Retapping

So I have read comments and understand that the hole creates a wound that eventually becomes a 2 foot tall by two inch or so wide, stretch of dark wood that will never flow again. I wonder then, if the 'scab' for lack of better term, as the tree initially heals and closes, takes time to generate up and down from the hole. If one were to tap another hole just two inches above the first, dried up hole, would it run for a few weeks. If it did, then the stain would not be significantly bigger, and may not affect the tree at all. Or similarly, a new hole couple inches below. If however the scab, stain area takes on the entire size immediately and progressively shuts off and darkens, then this would not work at all. In this case, again, no more real significant damage to the tree.

Right now, mixed bag. One good producing tree has shut off, others are doing as good now as ever, all put in Feb 5.

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Originally Posted by Helicopter Seeds

So I have read comments and understand that the hole creates a wound that eventually becomes a 2 foot tall by two inch or so wide, stretch of dark wood that will never flow again. I wonder then, if the 'scab' for lack of better term, as the tree initially heals and closes, takes time to generate up and down from the hole. If one were to tap another hole just two inches above the first, dried up hole, would it run for a few weeks.

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There is a better term for the "scab". It is referred to as a "wound", or "compartment", or "stain."

What you are suggesting (tapping above or below) is currently being researched as a whole suite of different strategies for keeping tapholes viable for a longer period of time. I wrote about this on another thread some months ago. Can't tell you the results of that study for another 2-3 years (it just started in October 2017), although perhaps I can give an update of the work season-by-season. We typically don't like to do that, as then people will jump on it immediately and then get upset (the polite term) if/when the results change as we learn more. So I guess the real answer to your question of whether this approach will work in producing more sap (at a reasonable cost) and also not create substantially more stain, is unknown at the moment. Any other answer is speculation.

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Originally Posted by DrTimPerkins

There is a better term for the "scab". It is referred to as a "wound", or "compartment", or "stain."

What you are suggesting (tapping above or below) is currently being researched as a whole suite of different strategies for keeping tapholes viable for a longer period of time. I wrote about this on another thread some months ago. Can't tell you the results of that study for another 2-3 years (it just started in October 2017), although perhaps I can give an update of the work season-by-season. We typically don't like to do that, as then people will jump on it immediately and then get upset (the polite term) if/when the results change as we learn more. So I guess the real answer to your question of whether this approach will work in producing more sap (at a reasonable cost) and also not create substantially more stain, is unknown at the moment. Any other answer is speculation.

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Dr. Perkins,

I am very interested in the results of this study. In PA (with the exception of NE and North Central PA), we have been having an extremely long sap season this year. It began around February 8, is still going strong and could continue until the beginning of April. Seasons this long occur less than once per decade. Some of those who retapped are reporting record-breaking seasons while some of those who did not are reporting sub-normal seasons.

As I see it, there are two aspects involved with retapping that I hope you explore:

1. The wound. Retapping creates double the amount of wounds in a tree. It seems to me that this factor could also be explored by comparing 3/16 and 5/16 holes (and perhaps, as this is a study, the 7/16 holes that were used in the past). It would seem to me that larger diameter holes would create larger wounds.

2. The sap. Retapping can cause twice as much sap be bled from the tree. It seems to me that this factor could also be explored by comparing vacuum with gravity line systems, as people who use vacuum usually get more sap per tap.

Please do share the preliminary results of your study as soon as they become available. I am especially interested in whether these factors influence the amount of syrup collected the following year.

Dr. Perkins,

In response to an earlier post by you on this thread, I wrote:

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Originally Posted by HowardR

1. The wound. Retapping creates double the amount of wounds in a tree. It seems to me that this factor could also be explored by comparing 3/16 and 5/16 holes (and perhaps, as this is a study, the 7/16 holes that were used in the past). It would seem to me that larger diameter holes would create larger wounds.

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I just discovered that you conducted the most relevant study, which can be read on the web at the following URL:

http://www.rothmaplesyrup.com/Documents/SpoutStudy.pdf

You were comparing small (5/16") spouts with large (7/16") spouts. Doing the math, you noted that the 5/16 hole creates half the wound of a 7/16 hole. You found:

1. "For the five year period, the yields averaged 12.54 gallons/taphole for small spouts and 13.29 gallons/taphole for large spouts, or 94% as much sap using small spouts compared to large spouts."

