What Causes Ring Shake?

Speculations and discussion on science relating to ring shake. April 10, 2005

I have read all of the Knowledge Base and various studies, etc. on the subject of ring shake, and none of what I read seems to match what I see in nature to be the cause. It just keeps bugging me. I have a theory which I would like some of you to help me either prove or disprove.

Gene, you have been very clear on your belief that this is caused by a bacteria, but if there was another cause which was later infected by a bacteria, would your test show which came first?

I believe that ring shake is weather related. Here in Little Rock, Arkansas, there have been several years of extreme heat without rain. In 1980 between July 13 to Sep 16, every day was over 100 degrees and no rain. The same for 1954, June to July. I know that everyone here is thinking that would more than likely cause radial checks than anything. I agree. This is often present in association with ring shake.

I believe that ring shake is caused by the rain which follows the hot dry period, and the ratio between the rate of absorbency between heart and sapwood. After the hot dry spell, the tree has shrunk in diameter and circumference, then when the rain returns, the sapwood expands at a faster rate than the heart can absorb the moisture, causing the compressive tangential force perpendicular to exceed the weaker radial tensile failure point, which is typically about 1/3 of the other. Thus the sapwood tears itself away from the heart as it soaks up the moisture from the ground and through the bark, causing a ring shake.

I am not a scientist, but I love to study science, especially if it is related to wood. I have recently gotten some ancient cypress which is 45000 years old, which has more ring shake than is normal for most wood that I find today. I will be attending a conference with a number of scientists and other people interested in this wood. I am an artist and will be giving a presentation of my work, and would like to offer these insights and any feedback which you might offer, if this is a track which needs to be followed. I am not sure there has ever been a study which approached this topic from this angle, but this seems to match what I am seeing in the wood which comes my way.

If you have some wood which you would like to compare with any marker years in your part of the world, you must start your count from the sap-to-heart transition line, not from the cambium layer.

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Your last point first... The sapwood to heartwood line varies with species. In maple, it can be 75 years or more before you see heartwood. In others, the heartwood forms within three years of formation. What you state about counting makes no sense when all species are considered. Once the sapwood cell is formed at the cambium layers, within a day or two, the cells stop growing and do not change size as they age and convert to heartwood.

It is well documented that the bacteria enter the tree first, cause weakening, and then with the wind blowing or other traumatic stress, the wood "shakes."

The moisture content of sapwood and heartwood does not vary with the climate, as your statements imply. The MC within the tree is constant even when there is a dry spell in the weather. Trees do not shrink when it is dry outside. Your discussions are not supported by any scientific studies; in fact, studies have shown that the MC remains constant within the tree. Incidentally, if a tree were to shrink when it dries, you would have to reduce the MC to under 30% MC, as it is only below that level that wood shrinks. The normal condition in a tree is 75% MC and higher. Drying the wood in the tree to under 30% MC so it could shrink would kill the tree.

You say that you have read everything about shake. You need to read about tree physiology, which is the study on how they grow. If you have this understanding, then you would not have such strange ideas about tree behavior.

You have wood that is 45,000 years old? This is unbelievable. Is it petrified? How did you find it? Was it carbon-dated? I am unaware of any wood that is even 6000 years old.

From the original questioner:
I am aware that the thickness of the sapwood varies. Even within most trees it will often jump a few years, which is also a common trait of ring shake.

Your statement about MC in living trees is what I had always believed to be true, except that I remember seeing a standing living tree which had a radial check large enough to stick my finger in. Keep in mind that we had 64 days straight over 100 degrees, with no rain. It was miserable having to work when it was 108 out. I was working at two jobs, neither was air-conditioned.

I was given a yard tree back in 96 which a tree service took down with a crane, and delivered to my shop. I cut it into firewood lengths, and split it with a maul. It was a pleasure to split, because there was a total ring shake from the bottom section all of the way up for 40 or more feet to where the branches were the size of my wrist.

I was fascinated by this and wondered what could have caused it, so I came in and got a 10X loupe to see what that might reveal. There didn't seem to be any abnormal cells or sign of decay, only some splinters connecting each side of the split together. I had initially guessed that the cause had something to do with 1980, but when I counted from the cambium, it turned out to land on 1968 mid-summer. I was in For Polk La. that year.

When I got back to splitting, I looked around at how much more there was to split. I noticed that there was water standing about 1/8" deep all around the sapwood, while the heartwood was only moist. Ah ha, I thought. When I counted again, there were 12 years of sapwood, which when taken away from the count, fell exactly on 1980.

What made this tree so remarkable is that between 1980 and 96, it had never lost any limbs, or received any other wounds large enough to open this shake to the outside world, which would have given the insects and bacteria, etc. which is so much more common, from what I have observed since.

You can find a few paragraphs about this ancient wood in FWW Magazine on page 22 this month. Yes, it has been carbon-dated. It has lost much of its structural integrity. It was buried under 40' of wet sand. You may want to read some of Richard Guyette's research to get a handle on how many years before all of the carbon is gone under various conditions. It found its way to me through David Stahley, who is a dendrochronologist at the U of A in Fayetteville, and is studying this find. I got to know him by giving him some wood that I found over 20 years ago. His assistant based his master's thesis on my wood, and is another long story. I have learned a lot from studying their research. It has changed the way that I view nature.

