What causes spiral grain in trees?

[arojay]

I have pondered this question to myself many times.  I used to think that it was a heliotropic effect, then I realized that the predominant direction of spirality was wrong.  In this part of the world they turn to the right most often although I have seen schoolmarms, split at the stump, which turned opposite ways.  What's up?

[Tom]

You got me!!   I just figured there was right handed trees and left handed trees, same as people.  :D

[clearcut]

Spiral grain is thought to be an adaptation to harsh sites. Trees with spiral grain can distribute water and nutrients from the roots to the leaves more evenly across the tree.

The direction of the spiral is thought to be a factor of wind direction and the shape of the crown. Wind blowing across the crow twists the fibers (torsion) causing some damage. This slight damage causes the fibers to slightly misalign, beginning the spiraling.

The spiraling increases the strength of stems and branches.

[zopi]

trees can figure skate too...

[SwampDonkey]

I see it in fir, spruce, cedar, pines, white birch, pin cherry. It seems to be genetic and increases in magnitude with age.

Conifers trees tend to spiral left as they grow, then this grain reverses at one point and becomes more straight, then as the tree reaches old age it spirals right.

Spiral grain seems to be so common that it is considered a fact of life for most tree species.

Spiral grain also affects how smooth you can plane a rough piece of lumber.

There are lots of theories, nothing definitive.

[Source: Textbook of Wood Technology]

[WDH]

I agree with SD.  It is genetic.  A mystery of nature.  It is just how some tree species like sweetgum, blackgum, sycamore, hackberry, and elm choose to go about their business. 

Site conditions may cause it to occur in some species that don't usually exhibit the characteristic, but the above mentioned species almost always have it regardless of site. 

[Don P]

Actually I'd call those trees interlocked grain. They spiral for a few years one direction then switch and spiral the other way for a few years. I've turned gum around every which way at the planer only to tearout somewhere in either direction.

I've read somewhere in our previous discussions that softwoods normally tend to start as lefties and tend to end up with a right spiral where some hardwoods normally work the opposite way.

[WDH]

Yep.

Mahogany is the classic interlocked spiraler.  The grain spirals one way, then the next, giving us that classic ribbon striping so characteristic of the old colonial mahogany furniture.  Quartersawn sycamore also can give that beautiful ribbon striping along with that wonderful ray fleck.  If we could only make it be still long enough to make something out of it  :D.

[SwampDonkey]

Actually I'd call those trees interlocked grain. They spiral for a few years one direction then switch and spiral the other way for a few years. I've turned gum around every which way at the planer only to tearout somewhere in either direction.

BINGO!  ;D

[Don P]

If we could only make it be still long enough to make something out of it 

If you'll be needing any propellers just give a shout, we were blessed with ambitextrious wood 

I posted pictures a year or two ago of a batch of house logs that had a large percentage of left spiral. They were also loaded with compression wood and had grown pretty fast. Heartwood formation was just beginning in most. I think the cultural practices had kept these trees juveniles longer (or maybe just through more diameter) than normal. That started a train of thought I haven't researched. I know most conifers start out lefty, is the microfibril angle in the secondary lamella of the cell wall at that stage lefty  ???, I know it is angled. As a tree begins putting on straighter, stronger, good mature wood, (I see that period as the beginning of heartwood formation  ???) the MFA begins to straighten up in the cell wall. Does the "grain" follow this lead? As a tree ages the grain direction tends to become more right, has the microfibril angle gone right?

Or, is the visible grain direction following the lead of the cell wall "grain" direction. I wonder if there is a study of MFA in an interlocked species. Or are we spiralling with a normally built, straight microfibered, cell wall?

From a strength perspective is spiral grain doubly cursed or just the once.

[SwampDonkey]

Well think of it this way Don. DNA is a spiral helix and the building blocks of life, so don't expect a straight answer.  :D :D

[arojay]

"don't expect a straight answer".  That's a good one.  White Spruce is the predominant species around here so that's what I have become most familiar with.  With our short growing season and so on we have a ot of taper and plenty of spiral check when the wood is dry.  The degree of spiraling is different from tree to tree as is the direction, although more to the right than to the left.  I have heard from timberframers who will only select wood with a right spiral.  I can see why you wouldn't want checking in opposite directions.  Apparently spruce cones also have spiral in their 'construction'.  We have a research facility in our area that accomodates student researchers from many universities in Canada and the USA.  One of these projects is to figure out if red squirrels have a dominant side(right or left handed), or if they hold cones in whichever paw is best to get the seeds out of the cone spiral.  I'll keep you posted. 

[WDH]

Don, 

Those are good questions.  As I recall, juvenile wood has thin cell walls, so the impact of the microfibril angle in the S2 layer of the cell wall is more pronounced on the wood characteristics.  As mature wood begins to form, the cell walls thicken, so the impact of the S2 layer on overall characteristics is lessened.  I am not sure if the shift from one orientation to the other (left to right) in the growth ring is a function of the microfibril angle in the S2 layer shifting, or if it is the cells themselves. 

More research is in order for the inquiring mind.  Not that we can do a whole lot about it except understand the effect on the characteristics of the wood when we saw and use it :.   You can talk to trees, but elm, hackberry, sweetgum, blackgum, etc. just don't listen ;D.

[SwampDonkey]

Well it has to start with the fusiform initials of the cambium. That's what forms the xylem and phloem in the tree, made of longitudinal cells.

fusiform initial
     |->Cell
           |->nucleus long axis || to cell long axis
                  |->mitosis
                            |->chromosomes split longitudinally
                                         |->draw apart diagonally
                                         |->form daughter nuclei
                            |->cell plate between daughter nuclei, from vesicles of Golgi bodies
                                         |->protoplast divides into 2 daughter cells, 1 nuclei each
                                         |->formation of primary cell walls (S1) with middle lamina
                  |->cell enlarges to mother cell size
           |->cell wall thickens with secondary cell wall formation to the inside (S2)
           |->spiral thickening occurs in the S3 layer to the inside of S2
           |->warts and pitting occur to the inside of S3
                  |->special forms of cell walls:
                            Septa (in some Hardwoods)
                            Tylosis (in some Hardwoods/Softwoods)

[Source: Textbook of Wood Technology]
                                                             

[Tom]

That configuration looks like an old COBOL programming technique.

[SwampDonkey]

 :D :D :D Well, if we could only program trees.  ;D

Now, some nifty programmer can pick up the ball and run with it.  ;)

[james]

COBOL ...had a programmer friend that always claimed that language caused brain damage in its users
;D ;D
james