2. "In 1998 we also studied yields from holes of different depths with each size spout. Holes that were 1½” deep yielded 98% as much sap as holes 2½” deep for either sized spout, while holes ¾” deep yielded approximately 86% as much sap as holes 1½” deep." (Tapping more than 2" deep can cause significant damage to the trees' heartwood, especially of smaller or older trees where the heartwood is closer to the tree surface.)

3. "In two of these three years, both sized tapholes dried at about the same time; while in the third year (2000), the tapholes fitted with small spouts ran about two weeks longer than the 7/16” tapholes." (So there is a slight indication here that smaller tap holes yield longer than larger ones -- which is supported anecdotally by a March 17 comment by Paddymountain on the tapping Pennsylvania thread this spring. He reported, almost two months after tapping, "3/16 tubing [under vacuum] is running fairly good, 5/16 so so".)

4. "On average, the volume of stained wood resulting from the 5/16” holes was 80% of the stained wood resulting from 7/16” holes."

You only used stained wood area in order to explore the damage done to the tree. But there is another way of measuring the damage done to a tree -- the extent by which its radial growth is slowed. This was the factor used by Copenheaver et al. (2014) in assessing the amount that maple syrup production slows tree growth.

I hope that you include that factor in your new study. I suspect that two 5/16 holes retard tree growth by the same amount as a single 7/16 hole. If so, then the amount of damage caused by occasionally double-tapping trees during a long season is sustainable, just as 7/16 holes and the wounds that they caused were sustainable during the many decades that they were used.

Incidentally, the Copenheaver et al. (2014) study leaves the important question unanswered -- what factors actually retard tree growth? There are three important factors: (1) amount of sap taken, (2) volume of the wound, and (3) depth of the wound. In Pennsylvania and Ontario, maple syrup production reduced tree growth in the tested bushes, but not in New York. The authors reported that the trees in Pennsylvania and Ontario were tapped by inexperienced college students, while the trees in New York were tapped by professionals. My guess is that the college students drilled too deep, while professionals did not. The key factor, then, regarding sustainability, could be depth of tapping.

Tapping at a depth of 1½" to 2" could be key. I just bought Industrial Sharpie (13601) markers (for marking metal) and plan to mark each of my drill bits at 1½" and 2". Then I'll make sure that I and those who help me drill make holes between those marks in the future.

Without going into a real loooonnnngggg explanation....

- Yes, a bigger spout creates a bigger wound.
- Spout size is related to wound (stain) size, however it is not linear (as the graph I posted earlier showed).
- It is not typical practice to substitute 1 7/16" spout for 2 5/16" spouts, so the comparison is not apples to apples.
- Correct in that wounding is not the only impact on the tree, however growth is affected by several things.
- Of the several studies (published and unpublished) done so far, there is some ambiguity as to whether or not tapping has any impact on growth. Some studies say yes (with varying amounts), some say no. The Copenheaver study has several weak points, the main one being that the trees in tapped and untapped stands were NOT in the same exact area. Site history (thinning/pasturing) may play as large a role in radial growth as tapping history, so without having that factor controlled, the comparing the tapped and untapped trees in that study is nebulous. Studies done as part of the NAMP project for a couple of decades seem to indicate no difference in health, growth, or mortality of tapped and untapped maple trees. We have done two preliminary studies comparing growth of tapped and untapped trees (within the same stand), and the results are interesting in that they show a trend towards reduced growth in the tapped trees, but don't quite rise to the level where growth reductions are statistically significant.

To best get at this question, a long-term "controlled" study has to be done. That would involve finding a large group of trees that had never been tapped, and to leave some alone, tap some with gravity, and tap some with vacuum (this would provide three levels of carbohydrate extraction: none, low, high) and measure sap volume and sap sugar content over a long period of time. We are doing exactly that. We started the project 5 yrs ago and may release some preliminary results after we do the 5-yr growth measurements (along with several other parameters) this fall, but the experiment is planned to continue for at least another 5 yrs. The difficulty of doing this type of work is funding -- grants hardly ever run more than 3 yrs. I felt that this study is important enough that we are using "internal" funding for the project. Hopefully the results will resolve the question for good.

