Does the loss of sap or damage from tapping impact long term health of trees more?

[happy thoughts]

aw come on spud Where's your sense of humor? I thought perry's answer was pretty funny and now at least we know it's safer to be one of his maples than one of his children Life is short. We should all make room for more laughter and sweetness

[northwoods_forestry]

The comments made after the Doc's explanation I think are foolish.

And I appreciate your wisdom as well Spud.

[DrTimPerkins]

I think Perry's analogy is more apt. After years of giving a pint every year, now we're taking two pints, with the latest technology getting closer to three pints. At what point is it too much? That these studies are ongoing now after 25 or more years of vacuum seems a little after the fact. The answer at the moment then is that we don't know? We don't know how much sap is too much for the trees?

More appropriately, we've never really known. Studies designed to directly answer that question are very challenging and necessarily long-term, however a number of studies that have looked at this question over the last 150 years somewhat indirectly have all pointed to the fact that sap extraction has minimal impact on trees. There is one thing for certain, we are not killing trees rapidly through such high extraction rates with vacuum, otherwise it would be apparent by now. So while your concern is valid, I don't believe that the sky (or trees) are falling. Again, we're not ready to talk about our work in great detail yet, so I won't delve further into the results than that.

As far as the gravity question goes, 7/16 was the standard for many years. Why do you say that dropping to 5/16 does not allow more taps for the gravity producer? I understand that that tree wounding is the concern. Does that mean that the 7/16 taps were too much for all those years?

Someone else made that statement I believe, but I'll give my opinion. The wound caused by tapping (not just the taphole) is certainly smaller with 5/16" spouts. Given that the sap yield is about the same (at least with vacuum), there is no point in adding additional taps, and that is not a recommended practice. If you did, you're negating the benefits of the 5/16" spout. Secondarily, with good vacuum, the tapping guidelines can be more conservative, since we're able to extract more sap from the tree by pulling the sap from a larger portion of the stem. Putting in a second taphole in a tree under vacuum will not double the amount of sap, whereas in gravity, it frequently will.

Long ago when people hung multiple buckets (4-6) on large trees using 7/16" spouts, they were probably extracting far higher levels of sugar from an individual tree than we are now, even using high vacuum. So I'm not sure I fully buy into the argument that we're extracting unprecented levels of sugar now compared to what we used to. One could argue that we're actually being easier on the tree, because we're extracting the same amount of sugar, but with far less wounding.

[Stamford sugarmaker]

Very interesting discussion.

Could we speak to the gravity system a bit? I'm still using 7/16" taps but am thinking of going to 5/16" next year. If I keep the same number of taps per tree will I get the same volume using the smaller taps? I only do about 70 taps- half buckets and half tubing.

thanks, Peter

[Vermont Creation Hardwood]

I'm sorry I didn't make this clearer. I'm not interested in a vacuum system. A fair number of small producers can't justify the price and complexity of vacuum. So we're using gravity. The question I asked was: if 7/16 taps over many years didn't hurt our maples, why would not a proportional amount more of 5/16 taps to not exceed the equivalent wounding of 7/16 taps help gravity producers out? Some of us do not have more trees at our disposal. The extra taps would bring us closer, but certainly not close to what vacuum produces.

The advantage of vacuum is obvious; the advantage of vacuum pulling more sap from more of the trees' column through a smaller hole is obvious. I'm not discussing vacuum. I'm asking about gravity systems and how we might increase our production without doing more damage than 7/16 spouts do and did.

I suppose I shouldn't have mixed a more theoretical question about how much sap removal is safe with a practical question of increasing the number of taps.

[mapleack]

While a 5/16 tap hole removes approximately half the wood volume per hole as a 7/16, I don't believe that the dead wood area in the trunk produced is half. I believe it's larger than half, but the hole heals quicker. Dr. Tim will have the answer to that. Personally I'd tap smaller trees with 5/16, but not put more taps in a tree than I would've with 7/16. Even before I switched to vacuum I had eliminated alot of two tap trees, tree health is much more important to me than sap volume.

[DrTimPerkins]

OK...now we can start with a well-framed question.....thank you for clarifying.

First off, we want the amount of wood we cause to be non-functional (for moving sap) by tapping each year to be compensated for by the amount of wood the tree can grow back in a single season in order for sap extraction to be sustainable. That is a key concept. Secondly, those old trees with 6-8 buckets on them wasn't good for the tree. The basal (stem) growth rate of trees that large simply isn't great enough (in many cases) to support this, and what happens is that you end up cluster tapping, or you end up tapping into brown wood due to heavily compartmentalized wood in the stem, which doesn't transmit sap (well).

