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So I have an idea for a biome in which avian humanoids are the dominant intelligent lifeform. They live inside of trees that dwarf the redwoods of our world. The trees grow so tall and so thick (akin to a skyscraper) that they petrify from the inside out as they grow, forming a stony core a few meters from the surface. This stony core is obviously structurally weight-bearing, which begs the notion of the viability of boring through it to form cities inside of these gargantuan trees.

I would like to know the feasibility of trees that adapt like this and the way that they would support their own weight. What I would also like to know is what would the process look like for a tree to petrify itself from the inside out, as an adaptation for growing larger to out-compete other species for reaching sunlight.

These trees would, to my mind, be in the realm of 1000-1500 meters in height or larger, with considerably thick cross-sections (a tenth or more of their height at the midsection, a fifth at the base). I know not whether this is an appropriate dimension for these mountainous trees. I'm not sure about deciduous or coniferous yet either.

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    $\begingroup$ I don't think this is physically possible on Earth, but if you don't mind being on an alien planet with lower surface gravity it could be plausible. $\endgroup$
    – abestrange
    Aug 12 '20 at 19:10
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    $\begingroup$ Could be incorrect, but the process of petrifaction happens by minerals replacing the original material, not from becoming pressurized. If using real world physics, the pressure of the outer wood acting on the inner wood would just compress and make the inner wood extremely dense and hard, but not turn it to stone, I think. Again, could be mistaken. $\endgroup$
    – Tyler N
    Aug 12 '20 at 19:14
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    $\begingroup$ Tree height is not limited by the structural resistance of wood. Tree height is limited by the ability to pump water from the roots to the leaves. As is, pumping water up to heights approaching 100 meters is already very impressive; I cannot imagine how a tree would be able to move water up one thousand meters. $\endgroup$
    – AlexP
    Aug 12 '20 at 19:18
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    $\begingroup$ @AlexP, good point. Could a tree use the atmosphere (instead of the ground) as its primary source of water in an extremely humid and/or rainy environment? $\endgroup$
    – cowlinator
    Aug 12 '20 at 19:22
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    $\begingroup$ "Rain absorption or airborne moisture collection": in real life, absolutely not; in fantasy, maybe, why not? Trees consume much more water than what can be made available through these methods. Most plants which don't use their roots to get water from the ground are very small -- mosses and such. But there do exist large-ish plants, notably the wonderful Welwitschia mirabilis which survive (mostly) by extracting water from fog. (Note that Welwitschia is very much not tree-like -- it basically consists of two enormous leaves.) $\endgroup$
    – AlexP
    Aug 12 '20 at 19:48
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Minerals:

For a tree to deposit a stone core, all you need is minerals to be present in your environment in such quantity that they can be treated like a waste product. Look to coral, or sea shells, and imagine a plant depositing the same stuff. Fossilization can take very long or almost no time at all, if the appropriate dissolved minerals are present in the water.

I imagine trees eating away at limestone deposits, then depositing the carbonates in structural columns inside the tree. The stuff might be effectively a waste product, but a useful one. The tree is essentially filling the inside space with lime deposits, and protecting the lime deposits with the outside of the tree. The tree could be reclaiming the wood it laid down and replacing the lost structural material with what is essentially limestone.

This is an easy stone to work, very porous, and the tree may even leave natural cavities in the structure. This could aid in ease of tunneling. Limestone is used as a building material and ingredient in cement. As long as the outside of the trunk is alive, the inside is protected. The minerals soaking down would likely cause interesting deposits in caves people made, giving it a very organic feel. I've even seen basements in limestone that were growing crystal-like structures and had opalescent deposits.

The ability to transport materials is often the limiting factor on how high your trees can get. If you can have a natural way to pump the material up, though, the sky is literally the limit. How do geysers sound? These have (admittedly dangerously) hot, mineral-soaked water under pressure that the tree could direct upward in narrow tubes to fill a pool at the top. The water and minerals are soaked downward to make the tree and supply needed water and minerals (as well as the structural minerals for your exotic growth). The trees that grow near geysers become enormous, while the trees simply drawing on water in deep limestone deposits are "merely" huge. There could even be different varieties, and people carry geyser-type plants to geologically active areas and spread the species.

That gives you giant trees, symbiosis between man and tree, and geysers (what story isn't better with hot running water?) There could be a lot of different complications with this design that need to be hammered out, but unless someone has a huge and obvious objection, I think this could be a viable route for you.

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The core of the tree self opalizes.

Wood opal is a real thing. It is a type of petrafied wood. Opal is a hydrated amorphous form of silica.

I have read about artificial opals being made with sodium silicate. A soluble compund of silicon.

So for your trees they need the roots to produce Sodium Hydroxide which will dissolve silica in the rocks. Then the tree transports the Sodium Silicate to the heartwood, where the tree then using a Chlorine pump (like how your stomach makes hydrochloric acid) causes silica to precipitate out, opalizing the wood.

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  • $\begingroup$ I'll admit wood opal would be a cool material. Doesn't this need high temperatures for this reaction? Isn't the dissolved silica still pretty alkaline - kind of tricky to transport? Harder to explain, but neat idea if they can work out the bugs. It would need a fair amount of energy from the tree. Maybe the tree would only grow after a large volcanic eruption, so there would be abundant ash, or it survives a volcanic eruption and uses the ash for silicates and pH to fuel the transformation. Needs some thinking... $\endgroup$
    – DWKraus
    Aug 13 '20 at 15:37
  • $\begingroup$ The tree doesn't need to transport the Sodium Silicate in a concentrated form. It could slowly transport it up and then pump the water away. Trees play the long game. $\endgroup$ Aug 13 '20 at 19:44

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