Heartwood and Sapwood

Re: Heartwood and Sapwood

Sgian Dubh

That's a good question Don. I don't think there's a definitive answer to part of your question, the bit about "how many years". All I've found out during my researches on various aspects of timber technology is encapsulated thus:

In some species the transition between living xylem and heartwood is abrupt and clearly visible. With others it is hard to distinguish between sapwood and heartwood. The sapwood can remain as living protoplasmic cells for several years but this period varies from species to species, and even within trees of the same species.

My researches indicate that additional factors that may affect the speed at which sapwood converts to heartwood of a tree, whatever the species, include such factors as latitude, altitude, climate, supply of foodstuffs, e.g., minerals and water, whether a tree is forest grown or open grown, and so on.

As to the reason for conversion from sapwood to heartwood, I think the obvious answer to that is the growing tree needs ever greater structural support as it gets bigger, so the heartwood has to increase in order to sustain the loads a living tree experiences in life. And to why one growth ring a year: well, I guess that's just the way trees have evolved, and it seems to work for them, ha, ha. Slainte.

..Thought-provoking. Thank you.

Cells don't live forever

Bill Tindall, E.Tn.

There is heartwood, which is dead, because cells don't live forever. Heartwood has different minor constituent chemical composition because if the tree's heartwood had not evolved to be loaded up with fungus and bacteria toxins this dead wood would quickly rot and the tree would fall down.

Trees with mostly heartwood (walnut for example) may simply have cells that don't live as long as poplar or maple.

Re: Heartwood and Sapwood

Don Stephan

Now I'm more cornfused.

My recollection is that I read in Understanding Wood that new vertical wood cells made by the cambium don't live beyond a few months, and my expectation would be that sapwood as strong as heartwood in terms of supporting the tree. But I'm frequently wrong.

My guess has been that as the tree adds cross-section (moisture carrying capacity) each year at a rate faster than it adds leaves (moisture demand). Continuing along that guess, at some point in time, the moisture carrying capacity exceeds the demand, so the tree converts the innermost pair of growth rings (early season and late season) to heartwood, taking that wood out of the moisture carrying racket. But that's just a guess.

Re: Heartwood and Sapwood

Barry Irby

Why don't you look at the Forest Products Laboratory and see what they have to offer? Lots of carefully studied information there.

Things that happen must be possible, but sometimes we never know the WHY.

Re: Heartwood and Sapwood

Philip Duffy

Don, the school of Dendrology at Virginia Tech is has an excellent web page with tons of good info. You may find your answer there. Philip

Re: Heartwood and Sapwood

ebd

If I can find it I will look the answers up in my Plant Anatomy textbook. I don't remember the answer off hand.

Re: Heartwood and Sapwood

Keith Newton

Don, I've been pondering this question for about 25 years also, and even though I'm not a tree scientist, have read everything I could find on the subject, and some hypothesis worth considering. I also have a dendrochronologist friend that I've learned a lot from. A dendrochronologist is someone who studies the size of annual rings relative to weather. Their studies require samples from lots of trees where they take little kitchen match size samples with an increment borer. The samples are glued into a groove of a small strip then sanded very fine so the rings are easily seen through a microscope. The scope has a bed with a digital readout in thousandths of an inch increments as the reader traverses and clicks on each ring. One tree won't tell you anything, because it could be covered with vines for a decade, or in the shade of a larger tree for a century. Only by averaging lots of samples can they tell for sure how much rain has fallen in a locality.

I guess everybody knows that the size of the rings will be larger in years with lots of rain and less during dry years. But I was surprised to learn that sometimes during extremely dry periods a tree may not be able to make a ring at all, or at least down near the Earth where they take the samples. The moisture may go up the sapwood to the leaves, but lots will be lost to transpiration, then what is left over may go back down the phloem to make a new ring, but not all the way down to the ground. So when they study lots of rings, certain patterns of good and bad year cycles show up in the averages, some trees may be missing rings that show up on others.

Getting back to the nuts and bolts. The moisture absorbed into the root system goes up the sapwood to the leaves. Thanks to photosynthesis the chlorophyll transforms Sunlight into sugars while taking in carbon dioxide, giving off oxygen. This sap then moves back down the phloem in the inner bark, and is used to grow new cells in the cambium layer. In Springtime, the open cells of a ring-porous, (like Oak) portion of the ring develops, and in woods like yellow pine, the soft portion of the hard/soft.

I've only seen cells half way colored between sapwood and heartwood a few times in mulberry, and I think it was early Spring, so this being the only species sample, I don't know if the transition from sapwood to heartwood happens gradually over the year, or end of season, or beginning of the next for all others.

One thing I have noticed in Juniperus v, Eastern Redcedar, is that there may be a correlation between the atmosphere and the transformation from sapwood to heartwood. We only have Yellow-belly Sapsuckers here during the Winter. When they peck the trees to open their wells, the sap oozes out, which attracts insects, that they consume along with the sap. After they leave in the Spring, the little droplets dry into a hard varnish like patch, not just in the well, but into the sapwood for about 3/16" radius horizontally, and maybe and inch up and down.

This darker permeated patch which was done at the surface ends up permanently in the historic record of the tree. Once it gets to the sapwood / heartwood interface, it blocks the sapwood behind the patch from ever changing into heartwood, so this seems to indicate there is a horizontal or radial aspect of movement. I notice this in a tree I found on the shores of L Ouachita back in the early eighties when I found the oldest Redcedar tree in AR, which led to meeting Dr. Stahle.

Another thing I've noticed is that when a cedar tree is mostly dead, and only a strip of living tissue grows up to support maybe one limb. Along the edges where the bark curls around covering the new growth, there isn't any sapwood at all. I suspect the air coming in around the edge through the dead dryer wood either oxidizes or concentrates the sap in the new cells as they develop.

I keep thinking about doing some experiments to see if I can make the heartwood rings jump by thinning the bark then latex bonding an aluminum patch out in the middle of a tree I expect to cut for firewood in the future. If it jumps one way, then the other under the patch, there would be the proof. If anyone reading this wants to experiment, give it a try yourselves.

I finally remembered to do experiment

Keith Newton

Hey Don, I spent a couple of mornings working on cutting some new trails through some woods that we had logged about five years ago. A 5” rain fell after they were in there, and the skidders left such a mess that I don’t think we’ll ever be able recover parts of the old lanes.

While I was there, I finally remembered to thin the bark in 3 trees, then bond a piece of flashing opt in the middle. If my expectation is right, when I cut them in about 4-5 years, there should be a abrupt change from the normal progression of sapwood into heartwood.

Now, I just hope I can remember to get back to cut them that far into the future. If you or anyone else here can remember, I might need a reminder to get back with the results, so feel free to drop me an email.