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The setting is in a region of a planet comparable to Earth's California in regards to location. The soil is extremely rich in nutrients and subsurface water. But for the past three million years the planet has been locked in an ice-age. Could 'trees' adapt to grow down through the ice and snow to reach the fertile soil beneath?

If the 'trees' had evolved to collect sunlight energy and convert it into heat energy in its roots would it be able to bore through the ice slowly while also absorbing the liquid water?

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    $\begingroup$ The seeds would likely still need nutrients to grow into the ice, and given that it's ice, there's probably a good deal of energy necessary to drill down into it. You may want to distribute nutrients throughout the ice or have plant matter decay into it so have a form a psudeosoil before reaching the actual surface. $\endgroup$ – Pleiades Apr 30 at 15:07
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    $\begingroup$ How thick is the ice? It would be easier for roots to get through several meters of ice as opposed to several miles of it. $\endgroup$ – Liam Morris - Reinstate Monica Apr 30 at 15:13
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    $\begingroup$ I read the start ofthis question as "planet comparable to California", and was really confused by quite a few moments. $\endgroup$ – T. Sar - Reinstate Monica Apr 30 at 18:25
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    $\begingroup$ There is no soil under a glacier. Glaciers have this habit of scraping off everying in their path down to the bedrock... $\endgroup$ – AlexP May 1 at 8:28
  • $\begingroup$ How much trees are we talking about? Remember that trees drop stuff, die, animals live in/near trees, feed and poop. After some while the ice near your tree is covered in leaves, poop, food left-overs etc. which will eventually create some kind of soil on top of the ice. Have you taken that into account? Can you comment on that? $\endgroup$ – Deruijter May 2 at 13:51
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Maybe seeds isn't the way to go. A seed would be hard-pressed to contain all the nutrients to build deep enough roots.

Instead, how about one of the many forms of asexual reproduction common in plants, such as vegetative propagation. Basically, a branch of the tree hangs low, touched the ice, begins growing roots until it hits the soil, then the linking branch withers, separating the now-complete plant from its parent.

Or, scrap the soil idea entirely. As others have said, under so much ice for so long the soil won't be anything to write home about. Plants with their roots in water exist. Maybe your trees' roots melt the ice chemically and drink that up for water. Ice that formed through layers of snowfall won't have much in the way of nutrients naturally, but if your glacier hosts a rich ecosystem with animals and plants living and dying on its surface, it could work. That poses another problem though: either your microbes have evolved beyond the real arctic ones and can decompose the corpses in the icy cold, or your ice is less 'nutrient-rich water, but solid' and more 'sterile, unforgiving ice with pockets of preserved corpses', at which point your plants spread their roots (via chemical melt) through it to find and chemically digest the corpses - like carnivorous plants that eat with their roots.

That is more of a creeper plant than a tree, though, so you'll need an excuse why the whole bark-tree-thing is needed. And, don't expect them to be pleasant either: the thorns of plants like briars are meant to hook into careless creatures and keep them tangled until they die and fertilise the soil - right where the plant is, not way over there. If the ice tree had to crawl its way through the ice to find ancient corpses that might be there, it would either develop the means to create new ones where they're close and easy to reach, or form a symbiotic relationship with something that does. Your forest floor will be covered in preserved bodies or their husks, mostly those of desperate scavengers that came to feed on the previous ones and proved as unlucky.

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Maybe, nature is incredibly inventive, but there are a couple of problems with the basic premise;

  1. Glaciers "bulldoze" soil out of the way when they move down valley. If there is any major volume of ice around the pre-freeze soils have been pushed off the slopes.

  2. The glaciers aren't going to stop moving for the trees that are growing through them either. The life expectancy of anything growing through an active glacier is measured in months; the time between first frost (when the glacier freezes to it's bed for the winter) and the thaw (when it starts to move for the spring and summer months). In temperate areas that can have winter rains it's even worse as winter storms can cause short melt spells, and glacial surges, in the otherwise stable cold months.

  3. They don't have to; trees, in fact whole forests, can and do grow on top of glaciers, soils often form on the lower sections of ice flows, supporting a variety of plant life. I myself have seen willow and poplar growing on soil covered ice near the toe of Fox Glacier in New Zealand and there are pine forests on the lower lobes of a couple of European glaciers.

As for roots melting through the ice chemical rather than thermal melting is probably easier to explain, salt excreted from the roots could raise the freezing point sufficiently to thaw down through the ice, water absorption would be automatic due to osmotic pressure.

