Some foods give us gas, but gas is what ultimately gives us maple syrup. If not for gas bubbles in the wood, sap wouldn’t flow. Who knew maple trees were CO2 powered?

A mere two decades ago, arborists were at a loss to explain what caused maple sap run. We'd typically mumble something about transpirational vacuum in the canopy before changing the subject. Everyone knows sap runs when warm days follow freezing nights. But it wasn’t until recently that the mechanism behind sap flow was better – although still not perfectly – understood.

Aside from maples, few species have a spring sap run. Birch and butternut do, but their roots generate pressure that forces sap upward. In contrast, maple sap flow is due to how its wood reacts to freeze-thaw cycles. Wood, or xylem, has vessel cells to carry liquids, and fiber cells for strength. Unlike most trees, maple fiber cells are partially filled with carbon dioxide and other gases, which can dissolve in sap.

At night, gases in fibers shrink as they cool, eventually dissolving into sap in the vessels. This drops the tree’s internal pressure, creating suction that draws sap from the roots. As daytime temperatures rise, gases bubble out of solution and expand, increasing internal pressure and forcing sap out tap holes at between 103 and 276 kPa.

Rather than flowing up from the roots and out the tap as was once thought, sap flows down from the crown (plus some lateral flow) toward a tap. When a warm day follows a sub-freezing night, sap may run from a few hours to several days, depending on the tree and barometric pressure. If it’s warm all night or freezing all day, sap won’t run.

Although sugar and black maples are most commonly tapped, producers also use silver and red maples when available. Even the humble Manitoba maple can be tapped. Maple sap is 2-3% sucrose on average, though this can range from below 1 to over 10%. In addition, sap contains organic acids, amino acids and minerals which contribute to maple’s flavour.

If great taste isn’t enough reason to use syrup, consider its health benefits. A 100-gram serving of maple syrup provides over 100% of the recommended daily amount of manganese and vitamin B-2, and it’s a significant source of magnesium, zinc and calcium. In 2016, Toronto-based researchers announced they’d identified a compound in maple syrup that inhibits clumping of beta-amyloid brain proteins, which may help prevent Alzheimer’s disease.

The freeze-thaw, dissolved-gas, pressure-differential explanation of sap flow has some holes, though. While the mechanism should work with pure water, sap only flows if it has a minimum level of sucrose. Flow should also happen in all xylem tissue, not just the living sapwood, but that’s not the case either. So the mystery of sap flow continues.

Recently, maple producers have been branching out into value-added products like maple candy. Another item is bottled, pasteurized and, of course, carbonated maple sap. What goes around, comes around, it seems.

ISA-Certified Arborist Paul Hetzler never shakes pop cans or maple trees before opening.

Views: 48

Comment

You need to be a member of CornellForestConnect to add comments!

Join CornellForestConnect

Forum

Replanting after timber harvest with climate change in mind

Started by Ben T. in Woodlot Management. Last reply by Patrik Schumann on Tuesday. 1 Reply

Hi Everyone,I’ve been wondering what tree species are going to thrive over the next 50+ years as the climate warms in New York and I’m curious if folks are enhancing plantings of particular tree species for future commercial harvest with warmer and…Continue

Rust Colored Hemlock Bark

Started by Carl Albers in Woodlot Management Dec 31, 2023. 0 Replies

Picture of a hemlock with rust colored bark.  When I cut a nearby tree, also with rust colored bark, it was infested with HWA.  Attached picture shows a Logrite ATV arch in use.Continue

Rust Colored Hemlock Bark

Started by Carl Albers in Woodlot Management Dec 31, 2023. 0 Replies

The hemlocks in my woodlots have been infested with hemlock wooley adelgid (HWA) for at least three years now.  Lately I've noticed some of them having a rust colored bark and I wonder if this is normal and that I just didn't notice it previously? …Continue

How to control mature white pine and hemlock to allow enrichment planting of hardwoods

Started by Peter Smallidge in Woodlot Management Nov 28, 2023. 0 Replies

I had a question about control of mature white pine and hemlock to improve sunlight for enrichment planting of hardwoods.  Following is my response, but I would like to know if anyone else has any experiences to share with control of these to…Continue

Story in Northern Woodlands Magazine on Deer Impacts

Started by Brett Chedzoy in Woodlot Management Aug 8, 2023. 0 Replies

This Spring we had an opportunity to speak with writer John Litvaitis about the big picture of deer impacts on the hardwood forests of the Northeast.  I posted the original story from the summer edition of Northern Woodlands to the…Continue

Ash blonding effect on lumber quality

Started by Jeff Joseph in Woodlot Management. Last reply by Jeff Joseph May 5, 2023. 2 Replies

Question: In Peter Smallidge's most recent "Ask a Professional" column for NYFOA's Forest Owner magazine he stated that some log buyers will reject ash that shows outward signs of "blonding" on the bark. Is this because the wood will change…Continue

The American Chestnut: A New Frontier in Gene Editing

Started by Brett Chedzoy in Woodlot Management May 2, 2023. 0 Replies

https://www.asbmb.org/asbmb-today/policy/042823/the-american-chestnutInteresting discussion the difference between efforts with the American Chestnut and other…Continue

Growing Black Locust for Pleasure and Profit

Started by Brett Chedzoy in Woodlot Management Apr 20, 2023. 0 Replies

In early March I was invited to present on the opportunities for growing black locust as a timber cash crop at the Rural Landowner Conference in Allegany County.  Ryan Trapani from the Catskill Forest Owners Association asked afterwards if I would…Continue

Badge

Loading…

© 2024   Created by Peter Smallidge.   Powered by

Badges  |  Report an Issue  |  Terms of Service