Possibly of Decay in Trees Wounded by Decay-Detecting Drilling Devices

"The tiny drilling hole closes itself up without any damage to the tree."
- says almost everyone who have used a resistograph or IML-Resi (decay-detecting drilling devices).

A resistograph or IML-Resi is a tool for tree inspections that detect decay in trees, wooden playground equipment, utility poles, and structural wood of houses and bridges. This tool was initially developed for the tree care industry, but its uses has apparently expanded to a few other industries.

It uses a stainless steel drill needle that is 3mm in diameter (head), and 200mm to 1000mm long. When the drill needle is pushed into the tree by the device, the resistance of the wood to it is recorded on a printed graph (in older models) or displayed on a screen that is on the device. Usually two to four drill points were made at lower part of the trunk and trunk flare, and where there are signs of decay such as cavity or mushroom.

 Head of drill needle, note the brad point.

The users of this device would either say that the fibers of the wood closes the drilling hole as the drill needle was retracted, or that the drilling hole left by the drill needle is so small that it is virtually not visible. Or that the drilling hole could be covered by the tree's growth in one or two year's time. The hole may be an entry point for fungal decay, and further excabated by the wood shavings that retain moisture.

To digress a bit, bits of the wood would be sheared off to allow the drill needle to enter further. The friction between the wood and drill bit head would produce wood shavings, wear down the cutting edge, and the integrity of the drill needle as a whole [1].
To digress a bit further, a drill needle for PD-300 could cost S$30 per piece, excluding shipping.

From at least two studies, what they found did not indicate that decay-detecting drilling devices should not be used [2, 3]. Trees that were already suffering from decay within the trees had their "rot cone" extend temporarily when drilled [3]. The compartmentalising ability of the tree and the aggressiveness of the fungus (determined by inoculum potential and colonisation strategy) are of crucial importance [4]. The studies conclude that the use of invasive diagnostic devices are less serious than felling the tree, or to prune major branches and roots, which typically allows fungal decay to set in.

References:

1. Wear Behavior of Drill Bits in Wood Drilling Resistance Measurements:

E. Sharapov, X. Wang, E. Smirnova and J.P. Wacker 2018, Wear Behavior of Drill Bits in Wood Drilling Resistance Measurements, Wood and Fiber Sciences, 50(2), 2018, pp. 13

https://www.swst.org/wp/wp-content/uploads/2017/06/wfs2678.pdf

2. Development of Decay in the Sapwood of Trees Wounded by the Use of Decay-detecting Devices:

Craig Hallam 2004, Development of Decay in the Sapwood of Trees Wounded by the Use of Decay-detecting Devices, Treenet Proceedings of the 5th National Street Tree Symposium: 2nd and 3rd September 2004

https://treenet.org/resources/development-of-decay-in-the-sapwood-of-trees-wounded-by-the-use-of-decay-detecting-devices/

3. K. Weber and C. Mattheck, The Effects of Excessive Drilling on Wood Decay in Trees,
http://www.arbormedics.com/PDF/PDFsample2.pdf, last accessed 7 Apr 2019.

4. Schwarze, F.W.M.R., Engels, J. & Mattheck, C. 2004, Fungal strategies of wood decay in trees. 2nd Ed. Springer, Berlin, Heidelberg.