Next concept, the 5/16" spout on gravity produces a wound that is up to about 20% smaller than in a 7/16" spout, and on gravity, and you get perhaps 80% of the sap volume (on one spout) you would with a 7/16" spout.

Last concept.....exudation of sap from maple trees under gravity act similarly to hollow pipes, or more appropriately, a pipe filled with straws filled with sponge-like material. The pipe is stuck upright in the ground and filled with water. If you put a hole in the pipe, you cut some of the straws (filled with sponge), and the water will drip out until the water pressure (or head, since flow is mostly due to gravity) inside the pipe is equal to that outside, at which point it'll stop. There is some amount of water transfer from straw to straw horizontally under gravity, but it is very little and very slow. Under gravity, the amount of sap you'll get is approximately proportional to the amount of straws (vessels) you sever.

So, all this put together means that if you put more X number of holes in the pipe (tree) under gravity, you'll tend to get somewhere near X times the amount of sap (minus a little perhaps). Not the same thing though under vacuum, especially high vacuum, because in that case you're pulling the sap horizontally a LOT more. Thus increasing the number of taps under gravity will increase the amount of sap linearly in proportion to the number of tapholes. But, if you use small spouts, you're getting about 80% of the amount of sap from a wound than you would from a 7/16" hole. So if you put in two 5/16" holes, you get 1.6X the amount of sap for 1.6X the amount of wounds.

1 5/16" spout = 0.8 sap for 0.8 wound (compared to a 7/16" spout)
2 5/16" spouts = 1.6 sap for 1.6 wound (" )
3 5/16" spouts = 2.4 sap for 2.4 wounds (" )
4 5/16" spouts = 3.2 sap for 3.2 wounds (" )
and so on....

So doubling the amount of 5/16" taps doesn't double the amount of wounds, but it is proportional to the amount of sap. So for a given volume of sap, you're not gaining anything in terms of tree health. In fact, if you double the number of holes from your 7/16" spouts, you'd increase the amount of wounding by about 60% (while gaining about the same increase in amount of sap).

Taphole closure though is much more rapid with small spouts, about 2X as fast.

[DrTimPerkins]

While a 5/16 tap hole removes approximately half the wood volume per hole as a 7/16, I don't believe that the dead wood area in the trunk produced is half.

Correct....the internal wound created by a 5/16" spout is about 80% the size of a 7/16" spout. http://www.uvm.edu/~pmrc/smallspout.pdf

[Snowy Pass Maple]

This is an interesting thread - I still think the original question is a bit open as to whether (2) 5/16" wounds are better than (1) 7/16" wound.

As you say, the purpose of a 5/16" seems to be to support a higher level of vacuum extraction and was never intended to be a replacement for 7/16" spouts. But analysis like you just showed will clearly suggest to any gravity producer that if they can get 1.6x the sap for equal wounding, then why not - and regardless of intent, it's a very valid question if we assume 7/16" tapping was also workable for a very long history. We are making the same assumptions now that vacuum seems to be doing no harm.

So far, I've just stopped using 7/16" and went to 5"16 for my gravity operation. But when I see people putting high vacuum on the trees and people generally accepting that vacuum is not bad, it tells us more sap extraction is not necessarily bad. And if more sap extraction is not a problem, and wounding is "equivalent" then it does really encourage using more 5/16" taps, or at least having a lower threshold in diameter to add a second 5/16" tap than you would for 7/16".

Maybe the part of this discussion worth exploring is whether (2) 5/16" wounds are equal, better, or worse than (1) 7/16" wound.

[happy thoughts]

This is an interesting thread - I still think the original question is a bit open as to whether (2) 5/16" wounds are better than (1) 7/16" wound.

And if more sap extraction is not a problem, and wounding is "equivalent" then it does really encourage using more 5/16" taps, or at least having a lower threshold in diameter to add a second 5/16" tap than you would for 7/16".

Maybe the part of this discussion worth exploring is whether (2) 5/16" wounds are equal, better, or worse than (1) 7/16" wound.

Yes, a very interesting discussion. If I'm following your line of thinking snowy, and changing your example a bit to something that might fit along the lines of how we might apply it, then it would seem there would be little gain in placing 4 smaller spouts vs 3 larger ones in terms of both wounding and sap production. Thus the tree saving function of smaller taps (post edit clarification- in this instance) would seem to be negated on gravity at least to my thinking.