Causes of Shake

      Bacteria is what causes shake in trees. September 24, 2003

Question
I have material coming in that has some shake in it. I read an article stating that wind shake is caused by a bacteria that weakens the wood. What is this bacteria called? Are there ways of detecting this bacteria in the wood, other than finding the "shock" wood? Even if the wood has not been "shock", is it possible that the wood could have this bacteria and is weak because of its presence?

Forum Responses
(Sawing and Drying Forum)
The bacteria belongs to the clostridium genus. The bacteria is often accompanied by an unpleasant odor. The MC is also much higher than normal.

The bacteria can be present and weaken the wood, but shake may not be present. In other words, the infected, damaged (poor machining, high MC, poor color, etc.) area extends beyond the shake area.

Gene Wengert, forum technical advisor



You are talking about shake, that which occurs between the rings of annual growth, right?


My understanding of shake is that wind shake and ring shake are two completely different things. Out West, wind shake is in reference to the star-like checks that occur in large trees, such as redwood. The shake is perpendicular to the annual rings, and not along the ring. Ring shake, as the name implies, is along a ring.


Wind shake = shake = separation parallel to the rings (not across). Sometimes shake will occur in trees that have been through a tornado, but other than that, all shake is bacterially related. (Very rarely, I have seen shake also called shoke, the past tense of the verb,)

When cracks or separations are related to the heart and go across the rings, it is called star cracks or heart cracks. I have not heard it called star shake, but it is possible.

Gene Wengert, forum technical advisor



I suspect the locals in CA still call it wind shake and know what they are referring to when they say it. They probably don't know the Midwest definitions very well.

I suspect "shook" is the past tense and not "shoke"? Can't tell if it is a typo or if it is a new word.



Shook indeed. I was not shoke up yet!

The definition of shake is worldwide, not just in the Midwest. CA locals must have their developed their own meaning.

Gene Wengert, forum technical advisor



So if I have understood correctly, the definition of shake found in the NHLA Rule book is what we're talking about.


A separation along the rings, the greater part of which is parallel to the annual growth rings.

Gene Wengert, forum technical advisor



Could you explain more in depth the "poor color" you talk about that accompanies wood in these bacteria-infected areas? Is the wood color darker, lighter, blotchy, multicolored?



Darker and streaked often.

Gene Wengert, forum technical advisor



I suppose the name "wind shake" is due to the long held belief that wind was the cause until scientists figured out what the cause really is? If it were really the wind, every tree within a mile of me would be shook.


Splits, sometimes very hard to notice, will accompany the darker colors, also.


Often the splits result because the bacteria weaken the wood severely.

Gene Wengert, forum technical advisor



Gene, correct me if I'm wrong, but isn't the fact that the wood becomes weaker the reason why the base of the wind shook tree swells so much? Compensating for weakness, with added density and footing? Is wind shake just an oak problem? I don't recall it being a problem with other species in these parts.


It occurs in many species (all?) that we have examined. Oak, cottonwood, hemlock (very common), etc.

The swelling is probably due to growth in a very wet site. Such wetness itself is favorable for the bacterial growth, as it is an anaerobic bacteria. The two go together but do not cause each other.

Gene Wengert, forum technical advisor



I recently sawed some 8/4 red oak from trees killed by oak wilt. Is this also a culprit in causing shake?

Is there any drying or machining difference as compared to live trees?



If anyone has spent time sawing enough red oak, they will know the bacteria infection symptoms. Heavy mineral, so much that the lumber will have a greenish hue to it and no presence of pink anywhere. You decide to saw 4x6's and get the log off the carriage. You know from previous experience that if you saw some lumber and put it on the top layer, that two days later when you go to ship it, you have to cut the bands of the pack and pull those boards off. The shake is so bad that it looks like a rattlesnake shedding its skin. That is bacterial infection, and in oak that board will blow apart quickly, sometimes in a matter of hours if conditions are right. Wind might exacerbate the problem, but I am sure it isn't the cause of shake. Perhaps if you live on the coast and a hurricane should come across land.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
This article about shake and bacteria holds very true for (WHND) soft maple, as this grows in low, often wet woodlots. In our local logging areas, we run up to 90% nd., and we find the infected streaks green to dark greenish in color. We have been successful in the drying process not to collaspe these poor areas in the lumber, however when you inspect these areas, you will find the shake. If these trees have the bacteria, it does smell like the swamp.



Comment from contributor B:
Here in B.C., Canada, what we call shake is cracks in the wood (usually in Douglas fir) which are usually perpendicular to the growth rings, and tend to be in the center areas of the "bole" of the tree. The cracks often are pitch-filled, and tend to weep after milling green trees. Apparently caused by high winds and also known as wind-shake. Lumber with shake in it is usually heavily degraded, often to the point where it is only useful as firewood. This sounds like a completely different "shake" than that which is being described in the mid-west!

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