Discussion in 'Biology & Genetics' started by pluto2, Oct 31, 2010.
What factors (besides photosynthesis) determine how tall trees will grow?
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Water supply, climate. and location
Species is probably the most important.
Soil quality and depth are also factors besides ones mentioned.
Why the location?
(...and water, climate, soil etc. as already stated.)
Most trees die as a result of trauma. Their trunks are strong enough to be quite resistant to disease-bearing organisms. But when a crack is created by lightning, or by a piece of a larger tree falling on it, the tree suddenly has an avenue for infection, and its days are numbered. That number may be very large, but it will die eventually.
Nonetheless, the ultimate height of a tree is limited by the friction of the fluid flowing up through its capillaries to provide nutrients to its extremities, in concert with gravity.
The maximum varies from one species to the next, depending on its geometry and the composition of its tissues. The tallest trees on earth are members of the species Sequoia sempervirens, the Coast Redwood in California, in the cypress family. The tallest tree now living is 115m, 379ft. The theoretical maximum is 122-130m, 400-425ft; that's the best precision we can get in the calculation.
The point is, they're already very close to that limit. Growth will obviously slow as they push against the limitations, so who knows how long it will take a 380-foot tree to grow that last 20 or 45 feet. It might be another two thousand years. That last inch will take a really, really long time!
Land plants evolved the ability to transport water vertically because they evolved lignin and cellulose polymerisation, and also evolved specialised stomata cells in their leaves. Xylem tissue, or 'wood', reticulates water from the roots of a tree to its leaves through osmosis and transpiration, which are the mechanics of water transport in plants.
As water evaporates from the crown it is replaced by water that is transported along xylem channels; trees retain water in their leaves during the day and transpire it during the night. The stomata cells in leaves control the transpiration rate.
So the height is limited by this process of transport which itself is due to capillary action, which is a function of surface tension and the fact that water is a polar liquid.
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altitude and latitude.
Another limiting factor everyone seems to have missed, including me, is that the transport of water occurs only along a fairly thin layer of xylem cells at the perimeter of the trunk. Most of the interior of a tree's trunk is dead tissue, but obviously serves a purpose by supporting the crown.
So the size of the crown overall is limited roughly by the surface area of its trunk. As long as there are sufficient numbers of xylem channels with unbroken columns of water in them the trunk can even be hollow, or large trees can survive some internal rotting.
I don't think gravity has much effect on the height of a water column, which is very thin and extends continuously from a root tip to a leaf. But gravity affects how much weight a trunk can support, so it's a sort of equilibrium between the mass of a trunk and its surface area.
Without having an active pumping system the highest a tree can grow and still get fluid to its top via capillary action is 130m, is that what your all getting at?
Not quite. Imagine you have a glass capillary tube, like the ones used to take blood samples from a finger/thumb.
So, how long can the tube be and still support an unbroken vertical column of water? How thin can it be?
I don't believe gravity will limit the length/height because capillary action is due to charged molecules attracting, and, well, the Coulomb potential is much stronger than gravity (about 10^35 times). There is no "pumping" action, it's all capillary, and is driven by evaporation through the stomata when they open at night.
Correct. The height of other trees is the major factor determining it's height. No tree can afford to be shorter than the trees around it. Of course, it's also a great investment in structure, so it's a comprimise between these two factors. Of course, there is no real need for trees to be tall, if they could all get together and set a maximum limit on height, they wouldn't need to be tall. But, evolution doesn't work that way.
Yeah yeah, look up water pumps and find out why we need to have the pump at the bottom, suction from the top beyond 8 m can't function because the pressure gets so low the water cavitates and all you suck up is vacuum vapor of water. So with just mass and suction alone its easily possible break hydrogen bonding and disrupt a column of water.
Cavitation doesn't happen in a capillary tube, because the ratio of the polarity of the traveling fluid to its mass is much larger than for a wide tube, as in a large bore pipe, so pumping is required to overcome a low ratio. The polarity of water has no effect in that case, in fact nonpolar fluids need to be actively pumped for the same reason.
Because water molecules have a polarity and so does the wall of the tube, Coulomb attraction overcomes gravity in a thin tube. A large bore glass tube isn't a capillary tube for water, because it has a low ratio as described above.
Aaah, but then were does this 130 meter limit come from assuming thee is no limit to capillary action?
From some other physical limit, which I believe is the ratio of the surface area of the trunk and all the woody branches in the crown, to the surface area of all the leaves.
The number of leaves is limited by the number of branches the crown can grow, which is limited by the trunk size. Trees are naturally fractal.
Trees have a genetic structure as well. This ultimately, like all lifeforms, is what drives them to grow and reproduce.
what sort of shape would atree make in zero g?
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