Revisiting the End of Maple Sugaring Season - Based on Growing Degree Days

Growing Degree Days are used to predict whether or not fruit trees will actually bear fruit; I'm applying this measure to Sugar Maples and predicting the end of season.

Sugar Maple buds, iPhonography through telescope 2017 Apr 04

Of course our maple season ended some time ago, the last sap was evaporated on March 21st; the end having nothing to do with Growing Degree Days and reaching budbreak, but having everything to do with the trees healing the tap holes to the extent that sap flow was stifled. As I looked out the window yesterday though, it was clear that the two mature Red Maples in our backyard were in the process of leafing out, and with the naked eye it looked like the Sugar Maples on the south side of the house were budding out, if not yet flowering or leafing out. That got me to thinking that it would be a good idea to revisit the Growing Degree Day calculations performed earlier this season (see "Maple Syruping Season - Starting, Ending, or Both?", and "Maple Syruping Season - Mid-Season Update", "Estimating the End of Maple Sugaring Season - Based on Growing Degree Days", and "Predicting the End of Maple Sugaring Season - Caveat Emptor"). Sugar Maple is expected to break bud when somewhere between 54 and 99 GDD_F (Fahrenheit) have been recorded.  So I asked myself again, "where are we now?" And what does bud break look like? To the last question first, I found a handy resource at the University of Vermont, which should surprise no one; a Field Guide for Monitoring Sugar Maple Bud Development. Here is a screen shot of flower buds, which more closely resemble what I am seeing than "vegetative" buds; it is also know that flower buds break a week or two before vegetative buds.  It seems that "budbreak" is when the flower bud opens at the tip.

Sugar maple flower budbreak Field Guide for Monitoring Sugar Maple Bud Development

In my picture at the top of this post, it is certainly not clear what is going on some 60 or 70 feet above the ground, though with the magic of digitally zooming in on a section of the image we can get a much better idea.  It looks to me that we have some pretty highly developed buds, but have yet to achieve budbreak; I am not seeing a split at the end of the bud.  True, the image quality is not great.

Digital zoom - Sugar Maple buds, iPhonography through telescope 2017 Apr 04

The GDD calculations based on OverGrown Acres Farm weather station data have been updated through April 3rd.  Perhaps surprisingly we are only at 27 GDD_F, half-way to the minimum necessary to achieve budbreak, 54 GDD_F.

Temperature history for 2017 to date, and Growing Degree and Heating Degree Days calculations

And we have also update the "prediction" as to when budbreak will be achieved.

2017 Apr 03 GDD Predictive Chart

The first prediction we made three weeks ago, in the "Caveat Emptor" post mentioned above, was for GDD_F 54 to occur March 26th or 27th, and GDD_F 100 to occur Apr 5th or 6th; those dates are now Apr 9th or 10th and Apr 21st or 22nd respectively.  So, the front end of the window has moved out 2 weeks, and the back end of the window has moved out 16 days.

One of the lessons being taken away from this season, is that staggering the tapping at the start of the season seems to make good sense.  Especially next year, with 500 taps, tapping over the course of 2-3 weeks, or more depending on the weather, would be something of a hedge against our inability to forecast the weather accurately, would extend our season, while reducing peak production, because fewer taps would likely be flowing at any one time.  Another lesson is that GDD is a pretty crude tool.  First of all, we know that sap is flowing (i.e., the tree is growing, no longer dormant) when temps are significantly less than 50°F, so the base temperature used for the calculation might be lower, say 40°F.  And, the range of GDD within which budbreak will occur is far too large at 46 GDD_F.

Other happenings of late have reinforced to me that we must learn faster.  The costs of not learning faster are simply unsustainable, especially in the business.  Somehow more feedback from the system needs to be obtained more regularly, and sharing more often and more widely is one way to get that, I hope.

Thank you for reading the blog, and for providing feedback!  The system needs it.  We need it.  I need it!

All the best,

John

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