Risk Assessment

Tree risk assessment and management is not precise, and is not accomplished by measurement and calculation. It is accomplished by observation, thought and judgement of the experienced and trained arborist.

We have years of experience operating a tree service, climbing and working in trees, with education and training in the mechanical properties of wood and trees. Our observation and analysis of hundreds of failed trees provides an advantage in risk analysis and assessment.

Performing a comprehensive examination of the tree may require excavation of soil to inspect the lower trunk and roots for decay. As necessary, we will climb the tree or use a lift or a drone to inspect for aerial defects.

In certain cases, important information may be revealed by an experienced arborist from simply sounding the tree with a mallet. When necessary, we use more sophisticated analytical instruments such as a resistance drill or sonic tomograph.

Equipment we use for Risk Assessment:

Mallet

We start with a mallet to “sound” the tree, listening for tonal variations that could indicate defects within the tree compromising structural integrity.

Resistograph®

We use a Rinntech R650 Resistograph® that inserts a 3 mm diameter probe to a depth of 50 centimeters (20 inch) into the tree. It measures interior wood density at selected points and converts the measurement into a graph that can be used to infer decay, cavities, internal knots, or other features. This is used to help analyze overall strength of the tested portion of the tree.

A typical resistograph reading can been seen here:

The low flat portion of the trace reveals an interior cavity or advanced decay in a tree.

Arbotom®

The Rinntech Arbotom® sonic tomograph utilizes impulse compression waves from an array of sensors to create both horizontal and vertical maps of the varying wave transmission speeds within the tree interior. These variances correspond to different defects that can be inferred from the images. Different graph types are available to assist in distinguishing one defect type from another.

This allows us to create an “internal scan” of mechanical portions of the tree necessary to stability.

To the left in the image above, the horizontal tomogram, to the right, the cross section approximately at the imaged section. A faint line outlines visible decay to approximately the extent shown by the instrument as slow sound transmission. A verti… — To the left in the image above, the horizontal tomogram, to the right, the cross section approximately at the imaged section. A faint line outlines visible decay to approximately the extent shown by the instrument as slow sound transmission. A vertical section can also be produced.

These instruments provide us with more information to make an informed judgment. They do not provide certainty. The final assessment is never a calculation, always a judgment.