Detailed tree inspections

When more information is required from a tree than can be obtained from a basic survey, a detailed tree inspection can be carried out. An initial visual tree assessment (VTA) may identify potential weaknesses within a tree, and the extent of these weaknesses may be better understood through a more detailed inspection.

For example, fungal fruiting bodies from identified wood decay fungi may be present. An indication of the extent of wood degredation within the tree can be assessed for certain types of decay by using a micro drill. We have a Digital microprobe (DmP) produced by Sibert Technology.

The Digital microprobe (DmP)

The DmP has a wire probe measuring one millimetre in diameter which rotates at a very high speed. This is pushed into the wood at a constant pressure. Data is relayed to a computer. Speed of penetration is measured by recording the number of revolutions for every 0.1 mm penetration. The harder the wood, the slower the penetration of the probe. Very accurate information on the wood hardness can be obtained from the probe. The information is converted to a graph format which shows the hardness of the wood at specific distances within the tree.

We only ever use the DmP on a tree when we wish to obtain more information about the extent of a
known or suspected defect. We will never use it on a tree as a matter of course.

Graph showing the relative hardness of wood, from a drilling test carried out by the DmP. Distance into the tree is represented along the horizontal axis, with the outside of the tree on the left. The depth in the tree is shown in millimetres. This graph shows wood of reasonable quality from 1.5 to 13 cm into the tree. Within this area, each peak represents an annual ring, from which historical growth rates, and an estimation of the tree's age can sometimes be made. From 13 cm, there is an almost complete absence of hardness, indicating advanced heartwood decay. By applying a series of tests at different locations on a tree, an accurate picture of the condition of the wood can be determined.

Information can be obtained from this test regarding the extent of decay, presence if internal cracks, and growth rate of the tree as the size of each annual ring is shown. This information can assist with the management recommendations.

Detailed inspections may also involve:

• Root excavations in order to assess the condition of the trees roots;
• Climbing inspections to closely examine the crown, where binoculars from the ground were insufficient.