maple sap flow

[old tom]

does the maple sap flow up from the roots and out the spile or down from the tree and out the spile? Does the first run sap flow different than the later runs?

Thank You Old Tom

[DrTimPerkins]

does the maple sap flow up from the roots and out the spile or down from the tree and out the spile? Does the first run sap flow different than the later runs?

Both.

Very briefly, during a freeze, water is pulled into the tree through the roots to fill the tree vessels. As the tree thaws, (in gravity collection systems) sap generally runs downward in vessels and out through any wounds. Locally it can be pushed upward a bit due to stem pressure. Eventually, on gravity, sap flow will stop when the moisture has been depleted. There will be little or only weeping sap flows until a subsequent freeze refills the stem with moisture.

On vacuum systems, same thing happens, but sap can also be pulled to some degree across the tree from further away as the sap run progresses due to the higher pressure differential (low pressure at the taphole, higher pressure on the side of the tree away from the taphole). Sap flow can continue much long than under gravity flow conditions due to the higher pressure (vacuum) gradient. With good enough vacuum and a long enough thaw you can reach a state where sap is being drawn up in the stem, and if continued, eventually water will be pulled out of the soil, up the stem and out of the taphole. Sap sugar content will drop off when this happens.

Keep in mind that this happens at different times throughout the tree. Some parts of the tree may thaw faster than others, especially deeper in the tree or on the north sides of the tree. Therefore sap flow in a tree is not a simple thing that can easily be described.

[johnallin]

Both.
……With good enough vacuum and a long enough thaw you can reach a state where sap is being drawn up in the stem, and if continued, eventually water will be pulled out of the soil, up the stem and out of the taphole. Sap sugar content will drop off when this happens…...

Maybe that’s why everyone’s woods got so dry a few weeks ago?

[old tom]

thank you.