From Professor Gene Wengert, forum technical advisor:
Bacteria that causes shake (by weakening the wood) moves about 1" per year up the stem. It enters the trees through the roots and not through the stem.

Shake is a separation of the rings of the wood parallel to the rings and not across the rings. Most shake is formed in the region between the heartwood and sapwood, but the bacteria exist in a much wider region than just the shake area.

The water can flow out of sapwood much faster than out of heartwood.

Cypress cannot be used for dendrochronolgy studies. Further, such dating only works for trees grown in seasonal climates. The dendrochronolgy base in North America is not much over 5000 years.

Because the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old. What do you want me to see in Richard Guyette's research pertaining to this matter?

The correct spelling is Stahle, not Stahley.

From the original questioner:
Thanks for correcting me on spelling Stahle. I'll be sure to pass on to him what you said about cypress being unsuitable for dendrochronology, since it seems to be the oldest wood east of the Rocky Mountains and has been the source of some of his most notable finds. You were joking, weren't you?

I don't claim to have a very good understanding of carbon-dating. That is why I thought you would like to read some of what Richard Guyette's studies show.

Back to the subject of ring-shake. From your sentence about water flowing out of sapwood fasterů Can I take that to mean evaporate faster? If so, do you agree that it will absorb moisture faster than heartwood, especially those with higher extractive content in their heartwood?

I have only done a few tests of my own, and would be very interested if there have been studies which show comparative ratios.

You have stated here that getting dry wood real wet on the surface can cause honey-comb, or internal checking. This is not so different from what I am proposing. So why are you resistant to accept the logic of what I am proposing?

What is left. Bark is such a good barrier against evaporation, that 60 days in a kiln above 100 + degrees would result in no appreciable loss in MC? I don't think so. I haven't built my kiln yet, but I can think of an easy test for some of you that do have one.

The next time you load a charge of lumber in your kiln, why not put a small red oak log in? Be sure to end-coat with Anchor-seal, so that all of the moisture has to evaporate through the bark. Run your normal schedule for whatever you are drying.

Whenever you take it out, cut the ends off, and put it back out on the yard under the sprinklers for a few days. It won't have the roots to suck up the moisture, but either way the moisture will be getting to the outside first, and if the heartwood has shrunk in diameter, the sapwood will be trying to pop loose.

This is also a good receipt for causing star-check in the heart, so if this occurs, it may relieve the stress which causes the otherů Although sometimes both are present when there is a lot of twisted grain near the pith, which keeps those checks from connecting well with each other.

Gene, I am sorry if I sound confrontational. Thank you for letting me voice my insights on your message board. As I stated earlier, I have been looking at this for a long time, and the studies that I have read made no connection to bacteria. (The studies which I mentioned were sent to me by the U.S. Forest Products Lab, and were by Arthur Koehler; R.W.Meyer & Lawerence Leney: E.A.McGinnes, Jr.) I believe that math will help prove this theory.

I have nothing to gain here. I don't think that I could get a grant or make any money from this if it is proven to be the real cause, but some of you probably could, or some of you may know someone in school who needs to do a study for a masters or Ph.D. If you do, please put them in touch with me. I will tell them everything that I know and can guide them through a lot of the resistance that I am sure they will meet along the way.

From contributor S:

I'm not arguing here, but my experience with ring shake in oak is that bacteria is invariably present along the lines of failure. This either indicates cause or that bacteria will quickly colonize the separated zone.

That said, I have seen ring shake in other species, most notably cherry, where no bacteria was obvious (no smell or stain), but in these cases, the tree was felled using a bulldozer, which I assume applied considerable shear forces while bending the trunk over.

From Professor Gene Wengert, forum technical advisor:
Sapwood is more porous to liquid movement than heartwood. In the living tree, sapwood has more moisture than heartwood.

"You have stated here that getting dry wood real wet on the surface can cause honey-comb, or internal checking." This is not totally correct. It is true only for partly dried wood, especially if stress reversal has occurred. It is true only for check prone species, like oak. (Note that your original posting was about shake in trees and you have switched to lumber at this point.)

"Bark is such a good barrier against evaporation, that 60 days in a kiln above 100 + degrees would result in no appreciable loss in MC?" Bark is not that effective. Even so, the shrinkage you will see if more tangential shrinkage which causes cracks across the rings and not shake. As you noted, there will be star-like cracks; these are not shake. These cracks effectively relieve the stress. For example, on a 24" diameter log, the outer tangential shrinkage will be about 3", while the radial or diameter change will be only about 3/4".

You should probably read some recent literature about shrinkage, moisture movement, and so on. Some authors would be Skarr, Siau, and Wangaard. Also, read the works of Ward about bacteria in wood. Check the Forest Products Society for recent publications at www.forestprod.org. There have been some significant advances in understanding since Koehler's time. After reading such works, you will be in a better position to formulate a theory. Certainly, these authors have spent many years working in this area; it is their work that forms the basis for my understanding. Your original comments about shake forming in the living tree need to be correlated with the tremendous amount of information on tree physiology. People have spent their lives studying the moisture in trees and how this moisture changes with seasons, weather, etc. Use this knowledge base to form your theories, rather than starting from zero historical knowledge of the subject area. I am certain you will find in this knowledge area a good and reasonable explanation for what you observed.