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    $\begingroup$ +1 for point number 1. If you had roots going all the way down through the glacier, they'd be destroyed in no time. $\endgroup$ – Alexandre Aubrey May 1 at 14:40
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    $\begingroup$ Ash, I'm not sure if you're actually making the point that @AlexandreAubrey is thinking of (and which was my first objection): If the tree extends from leaves at the top of the glacier to roots at the bottom, the flow of the glacier (up to hundreds of metres per year) is going to rip them apart from each other. I think explicitly stating that would improve this answer $\endgroup$ – llama May 1 at 17:26
  • $\begingroup$ +1 for the chemical melting idea (although salts might not be the right chemical melter; the plant has to find the salts, and sodium/potassium might be rare enough on ice that they shouldn't be wasted. But there could be organic ice-melters, like alcohol.) $\endgroup$ – Peter Shor May 2 at 12:41
  • $\begingroup$ The only chemicals available to a plant are the things it draws up through its roots and the things it makes starting with photosynthesis. If the roots are in ice, you obviously can't use stuff drawn up through the roots to melt that ice, so any chemical melting is going to have to be via organic compounds made by the tree itself. $\endgroup$ – David Richerby May 2 at 17:16
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    $\begingroup$ @DavidRicherby See my third point, trees don't need any special adaptations to grow on glaciers. $\endgroup$ – Ash May 5 at 18:11
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Up from below.

knotweed breakin thru pavement https://morgan-outdoors.com/?p=1443

Your glacier trees can take some pages from the playbook of the invasive Japanese knotweed, famous for its ability to break its way up through concrete.

  1. Your plants establish on the edge of the glacier. Runoff provides liquid water. The soil is good. Organic nitrogen is in short supply but these plants can fix their own nitrogen.

  2. They put down deep roots. Knotweed roots are 5 meters down. The soil next to a glacier facilitates this.

  3. They spread out in a clonal patch; if these are trees then like an aspen clone. Plants come up thru the adjacent ice.

  4. As new roots are laid down deeper into the ice field, the plant can encroach its way into the ice. Ice is broken as it goes. If this just an ice field, the plant will facilitate the dissolution of the ice. If this is a flowing glacier then it will fight back.

This sidesteps the issue of nitrogen and puts your plants over and under the ice.

Last piece: slider seeds.

These are big seeds, like coconut. They have enough resources in each seed to establish a hardy well rooted plant on minimal resources, like the coconut does for a sandy beach. These big seeds have sails and slide or tumble across the ice fields until they hit a low point and lodge. If this is a fissure or a bare patch or somewhere with access to the soil then the tree can get established and start a new clone.

Maybe instead of just seeds, during storms entire trees can break off from the clone and slide across the ice. Knotweed can definitely break off and take root in a new place from loose fragments with associated resources. . With access to water it can cannibalize its parts to grow the deep root needed to establish itself deeper in the ice field.

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    $\begingroup$ Clonal colonies... Nice! +1 $\endgroup$ – Joe Bloggs Apr 30 at 16:24
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    $\begingroup$ It's worth looking at the banyan model as well. $\endgroup$ – The Nate Apr 30 at 23:02
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    $\begingroup$ One thing to note, glaciers can often be very thick (a.k.a. tall), so your trees might have to grow very tall and break through a LOT of ice; or else they have to be restricted to thinner parts of glaciers. $\endgroup$ – cowlinator Apr 30 at 23:21
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Fertile soil is fertile, because it contains nutrients, and nutrients come from decomposed organic matter. If the place is covered in ice for 3mln years, and all organisms which live there live on the top of the glacier, I'm afraid the soil beneath it can't be fertile. Unless there is something else going on, like for example another ecosystem of organisms living under the ice. But in that case you would need much more than three million years for the evolution to make it work.

Back to your main question: Ice thickness on Antarctica, as well as thickness of glaciers during the most recent ice age, was about 2-4km. Trees growing 2-4km long roots from a single seed would be very difficult to rationalize, since only after touching the fertile soil beneath the tree would be able to get additional resources to build itself. Maybe you can say that the seed builds a carbon nanotube, drills it through the ice, and then sucks in nutrients and water. But again, three million years is not enough to evolve something like that. To be honest, I don't think any number of years would be enough - your readers will think you're just hand-waving things. Instead, maybe, the "seeds" could in reality be complex nanomechanisms, planted on the planet by an advanced civilization. The trees that grow out of them are real trees in every aspect except for that their own new seeds are really built by nanobots living inside them.

I hope that helps.

