Why not tap large limbs too?

[Homespun]

Happy Easter to you & yours!

My neighbor has a huge tree I've been eyeing. The trunk is about 45" in diameter.
About 10 ft off the ground it has 5 large limbs about 21" in diameter and 3 smaller limbs next to them about 16" in diameter.
Each limb is basically a tree in itself!

I'm wondering... could I put a tap in each limb a few feet away from the trunk, run the tubing down the trunk to the collection buckets, along with a few in the trunk (as usual) into the buckets?

Crazy?
Won't work well?
Same as overtapping a tree?
Ever been done before?

[gmcooper]

That would be over tapping. Depending on which guide lines for tapping you follow most would limit total number of taps to max of 3. Every time you add a tap you do get more total sap but the amount of sap per tap declines. Also remember even though it is a large tree the growth rate of those big trees is much slower than a 12-16" tree. Thus it takes longer to heal over those tap holes and provide new growth for sap carrying capacity.

[DrTimPerkins]

Crazy?
Won't work well?
Same as overtapping a tree?
Ever been done before?

Answers:
Definitely.
Right.
For sure.
Probably.

[happy thoughts]

Limbs carry a lot of weight stress. I imagine a tap wound could cause a weak area that might lead to limb loss down the road.

[mike z]

Dr.Tim:
Hilarious.

[RileySugarbush]

Answers:
Definitely.
Right.
For sure.
Probably.

I'm a little disappointed! Better questions for the Dr. : Has it been studied? If not, how do you know these answers? Ten years ago would you have considered sucking on chopped off saplings?

[DrTimPerkins]

I'm a little disappointed!

I didn't mean to disappoint you, but you didn't ask for explanations. And it was at a rather busy time of year as we were still sugaring and doing research.

It is crazy because people aren't going to tap using ladders. It's bad enough pulling spouts when tapping was done with 3' of snow on the ground.

It won't work well because the higher you go, the less head pressure you have and vacuum effectiveness is reduced, so sap flow would be considerably less. Think of it this way. You have a pipe stuck in the ground (a tree) filled with water. If you tap it low down, you get a lot of water out of it. if you tapped that same stem up high, you'd get far less out of it. Pressure and sap flow in a maple tree (not on vacuum) are dictated by the same pressure-related processes.

Putting that many holes in a tree each year is overtapping. A tree is an integrated unit. Tapping guidelines were based upon stem size, not branch size. That many taps in one tree would also have the potential of impacting the carbohydrate status of the tree.

It has been done before....when scientists (including those at UVM PMRC) were mapping pressure in maple trees to understand sap flow. To my knowledge nobody has tried it as a tapping/sap collection practice (see explanation at top under the "crazy" heading).


Has it been studied? If not, how do you know these answers? Ten years ago would you have considered sucking on chopped off saplings?

Yes, tapping in multiple places around a tree has been studied a few times by scientists looking at how sap pressure behaves in trees. Would I have considered chopping off saplings to collect sap 10 yrs ago....no, we hadn't considered that option until research led us to it. But then again, that is not at all unreasonable a practice for a wide variety of reasons once you understand the physiology of the tree and the mechanisms of carbohydrate storage and sap flow. Further....it is something we didn't talk about until we'd tried it for 4 yrs and knew that it would work.

So the take home is the same with or without the explanations....it is kind of crazy, it won't work well, it is overtapping, and it has been done before.

[RileySugarbush]

Disappointment.........canceled! Thanks!

Though the head pressure loss is (arguably) made up for by the suction head of the drop, up to 30 feet or so if on gravity lines.

[DrTimPerkins]

Though the head pressure loss is (arguably) made up for by the suction head of the drop, up to 30 feet or so if on gravity lines.

Which gets you exactly right back where you started....at the base of the stem of the tree.

[RileySugarbush]

Ok I give up!

[Galena]

Strictly fwiw....last year I did use a stepladder to tap my two huge red maples because they have burls from approx 3 ft above the ground to almost 6 ft up. So I used the stepladder to tap above the burls, using tubing (check the maple gallery link at the bottom of this post). They did produce some sap but very little compared to the usual workhorses in my lot. Overall I was disappointed, so doubt if I'll bother tapping them again :-/

[Jebediah]

A few times I've clipped off a tiny branch in the spring to see if sap is running--if it is, sap drips out of the end of that branch at a pretty good rate. Have been tempted to try to collect into buckets this way. May be far less than what you get from a regular tap, I realize.

I have a question about tapping guidelines--have these guidelines (taps per tree) been rigorously tested?

[DrTimPerkins]

I have a question about tapping guidelines--have these guidelines (taps per tree) been rigorously tested?

The UVM PMRC is in the middle of a multi-year, multi-faceted review of tapping guidelines. The majority of the work done earlier looked at tapping only from a wounding perspective. We are reexamining that, and also looking at it from a carbohydrate removal standpoint. Then there are lots of trade-offs, how deep to tap, how many taps, species differences, etc. that also need to be factored into the equation. Some of it is also very long-term, so it'll take at least 5 yrs to get a decent answer (and 10 yrs would be far better). We've presented some of this work at different maple conferences, but it'll be several more years before there is a comprehensive guide published.