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Yes, the title is strange, but hear it out. The inhabitants of my earth-like planet live high up in the atmosphere - living on giant trees. However, I don't want them to be able to see the surface far below them, so I need permanent cloud cover. Based on the question I asked, it seems like the easiest way to do that is with a greehouse effect similar to what is seen on Venus.

So I have giant trees on what is essentially Venus. Which... even I know is impossible. So what do I need to do to get giant trees on a Venus-like planet, that extend up into the atmosphere?

Notes:

  • The trees need to reach altitudes of between 50 and 60 km. This answer should help with that.
  • If it is simply impossible to have trees growing from the surface, I can have them floating in the atmosphere. It would need to be explained how they do this though. I would greatly prefer them to be anchored to the ground.
  • You can do anything you want to the base of the trees. They only need to be recognizable (having virtually all characteristics) as trees between 50-60 km.
  • The setting is medieval/fantasy, so natural processes are a must. You can use magic as a last resort to 'tweak' something if you have to.
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    $\begingroup$ Is technology allowed, or does the solution need to be completely natural? $\endgroup$ – Frostfyre Mar 10 '17 at 16:45
  • $\begingroup$ @Frostfyre Sorry, should have specified. The setting is fantasy/medieval, so no technology. Magic is present, but should only be used when there is no other way to get things to work. $\endgroup$ – Thomas Reinstate Monica Myron Mar 10 '17 at 17:57
  • $\begingroup$ 50 km is 160,000 feet, give or take - about 5 times higher than Everest. So, for survivable atmosphere at 50 km, the sea-level air density must be much, much greater than Earth's. This has all sorts of implications, including hostility to earth-like organisms due to oxygen toxicity. So you might want to rethink this one. $\endgroup$ – WhatRoughBeast Mar 10 '17 at 18:26
  • $\begingroup$ Thomas Myron - fantasy/medieval setting so no technology? Try telling a medieval blacksmith that he lives in a world with no technology. It is very hard to imagine scientific laws similar enough to ours for biological beings like humans to be able to survive, and yet different enough that science and technology don't work. So any plausible fantasy world must be one where science and technology can work but nobody in the society knows how to make them work. In LOTR, usually considered fantasy, the ancient Numenorens had technology in some ways more advanced than ours. $\endgroup$ – M. A. Golding Mar 10 '17 at 19:32
  • $\begingroup$ @M.A.Golding Okay, bad wording. No modern technology. Technology similar in era to medieval. $\endgroup$ – Thomas Reinstate Monica Myron Mar 10 '17 at 19:43
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I would suggest that your fictional planet might be less extreme than Venus yet still with total cloud cover and an uninhabitable surface.

In Poul Anderson's Orbit Unlimited Earth men colonized a planet of E Eridani (NOT Epsilon Eridani) with a thick atmosphere where only the highlands had air thin enough to breath.

In Larry Niven's known space stories Plateau, a planet of Tau Ceti, is Venus like and uninhabitable except on Mount Lookatthat, a California sized plateau rising up into breathable air levels.

It seems very illogical for the lower parts of plants to grow and survive in the conditions of the Venus surface and the upper parts of those same plants to grow and survive in conditions far above the surface where humans could survive. Those plant would seem to need to have different levels with totally different biochemistry on each level.

I could imagine plants like giant gasbags floating far above the surface, that send roots far down into thicker air to absorb nutrients, and send trunks and leaves high up above them to where the clouds are thin enough for the leaves to get enough light of the proper frequencies.

And on top of the trunks of those plants there could be parasite trees growing up higher and out above the cloud tops where your people could live. These trees would steal nutrients from the trees they grow on and their weight would keep the gasbags from floating too high and dying.

And possibly the deepest roots of the gasbag trees could get entangled with the tallest branches of other gasbag trees growing lower down with different biochemistry. Maybe there could be a chain of entwined gasbag trees with different biochemistries floating at different altitudes, going down to trees growing out of the surface. I don't know what the advantages of such a system would be.

Or one type of tree could grow from the tops of mountains where the conditions are not as bad as on the surface and parasitic trees could grow from their tops to pierce the clouds to Earth like conditions.

How tall can trees on Earth grow?

One answer is here: about 400 to 424 feet (122 to 130 meters).

http://www.livescience.com/14667-tall-trees-grow.html1

It is true that there have been some reports of trees even taller than 400 to 424 feet, such as the legendary Ferguson Tree possibly reaching 500 feet or 150 meters. But many researchers scoff at reports of super tall trees.

