles, spaced at 2m intervals, around the tree, with a pulse of radar being sent out every 1 cm of travel.  In the present study, this was 13 circles, with the outer most circle having a circumference of about 200 m.    

The tree radar machine
The tree radar machine
The tree radar machine

The results

Specially developped software allows analysis of the data, to provide a 3-D image of the root system.  Complications will arise when the root system of the oak overlaps with that of a nearby chestnut.

At its simplest, the data will show how good was our estimate of the extent of the root system.  The data from our ancient oak will then be combined with that from other investigations, to provide an expanding data base.  

The results will also show up gaps in the root morphology, so that we can consider taking remedial action. This could be by way of soil improvement or aerial pruning of heavily laden aspects of the tree with few structural roots beneath them.

Further Information

Further information on Tree Radar can be found at Sharon Hosegood Associates.