Would a 'World Tree' be feasible in real life?

Question

A livescience.com article claims that trees can reach a theoretical height of 400 to 426 feet (122 to 130m). This is due to the tree being unable to carry water up to the top at that certain point due to gravity. It also claims that

at a certain height, leaves (or, in the case of redwoods, needles) are not cost-effective — the energy they rein in through photosynthesis doesn't pay for the energy it costs to bring them water

I'm interested in designing a tree that's much taller than 130 meters. Specifically, I'm interested in creating a titanic "world tree" that exceeds the theoretical height limit. The world tree would have a ludicrous amount of leaves for photosynthesis.

Provided the perfect conditions for growth, what methods could the tree use to ferry the water upwards? And what would the limit be in that case? I'm assuming that there are other factors that could limit tree growth besides the inability to ferry water to the top of the tree; for example, after a certain height the wood of the tree may collapse on itself.

To be slightly clearer, I would like a list of evolutions/adaptations that would allow this tree to exist under perfect conditions and stability and what its height limit would be in that case. I can understand that such a tree with conventional earth trees impossible, that the limitations of wood would debilitate its height, and that it would not go over the troposphere due to temperature and air conditions

Thanks for the answers,tho I don't think I'll be messing with the gravity

Thanks to Brythan and Hamlet for the edits :D

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N.B. Read the requirements for the hard-science tag before answering!

Answer 1

Assuming you can fix the water problem using some of the other answers given, like having pools along the height of the tree, extracting water directly from passing clouds, etc., you will still have to deal with the tree crushing itself under its own weight. The following is an engineering kind of answer to the question.

Short answer

The equation that determines the maximum height of the tree is:

$$H_\text{max} = \frac{\sigma_\text{allow}}{\rho g}$$

Where $H_\text{max}$ is the maximum height of the tree, $\sigma_\text{allow}$ is the compressive strength of the wood, $\rho$ is the density of the wood, and $g$ is the acceleration due to gravity on your planet.

What does this mean? Well, the tree's height is directly proportional to the strength of its wood, so if the tree evolved to have ultra-strong wood it could grow taller. It is inversely proportional to density and gravity, so if the tree evolved to have extremely lightweight wood it could grow taller (maybe it uses some metabolic process to make balloons of lighter-than-air gas to support its weight too? that would be cool). Finally, as was mentioned in another answer, the lower the gravity the taller the tree. Halving the gravity doubles the possible tree height.

Note that it doesn't matter how big the tree's base is, it will still crush itself as it gets taller. This falls out in the derivation below if you want proof.

The math

Let's consider the simplifying assumptions that the tree has a constant cross-sectional area $A$ along its height (for example, a cylindrical tree would have $A=\frac{\pi}{4}D^2$ where $D$ is the diameter) and that we can ignore wind forces and things that could tip the tree over, focusing just on the compression experienced at the bottom of the tree.

The weight of the tree would be density × volume × acceleration due to gravity:

$$W = \rho V g = \rho A H g$$ (where $\rho$ is the density of the wood and $H$ is the height of the tree)

The ability of the tree to carry a load is described by its "compressive strength" which is basically the amount of "stress" the tree can take before breaking. Compressive stress at the base of the tree is the weight divided by the area of the base:

$$\sigma = \frac{W}{A}= \frac{\rho A H g}{A} = \rho H g$$

The area in the numerator and denominator cancels out. Now we can rearrange to find the maximum allowable height:

$H_\text{max} = \frac{\sigma_{allow}}{\rho g}$

Example

An oak tree on Earth could grow to a max height of $691\ \mathrm m$, given a wood density of $600\ \mathrm{kg/m^3}$, a strength of $4\,070\,000\ \mathrm{N/m^2}$ and acceleration due to gravity of $9.81\ \mathrm{m/s}$:

$$H_\text{max} = \frac{4\,070\,000\ \mathrm{N/m^2}}{600\ \mathrm{kg/m^3}\times9.81\ \mathrm{m/s}} \approx 691\ \text{m}$$

Material property sources: http://www.engineeringtoolbox.com/wood-beams-strength-d_1480.html http://www.engineeringtoolbox.com/wood-density-d_40.html

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Edit: Additional information

As mentioned in other answers, there are additional factors limiting tree growth. This paper from Nature describes the limiting factors in some detail. It mentions that the theoretical maximum water transport height may not be reachable because as the pressure drops it can lead to embolisms within the xylem, which can cause nearby branches to die. Trees can try to mitigate this risk by reducing the size of their stomata, but that also decreases photosynthesis, meaning the top of the tree has a much harder time generating nutrients. According to their estimates, this limits the maximum height of trees on Earth to somewhere around 130 m.

