Tree recharge

[blissville maples]

So I could probably write a list of crazy questions I've pondered. But I guess here's one I'll ask. And perhaps I am missing something simple...

So if a tree recharges with liquid from the ground when it's cold due to the fact that the tree creates an internal vaccum. Is it fair to say you would get a better or more robust recharge with our vaccum pumps on(given vaccum is making it all the way to the tree).
Even if the drop line is frozen with sap and prevents vaccum to the taphole the tree is still vaccumized from the day i would assume...
Why do we still need freezing nights, is it because the vaccum coming from the branches being much higher in the tree has more of an effect than the vaccum in our taphole 5' off the ground?

[DrTimPerkins]

So I could probably write a list of crazy questions I've pondered. But I guess here's one I'll ask. And perhaps I am missing something simple...

So if a tree recharges with liquid from the ground when it's cold due to the fact that the tree creates an internal vaccum. Is it fair to say you would get a better or more robust recharge with our vaccum pumps on(given vaccum is making it all the way to the tree).
Even if the drop line is frozen with sap and prevents vaccum to the taphole the tree is still vaccumized from the day i would assume...
Why do we still need freezing nights, is it because the vaccum coming from the branches being much higher in the tree has more of an effect than the vaccum in our taphole 5' off the ground?

Maybe you should've been a scientist...sounds a lot like what we do...sit around and think of interesting aspects to sap flow and production and then test them to see if we're right (or wrong) and how we can use that knowledge to improve sap yield, economic gain for producers, and sustainability of the process in terms of tree health.

Yes are (probably) correct in that vacuum hastens and augments the uptake of water during the freeze cycle. Vacuum does propagate into the tree and spreads out from around the taphole. How much and how far depends upon the length of the run and how much of the tree is thawed out. And you are also correct that the dropline/lateral line freezes up quickly so vacuum is cut off fairly quickly in a freeze. The tree doesn't freeze as fast, and especially not the shallow parts. Deeper in can stay thawed for a long time. So overall, the vacuum/pressure and freeze/thaw temperature patterns in (especially large) trees are complex. Parts of the tree can be creating pressure and exuding sap and parts can be taking up moisture from the soil all at the same time. However if the full tree is thawed, and vacuum has been on for a while, it likely enhances uptake. Vacuum not only makes it TO the tree, it makes it INTO the tree. We demonstrated this last season quite convincingly (hasn't been published yet). We can see this especially during extended thaws with strong vacuum. Even though there hasn't been a freeze for a while, sap production will drop off but continue at a steady, fairly constant rate. At this point we are pulling water out of the ground and up through the tree and out of the taphole. When this type of flow regime happens, sap sugar content will drop off. It takes another freeze to stimulate the conversion of starch to sugar.

We have done some monitoring of these patterns in trees. Tim Wilmot did a good amount of it with TREEMET for several years, but most of that was on gravity. Dr. Abby and I started doing this kind of monitoring several yrs ago, which is when we came up with the "sapling" method of sap collection. We noticed that we still have flow under vacuum for many days after a freeze, and concluded vacuum was pulling water out of the soil and out the taphole. The conclusion was that the top of the tree was not important at that point. To "test" this hypothesis, we cut the top off a sapling and applied vacuum, and could get sap as long as long as it didn't freeze (sap sugar drops off without a freeze though).

Last year we had a UVM undergraduate student begin an extensive monitoring project (see photo below), but then Covid shut every everything down, so we didn't get as much data as we wanted, but enough to demonstrate that some things we thought were happening. We'll repeat that again this year, but much more intensively. We're monitoring temperature in a stem at multiple points, along with pressure, and sapflow (within the stem) and sap exudation (what comes out of the stem). The results are very complex, so the issue becomes trying to find ways to portray them in an understandable fashion.

This monitoring study is probably one of my last big projects (along with some smaller projects) of my career as I approach retirement. Planning to drop down to 75% of full-time starting July 1, and then 50% in July 2022, before exiting fully June 30, 2023.

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[blissville maples]

Haha that tree looks like my neighbors!! Poor tree!! That's a very interesting take on vaccum. Do you ever find in research that you can't fully satisfy your hypothesis? Like maybe something applies and checks out here but not over there without explanation? If so do you try to perceive that there's a factor causing this or when can you say that this experiment is not practical and does that cause frustration or discouragement?


Ya know I'm a very simple person and if I had to do it all over perhaps I would have been something of the such. Knowledge is power,im intrigued by learning. and the brain is an amazing machine, the amount of info it can hold is simply amazing, and to pull up files day on day out for 50+ years without ever needing a reboot or file cleanup!! I consider myself to be a very intelligent with a unique way of looking at things in depth, and have also realized there's such a thing called " a feel for things" which cannot be talked about cannot be shown and cannot be read about it's a very intricate thing. At times i ask myself why I picked a career in which your abilities don't really matter compared to someone like a renowned lawyer or brain surgeon. At the end of the day I'd rather be bleeding out my fingers and coming home at the end of the day whooped and feeling like I put in a good day's work, I feel this is genetically encoding in my blood, I try to imagine how hard my forefathers worked. I have to say not many have the inner work ethic, and hopefully in 50 years from now some will still obtain these traits.

