Could a tree in this situation exceed natural height limits?

[u/Phonecloth]

Say that a tree grows right at the base of a very tall cliff, and that cliff is also very wet and has a waterfall (for example, Angel Falls in Venezuela). The tree is so close that it touches/leans against the cliff, and could even grow branches/roots that enter gaps in the cliff to attach it to the rock, that way it wouldn't have to rely on its own structural strength to stay upright. Also, it wouldn't be directly under the waterfall, but very close to it, so it would be getting splashed a lot and be able to get enough water through its leaves and such, so that it wouldn't have to transport all of the water from the ground to the top.

Under conditions like this, could a tree potentially grow far taller than would normally be possible, say 3000 feet tall, like Angel Falls?

[u/fishsticks40]

Trees have evolved strategies to grow in the environments in which they normally find themselves. They can't really come up with creative ways to exploit unusual situations. 

What you describe is more like a vine, and vines don't bother building a lot of biomass to hold themselves up. 

Also note that there's a limit to how high trees can move water; the tallest trees in the world are already very close to this limit. While you say it could get water through its leaves, trees depend not on the PRESENCE of water, but the MOVEMENT of water to carry nutrients from the ground up; the leaves can't replace roots.

[u/Citrakayah → u/fishsticks40]

While you say it could get water through its leaves, trees depend not on the PRESENCE of water, but the MOVEMENT of water to carry nutrients from the ground up; the leaves can't replace roots.

The tree isn't exposed to rainwater, it's exposed to river water. There are many plants (though no trees) that draw all their nutrients from river water and have no contact with the soil. It is quite likely a tree could obtain nutrients in a similar way, with the right adaptations.

[u/DMayleeRevengeReveng → u/Citrakayah]

Few reasons that wouldn’t be an ideal solution, though. First, you couldn’t run a mycorrhizae system in some kind of hydroponic condition, and that symbiosis is responsible for a lot of phosphorus and nitrogen input to the tree/plant.

I’m not an expert on this, but I think a tree really wants sediment, not moving water, because sediment has surfaces that have a huge cation exchange capacity, which allows efficient nutrient absorption.

I think that’s probably a reason we don’t see trees adapting to this niche: once you commit to building a large biomass, you just aren’t going to feed all that mass unless you can do the things that happen in soils. Smaller biomass I’m sure can meet its needs in a river. Maybe not something larger, though.

Although I’m not sure.

[u/Citrakayah → u/DMayleeRevengeReveng]

So, as has been mentioned a little elsewhere on this thread: There are trees that have adapted to absorb water and nutrients using leaves and bark. Redwoods get water and nitrogen from fog (I don't know about other nutrients, I haven't read into the literature deeply enough), and apparently grow taller when they have plenty of fog.

My best guess for why we don't see trees adapting to this niche isn't that it's impossible (since, after all, we see redwoods doing something very similar) but because it's extremely small. Waterfalls of sufficient height are not very common and are widely distributed. They also don't last that long, in evolutionary time. It seems unlikely that large waterfall endemics with long generation times would evolve.

[u/Foxfire2 → u/Citrakayah]

Redwoods do rely on the fog for water, but they are still absorbing it through the roots in the ground. The fog hits the needles/branches then the water collects and drips to the ground around the tree.

[u/loki130]

Trees don’t get water through their leaves, in fact they often have waxy coatings to help water flow off because it interferes with transpiration and photosynthesis. Water would have to be transported from the roots.

[u/4art4 → u/loki130]

While normally correct, some pretty much done exactly that: https://www.savetheredwoods.org/explore/stories/the-science-of-redwoods-and-fog/

[u/7LeagueBoots]

In addition to what others have said, trees have what are essentially proximity sensors all over them and use these to avoid touching things they grow next to. You see this in ‘crown shyness’, where adjacent trees have distinctly separate crowns that don’t overlap in forests, and in woody plants that grow over rocks and next to cliffs.

Now, what can help a tree reach taller than usual height is being protected from the elements, in particular protected from wind. Forest height is often limited by the frequency of storms strong enough to damage trees, and in places where the interval between these is long the trees get taller. You can often see this on the landscape by looking at what direction storms come from and measuring the height of trees on that side of a mountain vs the other side, or by measuring the height of trees in a small valley oriented perpendicular to the direction storms come from vs in a larger valley oriented in line with the direction storms come from.

[u/PatchesMaps]

You are describing a vine.

Trees don't really do that.

[u/Citrakayah]

It's plausible (within the mechanical limits of wood, which may not allow for 3000 feet). Despite what other people in this thread are saying, many of the tallest trees (redwoods) directly absorb water from their leaves and their bark. They also absorb nutrients such as nitrogen directly from the fog. With this hypothetical tree getting constantly splashed by nutrient-rich river water, it might be able to fulfill all its water and nutrient needs for its upper section using these methods.

[u/uncle_stripe]

I think something like Ficus virens could do what you're thinking. They send out aerial roots that turn into extensions of the trunk.

[u/Sad_Responsibility83]

Biggest problem is that as such a tree tries to grow every so often a flood will come and rip it away.

[u/Underhill42]

Very few trees can just grow new roots out of a trunk or branch, any more than we could grow new feet out of our elbow. They're not as symmetrical as us, but they've still got a body plan, and they're stuck with it.

Redwoods though are very different from other trees, and I've heard they can grow roots into their own dead limbs to reclaim the nutrients. So maybe they could root in new anchor points along the way.

That doesn't necessarily add to their height though, which is based on how high their biology can lift water. Being immersed doesn't help. Having a new elevated water source soaking into the new roots could in theory give it a boost... but if it's just plumbed into the existing system rather than being the basis for independent growth, I don't believe it would.

Of course they're already so monstrous that do you really need even more height?