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In my last question, I was asking what kind of shelter would need my arboreal civilization (Here is the link). To recap very quickly : they constantly live in heights of giant trees, and never go down (too dark and dangerous out there), so they are still hunter-gatherers.

But a problem came up : they don't have access to any kind of ressources that would allow them to create tools or weapon to hunt or gather in those hights. And since they can't reach the ground I needed them to have access to those ressources while staying up there. So why not bring the ressources to them directly ? (it will be divided in two questions)

For that I thought about having rock columns like those of Zhangjiajie National Park in China, in a way that the trees started to grow there way after the columns formed. The question is to know if such mix is even possible geologically.

What I know so far about this natural park :

There is about 3100 columns scattered on 86km2, and their hight varies between 120 to 350 meters high. 443 to 419 Mya, what is now the park was surrounded with oceans. When the two blocks who formed China collided, layers of sediment were lifted up, causing the drop of the oceans and the formation of moutain ranges. It's between 160 and 68 Mya that what allowed the formation of those columns appeared : big faults formed due to a second lift.

The giant trees, which grow more of less at a high of 250 meters, appeared in a similar area about 25 000 years ago, and grew litterally between the columns. What I was wondering is : would the trees destroy / weaken the columns, or, on the contrary, support them (if they can grow there at all) ?

I though that if the branches and trunk of the trees were growing around the columns, like a spiral, it would maybe support the structures of the rock columns ?

Thanks !

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  • $\begingroup$ Your title and the body of the question seems to be conflicting. Which of the two is your problem? $\endgroup$
    – L.Dutch ♦
    Nov 2, 2020 at 19:14
  • $\begingroup$ @L.Dutch-ReinstateMonica Ohh, I didn't understood what was the problem until I saw the word "support" ! My bad, in my language it can be used to mean something else. I wanted to ask if the natural park could " contain / be home to " huge trees (without being destroyed or weakened). Will it be clear if I use these words ? $\endgroup$
    – Emie
    Nov 2, 2020 at 20:25
  • $\begingroup$ No worries, I had the same doubt if with support you meant "be substrate for" or "allow the growth". See if my edit makes it more clear $\endgroup$
    – L.Dutch ♦
    Nov 2, 2020 at 20:40
  • $\begingroup$ @L.Dutch-ReinstateMonica It seems better, thank you ! $\endgroup$
    – Emie
    Nov 2, 2020 at 20:43
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    $\begingroup$ You're likely solving this problem incorrectly. If there are animals to hunt, they merely make tools from bone and leather, and occasionally wood. You might even make the trees themselves capable of providing some fiber for cloth. Additionally, they could have rare/precious stone tools that no one remembers where those came from. This is much simpler and more plausible than absurd geology that doesn't mix well with maximally-tall trees. $\endgroup$
    – John O
    Nov 2, 2020 at 20:52

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Cool idea!

Water erodes what's soft and leaves what's hard. That's good news for your people! High rainfall "upstream" in the past washed away soil, leaving columns of hard rock and, more importantly, metal.

Rather than columns, consider the idea of using ribbons. High-metal-content volcanism in the past pushed mineral-rich basalt up through fissures in an otherwise sedimentary plain. Rain washed the sediment away until grasses started blocking the erosion, giving trees a chance to grow and a fertile aquifer beneath the trees (and between the ribbons).

The result is a forest floor that really is dark because the ribbons are blocking more light than columns would. The trees are tall because that's where the sunlight is.

But the ribbons! They're a great place to mine for hard rock, metal, and many other minerals... other than salt.

The solution I just described would leave the area almost devoid of natural salt. I hope they're near an ocean.

Note that the rain still happens. Occasionally a 100-year-storm happens "upstream" (as it always has, which caused the erosion in the first place) and that means flood waters streaming between the ribbons of rock.

Conclusion

Ribbons give your story more to work with when it comes to mining for metal, hard rock, and minerals. However, if you prefer columns, I don't see a problem. Note that the ribbons are volcanically (and in my mind) a bit easier to justify than the columns in terms of lacing them with minerals and metals.

Either way, I believe the growth of trees amongst such as ribbons and columns is believable so long as the ground between is reasonably fertile (read: sedimentary) and there's moisture to justify the growth. This would suggest the columns/ribbons are hard rock, basalt and metals mostly, such that they're very hard to erode.

Tree roots do break things up, but only to a degree. Nature takes the path of least resistance. This is why I like the fissures and ribbons, the trees are growing down between the fissures rather than into the columns/ribbons.

However, given enough time, the trees will eventually win. The roots will eventually weaken the columns/ribbons and cause them to topple.

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  • $\begingroup$ Thank you so much !! I just have a question : what do you mean by "ribbons" ? (because when I search for translation it just says "a strip of fabric", and I don't think you meant that ahah) $\endgroup$
    – Emie
    Nov 2, 2020 at 20:36
  • $\begingroup$ @Emie I think JBH means something like grooves or gorges $\endgroup$
    – L.Dutch ♦
    Nov 2, 2020 at 20:41
  • $\begingroup$ I see, so instead of columns, I would have much bigger and larger pieces of rock ? $\endgroup$
    – Emie
    Nov 2, 2020 at 20:53
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    $\begingroup$ @L.Dutch-ReinstateMonica has the idea. Think about ribbon candy but stretched out much more. Or think about fabric ribbon turned on its edge. Or, as L.Dutch suggests, think about a lot of wide gorges separated by thin (say, 5-20 meters) walls. This kind of geological formation (if it really exists) would be rare, susceptible to erosion - but as a writer you're looking for suspension-of-disbelief, not scientific fact. Astronomers are regularly surprised by what they find in the universe. $\endgroup$
    – JBH
    Nov 2, 2020 at 21:38
  • $\begingroup$ @JBH That sound super interesting (and fun to create), thank you ! $\endgroup$
    – Emie
    Nov 2, 2020 at 22:03
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I just watched a video stating the tallest a tree can get is about 120m due to earth's gravity. So your 80-180m too high, for earth. A planet with 1/2 the gravity and therefore 1/2 the mass of earth would hit 240m. So you would need about 40% of earth gravity and mass and the trees would grow that tall.

However, a planet that small is going to have other issues.

You would be on Mars, and mars doesn't have enough gravity to hold on to an atmosphere so that is going to be an issue.

The capillary action doesn't work well above those heights.

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  • $\begingroup$ I had discussed this in an old post here : worldbuilding.stackexchange.com/questions/160545/… $\endgroup$
    – Emie
    Nov 2, 2020 at 20:57
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    $\begingroup$ Tree height isn't limited by gravity per se, it's limited by how high it can transport water up it's trunk. Increasing atmospheric pressure would increase this limit without effecting gravity. $\endgroup$
    – Zac Walton
    Nov 3, 2020 at 3:03

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