Frozen ground and sap flow.

[billschi]

New guy here.
This is my third year tapping trees. Last year I did 150 trees, this year I want to tap 2-250 trees.
I live in Northern Minnesota near Brimson. Minimal flow from the 6 test trees. It looks like the saap may start flowing this weekend.
My question is, if the ground is still frozen, how does the sap start flowing? I understand the sun can warm the tree up to get drips from my taps. I also understand the first flow is what was stored in the tree from last Fall. After the first flow, the sap has to come from the roots. If the ground is still frozen, how does the sap flow? Does the tree thaw out from the top down? I do notice the snow melting from the tree first but I am certain the rest of the ground is still frozen. What is actually happening?

[DrTimPerkins]

To directly answer your question, if the ground is (truly) frozen, there will be no water uptake and no sap run (after the first run perhaps).

However....totally frozen ground in the woods is not common. Typically snow provides an insulating layer and the warmth of the earth thaws out the ground to just under the snowpack (which is where the wee beasties live all winter....mice, moles, voles, shrews). Even if there is no snow, a good, deep leaf litter layer will insulate the ground. It is only when there is an extended period of cold weather and bare ground (no snow) that the ground will freeze solid more than a couple of inches, EXCEPT in areas that you run vehicles over.

More commonly however, the trunk of the tree can be frozen if there is deep snow packed around it, which will impede water uptake until the snow melts back away from the stem a bit to form a qamaniq (Inuit/Eskimo word meaning "depression in the snow around the base of a tree), which will allow soil water uptake and recharge to occur.

Tree roots are actually pretty sensitive to cold. Temperatures a bit below freezing are usually OK, but there can be frost injury if the temperatures fall much below that (which they don't often do in forest settings...unless there is woods road going through the area). The above-ground tissues of maple trees are far more cold tolerant....and can deal with temperatures down to about -40 deg C (which is also -40 deg F).

[lindnova]

To directly answer your question, if the ground is (truly) frozen, there will be no water uptake and no sap run (after the first run perhaps).

However....totally frozen ground in the woods is not common. Typically snow provides an insulating layer and the warmth of the earth thaws out the ground to just under the snowpack (which is where the wee beasties live all winter....mice, moles, voles, shrews). Even if there is no snow, a good, deep leaf litter layer will insulate the ground. It is only when there is an extended period of cold weather and bare ground (no snow) that the ground will freeze solid more than a couple of inches, EXCEPT in areas that you run vehicles over.

More commonly however, the trunk of the tree can be frozen if there is deep snow packed around it, which will impede water uptake until the snow melts back away from the stem a bit to form a qamaniq (Inuit/Eskimo word meaning "depression in the snow around the base of a tree), which will allow soil water uptake and recharge to occur.

Tree roots are actually pretty sensitive to cold. Temperatures a bit below freezing are usually OK, but there can be frost injury if the temperatures fall much below that (which they don't often do in forest settings...unless there is woods road going through the area). The above-ground tissues of maple trees are far more cold tolerant....and can deal with temperatures down to about -40 deg C (which is also -40 deg F).

Good explanation. That would explain why I got a ton of drips from some trees when I tapped, but nothing in the week since. Also explains why that one tree that was gushing over the weekend had a lot of snow drifted in and the others on more bare ground didn't run as much.

[billschi]

