How the water gets up a tall tree.
Frank P Russo – 2005-11-24
The ‘miraculous’ transportation of water up the stem of a tall tree like the Tasmanian blue-gum, has always amazed me a great deal. Actually so much so that I used to use it as evidence for “negative consciousness” – it’s easy for the water to go up, if it’s really coming down first!
However, a semi-jocular explanation never leaves you fully satisfied – you do keep searching! I think I hit the jackpot when I zeroed-in on leaves with my IQ sometimes last year! Why were all the stomata on the underside of the leaves and none on the topside? Sure you want to maximize light intake, but oxygen and co2 are more plentiful above the tree rather than in the stuffy undergrowth! I came up trumps for my null hypothesis: the water is really going up as water vapour and coming down as liquid water after being first taken up by the stomata. This would definitely back-up my childhood observation that the roots did not usually absorb a great deal!
What I needed was a dramatic experiment! Obviously the ground at the base of the tree would have to be unhindered and most trees do insist on this … furthermore, the roots or some other process such as high energy fertilizers would have to keep the base rather warm to foster evaporation.
I covered the base of an apple tree - that was not thriving being always in the shade – with clothes and placed a big thermometer on the trunk. I saw that thermometer go past 40 Celsius on non-hot days and the tree eventually died: a truly dramatic experiment!
So in conclusion, let’s be kind to our trees and keep their undergrowths both well fertilized as well as clear of any vegetative growth.
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