What Does "Old Growth" Mean

      The sawing and drying forum discusses what "old growth" means when used to describe lumber, and what qualities "old growth" wood may or may not have. May 14, 2006

Question
I am trying to understand what determines if a log is designated "old growth" or not. Some articles say that the first generation is old growth and the second generation is not -and has less quality than the first generation. What difference does it make? It seems that even the "first" generation wasn't really first - there must have been lots of generations before it. Some of the articles refer to the number of growth rings and their thickness, but growth rings are a result of the growing conditions (rain, disease, fire, soil, etc). These conditions might be more favorable for the second generation than the first... which would mean a better log, wouldn't it?

Forum Responses
(Sawing and Drying Forum)
From contributor B:
The way I understand it is that the old growth timber grew in dense forests, making for slower growing (more rings per inch). After the old timber was cut, the remaining trees got more sunlight, more water and food, making for faster growing conditions.



From contributor C:
One might think that better growing conditions would yield better lumber, but it is often the opposite. The tree that took 200 years to grow 3 feet across is going to have much denser wood than the tree that took 75 years to grow the same size. The rings are closer together in the oldest tree, meaning higher density, harder, and stronger. Also usually more resistant to rot and insects, and more stable. It makes a huge difference when talking about the quality of the wood.


From contributor G:
You cite one of the problems that we run into when folks that are trying to market something try to play upon our perception of what is rare/valuable. From the silvicultural standpoint, there are good scientific descriptions of what "old growth" forests are, but that doesn't help us understand what some folks are marketing as "old growth" lumber. Old growth forests are typically protected from harvesting, so I doubt that we would see much lumber from that source. I have seen lumber milled from logs dredged out of the bottoms of lakes and rivers advertised as old growth, and if the forests that those logs originally came from had not been logged, today they probably would have old growth structure.

As to the aesthetic quality of wood, it seems to be a matter of consumer preference. Some consumers think logging today's forests is bad but can justify using wood if the source can prove that it came out of the bottom of a lake somewhere. When they show off the piece of furniture made from such wood to friends they are trying to impress, they'll be able to say, "look how close together the rings are." There are high end markets today for logs that have high per inch ring counts, but most buyers don't care if the tree that a log came from was 100 years old or 300 years old - they're just looking for the desired grain pattern for their finished product. I have seen small logs from trees that had grown in partial shade, or in a poor site, that had rings so close together that a magnifying glass was required to count them. If lumber from such logs made it to market, there would probably be those consumers who would incorrectly assume, based on ring count, that it came from old growth trees.

As posters have noted, wood from pre-European settlement does tend to have a higher growth ring density, primarily because there was less logging and trees grew more slowly due to competition for sunlight. Maybe the wood scientists that help us on this site can help us with the issues of comparative density and stability. It has been my experience that at least with some hardwoods, the higher the ring count, the lower the weight/volume density because of the higher proportion of large vessels in the early wood. The opposite should apply to conifers.



From contributor S:
The boreal forest of Ontario is a fire-driven ecosystem. This means that what are referred to as "natural" stands likely originated from a stand-replacing fire. The growth characteristics of a given tree are thus driven by the time since disturbance as much as the site characteristics. "Old growth" in Ontario is defined by the age since last disturbance and is given a duration time - the time that a stand replacing fire is expected to occur. This system identifies, based on historical information, when a forest type acquires old growth characteristics - that is, characteristics consistent with stands which have grown in a competitive environment. In other words, stands which have not been disturbed, (remember, harvesting is a form of disturbance) and have new growth in the openings in the canopy created when older trees die, are developing old growth characteristics. Trees which grow in these post-succession stands tend to have growth characteristics similar to those found in virgin forests. So, in Ontario at least, we are defining old growth scientifically, rather than aesthetically. If you ask someone what they think old growth is, nine times out of ten they will define the tall majestic pine stands of Algonquin park or northern Minnesota or the Douglas fir stands of BC, or any other area with big, old trees with grass growing under them.


From contributor D:
"It has been my experience that at least with some hardwoods, the higher the ring count, the lower the weight/volume density because of the higher proportion of large vessels in the early wood."

That's been my experience, at least for ring porous woods like oak. Old growth is far weaker than faster grown modern oak. It is pretty stable, and I attribute that to the low actual density. My understanding is that softwoods are less affected by ring count. If I'm remembering right, within the range of ring density of 6-~35 rings per inch, overall latewood density is a better indicator of strength than ring count. Outside of those limits, I believe strength drops off rapidly.



From contributor W:
Out here in the west, they have the 20 inch rule on the public lands. If the tree is over 20 inches, it's called old growth and you can't cut it. At least that's until they figure out what old growth is.


From Gene Wengert, forum technical advisor:
Slow grown softwoods are indeed denser. But slow grown hardwoods can be the same (maple, birch, etc.) or lower in density for ring porous (oak, ash, etc.). They would not be denser.


From contributor C:
I like to learn something new every day. This is it for today. I work with reclaimed longleaf pine, and know that closer rings means more density. I would have assumed this would hold true for all woods. Interesting how it's the opposite for hardwoods. So old growth oak, or other hardwoods would be less desirable as far as strength, durability, stability, and rot/insect resistance, I assume?


