Accurate Wood Density Testing for Informed Tree Management

When a tree shows signs of internal decay, a visual assessment will not always reveal the full picture. A Resistograph tree inspection gives us the precise data we need to understand what is happening beneath the bark, so we can make sound decisions about a tree's future.

At Down to Earth Trees, we use the PD400 Resistograph as part of our advanced tree decay evaluation service. This method of testing allows us to measure wood density with a high degree of accuracy, confirming whether a tree retains enough structural strength to stand safely or whether intervention is required.

How Does a Resistograph Work?

The Resistograph uses a very fine micro-drill needle that passes through the trunk of a tree while recording resistance to penetration. As the needle moves through the wood, it produces a graph showing changes in density. Sound, healthy wood registers high resistance, while areas affected by decay, cavities or fungal activity show a clear drop.

This gives us a detailed picture of the remaining wall thickness of sound wood at any given point on the stem. Unlike visual inspection alone, the Resistograph provides measurable, defensible evidence that supports tree management decisions with real confidence.

When is a Resistograph Inspection Needed?

We typically carry out Resistograph testing when a tree has been flagged during a routine inspection or risk assessment and further investigation is warranted. Common scenarios include:

Fungal fruiting bodies visible at the base or on the trunk
Cavities, cracks or areas of obvious structural concern
Trees subject to a Tree Preservation Order where retention is preferred
Confirmation of findings from our PiCUS Sonic Tomography or Electrical Resistance Tomography surveys
Trees in high-footfall areas such as schools, parks, roadsides or commercial sites

In many cases, the results of a Resistograph inspection demonstrate that a tree still has sufficient structural integrity to be safely retained. This is particularly important for veteran and mature specimens where preservation is the preferred outcome.

Part of a Complete Diagnostic Approach

We rarely use the Resistograph in isolation. It works best alongside our other diagnostic tools, including PiCUS Sonic Tomography and TreeTronic Electrical Resistance Tomography (ERT). Together, these methods provide one of the most accurate assessments of internal tree condition available.

Following inspection and testing, we provide a full tree risk assessment report that includes structural condition analysis, interpretation of results, risk of failure evaluation and clear management recommendations.

Why Choose Down to Earth Trees?

Our consultants hold recognised professional qualifications, including LANTRA Professional Tree Inspector certification and advanced training in tree decay detection. We have carried out Resistograph inspections and structural assessments for local authorities, schools, public parks, estates, commercial property managers and private landowners across Kent, London, Surrey, Sussex and Essex.

If you have concerns about a tree's internal condition, get in touch. Call us on 01959 524 623 or email enquiries@dtetrees.co.uk to arrange a site visit.