latest reply to TCI
Here is the latest letter to TCI..
In a message dated 8/25/2004 4:07:47 PM Eastern Daylight Time,
[email protected] writes:
1. Several people at the ISA show apparently asked him to explain the saw-through on the cover photo. I know you and I had talked about it, but can you provide me a brief explanation of why you used that? I may want to print it as Lee thinks it needs to be explained.
Don and Lee,
The short answer is that the center plunge was made to remove overall fiber from the hinge, making it easier to pull over a backleaner.
Removing fiber from the center of the hinge allows the hinge to be thicker on its sides, which is considered by many, including me, to be beneficial. The corners of the hinge offer the most resistance against twisting and therefore hinge failure. Also one school of thought suggests that removing heartwood is beneficial, because heartwood has less flexibility than sapwood, which makes sense though I have not seen any science to support that thinking.
Center plunge is often used by loggers to prevent fiber pull, which can result in loss of value to the log, and can be used to allow room to set a wedge in smaller diameter trees. The technique has also been taught by Arbormaster to be used on back leaners, for the reasons described above. There is however some debate in the arborist community about the benefits of the center plunge on back leaners as some believe a thinner hinge has more flexibility and therefore greater ability to hold the tree in the intended falling path before breaking.
You may also have noticed that the center plunge is off-center. In this case, the tree had a slight side lean towards a house in addition to a significant back lean. The plunge was made on the compressed side of the hinge in order to leave as much fiber as possible on the tensioned side of the hinge, for reasons described in detail in the article. This left only a small tab of holding wood on the compressed side of the hinge, which was all that was required to prevent twisting and hinge failure.
I have complete photos of the entire removal of this twin lead red oak. The first lead had a head lean and the second a back lean. Each was about 24" dbh and 85' high. Perhaps I could write a short article about this job and call it "Anatomy of a Removal". In this case the drops landed perfectly, one directly on top of the other, which makes for some fairly impressive photos.