Broadback says...
Just curious. As I understand it the evaporation of moisture is what
draws the sap from the toots up the tree. Does this mean that the sap
does not rise until the leaves unfurl? If so where do the leaves obtain
the energy to be "kick started"?


I think that at least part of the mechanism involves the
roots pumping the water upwards. I seem to remember from my
student days that this was sometimes with considerable
force which can actually made the leaves "bleed" - a
process called "gutation" if I remember correctly.

There are also other mechanisms such as capillary action to
draw water along very fine tubules.
--
David in Normandy.
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