Sap Flow Mechanism from Peterson Farm – John Peterson
We are tapping our trees today (March 15) in hopes the weather will cooperate for the next couple weeks. The main sap run has started as early as March 9 and as late as March 29 for us.
It is widely known that temperatures must cycle above and below freezing to trigger Maple sap flow, but less is known about what happens in the tree to accomplish this. Here is the process to the best of my understanding. I originally did this in a flowchart, which made for a clear picture of the complicated process. The reference material was primarily the North American Maple Syrup Producers Manual.
- Temp drops below freezing causing branches and stems to freeze.
- Air filled fiver cells in the Xylem layer develop ice crystals on their walls.
- Humidity in the fiber cells drop, causing water to be drawn from adjacent cells, forming more ice and compressing the air in the cell.
- Movement of water into fiber cells causes a pull on sap in the Xylem vessels.
- Pull is transmitted throughout the branches and the trunk down to the roots (cohesion).
- Strong negative pressure (suction) results throughout the tree.
- If the ground is not frozen the negative pressure in the tree pulls up water from the roots as the temperature in the tree continues to drop.
- As temperature drops below freezing the sap begins to freeze in the tree.
- Frozen sap blocks the pathway (Xylem) for water to move from the roots up into the tree.
- Temperature rises above freezing (usually day) and the branches and stems begin to thaw.
- Ice thaws in fiber cells and the compressed bubble of air (in cells) expands, pushing water back into the Xylem vessels.
- Positive stem pressure develops through the tree aided by gravity and osmosis.
- Sap flows out tap hole (or other wounds).
- As time passes, positive sap pressure decreases due to evaporation of sap from branches and other internal leaks in the trees system.
- Sap pressure eventually equals atmospheric pressure outside tree.
- Sap ceases to flow under gravity.
- If there is another freeze thaw cycle, the process repeats itself.
I learned this in the depths of our long winter when it was too cold to enjoy the outdoors. Now it is time to forget about this stuff and get out and enjoy making maple in the woods!
Here’s an update from Butch & Amy Fideldy-Timber Sweet
Ready! Ready! Ready!
Checking in with Butch on Monday morning over the phone and the weather is the first item on the list. Cold weather continues and this morning temperature is a cool 23 degrees. Butch reminds me it’s normal to have winter linger, and looking at the forecast he’s hopeful that there will be a sap run at the end of this week.
The Timber Sweet crew have been out in the woods, tweaking the taps and making sure everything is in place after last weeks windy weather! There’s still a solid crust on the snow so it’s easy walking. Woodpeckers have active and Butch commented that the mainline running into the pump house looks more like a sprinkler system. Amy is looking to purchase owl decoys as a deterrent.
Amy has decided on the date for the Timber Sweet Open House- April 3 from 12:00 p.m. to 4 p.m. The Open House allows families to tour the sugar house, learn about maple syrup, and try some of their product.
Update from Spirit Lake Sugar Bush:
Minnesota Maple Syrup Producers Association annual spring meeting scheduled for May 20-21 at Wolf Ridge.
More from the 2011 Minnesota maple blog series
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