How Deep?

[FFFlying]

How deep is the correct depth to drill a tap hole?

I have heard from 1" to 4"...

Details, details, details.

What is the best depth?

[maplwrks]

2 1/4" will do it

[red maples]

on smaller trees (small being 10") I will usually go 1.5-2 inches. But on the bigger trees(big being 18+ inches) there might be 1" + thick bark. SO you need to adjust accordingly. But generally 1.5-2 inches into solid wood.

[FFFlying]

the other half of the question is can you tap too deep and what effect does that really have?

[Thompson's Tree Farm]

Old studies showed some sap gains with deeper tapping (up to 6 inches I think) but the additional sap after about 1 and 1/2 inches was pretty small. The drawback is mor injury to the tree. It will take many more years for a tree to cover an old tap with 3 inches of healthy wood than it will to cover with an inch of healthy wood.

[DrTimPerkins]

How deep is the correct depth to drill a tap hole?

Vacuum or gravity?

[BryanEx]

Vacuum or gravity?

Interesting question... I didn't realize there was a difference.

[DrTimPerkins]

Interesting question... I didn't realize there was a difference.

Vacuum results in far more lateral movement, and even upward movement of sap within the tree. Therefore with good vacuum the taphole need not be quite as deep.

[BryanEx]

As they say... you learn something new every day. :)

[red maples]

I had a tree come down in the wind storm last year it was a 12 inch diameter tree. only tapped once under vacuum I took that section with the tap hole and cut it in slices on the table saw. staining goes only about 1/2 an inch past the back of the tap hole but lateral staining at the longest point was just about 11 inches. and that was 1.5 inches into the tree. there was less than 1/8 inch staining on either side of the tap hole. the bottom 1/2 of the tree that was still standing was very healthy and believe it or not with no crown the tap hole was healed over and there was a little new growth at the break point which was about 25 or so feet. and that was in october when I cut down the base.

Granted this is only 1 sample I am sure there is more on this and there are other variables but, For me that shows basically at a depth of 1.5-2 inches into solid wood your going to "damage" wood 2-2.5 inches into the tree.

[FFFlying]

Ok...I am ready to learn more. We are on vacuum, usually about 19" of Hg. I thought you would need to go deeper with vacuum to reach around the tree.

This won't be too long... what would be the appropriate depth to tap a tree with a vacuum system and the what depth for gravity?

Thank you all for your interests and opinions...

[Groves]

What's the sweet spot for gravity? 3" ?

[DrTimPerkins]

Ok...I am ready to learn more. We are on vacuum, usually about 19" of Hg. I thought you would need to go deeper with vacuum to reach around the tree.

The anatomy of a maple trees is "constructed" to primarily move water vertically (up and down) in vessel elements within the wood (xylem) tissue. When you tap with gravity (buckets or tubing), the sap primarily comes from an area above the taphole, and flows out due to differential pressure....in this case, due to gravity. There are other things going on related to freeze/thaw and gas bubble expansion, but these are relatively minor in the overall scheme of things. So the pressure you get under gravity is due to the "head" of water above the taphole. An 82' tall tree tapped 2' above the ground = ~80' of head = 35 psi of pressure. As the sap drains from the vessels, the pressure gets progressively lower and sap flow slows down. Eventually, there is no pressure head left (all the sap has drained out), and sap flow ceases.

Under vacuum, sap can move around within the stem somewhat radially as well as vertically. It moves through rays and fibers in the wood due to differential pressure. It can move down, up, and sideways, essentially "tapping into" a larger pool of sap within the stem. It is possible under extended thaws to actually pull water right out of the soil up through the roots and stem (where sugar is added to the water) and out through the taphole.

All this to say....you needn't tap as deeply with vacuum.

Gravity 2.5-3" into the wood. Going deeper would get a bit more sap, but starts to detrimentally impact the "sustainability" of tapping due to wounded wood area after a few decades.

Vaccum 1.5-2" into the wood is sufficient due to radial movement of sap.

The other implication of this is that you can bump up the minimum size of a 2 tap tree with good vacuum. There is research currently ongoing (Tim Wilmot, UVM Extension) to define the additional sap you get with a 2nd tap under vacuum with different sized trees. It is NOT double the amount.

Now the other thing is -- vacuum does NOT cause additional wounding in the tree. The staining you see in the wood is a natural wound response that has essentially nothing to do with the fact that sap came out or the tree had vacuum or not. It is due to the fact that you put a hole there, and the tree is walling off that area to prevent infection (bacteria, fungi) from spreading throughout the tree.

Animal cells are readily injured by strong vacuum. An animal cell is kind of like a plastic bag (membrane) filled with jello. Put it in a vacuum and the bag expands like a balloon due to the low pressure until it eventually ruptures. A plant cell is similar, except that plant cells are normally within a cell wall (box). So you put a plant cell in a vacuum, the bag (membrane) can't get so large that it will be pulled apart....because it is confined within its box (cell wall). So vacuum has no real impact on plant cells....like those found in the wood of a tree.

[FFFlying]

Thank You Dr. Tim that is exactly the type of information I was looking for!!!

