Runout

[Kary Karahadian]

saw this while backpacking up in the Sierras. Makes understanding runout easy.

[Mario Proulx]

Yup... Just studying old telephone poles also clearly shows it, also.

But strangely, some trees will grow 100 years with zero runout, then suddenly begin to spiral like the one in your photo here!

[Barry Daniels]

I heard from an old luthier that the movement of the sun across the sky during daylight hours is responsible for tree twist because most plants try to follow the sun.

[Mark Swanson]

I have heard that too.
"But tomorrow may rain, so, I'll follow the sun."

[Mario Proulx]

I believe that idea was rebuked, Barry, with the more likely notion that the spiraling is simply nature's way of stiffening the tree trunk(which it certainly does).

If we think about it for a second, the twist would be a daily occurrence if it were truly "chasing the sun". Most plants simply twist their leaves a bit during the course of the day to expose the leaf to sun to its best advantage. The twist in a tree trunk is an actual laying-down of new fibers in spring and summer, at an angle, instead of perpendicular, to the ground.

[Chuck Tweedy]

If every (twisted) tree in the norther hemisphere twisted the same way (namely: clockwise as you look from above), there might be evidence that it caused by passage of the sun across the sky.
If counterclockwise in the southern hemisphere, that would be some pretty strong corroborating evidence.
I do not know if this is the case - just doing detective work.

[Barry Daniels]

Chuck, The luthier that told me this said the northern/southern hemisphere differential twist direction was a fact and thus was the corroborating evidence for this theory. However, the one piece of evidence we have (the photo in the first post) is twisting the wrong way for the northern hemisphere. Assuming the photo wasn't reversed. So the theory may be bunk.

[Chuck Tweedy]

Yep.
Good thesis for a student of forestry.

[Barry Daniels]

We have a forestry graduate on staff and I have posed the question to him. He promises me an answer tomorrow.

[John Hamlett]

Ever see ribbon grain mahogany? The grain twists one way for a time then the twist reverses for a time. Other trees do it too, like certain gum trees. I suppose those trees must move from the northern to the southern hemisphere every few years in order to do that...
Some trees, like western red cedar almost never show spiral grain.

[Chuck Tweedy]

John, many of those species are tropical, so in mid-summer the sun passes directly over head and actually does influence the tree from the other side during the winter.

Except the rings of alternating spiral do not occur twice a year.
No, those trees certainly do it for the strength - as Mario said.
Eucalyptus for one - Impossible to split a round. San Diego is warm, but not the tropics by any means.

[Mario Proulx]

I'm in the sub-arctic, yet we have some trees(willow, trembling aspen, and especially balsam-aspen, to name a few that come to mind) that often have interlocking grain. There's no friggin' way these trees reversed their "twist" every 5-10 years to follow the sun...., 'cause our sun is very consistently low up here, and for damned sure doesn't suddenly pop-up in the northern half of the sky for 1/2 the year(as it does in the tropics).

[Steve Rolig]

Has any one observed this before. This spring I had the chance to harvest a beetle-killed englemann spruce tree from Wolf Creek Pass in Colorado, about 30 inches in diameter. The outer 1-3 inches seemed to be the only part of the trunk that had any spiral (and not nearly as dramatic as in the picture above) the remainder split straight both radially and tangentially. Although I don't think it had anything to do with the twist only the outer 1-3 inches were blue stained from the beetle infestation. After splitting that off I was left with very straight grained wood without runout and without staining.
Steve

[John Hamlett]

Stuff like that happens. I have no experience with engalmann trees, only the wood in top-blank form, but certain species of tree are more or less prone to spiral grain, (wind, as it's called, not like the wind that blows, but like winding a clock), and the growth patters can change for no apparent reason. I've seen red spruce with variation in the amount of wind, nothing is too surprising when it comes to the inside of trees. (I've seen the inside of quite a few trees since I bought a sawmill in 1986, mostly eastern US hardwoods, though.)