And there is a newspaper report from 1927 of a petrified tree 896 feet long!

http://greaterancestors.com/ancient-trees-more-than-twice-the-height-of-the-tallest-giant-redwoods/2

Another discussion of possible tree height is on this same site:

How tall can a tree grow?3

Some of the answers offer suggestions for solving the problems.

So even on a strange alien planet where conditions are different, it will be a little bit difficult for trees to grow tens of miles high to tower above the highest clouds.

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The trees must float on Venus. Fortunately, floating on Venus is not as hard as floating on Earth. Your trees are autotrophic organisms relying on photosynthesis in their upper layers and chemotrophy in their "root" systems - hardened lower layers extant in the lower atmospheric layers of Venus that uptake the chemicals needed to build cell walls, create water, etc. These "roots" are much larger than the photosynthetic branches extant in the upper human-survivable layers, and are coated in a contiguous mucous which both protects the organism from the corrosive acid mists of the lower atmosphere and traps airborne particles for consumption. The same "root" system is filled with extremely numerous and large internal organs full of upper atmosphere piped down by the upper branches, which keeps the organism afloat easily.

The upper layers are green and purple, much like Earth plants, absorbing different bands of light for photosynthesis. They exist in the layers of the atmosphere where your trees actually begin life as wind-borne saplings - small seeds held aloft by large feathery appendages, gathering nutrition and sunlight from the upper atmosphere before becoming so heavy as to fall into the lower atmosphere, regain buoyancy, and begin growing their first tendrils back toward the sky from whence they came.

During the mating season of this organism, large floral externalities are visible everywhere on the upper region of the "tree," taking in windborne pollen exuded by male trees or exuding their own pollen. Pollen is generated in such quantities that in the regions of the atmosphere where these trees are most numerous, an entire season is known as the pollentime, or something similar - a period of the year during which temperatures and sunlight levels fall and the trees sink slightly lower into the atmosphere until the pollen disperses, allowing them to resume easily absorbing the sunlight which allows them to continue supplying their root systems with low-pressure atmosphere.

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  • $\begingroup$ Thank you. You have no idea how perfectly this fits with what I was envisioning. Would the 'trees' still have soft bark (soft as in the bark here) in the habitable area? Would the leaves change color and fall? $\endgroup$ – Thomas Reinstate Monica Myron Mar 10 '17 at 23:20
  • $\begingroup$ That's all up to you, isn't it? $\endgroup$ – Adam Wykes Mar 11 '17 at 1:19
  • $\begingroup$ I guess I'm trying to avoid the inevitable biologist who reads my books and exclaims, "That's impossible!" I mean, it's fantasy, but there are some scientific laws that I'm not aware of and could run afoul of without knowing it. That's all I'm looking for. $\endgroup$ – Thomas Reinstate Monica Myron Mar 11 '17 at 1:30
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    $\begingroup$ Just remind those people of all the things biological systems can do which we don't yet understand. Also explain that this is a world viewed through the hazy estimation of a pre- enlightenment civilization. $\endgroup$ – Adam Wykes Mar 11 '17 at 1:38
  • $\begingroup$ Good point there. $\endgroup$ – Thomas Reinstate Monica Myron Mar 11 '17 at 18:30
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Terraforming is the act of transforming a planet in order to resemble that of Earth. If your planet is terraformed, this should be extremely simple, just plant trees and watch them grow.

Venus is easy to terraform considering how similar it is to earth in mass, density, gravity, etcetera. Even without terraforming, it is still possible to do. The things you need to keep in mind are the poisonous atmospheres, crushing pressures, and high surface temperature. You need a way to coat the area of the planet in a cooling effect, and a way to strengthen the trees well enough to withstand the crushing force. I don't know if your trees can be poisoned, but I doubt an oak tree is going to fall over gasping for air because of poison.

The main problem is that you have temperatures hot enough to melt lead, you almost NEED to terraform the planet, and if you can terraform Venus, then you can do everything you already do on earth on Venus. I don't have any idea how you can have natural growing trees withstand temperatures of 450+ degrees celcius without terraforming or making an isolated area on the planet of Venus that has the ability to cool the trees down.

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  • $\begingroup$ The problem with cooling is that it (from what I can tell) will get rid of the cloud cover. $\endgroup$ – Thomas Reinstate Monica Myron Mar 10 '17 at 17:59
  • $\begingroup$ @ThomasMyron There is simply no other way, magic. This can't be done with medieval technology. Magic terraforming, cooling layer, etc. $\endgroup$ – Nate Dukes Mar 10 '17 at 19:59

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