Answer 2

Water Basins If every 300ft or so the tree grew water basins to catch rain, (or maybe as a place to deposit water that it had already pulled up from below?) the higher parts could draw from these basins instead of directly from the ground.

This can also lend itself to the fertilization as well. If these basins were large enough they could become small ponds or lakes that could support life. The animals/plants/fungi/whatever that migrate, live, and eventually die there could become the primary source of nutrition for the world tree.

The limiting factor would come down to how high can you stack wood before the bottom most block is crushed by the weight. Because this is an alien(magic?) world you could always say as the tree grows old instead of outright dying, it carbonizes into some carbon fiber structure that allows it to withstand the immense weight of itself?

Answer 3

• Transport : Due to transpiration, water can go upwards in trees, however after a certain height the pressure won't be enough. A way to counter this would be if the tree had a heart of some sort to act as a pump. Also, the tree can absorb water from outside, so the leaves at the very top can still receive water. ( You can also decrease gravity in that world.)
• Lifespan : It will take a really long time for a tree to grow to that height, it can't be done if it lives only for 30 years. So the tree would have to be pretty much immortal and fast-growing, because even 3000 years is too little. A way around this would be a tree whose offspring grow from itself (it is self-fertilizing, and the seed remains in the tree). So the tree will continue growing.
• Nutrition : A tree that big needs lot of minerals. Which is hard to get if it's stuck in one place. A counter would be if there were bacteria that excrete the minerals required for the tree, and also depend on the tree in some way. Also it can have some sort of 'basins' which emits a scent that attracts bugs. The bugs fall in and are dissolved to provide the nutrition.

Answer 4

If you significantly relax your concept of "tree", then consider this: an enormous buoyant "crown", attached to the surface via a long, lightweight, flexible "trunk". On a planet like Venus, with its very dense CO2 atmosphere, there are a variety of gases that could provide the necessary buoyancy.

One gas that comes to mind - oxygen! It has a lower molar mass than CO2 and, as a bonus, is a natural product of photosynthesis. The tree could start out growing on the ground, and then grow out some kind of bladder that captures the oxygen produced by photosynthesis. As the tree grows older, both the stalk and bladder grow, lifting it higher into the atmosphere.

For water, your atmosphere could have a reasonable water vapor content - not so high as to make the atmosphere lighter than the gas bladders, but enough that your "trees" can extract the water they need directly from the atmosphere. If your atmosphere is fairly well-stratified, the denser CO2 would sink to the bottom where it can provide more support, while the lighter water vapor would rise to the top, where your crown/bladder apparatus can extract it. This would give a double-incentive for trees to grow as tall as possible - more light and more water the higher up you go. The limiting factor would be at the point where the atmosphere no longer has sufficient density.

Potential problems

Gravity

You may need to play with the mass of your world such that the buoyant forces are enough to overcome gravity.

Respiration

Plants need to respire just like the rest of us - this means consuming oxygen. They could consume some of the O2 they've stored in their flotation bladder(s). They might start to slump a bit at night, when at peak metabolic rate ;-)

Answer 5

The tree's ability to lift water would scale quadratically if the gravity of the planet were lower. Thus, on a hypothetical planet with half Earth gravity (g = 5 m/s^2) the tree could attain a height four times as it would on Earth.

If your planet had the Moon's gravity, for instance, the tree could reach a height of four kilometers high.