Kevin

[cpmaple]

So with my gravity tubing system i should be tapping trees at 2.5 or 3 inches? Am i reading this right because last year i ran some 5/16 taps into 5 gallons pails and only tap 1.5 to 2 inches didnt get very much from them thought it was just the year we were having please help. cpmaple

[DrTimPerkins]

So with my gravity tubing system i should be tapping trees at 2.5 or 3 inches? Am i reading this right because last year i ran some 5/16 taps into 5 gallons pails and only tap 1.5 to 2 inches didnt get very much from them thought it was just the year we were having please help. cpmaple

A little deeper might help, but the primary reason you likely didn't get much sap last year is the lack of freezing periods.

After all the sap runs out of the tree by gravity, a freeze period is needed to draw the sap back up into the tree. The freeze causes a suction to deveop within the tree, pulling water out of the soil into the roots, and up into the branches and stem of the tree, where it mixes with sugars. Then when the temperature warms up again, the sap will flow out again.

One additional caution...if you're tapping smaller trees, definitely shallow up on the tapholes, whether under gravity or vacuum conditions.

Similarly, if your trees aren't growing well for some reason -- when was the last time you thinned -- poor site conditions -- environmental or insect damage -- then shallow up on the tapholes as well. Good growth of trees makes things much easier and makes sugaring much more sustainable.

[220 maple]

Great info on vacuum and gravity taphole depth. My first question is in reference to tapping with vacuum and having the ability to vacuum sap directly from the roots of a tree. I thought that the reason we got more sap with vacuum is because we are lowering the Barometric Pressure at the taphole and therefore fooling the tree into believeing it's a low pressure day everyday? Example last night it drops to 20 degrees for 12hrs then it warms up the following day to 45 -50 degrees under a clear sky, High Barometric Pressure. With that type condition we would get less sap than if it is cloudy and a storm brewing, preferably a snow storm.
The other question involves the trees recharging themselves during a hard freeze. I told a oldtimer that they take ground water in when they are froze. He said to me that frozen water does not move. I know it works but how? I need a answer for a guy who has been making syrup for 70 years.
Also Please let us know when your going to disappear from this message board, I know you always do when your season starts and your research projects demand all of your time.

Thanks for all the Info, Hopefully this spring I'm going to make it to the equipment dealers open houses, therefore meeting you and shaking your hand personally.

Mark 220 Maple

[DrTimPerkins]

I thought that the reason we got more sap with vacuum is because we are lowering the Barometric Pressure at the taphole and therefore fooling the tree into believeing it's a low pressure day everyday?

We get more sap because there is a higher differential pressure. Think of a tree as a pipe stuck in the ground filled a sponge and water. Drill a hole, if unfrozen, sap will run out until the pressure (head) equals the pressure (height=head) of the taphole. Now pull a vacuum on the taphole. You can now pull sap up from areas BELOW the taphole through the sponge (vessel elements). At the same time, you can also pull sap further laterally in the tree. Most of the time with gravity, there is little lateral (across the tree) movement of sap.


The other question involves the trees recharging themselves during a hard freeze. I told a oldtimer that they take ground water in when they are froze. He said to me that frozen water does not move. I know it works but how?

I'll have to give you the short answer. The long answer would take a chapter (and incidentally, Dr. Mel Tyree, the former Director of the UVM Proctor Maple Research Center and I are discussing writing a new paper on sap flow).

As the temperatures approach freezing, gas bubbles in the tree wood fibers start to contract (things shrink as it gets colder...we all know that :lol:). As these bubbles shrink (and there are billions of them), this creates a small suction on the water around them in the cell wall. This starts to draw water into the cells, creating a negative pressure (suction) on the vessel elements, kind of like sucking on a straw. This suction propagates throughout the tree, starting water movement into the tree. As the tree slowly begins to freeze (it happens slowly most of the time), frost starts to build up on the INSIDE of the wood fiber cells, kind of like it does on your windows on a cold day. The vapor pressure over ice is FAR lower than the vapor pressure over water (basically the humidity is lower over ice than over water). This drop in vapor pressure pulls more water to the surface of the frost, accelerating the process of ice/frost formation within the cell. The combined reduction in vapor pressure, and drop in pressure due to bubble contraction, results in a suction. The process continues throughout the entire tree. If the temperature drops slowly, we get a really nice recharge of water in the tree. If the temperature drops very fast, we get a poor recharge.

So the old-timer is right....frozen water (ice) doesn't move. But water just about to freeze sure does.

All this happens in maples due to a couple of unique anatomical features. The most important is that the lumen (the central area within the wood cells) within the wood fibers is filled with AIR. In most trees, the lumen is filled with WATER (sap). Air contracts FAR more than water with changes in temperature.


Also Please let us know when your going to disappear from this message board, I know you always do when your season starts and your research projects demand all of your time.

Will do. I will still watch the board somewhat, and answer when I can, but it won't be on a daily basis. I will respond to emails to Timothy.Perkins@uvm.edu, unless they get to be too many. I won't respond to PM during that same time though.


Thanks for all the Info, Hopefully this spring I'm going to make it to the equipment dealers open houses, therefore meeting you and shaking your hand personally.

I'll be there....at some of them at least. Always happy to meet and chat with maple producers.