Decay detection and dysfunction
We utilise sophisticated technology to detect tree decay and dysfunction, enabling us to provide evidence on which to base important decisions regarding the status of, and any potential remedial action on, the tree being tested. Each of these tools has it’s advantages and disadvantages, and some of these tools will be more appropriate in certain situations; over the years we have built up extensive experience in using these tools so you can be sure that the most appropriate will be selected.
We currently have available the following tools to analyse and research tree states:
- Sonic tomograph
- Electrical impedance tomograph
- Sonic hammer
- Tree motion sensors
- Resistograph microdrill
- Chlorophyll fluorimeter
This tool allows us to build up a picture of the potential decay inside the tree, by measuring the speed of sound through the timber.
The Tomograph can then use these measurements to create an image that details not just where the decay is, but how severe it might be.
The Picus Sonic Tomograph is a non-invasive tool for assessing decay in trees, working on the principle that sound waves passing through decay move more slowly than sound waves traversing solid wood. Most damage and disease causes fractures, cavities, or rot and these features will all cause sound waves to pass around the affected area rather than directly across it; by repeatedly inducing a sound wave from a specific point and monitoring the results on the other sensors, a picture can be formed of the stem interior.
By sending sound waves from a number of points around a tree stem to a number of receiving points, the relative speed of the sound can be calculated and a two-dimensional image of the cross-section of the tree can be generated.
Electrical Impedance Tomograph
The Electrical Impedance Tomograph uses electrical current to test the state of decay within the tree. Wood is influenced most of all by the water content, cell structure and chemical elements which change according to the status of wood, and the Electrical Impedance Tomograph can detect these alterations in resistance across the timber.
Like the Sonic Tomograph, the Electrical Impedance Tomograph can only take a view through a slice (2D) of timber, so selection of a suitable height to assess is important to avoid potentially misleading readings.
The Electrical Impedance Tomograph can be used in conjunction with the Sonic Tomograph to provide even more accurate analysis, helping to analyse the type of damage, with the potential to distinguish between cavities and ‘wet’ diseased wood; it is also possible to detect the early stages of decay in the tree.
The Tomograph images can clearly indicate the state of the wood by using different colours to illustrate the tree’s resistance to the electrical current – giving a clear indication for use in reports on the potential action to be taken.
The sonic hammer operates in a similar manner to the sonic tomograph in that it uses sound velocity measurement to assess potential decay in the tree.
The unit does not produce images as the tomographs would do, but it does provide a relatively quick means to assess the tree prior to further measurement; it needs just two screws fitted to opposite sides of the tree stem to allow the measurement to be taken. As this unit is simple to deploy and readings can be obtained in a timely fashion, this unit can be ideal where confidence to progress to other, more complex, forms of data collection is needed.
The sonic hammer can help in the detection of early stage decay, brown rot (so called because it decays the cellulose and hemicellulose in wood, leaving the brownish coloured lignin) and white rot (which decays lignin and cellulose, leaving the rotted wood white in colour), cavities, wet cores, and cracks in root areas.
Tree Motion Sensors
These units are ideal for long-term measurement recording of trees in urbanised areas or other high-activity areas, and can record data regarding root deflection and tree stem stability.
The Tree Motion Sensors are affixed to the stem of a tree and through extremely accurate measurements can record the movement and flex of the tree in high winds. This information can then analysed to provide an indication of how susceptible the tree is to failure.
The units themselves are compact and can be left unsupervised whilst data collection occurs; typically fitted at the base of the stem and another placed higher up the main stem, the flex induced from high winds will be recorded. The units utilise a series of sensors – GPS, compass and an inclinometer – to accurately record the position of the tree, the directions in which it sways and by how much.
The tree species will have an effect on how much one can expect the tree to sway under ‘normal’ conditions, but this can be affected by whether the tree is in leaf (creating a greater ‘sail area’ in the canopy), or whether poor tree work has resulted in a potentially unstable tree through the removal of too many branches (branches tend to have a dampening effect on stem oscillations).
The Resistograph has a number of uses, and for arborists it is used to determine the amount of decay in living trees or dead stems. The unit powers a small diameter drill into the tree stem and records the resistance provided by the wood to the turning drill – simply put, if the unit senses a reduction in resistance as it drills through the tree, this is likely to indicate rot and decay.
Our resistograph can drill up to 40cm in depth, and it has the great advantage that it can be used at any height as operation of the unit from a rope and harness (or MEWP) is entirely feasible; it can also be drilled at an angle downwards to assess the rootplate as well.
We also use it in root assessment following air-spade investigations and during climbing inspections.
The Resistograph will provide you with measurable data which will determine to what extent a tree is at risk of failure; it is also invaluable for assessing structural roof beams, bridge timbers, wooden framed houses and playground furniture.
Chlorophyll fluorescence as a measure of the photochemical efficiency of plants is widely used in field studies as an early diagnostic measure of stress in plants caused by adverse environmental conditions.
The process is non destructive if undertaken on site, alternatively samples may be collected and sent to us for analysis; from sample measurements we can assess stress levels and provide remedial advice.