Maple sap is flowing – briefly

Maple syrup production report for February 4, 2016

Welcome to the 2016 Ontario maple syrup production report. The maple report will be updated on a weekly basis and will continue to the end of sap harvest and bud break in spring.  A seasonal summary of the production year will follow in late spring, once the syrup industry has had a moment to take stock of the resulting syrup and sugar crop.

The syrup season has begun early this year

The winter of 2016 has been relatively mild so far.  This week, many syrup producers have been busy tapping maple trees in the sugar bush.  In southern regions, a few producers have completed tapping and are collecting sap this week, taking advantage of early sap flows.  Some will be boiling the first batches of syrup before the weekend.

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Sap will flow from thawed maple trees when consecutive daytime temperatures reach +5 to +8 ⁰C followed by freezing nighttime temperatures of – 5 to – 8 ⁰C. Nighttime freezing recharges the maple tree to flow sap the next time it thaws.  Sap will flow faster when a low atmospheric pressure occurs during each thawing event.  Maple syrup producers often monitor both the ambient temperature and atmospheric pressure, to judge when the sap will flow and how fast.

University of Vermont’s Maple Specialist, Mark Isselhardt, is reporting similar tapping and sap flow conditions for their Vermont syrup producers this week.

Although daytime temperatures have been above freezing this week, the buds on maple trees remain fully dormant, thanks to the short day lengths of early February and freezing nighttime temperatures.  The long-range weather forecast is predicting a return to cold freezing day and night temperatures, which will stop sap flow and keep the sugar bush dormant for now.

It is important to note that while trees are dormant now, the buds on trees have likely accumulated enough chilling requirement to overcome internal physiological dormancy.  This means the buds will be kept dormant by external environmental conditions,  mainly by cold temperatures, overcast days and long nights.  Not to panic however.  The season is still young.

While many producers are still waiting a few more weeks to begin tapping trees, larger commercial producers in most regions are taking advantage of the mild weather over the past few days to begin drilling tap holes and installing spiles.  It can require several weeks for large syrup operations to complete tapping a sugar bush, for example, installing 15,ooo taps is a sizeable task.

Protect yourself in the bush

While working in the sugar bush, maple syrup producers should take all necessary safety precautions to ensure the risk of injury is minimized, such as:

  1. Have a daily plan to let family members and other workers know exactly where you are working, and when you intend to be home.
  2. Wear appropriate protective equipment including a helmet, hearing and eye protection. Wear certified protective clothing and footwear when using a chainsaw. Take a chainsaw safety course.
  3. Watch out for hazards in the bush, such as dead trees, hanging limbs and any trees showing weakness above ground.
  4. Tractors or other heavy equipment should have roll-over protection and impact frames installed over the driver.  Wear the seatbelt.
  5. Never work alone in the sugar bush, especially when using chainsaws.   Have cell phones or a radio with you to call for help if necessary.
  6. If you need to call 911 in an emergency, know your exact address in advance.

Conservative tapping guidelines

The objective of tapping a maple tree is to optimize sap yield while causing as little injury to the tree as possible. Drill tap holes only when the sapwood is thawed to a temperature of – 5 ⁰C or warmer, to prevent splitting of bark.

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Tapping into deeply frozen wood can cause the bark to split above and below the hole as the spile is seated into the hole.   With splitting, vacuum in sap tubing can be reduced due to a poor spile-to-tree seal, and sap can leak down the trunk instead of into the spile.

Tapping at an upward angle

Drill tap holes 1 ½ to 2 inches deep, at a slight upward angle using a sharp sanitized tapping bit. A downward sloped tap hole will drain by gravity to prevent sap or rain water from collecting in the hole after sap harvest has ended.

Tap hole healing - side view

Keeping old tap holes dry will help prevent infection by wood decay organisms and result in better healing by the tree.

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Check the appearance of wood shavings on the tapping bit.  Cream coloured or white wood shavings tell that a good tap hole has been drilled into healthy sapwood.  Darker or brown shavings on the drill bit indicate decayed wood or non-conducting stained wood has been hit, therefore a second tap hole will be needed to locate healthy sapwood.  Unfortunately, hitting stained wood causes additional injury to the tree due to multiple tap holes.

Tapping guidelines for vacuum tube collection and bucket collection

Trunk diameter at chest height

Number of taps per tree

          less than 10 – 12 inches

0

              12 to 18 inches

1

          greater than 18 inches

2

Large old sugar maple trees that are nearing the end of their useful life can be tapped more heavily where removal is intended soon. The final decision on tapping maple trees is the responsibility of each syrup producer.

Preserving healthy sapwood

Near the end of the sap harvest season and onward into spring, trees will react to tap holes as a wound response and will begin halting sap leakage by permanently plugging the hollow wood fibres inside the sapwood above and below the drilled holes.

Taps and stain columns

The plugged fibres are called stain columns, or non-conducting wood by maple researchers.  Once formed, the stain columns remain permanently fixed inside the sapwood and will never flow sap again.  Non-conducting wood accumulates inside the trunk with each passing year as trees are tapped.  Therefore, minimizing the number of holes drilled into the tree will help preserve more sapwood for future tapping.

Volumn of stain column graphic

Tapping bits range in diameter including: 1/4, 5/16, 19/64 and 7/16 inches, depending on the size of spile to be installed.  A small diameter tap hole will generate a smaller volume of non-conducting stain column in the sapwood.  The ratio is approximately 50:1 of stain column volume to tap hole volume.  Lower volumes of sap are typically harvested as the tap hole diameter decreases.

For example, using a ¼ inch tapping bit for a ¼ inch diameter spile can protect approximately 25 – 30% more healthy sapwood for future tapping, compared to using a larger 5/16 inch diameter tap.  The total sap yield per tap is reduced on average by 12% using 1/4 inch diameter taps versus 5/16 taps.  Smaller tap holes may be useful for sugar bushes that are located on less-than-ideal sites, where the annual growth rate in trees is lower than the average growth rate.

Healthy sugar bushes that are located on fertile soil and are managed using good forestry practices can generally sustain larger diameter tap holes, assuming that tapping guidelines are followed.  Here, new sapwood will accumulate each summer to ensure there will always be an adequate tapping area on the trunk for maple syrup production.

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