| ▲ | Giant trees have no trouble pumping water to top branches(news.exeter.ac.uk) |
| 45 points by hhs 2 hours ago | 21 comments |
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| ▲ | calibas 3 minutes ago | parent | next [-] |
| The largest tree on record is rejected in part because it's over the theoretical limit: https://en.wikipedia.org/wiki/Nooksack_Giant Too bad we cut it down, along with almost every other giant Douglas-fir. |
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| ▲ | nullorempty an hour ago | parent | prev | next [-] |
| >Giant trees have no trouble pumping water to top branches Hm, may be because they are not really "pumping" the water? |
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| ▲ | leni536 an hour ago | parent [-] | | What would you call it? | | |
| ▲ | cj 44 minutes ago | parent | next [-] | | Not that it really matters, but the article also refers to it as “drawing water to the top”. That seems more representative of reality than “pumping water from the bottom”. | | |
| ▲ | chowells 21 minutes ago | parent | next [-] | | If you think of it that way, you have a real problem. It only takes about 10 meters for the weight of a column of water to create enough downward force that it starts vaporizing, at which point no pumping action works. This is why any deep well has a submerged pump. You simply can't pull water upward further than that with negative pressure in the Earth's atmosphere. It must be pushed with positive pressure instead. This is why the question is interesting. You can't just suck water to the top of a 60 meter tree. There must be some kind of positive-pressure pumping involved. | | |
| ▲ | pulvinar 10 minutes ago | parent [-] | | The trick for trees is capillaries, which change the equation. The 10 meter limit only applies to larger columns. With capillaries there's a high negative tension that allows evaporation from leaves to pull the xylem sap up 100 meters or more. There's no free lunch here. The Sun drives the evaporation, and if the tree were in a closed system with no solar input, the humidity would eventually get high enough to stop it. |
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| ▲ | margalabargala 41 minutes ago | parent | prev [-] | | Yeah it's the difference between creating low vs high pressure. | | |
| ▲ | card_zero 35 minutes ago | parent [-] | | The low pressure is up there already, for free. Or the high pressure is down here, whichever way you want to look at it. |
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| ▲ | gitaarik 42 minutes ago | parent | prev | next [-] | | “Trees contain lots of thin, hollow vessels and they suck water upwards by creating low pressure at the top,” So sucking / pulling? | | |
| ▲ | IsTom 39 minutes ago | parent [-] | | So a suction pump? | | |
| ▲ | card_zero 37 minutes ago | parent [-] | | Same principle as chimneys. But I also noticed this line: > leaves which have adapted to withstand greater water stress before wilting. That must be one of the "adjustments to water transport" mentioned. So I suggest that they do, in fact, have trouble pumping water to top branches. | | |
| ▲ | gitaarik 26 minutes ago | parent | next [-] | | Maybe it's not more trouble pumping, eh, sucking water up. But that the top branches are the last ones to get water in periods of draught, and have therefore more resilience? | |
| ▲ | DANmode 28 minutes ago | parent | prev [-] | | Or, it’s simply a rate to variably adjust to, so the tree is neither flooding nor parching the leaf. |
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| ▲ | rolph 33 minutes ago | parent | prev [-] | | more like capillary action. https://en.wikipedia.org/wiki/Xylem#Cohesion-tension_theory | | |
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| ▲ | nomel 22 minutes ago | parent | prev | next [-] |
| This goes against all previous research/measurements for actually tall trees (looks like they only considered up to 80m) and the fact that there are exactly zeros trees in the world taller than 130 meters [1]. Wide capillaries at the base, like stated in the article, don't seem to be related. [1] https://www.sfgate.com/science/article/REDWOODS-How-tall-can... |
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| ▲ | m463 18 minutes ago | parent | prev | next [-] |
| on the other hand, many giant trees get the water out of the air via fog: Coalescence of coastal fog accounts for a considerable part of the trees' water needs.[23] https://en.wikipedia.org/wiki/Sequoia_sempervirens#Fog_and_f... https://en.wikipedia.org/wiki/Sequoia_sempervirens |
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| ▲ | alldayhaterdude 34 minutes ago | parent | prev [-] |
| Happy for them. |
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