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Trees with their roots and everything basically hold on to a section of land(dirt/stone/whatever) if one thinks about it.

A certain species of tree has fibrous roots and a poisonous, flexible, vine-like trunk that gets longer as the tree ages. It has evolved to form a giant hydrogen gas balloon, instead of branches and leaves, whose translucent membrane is filled with chlorophyll to make use of light bouncing around inside it, the hydrogen being produced from the water it takes in and expelling waste oxygen. The balloon eventually gets big enough to lead to the tree uprooting itself and popping somewhere high above due to the eventual too great pressure differentials and it is this way that it spreads its seeds via the wind carrying it somewhere else.

Since the balloon both carries the tree and rips it out of the ground it should provide enough buoyant lift to carry the tree and some extra that's possibly stuck to its roots. Animals have next to no use for them, with only the eventual seeds providing sustenance, so they tend to be left undisturbed until they pop. Their native biome does not experience hale or too strong storms so rain isn't an issue for a premature pop before the seeds are ready. I'm calling it a 'tree' because of the size of this flora, even if its features would not likely lead to it being classified as one.

Is it possible for a closely-grouped collection of these trees to uproot at the same, carrying more dirt along than they usually would due to their roots growing close together, and not going too high into the air where they would've popped but instead have become what one might call 'floating islands'?

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  • $\begingroup$ Were you to want an answer based on science, I would have pointed to you that hydrogen has the bad habit of escaping from any material known so far (so those bag need to be replenished) and a tree flying up into the sky loses an important advantage of the soil, namely the ability to soak water reserves for longer than a bare root could do (so the hydrogen replenishing phase becomes a wee more difficult) $\endgroup$ Oct 8, 2021 at 10:35
  • $\begingroup$ As you're still a new user, I'm not going to vote to close your question, but please understand: from the help center we read, "To prevent your question from being flagged and possibly removed, avoid asking subjective questions where there is no actual problem to be solved." And you're not asking for help solving a problem. Frankly, you appear to be asking for our approval (aka, "do you like this idea?") because there's nothing to judge the question against. Can the trees become floating islands? Sure! It's your world, you set the rules, and there's enough there to say "yes." So why ask? $\endgroup$
    – JBH
    Oct 9, 2021 at 4:39

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It's Complicated:

As examined in THIS question, it's hard to justify your islands floating. But you could have floating islands. You'd need some preconditions to make this plausible. I DON'T think these plants would likely uproot in the style you are suggesting, but would either break off from an existing floating island OR would grow from a seed on the ground and deliberately have a design/structure to sheer off the surface once sufficient buoyancy was achieved (possibly seasonally). As written this may be a bit of a frame challenge.

  • Abundant water or constant bobbing up and down. You need a ready supply of water, so the island doesn't need to retain a vast amount of (heavy) water to stay hydrated. The sky is a very dry place generally, and water will drip off your plants. So you either need constant light rains, or you need your island bobbing up and down to slurp water from the surface. Regardless, your plants will still probably end up looking a lot like a cross between a dirigible and a cactus. The bobbing motion could come from thermal means, with the plant warming and rising in the sunlight (taking advantage of solar both for food and additional lift) while cooling and descending to the surface at night.
  • Nutrient supplies: While the bobbing up and down sounds like a really awkward idea, your plants could also "eat" other plants in this process, extracting water, nutrients and possibly energy from the other vegetation they encounter. The alternative is if your floating islands provide a nesting ground for some animal that brings nutrients (guano, for example) to the plants.
  • Reproduction by budding: Your plants are unlikely to gather other plants together to make floating islands, but they could certainly reproduce clonally by budding off and running suckers out to create new plants that are genetically identical or derived from the originating plant. This would occur while flying. So the islands would be grown conglomerations related plants. of Generationally, your islands would look like blimps (bulbous/spherical, then flying saucers, (disks around a central hub) and eventually flying rings (as the oldest plants die and are recycled).

Some additional ideas would be for your islands to actually tether themselves periodically to the surface to extract water and nutrients they need. Storms coming up seasonally would represent the migratory/reproductive season for the plants, as the tethers sheer away, islands might break up, and individual new floating "seed" individuals scatter to the winds.

If there are abundant seas/oceans, your islands may spend a significant amount of time floating on the water. They might even "fish" for nutrients like an aquatic version of the Venus flytrap.

Your islands could also use ammonia production (possibly in tandem with symbiotic bacteria) to trap nitrogen for the plants to use. Spare ammonia can be dumped into the same space as the hydrogen, as ammonia is also a liftings gas. It has the added advantage of being condensable (not sure how a plant would do this, but...), but also readily soluble in water (so a plant could extract it from the air) allowing changes in buoyancy so the island could adjust its altitude. Ammonia is less flammable than hydrogen, and the molecules are larger so it's less apt to leak.

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  • $\begingroup$ Epiphytes can apparently get the nutrition they need without coming to ground. So these floaters should be able to do the same. Especially if they acquire a bird colony. Bird poop would be a ticket to success for a flying tree island. Flying tree island would be a nice safe place for birds also. $\endgroup$
    – Willk
    Oct 9, 2021 at 1:51
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It seems unlikely.

Uprooting a tree is not easy, and if you pull it by the branches it is way easier to snap the branches than anything else. And I think trees evolved to snap like that, because it's easier to survive and recover a broken branch than an uprooting.

On top of this you want also to carry some soil trapped among the roots, not only the roots. So it means your branches and your roots need to have more resistance than the soil itself.

This apart, we come to the problem that the lifting capacity of hydrogen is not that high: about 1 $kg/m^3$, or 10 $N/m^3$, while the least dense wood has already a density of about 1100 $N/m^3$. But, again, you want also soil, which has a density starting around 15000 $N/m^3$.

And you don't want just to lift that stuff, you want to break the resistance of the soil. Everything seems pointing in the direction of a big nope. It's way more easy to just attach a single seed to a lifting balloon, if you want to go the balloon way.

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  • $\begingroup$ I have this feeling he wants his floating-in-the-sky organic island, rather than just a simple balloon. Then, "1kg/m^3" is the lifting capacity under normal conditions (which are quite terrestrial). Other contexts may offer slightly better chances. $\endgroup$ Oct 8, 2021 at 10:39
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Yes, plants produce their own soil

Some ivy garden plants do this trick, while climing up a building. They stick together. They don't take enough soil up, plants can't do that. At first, long stems will keep providing the food. But further proceeding growth on the walls and on the roof will cause dying branches and leafs there, creating new soil, on the spot ! The ground won't need to provide soil anymore. After some years have passed, plants will cover the complete building.

Symbiotic companions to keep the floating trees together

When talking trees with big balloons on top, it may be difficult to stick together. In order to circumvent this problem, there could be bamboo, or a mistletoe-like plant growing in the trees to keep trees connected, while they take off.

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