About the tree.

[Mapler Jim]

Where is the demarcation line between where the sap goes up the tree and were it comes down the tree?

[happy thoughts]

I'm not sure I understand what you're asking but to the best of my knowledge maple sap flow during sugaring season specifically occurs in the trees xylem and can go both upward and downward. Sugar sap flow is dependent on freeze/thaw cycles and pressure gradients that develop inside the tree vs outside. When temperature conditions are right, pressure that builds inside the tree causes sap to flow out the taphole to the outside... toward lower pressure. There is no demarcation point you can point to on a tree as sap can flow either way in the xylem depending on the conditions that affect the trees internal pressure and as long as the sap remains unfrozen. If that isn't what you're really asking maybe you could clarify your question :)

[bigschuss]

Where is the demarcation line between where the sap goes up the tree and were it comes down the tree?

Not sure what you are asking?

[maple flats]

My understanding is that it does both in the entire trunk, rises when temperature rises and falls as it cools. I don't think there is a highway as such where one side is for up and the other is down. I think it is just a common corridor. Likely Dr Tim will chime in and tell me I have it all wrong.

[bigschuss]

There is not a common corridor or a demarcation line on the tree where it flows up/and or down. The xylem (dead cells) is for transport of water, minerals, nutrients UP the tree and the phloem (living cells) is for transport of nutrient rich sap to all parts of the tree...up or down.

The movement of sap in these tissues is a complicated one based on water potential (pressure potential and solute potential), capillary action, adhesion, cohesion, and yes temp., humidity, wind. etc.

[NW Ohio]

An article from ScienceDaily: http://www.sciencedaily.com/releases/2013/03/130307110718.htm
The study it is refering to: http://epubs.siam.org/doi/pdf/10.1137/120880239

Not that I think the new study (above) means much to most of us, but... ...it appears that we are zeroing in on having an equation that will allow syrup producers to calculate a days potential sap flow based on: the average temperature from the three previous years, average diameter of the trees in year sugarbush, coldest temperature experienced over winter, temp. on Jan. 1, and temp. and wind direction at 6:00 am on any given sap collection day. When we have that I should be able to calculate when I'll get to bed, given my evaporator's gph. Just another example of science and math ruining the surprise. :D

[DrTimPerkins]

I'm not sure I understand what you're asking but to the best of my knowledge maple sap flow during sugaring season specifically occurs in the trees xylem and can go both upward and downward. Sugar sap flow is dependent on freeze/thaw cycles and pressure gradients that develop inside the tree vs outside. When temperature conditions are right, pressure that builds inside the tree causes sap to flow out the taphole to the outside... toward lower pressure. There is no demarcation point you can point to on a tree as sap can flow either way in the xylem depending on the conditions that affect the trees internal pressure and as long as the sap remains unfrozen. If that isn't what you're really asking maybe you could clarify your question :)

This is correct. In the spring, sap can move up or down in the xylem depending upon whether you're in the freeze (uptake) portion of the cycle, or thaw (flow-exudation) period. Under gravity (buckets, tubing, bags), typically bulk flow is downward. To complicate it even more, with tubing on vacuum, sap can move up or down towards the taphole.

When trees have leaves, most of the bulk sap flow is upward in the xylem and most of the bulk sugar flow is downward in the phloem....but that is a real generalization.