The Wind-Reaction-Measurement records the dynamic sway motion of a tree in naturally occurring wind, by measuring the root plate tilt.

Advantages:
The reaction of a tree is measured directly, including all environmental influences.
These include tree specific parameters (size, form of the crown etc.), wind strength and wind exposition (buildings and other trees in the vicinity).

In contrast to this the tree pulling test (Wessolly & Erb, 1998), an established method for assessing root defects, uses an artificial wind replacement load. However, an estimate for the correlation between actually occurring natural wind and the artificial wind replacement load is rather difficult because of the previously mentioned environmental influences.

Confirmation of stability
If trees only show a small root plate tilt, even in strong wind gusts, one can assume a stable root system.

Identification of trees with root anchorage problems
After measuring tree groups comparing the results can identify trees with conspicuously large root plate tilt.

Combination with static tree pulling test with regards to stability
If a tree with increased tilt angles has been identified, it is often meaningful to follow up with a static pulling test to measure the trees reaction to a known force.

Addition to sonic tomography target PiCUS Sonic Tomographand resistance tomography
Trees with large defects in the lower stem area (with assumed root defects) should additionally have their stability tested in natural wind

Surveillance of trees near construction
Sustained changes in a tree’s tilt angle during groundworks (e.g. placing of sheet pile walls) can be detected with the PiCUS TMS.

Long term monitoring of trees
Trees suspected of having root anchorage problems can be inspected in regular intervals to check whether:

• The root plate tilt in wind decreases (tree grows new and stronger roots)
• The root plate tilt in wind increases (roots are dying off or get damaged otherwise)
• The reaction remains constant