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The trees in question are 150-300-meters-tall, 18 meters in diameter and have no branches except at the very top where each branch has a single leaf that takes up the whole branch. Its bark is thick enough to prevent fire and nonarmored-piercing bullets getting through and has strong roots that can go through concrete. They reproduce by way of nuts. What would be fastest rate of growth and reproduction cycle I could give these flora freaks that is at least somewhat believable?

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    $\begingroup$ Are these trees on earth? Because if so, they're already exceeding the maximum height trees can grow on Earth. They're already unrealistic, so you could have them grow in an unrealistic time to boot. If they're not, then you could look at bamboo, which can grow at up to a metre a day, as an upper bound. $\endgroup$
    – jdunlop
    Commented Jan 11, 2022 at 7:01
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    $\begingroup$ Please do some proof-reading and clarification: 1. Do you really mean metres for height and feet for diameter - please pick a unit? 2. Are you saying that each tree has one leaf/branch only (which happens to be at the top)? 3. What are "stranded bullets"? 4. "They reproduce by way of nuts by way of pollution." - nuts I can understand, but how is pollution part of the process? $\endgroup$ Commented Jan 11, 2022 at 7:45
  • $\begingroup$ Bamboo can grow about a meter or yard per day. But bamboo is not a tree in the botanical meaning of the term. (It is a grass.) For botanists, a tree is a woody plant with secondary xylem; meaning that a true tree cannot grow at such impressive rates. As for the rate of reproduction, plants can and do produce a lot of offspring in favorable conditions. (And it is very common with trees to have some means of vegetative reproduction in addition to sexual reproduction.) $\endgroup$
    – AlexP
    Commented Jan 11, 2022 at 9:07
  • $\begingroup$ I so want to answer this, but I have questions. Local gravity? By way of nuts by way of pollution? $\endgroup$ Commented Jan 11, 2022 at 10:40
  • $\begingroup$ ALso, put the question in the body of your question, not just in the title. Also, fastest possible under what circumstances? If there was some kind of disaster that removed all but a few trees maybe they can produce enough seeds to re-start an entire forest in one season, then it takes centuries for those seedlings to reach maturity. $\endgroup$
    – Dan
    Commented Jan 11, 2022 at 14:08

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These are bamboos. A meter a day at least.

These freakish bamboos are grasses are not limited by xylem cavitation in the way tall trees are.

. The maximum height of grasses is determined by roots

Although root pressure appears to occupy a central role in the functioning of the water transport system of many monocot plants, among dicotyledonous species there is no evidence of any reliance upon root pressure for refilling xylem...

In addition to the regular and awesome bamboo repetoire, in this fictional plant the leaf at the top is a water capture device in the manner of a tank bromeliad. Water is retained within the hollow stem, which helps produce a pressure head for the roots and also a source of water already at elevation.

The 60 foot diameter is because these are actual multiple stalks which grow fused together, supporting each other.

But the question: growth rate. Existing bamboo can grow as fast as a meter a day.

https://www.sciencefocus.com/nature/speed-bamboo-plant-grow/

Some of this might be because the cells are in effect being "pumped up" from below with hydrostatic pressure. The pressurehead from the internal reservoir would help with this phenomenon.

The fastest growth will be at ground level where pressure is highest - new stemps erupting from the ground to add their mass to the main trunk. New growth will be soft and wet and not as bullet resistant (bullet resistant?) as the mature woody stems. Maturing that part takes longer.

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  • $\begingroup$ Bamboo will grow extremely fast, but it does depend on the "live fast die young" motto. Some bamboo may grow 1m/day (that may not be the biological limit), but if its to grow at that pace for 300 days to produce a 300m tree, it would contain 25500 m^3 of mass. Thats a lot of material that needs a steady supply of material to maintain such a growth rate. It could be possible, but the soil around the tree would be dead $\endgroup$
    – Sonvar
    Commented Jan 11, 2022 at 22:24
  • $\begingroup$ @Sonvar - I suspect those rates are possible when there is a lot of available fixed carbon already in the roots, and maybe a lot of water. I dont think a photosynthetic organism could fix carbon that fast. $\endgroup$
    – Willk
    Commented Jan 11, 2022 at 23:24
  • $\begingroup$ There is more than just carbon that goes into making trees/bamboo. Nitrogen, phosphor and potassium are very important nutrients. Calcium, Magnesium and iron are important minerals plants need to grow. Something this massive appearing quickly would need a MASSIVE root structure and/or stripe every atom of nutrient out of the soil it can reach $\endgroup$
    – Sonvar
    Commented Jan 12, 2022 at 14:18
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Frameshift: Exactly what do your terms mean?

How about a plant that grows as a mass of shrubs--connected underground, it's all one plant. The mass of shrubbery gets bigger and bigger until it's stores are great enough, then when the time is right it sends up this most epic of flower spikes.

The objective of this is to disperse it's progeny. Each of those "leaves" is connected to a nut, when enough of a storm comes through the "leaves" get ripped off, carrying the nuts with them. The spike has to be tough enough to resist some menace that likes to damage trees, but the tree can't simply slowly grow tall enough because the environment doesn't permit long term survival of something like that.

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1.5 meters a year

the fastest growing large tree on earth can grow between 5-8 feet per year on average. with a very large tree I would use the lowest range on that so 5ft a year or 1.5 meters.

keep in mind giant redwood average 2-3ft a year so 5 is not that absurd. But this is under idea conditions, if it is dry or cold it can drop to a few inches a year so if you want more realism and non ideal conditions stick to 0.5 meters/ year .

Most trees can start reproducing in their first year so the reproduction cycle us up to you.

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