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Comment by MiguelVieira | Hacker News Reader

It's interesting to point out that the wood has tighter rings and is more durable not necessarily because it came from old trees, but because the old growth trees grew in mature forests where they were in the shade of other trees, and thus grew more slowly and had tighter rings.

Trees growing in full sunlight grow quickly and have more widely spaced rings. Balsa wood for example, which is very light and soft, comes from balsa trees that have evolved to grow very quickly in sunny gaps caused by fallen trees in tropical forests.

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The main reason old growth trees have tight rings is not that the tree is growing slowly (in mass) but that the diameter and height of the trunk is so large that the rings are very narrow. A 200ft tall tree with a 8ft diameter trunk with a 50 foot sunny top will put on a lot of mass but it is spread out over the surface of the truck. The added ring each year will be thin. Old growth forests are rare and I think people don't have a good idea of how big old growth trees can be. The old growth redwoods are admired for their size but other trees also get very large. At a small museum in the northern Sierra foothills I saw a photo of a 16ft diameter Douglas fir. It's too bad none of these trees survived (that I have found). Many pictures of logging trucks with just one log on them.

You do definitely get thin rings when the trees are shaded but the monster old growth trees, the thin rings are usually due to the size of the trunk.

I know nothing about wood but does this mean that the heartwood has relatively wide ring spacing (since it grew when the tree was low and small?

You see this in trees that have grown up in forest conditions. They sprout in a patch of sunlight, but then they eventually fill the space and can't grow as quickly anymore.

In trees that are grown in more open conditions with plentiful sunlight, water, and nutrients, the growth rings are more even because there is nothing holding back their growth and forcing them to slow down.

> The main reason old growth trees have tight rings is not that the tree is growing slowly

No, it really is. Old pine from and some hardwoods grew in densely populated forests and there was a fight for sunlight. This severely limited how quickly the trees could grow per year resulting in tighter rings and far superior lumber.

Tree plantations are specced out to plant trees the perfect distance from each other so they can grow super fast. Spiked with fertilizers a pine can be harvested in year 15 for modern lumber. It's amazing how fast they can grow trees with enough sunlight and food.

Larger trees grow more slowly due to increasing competition (especially for canopy space) with their neighbors.

If trees are planted with sufficient spacing, an old tree's outer growth rings will be the same density as the inner growth rings. Trees grow to the water, sunlight, and nutrients that are available to them -- up until they become diseased or they grow so large that they struggle to support their own weight (at which point they start losing branches, which means they no longer get enough sunlight). To counteract the pull of gravity, older trees stop gaining height and instead focus on adding girth (i.e., thicker growth rings).

Tree plantations achieve a higher wood output by progressively thinning the plantings as the trees mature. This allows the remaining trees to keep growing at a fast clip and results in more even grain in the lumber.

I was talking about really large trees like you get in true old growth forests (ie never cut. Many people see 100 year old second growth forests and think they are old growth, but they are not).

Tree plantations are a whole different eco-system (a very improverished one like a cornfield) from an old growth forest (not really an eco-system). I would love to see tree plantations grow trees for 500 years, but I have never heard of that happening.

Check out this paper where the oldest tree in the study (651 years old) was producing the most heartwood per year of any tree in the study area[1]. Or use google scholar and search for "wood production of old growth forests" The rings on this 651 year old tree will be very thin but the volume of wood produced is large due to the huge diameter of the trunk. Have you every seen a 16 ft diameter tree? They are rare but amazing.

[https://www.sciencedirect.com/science/article/pii/S037811270...]

Great explanation of why certain species of trees are both fast growers and 'fast fallers'. Tulip Poplar trees for example are often first/second growth, and they are also often the trees that will break/fall during storms too. They trade that fast growth for durability it seems.

In my observation, tulip poplars, get a bad rap. They do drop limbs routinely, but I don’t see them getting knocked over by wind. I see pine trees blow over the majority of the time. Of course, different forest composition might change the odds, but for my area tulip poplars seem pretty strong

Thank you! this was the information that was missing from the blog, and I scratching my head a bit.

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