[Mario Proulx]

Steve, I've seen it often, while splitting firewood...

One suggestion, and one that makes perfect sense, is that as the tree reaches a height to where it needs more strength, more quickly than simply laying-on more growth provides, either from the height it has now reached or perhaps because a nearby tree, or many trees, have died and fallen and it it no longer protected from strong winds. So, it begins to lay-down it's new growth at an angle, instead of vertically. As a small, young tree, the ability to bend, instead of breaking, is an advantage, and laying-down new fibers vertically is also the most efficient method of gaining height and growth, so it makes perfect sense that a young tree would not "bother" to 'twist'.

Also, if the tree was physically twisting, -all- of the trunk would be twisted, not just the outer layer.

"Following the sun" makes no sense at all, and the real-world evidence dismisses it as folklore, methinks. But as long as folklore continues to be passed-on by otherwise reputable people, it will never go away.

[Barry Daniels]

Speaking of wood folklore; check this out. It is from the same source I heard about the cause of twist:

http://www2.gibson.com/News-Lifestyle/F ... -2012.aspx

I think the obvious falacy of this "theory" is that even if the moon cycle affected the amount of water in the wood, this would be removed during curing.

Werewood indeed!

[Mario Proulx]

Oy!

[Alan Carruth]

I've got a book entitled 'Growth Stresses and Strains in Trees', by Archer, that has some information that got me thinking about the origins of spiral grain in a different way. Inserted in the back is a short paper by the same author, that seems to substantiate my ideas, if my poor math skills are following it right. This gets a little involved, so bear with me.

The primary stress he talks about is the buildup of tension in the outside layers of the trunk, and the concomitant rise in compression toward the center of the tree. Basically, green wood tends to fail first in compression, so the tree has a mechanism to reduce the compression stress in the outer layers. As each new layer of wood cells is formed, and before the cellulose fibers are glued together with lignin, the tree increases the pressure within the cells, enlarging their diameter. Each cell contains three layers of cellulose fibers: two that run up and down the length of the cell, and a layer in between (the 'S-2' layer) that spirals around. You could think of the cell as along, skinny balloon, with the S-2 layer as a spiral of tape that was put around it when it was partially inflated. Blowing it up more will cause the balloon to twist and get shorter, as the tape won't expand the way the wall of the balloon can. Of course, a cell in a piece of wood can't get any shorter to speak of; it's tied down, but the increase in pressure does introduce a tension stress in the wood. The fibers are glued together when the pressure in the cells is high, and this locks in that tension.

It's pretty easy to see this in wood. If you rip strips off the bark side of a quartered plank, they will often bend away from the plank. This used to be the standard way of assessing the built-in stress. A plank was cut from the center of the log, so that it was well quartered all the was across, and contained the central pith of the tree. Two parallel marks were made across the plank, 100" apart. Then the plank was cut into strips. If they are kept in order, they'll look like:
)))))))|(((((((.
The strips are then clamped back together in order. The central strip will be longer than the plank was originally: releasing the tension of the outer layers removes the compression stress and allows it to expand. Similarly, the outer layers will be shorter than the original plank. The parallel lines that were 100" apart are now chevrons facing away from each other, and the difference in distance between the points of the chevrons and the tails is a measure of how much stress there was in the log.

It's pretty obvious that this stress will be controlled by the tree, depending on conditions. Removing a large branch on one side will throw out the stress, and cause the tree to react: according to Archer this can happen in less than a week. Trees that lean, or ones that get tipped partly over, will have much more tension on one side of the trunk than the other. I imagine much the same would happen to a tree that grows on a steep slope, even if the trunk is vertical: there are likely to be more branches and leaves on one side than the other.