Note that BarbalatsDilemma mentions in her answer that once we remove the limit of water transport, the limiting factor of tree growth will become the wood's ability to withstand compressive stress, which increases linearly with height. In fact, the strongest woods are from those trees which grow the tallest. Therefore once the water transport limitation is removed, the tree may have reason to develop yet stronger woods.

To address concerns of lesser gravity affecting the planet's atmosphere, I present Titan, a moon of Saturn. This moon has an atmosphere thicker than Earth's atmosphere. To address arguments that the atmosphere may be possible only due to the lower temperate at Titan's location, the leading theory of the origin of Titan's atmosphere is that it is caused due to low silicate content in Titan's crust, so everything is volatile. Thus, a higher temperature would actually increase the sublimation rate and thicken Titan's atmosphere. The higher temperature would expand the atmosphere, but so long as that atmosphere remains inside Titan's Hill sphere it would remain and cause even higher pressures. Titan's Hill sphere is about 50,000 KM, current atmosphere reaches about 1000 KM above it's surface, and volume increases by the third power with increasing radius. Note that these volatiles are organic materials, in particular hydrocarbons, so they would actually support plant growth very well.

Answer 6

the tree can utilize some form of https://en.m.wikipedia.org/wiki/Atmospheric_water_generator which would allow it to collect water from air itself. It would get water directly from the clouds and water vapor itself. I guess the leaves can act as a net to allow water to condense and is then absorbed by the leaves itself.

With the help of Google,https://en.m.wikipedia.org/wiki/Troposphere#Temperature

I highly doubt the tree can survive past 6000 km depending on where the tree is situated as temperatures would start decreasing drastically near the tropospause and air would get thin. As for the trees support and weight, I'm thinking that it would have to evolve a kind of multiple tree trunk that winds together? A trunk that twists together might be a better support for the lower part but it would straighten out as it gets higher to avoid even more weight pressing down. For the amount of leaves needed to support a massive tree, the branches would need extra strength by either supporting each branch by intertwining[might be disastrous if the bottom branches break] or by 'braiding the branches' which should increase the weight it can hold.

Otherwise, it might be a nice little cheat to have your tree be supported by a really really tall steep cliff[part mountain part tree]?

Answer 7

Symbiosys Life forms like little insects and birds search protection in the tree, the tree get water from animals urine and from air umidity (using sponge like leaves).

Primitive refrigeration The leaves could have a shape like a double "u" that is great for converting wind energy into mechanical energy, the side effect of that is that wind get cooler, allowing condensation of water (even if in very small amout).

Symbiosis II Certain life forms could actually evolve to bring water to the tree and get in exchange small fruits, if the tree is that big it is likely it has a complex ecosystem inside it wich would make the tree also a isolated system.

This is for getting water.

For getting instead great height instead we have more problems, the tree would have a shape that resembles a reversed cone (base on ground and vertex upside).

Wood is light but also weaker than iron, so the height maximum reachable (to avoid mechanical breaking of the tree) should be slightly above or below the highest buillding, so don't expect it to be higher than a kilometer, however you could partially cheat if the tree grows on the highest mountain in your world.

EDIT: since tag advocates are becoming increasingly boring, here's for the hard-science part:

Symbiosys: no know micro-organisms have such a behaviour, however there's a spider that is able to transfer air bubbles below water level to create a nest. Since there are already life forms that move air somewhere, it is plausible to assume are possible life forms that move water somewhere. Also, snails have a protective coating to avoid dehydratation when sleeping, the tree and its life forms could use a similiar mechanism to preserve water.

Regarding the refrigeration: simple physics law, if air do any work it spends energy in doing so and hence lower its temperature, also certain shapes (double "U") are really helpfull in draining thermal energy and converting it in kinetic energy

Since a big life form is highgly susceptible to die by any disease (single DNA), it is more realistic if the tree is in reality a composite life form so that it has enough DNA variety to not die entirely due to diseases. We have already proofs of this being possible (moss is in reality made by 2 different life forms cooperating), also it is possible to do vegetable grafting (put a plant branch to a foreign plant to obtain new type of fruits), another proof that a vegetable life form wich is in reality made by different life forms is entirely possible.

