Is 48 Hrs. enough to recharge trees ??

[TerryEspo]

We have a bit of a cold snap here and I am wondering if two days is enough to recharge the trees to give a good run after it warms up again.

The next two days it is not going above freezing even in the middle of the day.

What is the advantage of this ?

Thanks.

Terry

[DrTimPerkins]

We have a bit of a cold snap here and I am wondering if two days is enough to recharge the trees to give a good run after it warms up again.

It isn't really got much to do with the length of the time below freezing. More important is how rapidly the freeze occurs. A really nice slow (many hour long) freeze is optimal for causing good water uptake from the soil and distribution throughout the tree. If the temperature drops too rapidly, freezing of vessels can occur too fast, blocking the further uptake of water. The succeeding sap run may be less if that occurs.

During the time when temperatures are below freezing, there isn't a lot going on. There can be some conversion of starch to sugar, but that too can happen fairly quickly (hours). Having a freeze last for many days doesn't do much for the trees, but it gives the sugarmakers a chance to rest.

[PerryW]

More important is how rapidly the freeze occurs. A really nice slow (many hour long) freeze is optimal for causing good water uptake from the soil and distribution throughout the tree. If the temperature drops too rapidly, freezing of vessels can occur too fast, blocking the further uptake of water. The succeeding sap run may be less if that occurs.

Interesting! I always figured that the amount if "tree recharge" was proportional to the (amount of time below freezing) X (degrees below freezing) or essentially the area of the temperature curve below freezing (think integral if you know Calculus).

My test is: "If the ice is thick enough on the puddles to walk over without breaking, it's gonna be a good run when it warms up. If the ice is just a skim, you will get only get a small run that will end early."

[wnybassman]

We might be in decent shape here then. We spent much of the day hovering right around the freezing point before it finally dropped below.

[not_for_sale]

A really nice slow (many hour long) freeze is optimal for causing good water uptake from the soil and distribution throughout the tree. If the temperature drops too rapidly, freezing of vessels can occur too fast, blocking the further uptake of water.

So we are talking about capillary action here? The freeze slowly restricts the diameter of the vessel and flow increases until its blocked?

[DrTimPerkins]

Interesting! I always figured that the amount if "tree recharge" was proportional to the (amount of time below freezing) X (degrees below freezing) or essentially the area of the temperature curve below freezing (think integral if you know Calculus).

Nope. Recharge cannot happen if the temperature is much at all below freezing, since water (sap) will freeze and "block" the pipes through which recharge would occur.

[PerryW]

Nope. Recharge cannot happen if the temperature is much at all below freezing, since water (sap) will freeze and "block" the pipes through which recharge would occur.

Maybe I'm confused about the term recharge or maybe by gravity taps react differently that high-vacuum taps but....

For me, it's, the harder the freeze, the harder the run. If I have good run today, my trees will NOT run tomorrow significantly unless the temp drops below 28-29 degrees. The only exception to this rule is if the temp drops to 28 degrees for an extended period, then the trees will run well.

After a good run, I can pretty much estimate the amount of sap I will get the next day (assuming it warms up) by noting the low temperature.


32 deg low - <50 gallons
30 deg low - 75 gallons
28 degree low - 125 gallons
26 degree low - 250 gallons
24 dergee low 400 gallons
20 degree low - 500 gallons
15 degree low - 600 gallons.

There are always exceptions to this rule, (like how long the temp stayed cold) but noting the ice thickness on puddles can usually help me predict these exceptions.

[DrTimPerkins]

So we are talking about capillary action here?

No. Capillarity has some effect, but the major driving force for uptake is vacuum (suction) pressure created in the xylem (fibers) of the wood. As the temperature drops, gas bubbles in the fiber lumen contract, creating a suction. At the same time, ice begins to form on the inner cell walls of the fibers (like frost on windows). The saturation vapor pressure (like humidity) of ice (frost) is FAR lower than that of water, so the vapor pressure drops precipitously, adding to the suction kind of like a turbo-booster just at the time that water freezes. This creates a fairly large suction pressure (5 psi, ~ 10" Hg), which moves water from the xylem vessels into the fibers. The movement of water from the vessels transmits the suction down through the wood and roots and moves water from the soil into the roots. The process stops either when a critical water content is achieved, or when ice forms in the vessels, blocking further uptake. Most uptake probably occurs over 15 minutes to 2-4 hr timeframe.


The freeze slowly restricts the diameter of the vessel and flow increases until its blocked?
Again, close, but not quite right. The freeze occurs first mostly in the bulk wood fibers (they are smaller, so freeze more quickly). There is more water in the vessels, so it freezes after the fibers (somewhat). Also some vessel elements can freeze, but there are lots of vessels, and they are interconnected, so somewhat redundant in design. Thus if some vessels freeze, water can still enter via other vessels. Once a vessel freezes, it freezes pretty much evenly throughout the vessel (there is nothing stopping it from freezing throughout the entire vessel). So it isn't a progressive blockage of the vessel that is occurring. It is progressive freezing of fibers, followed by freezing of vessels. Of course, a large tree and the fine branches are not isothermal, and the entire organism doesn't freeze homogenously, so some parts of the tree may still be exuding sap at the same time as other parts are taking up sap.