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    $\begingroup$ How do you know life as we know it isn’t built of complex nanomechanisms designed by an advanced civilisation to serve some unfathomable purpose??? #existentialcrisisoverhere. $\endgroup$ – Joe Bloggs Apr 30 at 15:22
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    $\begingroup$ There are plants which grow in the least promising of soils, or out of the smallest fissures in bare rock. Some die when the soil becomes too fertile for them. Some just grow even better, and become known as invasive weeds. Plants don't require any organic matter in their soil. The vast majority of a plant is built out of carbon dioxide from the air, water, and nitrogen (which can be fixed from the air by symbiotic bacteria). They just need small amounts of various mineral nutrients which dissolve out of rocks (sometimes with help from the plant). $\endgroup$ – nigel222 May 1 at 12:05
  • $\begingroup$ nigel222: To be able to use nutrients and CO2, the plant has to be already developed. When it's a seed, all the building blocks of a plant, except air and water, have to be contained inside it. Environment triggers the seed to open, but during the first phase of growing the plant has to use what's there in the seed. Only when the root finds nutrients in the soil, they can be used for further growth. In this case, the plant lacks nutrients until it digs through a thick layer of ice. It needs to build a very long and strong root from the seed, and it needs lots of energy to dig through the ice. $\endgroup$ – makingthematrix May 4 at 18:33
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Lightning trees!

The first law of living in extreme environments is: never expend resources you don’t have to. In your case, why do hard work getting down to the soil if you can get a lightning storm to do it for you?

Assuming that some part of the year, the surface temperature is above freezing (or you can’t have plant life anyways) your glacial plateaus will have lightning storms, with liquid water coming down, to boot.

Ice is a terrible conductor, and your trees are a tall and jutting path to ground. Cue:

enter image description here

“Ah!” but you say, “But then my tree has exploded!”

Well, that’s okay. That’s exactly what your tree wanted! It’s an active pyrophyte. https://en.m.wikipedia.org/wiki/Pyrophyte

So it explodes, and sends chunks of itself skittering around the whole damn surface of the glacier! Maybe like eucalyptus trees, its entire canopy can detach and get blown miles away... where it attracts a second lightning strike, which cracks and melts a path down to the soil beneath, where your pyrophyte seeds happily settle in to grow in newly wet soil.

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The main issue with roots going all the way through the glacier is that glaciers move.

More importantly, they move through deformation. This means that the base of the glacier is moving at a different speed than the surface. A solid object going all the way through the glacier (e.g. root) will get stretched, torn, and destroyed.

Many other answers provide alternatives that would still allow you to have a glacier covered in forest.

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Not all glaciers are sparkling white. Some are dirty, in that they contain a certain amount of soil. The soil could be churned up from the ground the glacier flows over and rises to the top, or it can be deposited by other means, such as wind storms or volcanic eruptions.

This soil could be the source of your nutrients in the same way hydroponics works. Granted, the nutrients won't be in large amounts nor will they be quickly replenished, but you have 3 million years worth of soil buildup as well as old trees dying and decaying.

If there is any fauna, that would add nutrients as well. This would be due to their dragging their own edibles onto the ice, manure, urine, or their own corpse.

Because of the minimal nutrients, you're likely to see longer lived trees rather than massive forests. Even on Earth, there are trees that are hundreds, if not thousands, of years old. On this planet, they might be tens of thousands of years old. They may also be really massive, or relatively small for their age. Their growth rings may also be so small as to not really be distinct enough to be rings anymore.

Once a tree dies, it leaves it's nutrients to it's descendants, so maybe there are pockets of trees as well as large individual trees.

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Could trees adapt to grow down through the ice and snow to reach the fertile soil beneath?

Plant, like any other form of life we know on Earth, depend on liquid water to perform their biological functions.

The main issues with a frozen planet surface is that it lacks liquid water, and that the low temperature really slows down biological chemical reactions.

Moreover, I suspect that after 3 million years of ice age the ice sheet would be rather thick, too thick for whatever root to pierce it starting from the top.

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  • $\begingroup$ There are very easy ways to get liquid water from ice. The only question would be whether the plant can produce enough energy to use them. Maybe the plant can use photosynthesis for this – how bright is the sun? And there are fish that live in freezing water, and their chemical actions seem to proceed quickly enough for them not to die (although they have adapted to this environment through evolution). $\endgroup$ – Peter Shor May 2 at 12:44
  • $\begingroup$ @PeterShor, if plants could use photosynthesis to melt ice there would be no ice in first place $\endgroup$ – L.Dutch - Reinstate Monica May 2 at 14:41
  • $\begingroup$ @L. Dutch: Have you ever heard of skunk cabbage? What is the albedo of ice? What is the albedo of plants? And if you collect the sunlight that falls on one square meter of ice, does it contain enough energy to melt 10 cubic centimers of it? I'm not suggesting that the plants should melt the entire glacier, just enough to get some liquid water. $\endgroup$ – Peter Shor May 2 at 15:20

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