Answer 8

Wind is a killer. There is a reason that the tallest trees have few branches below their crown. Catchment basins would act like sails and tear the tree apart. Sorry to rain on your parade. The highest building in the world is 830 meters tall and I doubt that mother nature could do more than double that with a living organism, but I'm just guessing...

Answer 9

Just passing through and thought I'd leave my thoughts on this topic...

Have a look at the latest (last) book in Terry Pratchett and Steven Baxter's Long Earth series, "The Long Cosmos". One of the worlds there has ginormous trees. Water transpiration to the upper branches is effected by the trees capturing / generating hydrogen, and using this to float sacs of water up to the upper levels.

Of course, the wood of the trees were highly imflammable, being chock-a-block full of hydrogen. The existence of such a world and such curious trees was never reported, probably because any traveller who stepped in, and stayed long enough to note the size of the trees, probably stayed long enough to collect some wood and make a fire... BOOM!

Answer 10

No. As trees are today it is impossible. In trees water is drawn up the tree passively. To get the kind of heights your looking for the tree would have to pump it own water. I can't see how a tree could produce enough energy through photosynthesis to power an active method of water transportation at that height. Furthermore if the tree grew too high the air would be too thin for photosynthesis or respiration. In order to survive our tree would have to eat other plants for sufficient energy and would have to pump oxygen up to the top of the tree.

Answer 11

A smaller version is possible, especially if it is adapted for that sort of thing: It can have a very thick base and thinner at the top (so it won't break), and very long roots that are spread out (so it will get minerals).

If it is near a river, in a relatively windless area then it can grow to large heights. This solves the problem of nutrition (the waste in the water provides nutrition, as well the other stuff stated by KingOfSnakes and it can have a heart which provides additional pressure to draw the water to its leaves.

Answer 12

It depends on your definition of "tree".

First, there are multiple answers here that propose a heart--this doesn't overcome the problem that lifting the water costs more energy than the photosynthesis yields. This means either we obtain the needed water directly from the atmosphere (which means a humid climate) or we need some radically different chemistry. Since we want something tree-like lets start with photosynthesis--but the high energy molecules aren't sent down the tree, but only laterally to the trunk where they are converted to electricity. The products are sent back out to the leaves to be combined again--you only need to lift for growth or leakage, not for energy production.

Now, we need a very strong tree--instead of wood lets figure a core of metal foam. Once the roots find suitable ore deposits they grow a metal foam core in each trunk. For the sake of strength you need multiple trunks with many cross connections. Look at how antenna towers are built for how the tree has to do it.

As the tree gets big enough we can take some of the load off it. The tree grows a transparent but airtight canopy over itself. The leaves are inside this canopy. The canopy acts like a greenhouse--the insides are warmer than the ambient air which is good as it gets cold up there and you have in effect a giant hot air balloon. If it's big enough the only elements in compression are those holding out the waist of the bubble, the rest of it is all in tension and therefore much easier to support.

The tree needs to have full regeneration capability or else the ravages of time will kill it before it gets to the size of a world tree.

Answer 13

I can think of a few options, some of which will just be additional notes on existing answers:

1. Capillary Action

Capillary action could possibly circumvent gravity - it already does on a small scale in all sorts of real world situations. The basis for capillary action is surface properties and surface tension of fluids allowing them to rise (or fall) through extremely narrow channels. A fountain pen is a great example of this. If you take an empty fountain pen and rest the nib in an ink well, ink will slowly rise through the nib into the ink feed.

2. Water Collection Basins

A tree could have natural collection basins, akin to a strawberry pot. This would allow the tree to naturally collect reserves of water anywhere along its surface. This could even be done (through some twist of evolution) at each location where a branch meets the trunk. Actually, I'm almost surprised there are no Earthly trees (as far as I know) that do this. Or possibly it's leaves could be designed to funnel water into such a system. Hostas work like this on a much smaller scale - drawing water into the base of the plant.

3. Atmosphere

If your planet is not strictly Earth-like, and the tree is tall enough, a persistent or near-persistent vapor base (clouds) at or near the crown of the tree could provide ample water, especially if the tree had adapted structures that would help capture and channel water. This could even be as simple as interestingly channeled bark-like structures trapping and condensing water from the vapor.