Dr Tim, thank you for your quick response.
With all due respect I will share the findings from living in Minnesota. First, I will give you a little information about my background. I owned a plumbing and drain cleaning company for 25 years. I've always heard in my younger years about the frostline being at around 42" in the Mpls/St Paul area. And therefore it determines the footings set for houses. Up where I live now, the frostline is at 5'. I've realized the difference in each winter and the effects on how busy my company was. As you said, more snow and the frost didn't go down as far. One year, we had extended days of subzero temperatures, I had to design a heater to thaw out septic tanks for people that went on vacation for 2 or more weeks during Winters with little snow cover. The inlets of septic tanks are by code, 18"-36" below the ground surface. A drippy faucet, toilet or a 85% or better efficient furnace, will cause a sewer line to freeze in most Winters. The deepest I've seen the frost 'driven down' in the streets was ~14-15'. We were thawing out water lines for municipalities then in 2014.
What I do know is our water temperature comes out of the ground in the summertime at 41.5 F where I live now. We are at the 47 degree latitude. Removing tree roots out of sewer lines for 25 years, I understand the tree is about as big underground as it is above ground.
My theory prior to this post is that the tree is warming up from our daytime temperatures and knowing below the frost line is slightly above 40 degrees, are the trees thawing out before the ground around the tree? I mean, because trees have energy, they must be naturally warmer, right?
Just an unrelated side note, We moved up here 2 years ago and have experienced -30F quite a few times in a winter. That is the first time I heard our trees pop. I think the Maple trees need colder temperatures to pop but there are vertical lines up the Maple trees to tell me it has been cold enough at a time or two to make it happen.

[DrTimPerkins]

My theory prior to this post is that the tree is warming up from our daytime temperatures and knowing below the frost line is slightly above 40 degrees, are the trees thawing out before the ground around the tree? I mean, because trees have energy, they must be naturally warmer, right?
Just an unrelated side note, We moved up here 2 years ago and have experienced -30F quite a few times in a winter. That is the first time I heard our trees pop. I think the Maple trees need colder temperatures to pop but there are vertical lines up the Maple trees to tell me it has been cold enough at a time or two to make it happen.

Your experience is not different from what I said. In areas where there is no snow, no leaf litter, and no roads/sidewalks, there tends to be fairly little ground freezing. When it does freeze in the woods, it tends to be temporary. A snow layer will generally result in the frost in the soil melting back to within a few inches of the ground.

No, trees don't generate enough energy by metabolic processes to warm themselves. They do however accumulate some heat during warm spells or when it is sunny, and since they are large and thermally buffered to some extent, they tend to change temperature far more slowly than the air does. So a tree trunk can warm above freezing and then stay that way for a while after the air falls below freezing -- which is why sometimes you'll have sap still flowing while it snows or drops below freezing for a while. The accumulated heat can also melt the snow back away from the tree trunk, forming that depression in the snow around the stem (particularly on the south side).

[minn]

[QUOTE=DrTimPerkins;351371]Your experience is not different from what I said. In areas where there is no snow, no leaf litter, and no roads/sidewalks, there tends to be fairly little ground freezing. When it does freeze in the woods, it tends to be temporary. A snow layer will generally result in the frost in the soil melting back to within a few inches of the ground.

Apparently you have not experienced winter in northern Minnesota. I agree with your statements with Vermont frost or lack of.

[RileySugarbush]

Also from Minnesota and ground here is indeed frozen! Not sure how deep. But the most important question is:

How do you pronounce "qamaniq"

I like that word and there are a lot of them forming around our maples right now, though the trees are still somewhat recalcitrant.

[DrTimPerkins]

How do you pronounce "qamaniq"

Kah - mah - nique

Like the crow

Your mother

End of the word "tech-nique"

[212Maple]

I live about an hour west of Minneapolis and the frost two weeks ago was 4.5- 5 feet deep. We have had very little snow cover for most of the winter until the last 3 weeks and since then we have received about 2 feet of snow. I have collected 400 gallons of sap on 325 taps in the past week.

[DrTimPerkins]

We have had very little snow cover for most of the winter until the last 3 weeks and since then we have received about 2 feet of snow.

Lack of snow cover in the woods can result in soil frost. Once covered with snow, the frost starts to move out again. I'm not in Minnesota, so you got me there, however IF there is frost in the ground, you're not going to get any sap (after the first run) until the ground thaws. Basically the same thing as if you have snow tightly packed around the tree stem. Water and sap freezes at 32 deg F, so any frost, whether in the soil or in the stem, will prevent recharge.

Maple roots are NOT very cold tolerant, and most maple feeder roots are in the upper foot of soil/litter.