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I was trying to create a world that has extensive massive rain-forests unlike anything on earth where the trees interlock with thick branches to allow them to rise much higher into the air (several hundred meters) and provide stable support. This is heavily inspired by a hypothetical alien planet I saw on a National Geographic documentary when I was younger, which you can see here: https://www.youtube.com/watch?v=Pw2tggyZeAQ

Now they argue here that they got assistance from biologists and ecologists to see if such an ecosystem would be possible, but I wanted to run by here to see if that's something that can really be justified.

The thinking goes that on earth, we have trees going up to around 95 meters, their size is restricted by the simple problems involved in creating something tall enough that can go higher and still stand on its own without collapsing, but also the ability of the tree to transport water up to that height from the ground, which eventually becomes unfeasible with the xylem system.

In the show, the solution is that the trees take advantage of endless, heavy rains and fogs, catching water directly at the very top and funneling it down rather than fighting gravity, while they grow struts and supports that interlock and support them against each other over a huge area, allowing them to rise much higher into the air.

I poked around a bit and it seems that both of these solutions appear a bit on earth, giant sequoias collect some of their water from the top, making use of extensive fog: http://articles.latimes.com/2002/sep/01/news/adme-redwoods1

Additionally Banyan trees(http://en.wikipedia.org/wiki/Banyan) seem to lock into place against each other with support roots over a wide area, though they don't go nearly as high as I'm proposing.

The Documentary also supposes that this planet has a much denser (3atm at sea level) atmosphere than earth, would this assist in carry water vapor and such?

If somebody better educated in biology and physics could help me out with this, explain where this idea may break down and why it would be much appreciated, thanks!

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There are a few limitations to the height of trees.

The first is the strength of the building materials they are made of. Wood is actually a very strong material so in theory trees can grow very tall.

The second is stability - the taller you go the harder it is to not fall over. In the youtube video the trees solve that problem by interlinking with each other at the top. This would certainly work.

The third is getting water up from the roots to the top of the tree. This is the main limitation preventing trees on earth growing any taller. If enough regular rain was coming then a catchment system as proposed in the video would solve that problem.

So in other words yes, the trees as described in the program are plausible.

The denser atmosphere will help slightly by providing a small amount of lift to the trees - although it will also make wind more powerful. This would make the interlocking even more important.

The main limitation is going to be at the edges of the forest, where you have trees not supported on one side. Additionally you have the problem of where new trees come from - as they would not be able to grow up from the darkness below to reach the light.

Trees near the edge may well be shorter, then the height increases as you go deeper and deeper into the forest.

Trees deep in the forest would most likely reproduce using a sucker type arrangement where a new tree growing is provided materials by the ones around it rather than using seed dispersion. This would be needed because the seeds would be in complete darkness so have no chance to grow.

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