Answer 14

All other answers assume the tree is growing in a gravity well. This need not be the case - however, other constraints will apply (read Niven's 'The Integral Trees').

There is also a question of scale. A perfectly normal tree could be considered a 'world tree' by a very very small intelligent race.

Answer 15

The tree could get "help" from other organisms, willy nilly. People could feed it (they'd need a motive). Or it could consume other plants. Then it could have access to more energy and different materials than a normal tree.

I highly recommend that you read the novella The Son of the Tree by Jack Vance. It also has a world tree. Its feeding patterns may be...instructive.

It could also do something with solar power in order to generate energy, either by heating water in basins through reflective leaves, or by using metals that catch light and convert it into electrical power. It may be far-fetched, but it could work in a novel.

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Another idea is that the world tree could get it's nutrients from the waste products of animals that live on it.

Answer 16

I believe that in order to make the tree possible the tree would have to be constructed with genetically modified tissue vertically with an ascending team of 3D printers as if a spider wove its cloth upwards, and this would have as main objective to have a "living" To shelter human life like living in a biological skyscraper, I believe that with all current and future technologies and the most brilliant minds in engineering and design it would be possible to build a tree that could reach 40,000 feet, ok no :P.

Answer 17

Lets say world trees really could have existed on earth it would need immense water to sustain itself i think of natural pure and warm spring water under it that flows up under higher pressure created under ground aiding the tree to pump the water up higher into its self and to prevent it from crushing into its own weight parts of its stem/trunk and root system must have been crystallized by the pressure of its weight together with the minerals within the spring water as it grew over time (like some of that evidence is found in tree stumps/trunks on this site https://secretenergy.com/news/are-these-giant-prehistoric-trees/)

Answer 18

After looking at all of the comments, this is my personal conclusion for the ultimate "world tree".

Leaves with very short hairs. These leaves would not only produce energy through photosynthesis but absorb water like roots, where the hairs act as root hairs. With slightly different physiology this is certainly possible.

Location in a valley providing relative shelter from winds. The tree would also be very thick at the bottom and get progressively thinner to avoid breaking.

No more than 2000 meters (2 km) high to avoid constant, ultra-low temperatures, but still have a massive size. This would also remove the need to make ridiculously strong wood or other, more complicated and/or unrealistic elements.

Light but relatively strong wood. The tree would also (as with most plants) have a high lignin content, from which it would somehow produce its own carbon fibre and implement it into its own structure in high quantities, greatly strengthening the tree to keep it from essentially imploding.

Pools of water from interlocking branches and/or leaves above ground-level, drawing in critters and providing energy reserves if needs be. Microbes, insects, small mammals, and other organisms would be attracted to the relative safety/shelter of the tree, and with water, they would be even more likely to wish to take up refuge there. They could provide minerals and other nutrients in the form of their waste, and could even form a stronger symbiotic relationship of some kind (use your imagination). The pools would also work as energy stores, where the water could be saved and then used by the water-absorbent leaves.

Very thin channels in the tree. Water and other nutrients could travel throughout the tree based simply on the behaviour of fluids in very small channels (see Jesse Williams’ response for a somewhat more detailed description).

Large root system capable of bringing other nutrients and support/stability.

Multiple "trunks" winding together. This would divvy out the trees own pressure more evenly, among other things.

Answer 19

In my opinion, a world tree would be impossible to make if the trunk is only composed of one part. But if we take into consideration some trees like the Banyan, or much more known in our country as balete, I think it could grow to become a world tree, provided that it has sufficient nutrients to support it.

A banyan tree is really a small tree if it is alone. However, it makes multiple aerial roots. And these roots grow big until it becomes like it's mother trunk. Its aerial root system made it possible for it to become bigger and bigger without fearing of being toppled down by gravity.

So, that's it. If our world tree has multiple aerial roots, it can support itself and not fear the ferocious hand of gravity. And it will grow taller and taller, but it will expand more and more, taking up more space than we would like it to be.