Artificially warming trees

[Kamina]

I tried looking online before asking here, to no avail.

Has anyone ever tried artificially warming the trees to get a better flow? I was thinking that you could, theoretically, put black trash bags around the roots and base of the trees to melt snow around the roots, warm the base, and warm the trunk under the spiles...

Not sure if anyone has ever experimented with this before. This season has been such a slow start, I've been thinking of ways to jump-start it earlier next year.

[ecolbeck]

Patience, maple jedi. The solar forces will be with us soon.

[maple flats]

Sounds like someone who can't wait. The way sap flows is when the tree freezes it pulls the sap up in the tree, and "think" of it as filling the trunk, then as the trees warms it drains down and out the tap. It doesn't get pushed up from the roots to your tap(s) and out. For your idea to work, you'd need to thaw and warm the trunk above the tap hole, for several feet. I just don't see it ever working satisfactorily.

[Kamina]

Sounds like someone who can't wait. The way sap flows is when the tree freezes it pulls the sap up in the tree, and "think" of it as filling the trunk, then as the trees warms it drains down and out the tap. It doesn't get pushed up from the roots to your tap(s) and out. For your idea to work, you'd need to thaw and warm the trunk above the tap hole, for several feet. I just don't see it ever working satisfactorily.

Thank you for the explanation. Not impatient - just more curious than anything. I am going to try it with a couple of trees next year just for fun. I’ll report back with findings.

[berkshires]

Remember the guy a couple years ago who posted here saying he was going to be visiting for a few days only, so he planned to light torches or something under his trees to make them run? He was dead serious, too. What ever became of that guy?

GO

[richwilly]

I seen him yesterday at the hardware store buying more torches.

[bigschuss]

There's an old 1970's British sitcom I like to watch called "Dad's Army." In the show Corporal Jones often comes up with kind of "out there" solutions to problems and Capt. Mainwarring responds "I think you're getting into the realms of fantasy now Jonesy." Kind of reminds me of that.

I think you're going to find that the variables that affect sap flow go well beyond warm roots. Trying it isn't going to hurt anybody of course. I just hate to see you wasting a lot of your time...and trash bags.

[fred]

similar to Red Green

[maple flats]

Now that's a great comparison.
If you try it, I wonder if the little micro climate you create between the black bags and the tree will get some unwanted insect damage or other harm to the tree itself.

[Openwater]

The way sap flows is when the tree freezes it pulls the sap up in the tree, and "think" of it as filling the trunk, then as the trees warms it drains down and out the tap. .
Does the tree actually have to "freeze" to pull the sap up? I assume this is created somehow by negative pressure in trunk, but how critical/specific is it to actually reach 32 deg to pull sap up the trunk? Or is it more due to the temperature swing/differential within a 24 +/- hour period?

[DrTimPerkins]

The "freeze" is critical. The transition from liquid to solid is accompanied by a huge drop in vapor pressure, which aids in creating the vacuum which pulls water out of the soil into the roots, stem, and branches.

[Openwater]

Thanks Dr Tim.
That's what I assumed. I knew that vapor pressure and temperature are directly proportional, probably not linearly, but wasn't sure if there was something "magical" that happens with the phase change resulting in the large vacuum created. To get that same drop in vapor pressure above freezing temp, I assume it would take a large temp drop at a velocity that is almost impossible in nature.
Sorry for getting theoretical; it's been a while since physics and chem.

[ChrisMFF]

The "freeze" is critical. The transition from liquid to solid is accompanied by a huge drop in vapor pressure, which aids in creating the vacuum which pulls water out of the soil into the roots, stem, and branches.
Question - how does sap flow from crown to roots and vice versa during the spring and summer when the temp is above freezing?

Thanks

Chris

[DrTimPerkins]

Sap will always move in response to a pressure gradient from areas of high pressure (water potential) to areas of low pressure (water potential). This can be in response to several different types of forces...gravity (water flows downhill), osmotic (in response to solutes...sugar in tissues), matric potential, capillarity or other forces. Doesn't much matter where the force originates...the main thing is water always flows from areas of high to low pressure (water potential)....kind of like what happens when a car tire has a leak....air comes out until the pressure in the tire equals the air pressure outside the tire.

So how does a tree cause water to flow up?

In the spring (no leaves on the tree), water is pulled upward into the tree throughout the roots, stem, and branches in response to contraction of air within the lumen (center space of cells) within fibers as the temperature drops and the change in vapor pressure when water transitions from liquid to solid (ice). So bulk flow of liquid during the freeze phase is upward. During the sap flow (exudation phase), the sap flow is initally downward in response to gravity (head pressure) and can continue over a few days due to expansion of gas bubbles. If vacuum is used, sap movement occurs from both downward and sideways movement initially, and over a long run, can change to be upwards. If it is an extended thaw, water can be pulled up from the soil through the stem and out of the taphole.

This development of stem pressure in maples is an evolutionary adaptation to the fact that water freezes in the winter. When that happens, gases come out of solution (cold water can't dissolve as much as warm water). That creates a problem in the tree vascular system. It is hard to "pull" water through a vessel element in the wood that has air in it. Trees have to somehow either rid themselves of these bubbles (emboli), or they have to be very redundant, or have very small vessels that don't cavitate (form emboli) as readily (but that impacts efficiency of water movement), or they have to refill gas-filled vessels. Different trees do it differently....maples generate stem pressure to redissolve the bubbles.

In the summer, water/sap moves upward in response to water evaporating from inside the leaf cells and transpiring out through stomata (tiny pores) in leaves. This force "pulls" water along through through the vascular system of the tree and pulls water out of the soil into the roots. This works because water is sticky (it likes to cling to itself due to its polarity...which is why water forms droplets) and capillarity.

A more detailed description of the sap flow process can be found starting on page 81 at:

https://holmes.osu.edu/sites/holmes/files/imce/Program_Pages/Maple/North%20American%20Maple%20Syrup%20Producers%20Man ual%20full%20pdf.pdf

So if you think that's too much...the actual mechanics of maple sap flow uptake and exudation is about a 32 page scientific treatise that even I have a hard time with at points unless I read it a little at a time and stop to think about it every now and then. Dr. Melvin Tyree, a former Director at UVM PMRC, is undoubtedly the person with the best understanding of maple sap flow. He is still active in science, and is one of the world's top experts in water relations of trees.

[ChrisMFF]

Awesome stuff! Thanks Doc!!!

I absolutely love your posts.

Thanks again,

Chris

[saphound]

Fascinating..but a little deep for me. I just take what the tree gives me. But I do have one question on something that caught my eye.."If it is an extended thaw, water can be pulled up from the soil through the stem and out of the taphole."

Does that mean it will be more water and less sugar; Dr Tim?

[DrTimPerkins]

Fascinating..but a little deep for me. I just take what the tree gives me. But I do have one question on something that caught my eye.."If it is an extended thaw, water can be pulled up from the soil through the stem and out of the taphole."

Does that mean it will be more water and less sugar; Dr Tim?

As the run continues under those conditions (after an extended thaw of several days), the sugar in the sap will drop off. A freeze will both reinitiate refilling of vessels and the conversion of starch to sugar.

Note that this does not mean that all sap on vacuum is diluted. This phenomenon will only happen with an extended thaw. In general, the sap from gravity and vaccum flow tends to be (essentially) identical for most sap runs.

[Sugarmaker]

I have used electric blankets for years now. Isn't every one doing it??
Regards,
Chris