Sap uptake and exudation in maple (probably) evolved as a mechanism to repair emboli (bubbles in the system) that form during winter/freezing conditions. Birches do it via root pressure, maples do it via the formation of stem pressure. The high pressure in the wood (of birch, maple, or walnut) redissolve any bubbles in the system, re-establishing the functionality of the tree's "plumbing" system. Other trees (conifers and ring-porous tree species) have other mechanisms.

Please understand this is the short version of the story. We are currently submitting a review paper on how the process works.

[PerryW]

to clarify, I'm not disputing that a slow freeze is better that a fast freeze. I'm just saying that the overall freeze has to be a hard freeze for my 600-700 gravity woods taps and mu 50 buckets.


And thanks for your 7:51 AM post. It's the best description of what make sap run I've ever heard!

[TerryEspo]

Dr Tim....that 7.51 a.m. post is the best description ever to describe sap flow science.

Thank-you for that.

It is back to winter here, below freezing cold, snow and blowing.
I will see in a couple days what reaction my trees have to this re-introduction of winter.

My last boil 2 days ago gave the light fancy syrup again. Does that mean my trees are still giving early sap and I still have lots of boils left ? Could I get only light syrup this season? Am I for sure going to get some medium or dark syrup before buddy sap?

This post is very educational for me , anyway.

Thanks to all.

Terry

[PerryW]

Terry, I'm pretty much in the same boat as you. 92 gallons total in all but the last 5-10 gallons is fancy.

I suspect that as long as we don't get 60-70 degree weather (like last year) and get a few freeze-thaw-freezes, we will make plenty of lower grade syrup.

My taps have been in almost 5 weeks ao I'm hoping for another week or two before they dry up.,

[DrTimPerkins]

My last boil 2 days ago gave the light fancy syrup again. Does that mean my trees are still giving early sap and I still have lots of boils left ? Could I get only light syrup this season? Am I for sure going to get some medium or dark syrup before buddy sap?

Sap color is more related to the microbial content in the sap than anything else. Microbes convert some of the sucrose into glucose and fructose, which caramelize (darken and form color) at lower temperatures (such as those found in evaporators) than does sucrose.

You're very likely to make at least some dark syrup before the end.

[TerryEspo]

Thanks Dr. Tim.

It makes sense.

I usually boil same day, filter sap as I put it into my 50 gallon barrel to bring to the house, filter again before going into Feeder tank, constantly skimming foam, then filter almost syrup as it comes out of batch boiled flat pan, then a final filter once it is syrup.

Guessing around 5,maybe 6 gallons so far and all blond ,blond, blond, light. 7655 7656

I also read here that sap that gets in and out of the arch boil in a hurry is less dark too.

BUT, I did think too that syrup will be darker as the season progresses.

Its all good no matter what shade/grade it is.

Thanks for the input.

Maybe I need to let the sap sit and rot a couple days, LOL. Then I can get darker syrup.

Good luck to all.

Terry

[abbott]

So I would assume, then, that there is still a minimum amount of time that the air temp needs to be below freezing for the tree to do its thing. I'll certainly try to pay closer attention in the future to how long the freeze-up takes.

How does this relate to sugar content? On vacuum in particular, the sugar content goes down steadily if there is no freeze at night. A few good freeze/thaw cycles will often bring it back up. Is it just that the tree needs to re-develop the pressure to bring new sugar up from the roots?

[PerryW]

So I would assume, then, that there is still a minimum amount of time that the air temp needs to be below freezing for the tree to do its thing.

Absolutely! You need a good enough freeze to shallow puddles to freeze solid (for gravity taps, at least).

If you left a half full beer on the porch and in the morning there is no ice in it, my trees will not run.

If the snow is NOT hard and crunchy, you will NOTt get a run.

If your driveway is still muddy in the morning, you will NOT get a run. If the ruts are frozen up tight, it will run like gang-busters.

There are always occasional exceptions. Last season, I got partial sap runs without a freeze, but the temps were hitting 80 degrees!

Also, sometimes, when the conditions are just right, the sap will continue to run through the night and you will get a double run, without a freeze. I'm thinking this effect may be slow freeze effect that the Doctor mentioned?

I have no theory, but I've been tapping essentially the same 700 taps for 24 years and using the same equipment.

[maple flats]

I guess I never got that much detail. I only notice that if the temp drops to about 28 or lower, I get sap when it warms up again. I seem to get more when it dropped even lower, but this increase seems to remain steady at about 25 and below. I wonder if the insulating properties of the wood itself don't help get more water drawn in , since the outer will freeze before that deeper into the trunk. (Dry wood is about R1 insulating factor, I don't know what a live tree R factor might be, but the sheer mass has to help some.