First year gravity tubing questions

[maple flats]

Going that high in the tree will result in less sap because you have less internal pressure the higher you go in the tree.

[Jebediah]

I believe that. On the other hand, when I break off twig of tree, sap drips out, so doesn't decay to zero.

[DrTimPerkins]

I believe that. On the other hand, when I break off twig of tree, sap drips out, so doesn't decay to zero.

Think of a tree as a large pipe (actually, it is more like a huge number of tiny straws inside a large pipe) stuck in the ground that is filled with water. If you tap it high up, it will drain down until the level of water (sap) in the pipe is equal to the hole you've drilled, then it will stop. If you drill lower down, you'll get more water (sap) than if you drilled higher. Of course if this is the only way you can manage it, then less sap is better than no sap, but this practice does result in reduced sap compared to tapping at a normal height.

And, as always, vacuum results in a slightly different situation since you can pull sap upward through the straws/pipe.

[NhShaun]

I also take all of my tubing down every year. I have 860 taps with each lateral having anywhere from 15-30 taps each. I use a water and hydrogen peroxide mixture. I blow it through the tubing using a sand blaster making a water and air mixture. It does an excellent job cleaning the tubing. There is no mold or evidence of anything left behind. I do it within a couple weeks of seasons end.

Sounds like a great method. Does is stay clean for the entire off season? No mold growth from moisture build up inside the lines?

[randomseeker]

I wonder if the sap flow is proportional to the distance up the tree it is tapped? If tapping 4 feet off the ground produces x litres/day on a 60 foot tree, would tapping 15 feet off the ground produce something like 20% less (very rough math)? Pressure in a water pipe is independent of the width of the water pipe, so would the sap pressure in the tree be independent of the fact the top portion of the tree has less width? Also, this speculation ignores the root system, which contributes to the total height of the tree (unless the water table is above the bottom of the root system ... this is getting too complicated ! . Finally (maybe), is not the flow a function of the sap flow itself going up and down the tree? I mean, if the tree produces more sap as the heat hits it, surely the sap is flowing upwards and the taps are 'draining' off the upward flow making the function less dependent on 'standpipe' pressure?

Think of a tree as a large pipe (actually, it is more like a huge number of tiny straws inside a large pipe) stuck in the ground that is filled with water. If you tap it high up, it will drain down until the level of water (sap) in the pipe is equal to the hole you've drilled, then it will stop. If you drill lower down, you'll get more water (sap) than if you drilled higher. Of course if this is the only way you can manage it, then less sap is better than no sap, but this practice does result in reduced sap compared to tapping at a normal height.

And, as always, vacuum results in a slightly different situation since you can pull sap upward through the straws/pipe.

[DrTimPerkins]

... is not the flow a function of the sap flow itself going up and down the tree? I mean, if the tree produces more sap as the heat hits it, surely the sap is flowing upwards and the taps are 'draining' off the upward flow making the function less dependent on 'standpipe' pressure?

First, keep in mind that the "pipe model" of a tree is a gross simplification of what is really happening, but it is pretty good to explain flow (sap exudation) under gravity conditions.

No, heat does not make sap flow upward.....in fact, cold (specifically the transition of the sap from liquid to frozen) drives water uptake (recharge) from the soil, at which time the tree is under a negative pressure (thus sap will NOT flow from the taphole). Heat can increase sap flow by increasing pressure within the tree to some extent (gas and liquid volume increase in volume as temperature increases), however this isn't what drives bulk exudation in gravity flow situations. The other way that "heat" can increase flow is by melting sap that is still frozen within the tree, thus releasing it to flow out by gravity.

[DrTimPerkins]

I wonder if the sap flow is proportional to the distance up the tree it is tapped? If tapping 4 feet off the ground produces x litres/day on a 60 foot tree, would tapping 15 feet off the ground produce something like 20% less (very rough math)? Pressure in a water pipe is independent of the width of the water pipe, so would the sap pressure in the tree be independent of the fact the top portion of the tree has less width?

Yes, to some degree sap flow is proportional to the height of the tree above the taphole. And yes, tapping higher on the stem (in gravity collection systems) will result in somewhat less flow than tapping lower on the stem. Yes, sap pressure is independent of the width of the tree (height is the critical factor determining pressure, or "head"), however keep in mind that the tree is not a simple pipe, but a large series of somewhat interconnected pipes (straws) inside a larger pipe, so the critical thing is the height of the interconnected straws from the taphole to the top of the tree. Sap in gravity collection mainly moves downward from an area above the taphole, which is much less than the cross-sectional area of the stem at that height. There is quite a bit more resistance to lateral (sideways) movement of liquid in stems. Thus the wives tale of "tapping above a large root or below a large branch" is not terribly valid and won't result in more sap flow. While the total reservoir of sap above that point is definitely larger, the area you tap into (the pipes you sever in tapping) is still one of the primary determinants of flow, so the effect of that large branch or root is not great.

Also, this speculation ignores the root system, which contributes to the total height of the tree (unless the water table is above the bottom of the root system ... this is getting too complicated

In gravity flow, what is below the taphole is largely immaterial. Without some driving force to make sap move up and out of the taphole (such as vacuum), then there won't be any sap flow originating from below the taphole. Same as if you dig a hole in the ground, water doesn't run out of it unless it is under some sort of pressure.

This explanation relies entirely on the physical model of sap uptake and flow from trees. There is also a biological component due to osmotic pressure, but it is really quite complicated, and only a slight refinement of the maple water uptake/sap exudation model. Hopefully we'll have the full paper describing the process submitted soon (just one thing in a big stack of stuff to work on).

[coyote]

NhShaun-I have the tubing in rolls when I wash it. It still has lots of solution remaining in the roll all off season. When I rehang the lines in early spring the solution drains out. It is still crystal clear and has no smell or taste. No mold in the lines.