In addition, there has been some research looking at 1 vs 2 taps and depth of tapping, and more are planned as part of a total analysis of "sustainability", a theme that has been ongoing for about 7-8 yrs here at UVM PMRC. As before, we don't talk much about these studies until we have 2-3 (or more) years of study under our belt. Some of the individual components have been completed and published, others are still ongoing (and even just starting). All I can say right now is "stay tuned", and our hope is to have a comprehensive document describing the entire theme in about 3-4 yrs (about the time I retire).

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Originally Posted by HowardR

Tapping at a depth of 1½" to 2" could be key. I just bought Industrial Sharpie (13601) markers (for marking metal) and plan to mark each of my drill bits at 1½" and 2". Then I'll make sure that I and those who help me drill make holes between those marks in the future.

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Use a short piece of 5/16" tubing slipped over the tapping bit as a bit stop. You can easily cut it so the tapping depth is whatever you want. A sharpie mark will disappear quickly, and is easy to overshoot.

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Originally Posted by HowardR

1. The wound. Retapping creates double the amount of wounds in a tree. It seems to me that this factor could also be explored by comparing 3/16 and 5/16 holes (and perhaps, as this is a study, the 7/16 holes that were used in the past). It would seem to me that larger diameter holes would create larger wounds.

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I tapped several trees 3 seasons ago with bits from 1/8" to 7/16". They are scheduled to be cut down this summer (when we are cutting other trees for different projects) and the volume of internal stain from each size measured.

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Originally Posted by HowardR

2. The sap. Retapping can cause twice as much sap be bled from the tree. It seems to me that this factor could also be explored by comparing vacuum with gravity line systems, as people who use vacuum usually get more sap per tap.

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Yes, this is why we always tend to measure sap volume and sugar content in these studies, so that we will know the total amount of carbohydrate extracted from the trees. We have had several studies looking at carbohydrate extraction compared to tree reserves, and others that are ongoing. Understanding the relationships and transformations in carbs in an organism as large and complex as a maple tree is challenging. There is little good scientific literature on the subject for that very reason (it is hard to do)....but that doesn't stop us from trying various ways to understand it, and we have published some papers on it.

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Originally Posted by DrTimPerkins

Use a short piece of 5/16" tubing slipped over the tapping bit as a bit stop. You can easily cut it so the tapping depth is whatever you want. A sharpie mark will disappear quickly, and is easy to overshoot.

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Dr. Perkins, thank you for the tip!

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Originally Posted by DrTimPerkins

It is not typical practice to substitute 1 7/16" spout for 2 5/16" spouts, so the comparison is not apples to apples.

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Using different tap diameters (3/16, 5/16 and 7/16) as the independent variable and radial growth as the dependent variable could answer questions about the extent to which hole volume slows growth (if at all). My hypothesis would be that the correlation between hole volume and radial growth would be insignificant for holes that are 1.5" deep and linear for holes that are 2.5" deep.

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Originally Posted by DrTimPerkins

In addition, there has been some research looking at 1 vs 2 taps and depth of tapping, and more are planned as part of a total analysis of "sustainability", a theme that has been ongoing for about 7-8 yrs here at UVM PMRC. As before, we don't talk much about these studies until we have 2-3 (or more) years of study under our belt. Some of the individual components have been completed and published, others are still ongoing (and even just starting). All I can say right now is "stay tuned", and our hope is to have a comprehensive document describing the entire theme in about 3-4 yrs (about the time I retire).

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You are doing the most helpful research for maple syrup producers! Please do look at radial growth as one of your dependent variables.

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Originally Posted by HowardR

Please do look at radial growth as one of your dependent variables.

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Where it is possible, and where it makes sense, we do. Unfortunately, in many cases, the length of the study, which is dictated by the length of the grant funding, precludes studies from being long enough for any growth response to be observed.