From contributor D:
I was just talking strength. We kind of took a turn into density and that's where I was coming from. I'm calling shrinking and swelling "stability." I think, extractives aside, a less dense piece of wood is going to be more stable. Durability, which I'm reading as insect/rot resistance, would to my thinking come from extractives. I'm guessing a slower growing tree would have more? Even that is up for debate in what I've read.

I'm not buying it on softwood density being linked to ring count. I can bring to mind plenty of tight ringed unusually light pieces, as well as unusually light coarse grained pieces. If strength is what you're after, look for a piece with a large proportion of latewood. (It'll be the clear, dense heavy board with lots of dark ring showing. Who cares how many rings it's got.)

I looked this up in Peter Koch's "Utilization of the Southern Pines":

Growth rate;
From section 4-3 it was noted that growth rate of plantation trees, when manipulated by changing environmental or silvicultural condition, may not be closely correlated with wood specific gravity.

In natural stands of shortleaf pine in MO, Ralston and McGinnes (1964) found that specific gravity of mature wood sampled at breast height was not influenced significantly by diameter growth rates from 8 to 40 rings per inch.

From a study of 40 loblolly pines aged 31 to 76 years cut on a single 160 acre tract in northeast MS, Yao (1970) after considering all heights and radial positions concluded that unextracted wood specific gravity was positively correlated with number of rings per inch in the range of 3-6 rings per inch; in wood with more than 8 rings per inch, however, specific gravity was generally unrelated to growth rate.

Don't get me wrong, that wood that contributor C is describing is some of my favorite stuff. I'm just putting up what I think I know for the sake of learning more. I built a kitchen cabinet for a remodel job last year out of reclaimed oak from earlier in the job. 1 piece door panels, drawer fronts, very beautiful, tight ringed, stable wood. When I broke scraps to toss in the stove they would break easily, short and brash.



From contributor C:
I have done a lot of reading on longleaf, and how it is so much more stable/rot and insect resistant/stronger/durable than any other American pine. Best I can tell, this is because of both the pitch content and the high ring count. Maybe it also has something to do with the species' chemical properties that sets it apart from the other pines? I don't know.

In my own experience (I deconstruct the buildings this wood comes from), the more open grained boards are most likely to be the ones that are rotten or bug eaten, or sagging/broken. Sometimes boards with high ring count are right next to boards with lower ring count (all longleaf boards have relatively high ring count, but some more so than others). Sometimes the board with less rings will be eaten up beyond use, and be right next to a tighter board that is untouched. Walking on old floors, sometimes boards will break, but one or two in the spot will be super solid, while boards on either side are breaking away. The ones breaking away usually have less rings.

I have also noticed that when the boards have so many rings you can't count them, sometimes they seem to have similar properties to the boards with low ring count. In any case, if the board is full of pitch (what we call "fat lighter"), it's usually in top condition, regardless of ring count.

Although this isn't a scientific test by any means, it has reinforced my thinking that more rings is better. Not only visually. I'm open to suggestions that are contradictory, though. I can't argue against science.



From contributor K:
I think the term "old growth" came into popular use as a replacement term for "virgin forest" since we have been in the business of controlling forest fires that would regularly burn the litter and under-story trees. An old, perhaps uncut tract of land would not retain its virgin status because of being over-managed. On the subject of greater density in faster growing/more late wood to early ratio, this will obviously contribute to greater density, but do more, shorter blocky cells of higher density contribute to other structural benefits other than compression, or resistance to denting? What about tension, shear and bending?


From contributor R:
The dendrology books give an accurate description of the characteristics which indicate an old growth tree. Keep in mind that it takes several characteristics to make up this designation. Recently some in the environmental community have been trying to redefine old growth as any tree over 150 years old or with a DBH of x inches. In the Tahoe basin the number is 30" DBH. However; since almost the entire basin was logged during the heyday of the Comstock era, it is doubtful that most of the existing 30" trees were there 150 years ago. In ponderosa pine and sugar pine, I have observed that most trees will start off somewhat slow if growing under a canopy, then take off until they reach a DBH of about 24 to 28", then as their needs increase with their size, they slow down again. This is not to count suppressed trees attempting to grow under a dominant tree. It is my opinion that we in the industry should carry a dendrology book and when some idiot makes a factual misstatement concerning the term old growth, we should whip out a scientific definition rather than allow them to propagate their nonfactual idea.


From Gene Wengert, forum technical advisor:
The definition of "old growth" will vary considerably from the Western forests to the Southern and Eastern forests and Canadian forests. There has been quite a bit written about this definition; always check for the geographical area that the authors are discussing.


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

Comment from contributor A:
I have worked with a lot of old growth material hardwood and softwood, recovered from old barns built over 100 years ago, and in my area that is when the old growth forests were cut. I have also worked with new growth as I was a logger for 5 years before I began reclaiming wood from barns. After reading this article I have lost a lot of respect for "science". I can tell you that the wood I reclaim be it hard or soft wood is much more stable and dense than the new wood. It could be the fact that it has air dried for 100 years or it could be that it is old growth, or both. Either way it is just plain better. I would say you would have to ask a woodworker not a scientist on this one.



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