At any rate maple trees must be the most amazing and interesting tree out there, besides some of the ones that will kill you if you stand under them in the rain!!

[DrTimPerkins]

Scientists generally don't try to "prove" something....it is nearly impossible. Rather, they attempt to show that the opposite is not the case (the null hypothesis). So instead of saying "these two things are different", we say, "these two things are not different." Then we test that by limiting as many possible outside influences as we can so we are ONLY comparing the two things of interest (so for example, spout A vs spout B), but measuring it the same way in the same time period for sets of trees that are as closely similar as possible in the same place (or over a wide selection of places). Then we have to get multiple measurements of sap yield from each of the two spout types, and preferably do it over the several seasons. Then we take the averages and the amount of variation and statistically determine the probability that the two populations of samples are the same.

So using that example, comparing sap yield from Spout A and B. We would choose several trees or several groups of trees. Each tree (or small group) would be randomly assigned to one or the other spouts. We would take great care to be sure that the average size and health of the trees was as similar as can be. Typically this means the average difference in dbh of the two groups is less than 0.2% and that all trees are healthy and growing in the same general stand. That eliminates (to the extent possible) that any difference we see is due to differences in tree dbh. Then all the trees will be tapped by one person with the same drill/bit on the same day and same tapping hammer on the same side of the stem in random order (so one tree might be Spout A, then next Spout B, etc.). The vacuum system for all the trees will be the same pump, and vacuum is monitored at the beginning and end (and sometimes in the middle) of the line to be sure they are all getting the same vacuum level for the whole season. Each tree has its own chamber, but they are all identical. The same person measures the chambers (either daily or at the end of the season) for depth (to convert to volume) and sugar content to get a total yield for the year. We will then calculate totals, but very frequently won't present the results until we do the same study the next year or even for 3 yrs (or longer) to make sure the results are consistent. We statistically compare the total yields to see if the two populations are the same or they are different. If different (statistically), we will be able to say that (within a certain chance of being incorrect), the two spouts perform differently.

Eliminating extraneous influences is critical. Say Spout A and Spout B are very different designs and that is the thing of interest. We would want to make sure that the ONLY difference is the design. So we wouldn't want Spout A to be one color and Spout B to be a different color...because maybe the results would be due to color, or maybe they'd be due to design. They have to be exactly the same EXCEPT for the one thing we want to test.

The other important part of this is what is called "control". Typically this is something that we have a good deal of information and expectations for a certain result. So for example, we might have already worked with Spout A for several years and understand how it produces, and Spout B might be a new and different design that we are not sure how it will perform. Controls are very important.

Having an adequate sample size is also important. Comparing the production from one mainline vs another doesn't tell you much. Maybe you have two different spouts, but one of the lines had more leaks on it. Is any difference in sap yield due to the spouts or to the leaks -- there is no way of telling. By having a lot of individual trees or several mainlines, we can get averages for any "treatment", which helps to dampen the influence of those types of "noise" in the study.

In other words...when we can finally come out and say something is the same or different...we're pretty darn sure that it is only ONE thing (in this case spout type) that has affected the result.

Doing it this way is not easy and is not cheap, but it is correct scientifically, and allows us to state with some level of confidence what the results are.

So all in all, while it is good to hear what producers experience in the real world, given the normal year-year variation in yield, it is often not possible for them to know whether a 25% change in production for one year is due to some change they made, or just a good/poor season. That isn't a criticism so much as a reality....their focus is on production...rightly so. Our focus is on science, so we can do things differently. Very frequently we will dump sap (as painful as that is) because trying to collect it and process it would make it more difficult and compromise the science. Producers can't afford to do that. For us the value is not in the syrup, but in the science. So by doing it the way that we do we can typically tell if something is different if it varies by as little as 5% or less. It takes an awful lot of planning, care, and effort to do that. That is the value of scientific studies in maple production...or in anything really.

Lastly, it is great to have different groups doing similar research. For many years now Cornell and UVM PMRC have done similar work. Sometimes our results point in the same direction, sometimes in different directions. Either way is good, as it allows us to dig a little deeper and try to understand the similarities or differences and whether they are due to differences in approach, site, or something else. We've met as a group now each summer for many years to preview findings and discuss them before we present them to producers. Sometimes Centre Acer from Quebec has participated...sometimes not. But anytime we do meet, we always end up understanding the issues better. That is good for the entire maple industry.