8
$\begingroup$

Why is it beneficial for trees to grow that tall?

This sounds like a kid's question Mom, Dad... why are trees so tall?

Costs and Benefits

There are some obvious costs:

  • Need much Carbon and other nutrients
  • maintenance cost
  • energy cost (for growing, to bring water (and nutrients) up to the higher leaves, etc...)
  • Sensitivity to wind
  • etc...

Potential benefits I can think of:

  • Competition for sunlight
  • Better dispersal
  • protection against predation
  • Some birds (maybe especially those that are potentially good seed dispersers) prefer to land on high trees (avoiding the cost of regaining altitude). Being high attract these birds which eat the fruits and disperse the seeds.

Are there other potential benefits?

Specific to palm trees

I am currently in Bali, Indonesia looking at palm trees that seem to have a very low competition for sun light (the forest is not dense, the light is intense), there are no tall predators (but being tall might be a protection against climbing predators as well and there are indeed monkeys and other potential climbing predators) and looking at coconuts, papaya and banana I can hardly think that being tall helps to disperse further away (seeds dispersal by barochory). So, why (evolutionary reasons) are palm trees so high?

Improve this question
$\endgroup$
3
  • $\begingroup$ Tsunami seems to rare. I thought maybe high enough to crack the nuts from the drop that are hard enough to resist being eaten by animals. $\endgroup$
    – user11556
    Dec 14, 2014 at 8:07
  • 1
    $\begingroup$ Are the palm trees in a natural forest? You might be looking at an artificially grown oil palm plantation, since it sounds like your description is referring to that. $\endgroup$
    – March Ho
    Dec 14, 2014 at 8:11
  • 1
    $\begingroup$ It might be that non-dense forest you are observing the palm trees in isn't the environment they evolved in. meltingasphalt.com/parable-of-the-redwoods explains this quite well. $\endgroup$
    – Thomas Colthurst
    May 30, 2015 at 21:34

2 Answers 2

Reset to default
4
$\begingroup$

Beside the reasons you've given I would add environmental disturbance (e.g. flooding) as a evolutionary factor that could explain selection for taller individuals. Many palms also inhabit and thrive in disturbed habitats (Frangi & Lugo, 1998; Salm, 2005), which indicates that this could potentially (i.e. speculative) be an important factor for this taxon. Palms also have the combination of tall height and a relatively low "wind profile" (relative to many other groups of trees), which indicates that they are adapted to exposed/disturbed habitats.

This, along with the reasons you've already given, seems to cover the most obvious evolutionary reasons for selection on tree height. However, these will naturally trade-off against negative effects on e.g. fecundity from investing and maintaining biomass.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Thank you, this kind of speculations was exactly what I was looking for! $\endgroup$
    – Remi.b
    Oct 23, 2013 at 10:20
3
$\begingroup$

The height of tree species varies, of course, as each tree fills a given niche, much like animals do; you might as well ask why blue whales grow so big. The answer, of course, is that they seek out and successfully get the nutrients they require. It is advantageous for some trees to be huge and get the most sunlight possible and so some trees do.

In the specific case of palm trees, however, they aren't true trees but rather a grass, which means they are a monocot and (I'm a little shaky on plant physiology but...) that the outside isn't living but the inside is. Monocots grow straight up, in one main shoot, and palm tree follow the same pattern. Tons of sunlight, nothing to come mow or it down, and nowhere to go but up means they'll be big. True trees, on the other hand, have what is called heartwood in the center, which is technically dead tissue.

Another thing to think about is that trees aren't moving, so they only way they can improve their condition is by growth. An animal, on the other hand, can migrate to follow food; growth, particularly for mammals, also has a huge heat cost.

Improve this answer
$\endgroup$
11
  • 2
    $\begingroup$ Thanks for your answer. It doesn't provide the answer I was seeking though. I was looking for functional evolutionary reasons for a tree to be tall (like the three examples I provided). I know it is a reaction to natural selection, I know the concept of ecological niche. You're saying that tree can improve their condition by growth but my question is why? Or more specifically why growing tall? $\endgroup$
    – Remi.b
    Sep 13, 2013 at 6:18
  • $\begingroup$ For the case of palm trees, saying that they cannot grow wide but only tall is some kind of answer although it still does not answer to why growing tall rather than not growing (and invest more into reproduction)? Hope my comment makes sense! $\endgroup$
    – Remi.b
    Sep 13, 2013 at 6:18
  • $\begingroup$ @Remi.b I tried to say that in my first paragraph, and again in my last. It's straightforward, and you guessed it: The taller the tree, the more sunlight it can get. Other factors like soil and temperature can play a role as well. $\endgroup$
    – Amory
    Sep 13, 2013 at 6:28
  • 2
    $\begingroup$ @Remi.b just because a particular individual (tree) has no competitors does not imply that the species evolved free of competition. I would guess that it always comes down to getting more sunshine. For example, a polar bear born in a zoo in Brazil will still be furry and white even though those characteristics don't help that particular individual. $\endgroup$
    – terdon
    Sep 13, 2013 at 14:12
  • 1
    $\begingroup$ @Remi.b And I (we?) are wondering why that's not enough for you? Trees require sunlight to survive, and growing taller means more sunlight, so why shouldn't they? A taller tree would have a fitness advantage that would be selected for. I'm sure in some scenarios predation could play a role but not as strong as the desire for sunlight. $\endgroup$
    – Amory
    Sep 14, 2013 at 6:31

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .