Equipment » Root Plate Stability

The roots and soil anchorage are the foundation of tree structure and any excessive movement indicates a reduction in stability, and the tree may be at risk of failure in high winds.

ENSPEC assess tree stability using tilt sensors that accurately measure root plate movement under natural wind conditions to identify trees at risk of failing. The tilt sensor is a small electronic instrument that records dynamic root plate movement to accurately measure the tree’s response to winds. This is the only method currently available that accurately measures wind loading and directional information on root plate movement.

ENSPEC can identify trees that are at risk of failure and trees that are stable. Trees that are at risk of failure move excessively in winds due to poor root anchorage or root plate instability, whereas stable trees have little movement of the root plate even in strong winds because the root and soil anchorage is sound.

Root damage to trees is common in urban areas when digging trenches to install gutters or underground services.  The stability of a tree can be affected if structural roots are cut, or if fungus or disease enters the tissue through root wounds. If this happens the root anchorage in the soil will be compromised and the tree root plate will move more in windy conditions.

Wind direction is important when assessing tree stability because wind comes from many directions and often the most destructive wind comes from the unexpected direction. Data from tilt sensor tests is valuable in urban areas where nearby buildings can affect wind direction and cause unexpected tree failures.

Fully trained and experienced ENSPEC staff attach the tilt sensor to the base of the tree trunk at the top of the root plate where it continuously monitors root plate tilt during natural wind conditions.

If low levels of tilt are recorded the tree can be identified as stable and unlikely to fail in high winds. If high levels of tilt or excessive movement are recorded the tree can be identified as unstable and at risk of failure in high winds.

ENSPEC personnel analyse the data from the tilt sensors and provide a detailed, professionally written report to the client. The information in the report can assist managers in evaluating trees that are at risk of failure in high winds and to plan appropriate pre-emptive strategies to mitigate the risk of tree failure.

Accurate data on root plate movement can be used to assess likelihood of failure and risks associated with different management strategies for trees, especially in public spaces, and provide evidence to support tree management decisions.

ENSPEC can use the tilt sensor to evaluate the effects of digging or trenching on tree stability by measuring and recording tree tilt before and after the construction works have been undertaken.

The tilt sensor enables the early detection of trees at risk of falling thus allowing managers to plan and implement
remedial works that can prevent failure and damage occurring and safely retain the tree.

Although a tree may be moving at the root plate, it can be supported until roots regenerate and so may not need to be removed. ENSPEC offers tree stability assessment and preservation systems for trees at risk of failure, enabling time for the roots to recover and eventually support the tree. Tree stability can be verified using the tilt sensor to monitor the root plate movement over time to show that the tree anchorage is improving and the tree is becoming more stable.

Data obtained from tilt sensor tests may also be useful in proving that a tree is actually stable and therefore not in immediate danger of falling. This information allows managers to concentrate resources on high risk trees whilst preventing the unnecessary pruning or removal of stable trees.

Figure 1, shows an Electronic tilt sensor secured to the tree to continuously monitor dynamic root plate movement.  During winds the root plate tilt is measured to assess wind loading and tree stability.
 
Figure 2, shows a graph of two adjacent trees in high winds. Stable tree has little root plate movement; other tree shows excessive root plate tilt in the same wind and is at a higher risk of failure.

Figure 3, shows a graph of dynamic root plate tilt for a Eucalyptus rubida (31.5 m high) during a wind storm on 21 July 2011 with a maximum tilt of 0.85 degrees. The circle indicates the tilt limit that is expected from a stable tree under the same wind loading. Wind was from the northerly direction, which caused the tree to tilt in a southerly direction. Failure of a neighbouring tree indicates that this wind was strong and that this tree is moving more than a stable tree and is therefore considered at high risk of failure.

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