Now, here's the speculation... It occurred to me that all of those little wood cells trying to twist could be seen as rather like gears around the periphery of the trunk. As they all twist one way, the trunk will be twisted the other way. They're small, of course, and don't have much leverage, but they are also persistent, and we know how wood cold creeps under persistent loads, even when those are 'small' relative to the strength of the wood. Over time, this could cause the trunk to twist, and that would displace the branches of the tree from where it 'wants' them.

By the same token, if the cells are laid down at an angle to the axis of the trunk, they will tend to cause it to twist due to the increase in tension in the outer layers of the tree. This is also not desirable. _But_, if the cells are laid down at just the right angle, the 'gear' twist will be counteracted by the 'tension' twist, and the tree will remain in the position it wants to.

So; trees don't exactly twist to follow the sun, but it's possible that the alternation of wet and dry seasons, and changes in shading as the sun moves north and south, could have a bearing on the formation of 'stripe' figure in tropical woods. This would not explain stripe in temperate zone wood: I'm working on a Red spruce top now that has some striped runout. The long period of the change suggests that it could have something to do with periodic logging of the area where the tree grew, but that's just conjecture without any data.

Here's a datum:
Moisture cycling over time causes wood to progressively shrink, and also tends to relieve any built-in stresses. My old barn roof has a kingpost truss construction; with upright timbers supporting outer ridges of the the gambrel roof. Some of these grew with a twist, and some did not. The ones that grew with a twist have become more twisted over time: the upper ends of the square posts are no longer aligned with the lower ends, having twisted as much as 20 degrees or so, in a sense that increases the twist angle of the grain runout. We can think about why this might be so.

Alan Carruth / Luthier

[Mario Proulx]

That makes sense in many ways, but doesn't explain interlocking grain, and for sure doesn't explain how a tree can grow for a 100+ years, straight as straight gets, then suddenly begin to put-down new fibers at an angle. Again, if the tree, or trunk, actually did physically turn and twist, we would see the runout throughout the entire tree, and not as a distinct change.

And of course, all of the possibilities can hold true, for various species and for various reasons(climate, genetics, environment, etc...

BTW, I've also noticed old beams, and even older 4x4, that continued to twist for decades, some breaking the concrete they were set into! Reaction wood is force to be reckoned with!

[Alan Carruth]

Mario Proulx wrote:
"That makes sense in many ways, but doesn't explain interlocking grain,..."

The sort of interlocking grain that you see in wood from branches, and sometimes in the trunk, is 'reaction wood', which was not part of the above discussion. (I'm assuming you're not talking about 'stripe' figure, which I did discuss) As we know, wood does not resist a sustained load that imposes shearing stress well, tending to deform progressively over time. That's why we need to use truss rods. Gravity acting on a branch will also tend to pull it down. Interlocking grain is the tree's way of dealing with this. Diagonal fibers can take the stress that would act as a shearing load between cells as tension, and this stabilizes the branch. You see this sort of reaction wood in the trunk when the tree has taken a lean (say, by being partly uprooted in a wind storm) or simply has lost a major branch on one side. Hardwoods and softwoods do reaction wood differently: if memory serves hardwoods have the reaction wood on the bottom of the branch, and softwoods on top, but I may have backwards that. In any case, a really horizontal branch will tend to be egg shaped in cross section, and point up or point down depending on whether it's hard or soft wood.

"..and for sure doesn't explain how a tree can grow for a 100+ years, straight as straight gets, then suddenly begin to put-down new fibers at an angle. "

It might: as stated, trees can react quickly to the loss of a major branch or other change that imposes an unbalanced load and puts one side at risk for too much compression load. That side would see an increase in built-in stress, and, if my conjecture is correct, in runout. I have billets of wood from a spruce tree, some of which show no twist on a split surface, and others of which do. If I'd known as much in '88 when I got the tree as I do now,I'd have probably paid more attention to where in the tree the billets came from.

I'm not claiming to have all of the answers, and gosh knows I may have misunderstood some of what I read. However, it does make sense of a lot of observations, so I'm sticking with it until I get a better explanation.

Alan Carruth / Luthier