Climate

Another Unpredictable Winter Ahead???

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A big thanks to Les Ober, Extension Educator ANR, Geauga County OSU Extension, for this article.  This is a hot-off-the-press refresh (newer outlooks and forecasts!) from a piece that was just recently published in a couple other outlets.  

What do snowflakes and weather systems have in common?  Other than the obvious!  Snowflakes never duplicate themselves, and each has a unique pattern.  It is beginning to look like the same is true for winter weather in the eastern United States.  The weather for the next two months will play a major role in determining the outcome of the 2026 maple season.  Because of rapidly moving weather systems, there is no longer an average winter. According to OSU Climatologist Dr Aaron Wilson, we are in for a pattern that looks quite similar to last year.  The weather pattern over the Pacific is going to drive warm weather into the central part of the country.  That warm air will then push northward creating a bulge into Canadian provinces which then drives cold air south.  This chain reaction essentially creates a cold air outbreak into the Northern US.  Too complicate things even more, La Nina is weakening and there is a chance of El Nino taking its place. This results in a lot of variability and possibly even extreme weather.  This winter could be more of a roller coaster than last.

If you live in one of the Great Lake snow belt regions, this system is likely to result in snow.  Regions like Western New York and Eastern Lake Ontario can almost always expect large volumes of snow when this happens.  As for the Lake Erie snow belt, it depends on wind velocity, wind direction, and lake temperature.  This year, Lake Erie is warmer than normal for this time of year.  As a result, we have already seen significant Lake Effect rain and snow across Ohio.  Northeast Ohio had up to 6 inches of rain in the third week of October and 12 inches of snow in the snow belt at the end of November.

If you look at the NOAA 3-month outlook maps, it appears that we are headed for another mild winter.  Is it time to get out the tappers and head for the woods?  The Lake Effect snow we experienced in November is already reappearing here in early December.  The Great Lakes are still warm, but temperatures are falling with this pulse of polar cold that has invaded.  The monthly outlook for December clearly shows that there has been a shift in the weather forecast, and the first 4 days of December have matched the predictions.

As December fades and January looms, the thought of tapping trees and making some early syrup begins to creep in to mind.  I think you can rule out making December syrup from Northern Ohio up into New England.  That does not mean some individuals will not give it a go, there are always tappers who want to be first to carry new syrup out of the sugarhouse.  What to expect for January?  I am not ready to discuss what might happen as the forecasts are a mixed bag.  If I was betting man, and I am not, I would say we are in for a cold start for January.  This may keep the early tappers out of the woods a little longer, but this is where we hit a fork in the road.  After the New Year, producers in the southern tier: southern Ohio, West Virginia, southern Pennsylvania, Virginia, Kentucky, and Indiana need to get ready to go on a minute’s notice.  The rest of us can sit back and watch the weather unfold.  After years of experience, you will know when the time is right.

I will continue to watch the forecast very closely as we move through the month of December.  The closer we get to the season, the more timely and thus accurate the forecasts will become.

Climate Trends & Maple Production STORYMAP

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Thanks to one of our own – Kathy Smith – for passing along information on this new StoryMap released from UW-Madison Extension and the Midwest and Northern Forests Climate Hub.  The density and quality of the information contained inside is impressive with more than enough data to completely nerd out on climate impacts to maple.  Though the news is not necessarily great for our region, thankfully producers can adapt to changing conditions with several strategies.

Thanks to the UW-Madison Extension team for a wonderful resource!

Maple & Popular Mechanics…???

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Maple for the masses – of course that’s our goal when we think about the tasty product we produce and the many millions of people who aren’t yet customers but should be!

Maple for the masses – from a researcher’s perspective, there’s always the goal for our work to be translated from research into applied guidance that can be adopted by producers all over the landscape.

Maple for the masses – from a general knowledge and curiosity perspective, producers love to tell others about the maple culture and practice that we love so dearly.

One could argue these elements leverage Curiosity into Consumption which eventually turns into Concern for the resource – a beautiful way to think about how our human curiosity can find engagement that ultimately leads to a stewardship ethic around an issue or topic or resource.

Very seldom does a single piece of media capture all of these perspectives and more so wonderfully.  Sticking with the personality of Aaron Wightman from Cornell (see last week’s post about the Sweet Talk Maple Podcast), I think you’ll agree this Popular Mechanics article is a real doozy.  Enjoy!

Dealing with Storm Damage

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A big thanks to Kathy Smith, Program Director of Extension-Forestry, for putting together this great resource of how to cope with storm damage.  Unfortunately, it has been a reality for far too many maple producers in the past 3 years, and I’m sure for many more before then.

Click back into our archives to read a post after the 2022 derecho that ripped through north-central Ohio in mid June.

Lots of work went into creating this resource-rich PDF, so I’ll simply link it below for download and use.  Enjoy!

Storm Damage Article – Smith & Karns 2024

Ohio’s 2024 Drought & Next Year’s Maple Season

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Ohio is part of a severe drought that has affected many states east of the Mississippi and is experiencing what many Western states have had to live with for years.  This is all part of the seemingly endless series of weather events that stem from changing climate.  Of major concern to maple producers is the effect this drought will have on maple syrup production during the 2025 season.  Let’s look at the current U.S. Drought Monitor map.

As you can see the extreme and exceptional drought ratings are in southeastern Ohio, and an even larger portion of the state is categorized in the Abnormally Dry to Moderately dry conditions. One saving grace is that the one area currently unaffected is a portion of northeastern Ohio that includes Geauga County and most of its adjacent neighbors.  From experience in the 1988 drought, conditions can change very quickly; however, autumn is a bad time for a drought because you tend to go into winter with lower subsoil moisture reserves. How might all of this affect maple production?

Rather than paraphrasing a brief article by Dr. Timothy Perkins written at the time of the 2022 drought, I will simply quote his thoughts on how drought affects sap flow.

Sap flow is more dependent on soil moisture during the spring itself…so snowmelt and rain during the spring are quite important. However, there seems to be a couple of impacts on sap sugar content and tree growth. Think of leaves as the engine of the tree. The fuel is sunlight. But in order for that engine to run at peak levels, everything else needs to be operating correctly. If soil moisture is lacking, stomates in the leaves close, so carbon dioxide cannot enter the leaves and be “fixed” into sugars. So, drought reduces photosynthetic carbon gain (production of sugars), resulting in reduced growth and less storage or sugars in that ring of wood formed during that time. Fortunately, the sugar we collect as maple producers in sap comes from many tree rings (20-30 depending on tree growth rate and taphole depth), but the outermost tree rings tend to be the most productive (more sugar and higher hydraulic conductivity…meaning the younger pipes/vessels work better), so there can be some small reduction in sap sugar content due to drought. This is more apparent when we have several years of drought in a row.

From personal experience, I would be more concerned with this drought if it extends and expands into the winter. Winter snow accumulation has a major impact on recharging the subsoil and sap flow, and subsoil moisture is everything when it comes to sap production.


Photo courtesy of Bret Kaufmann

As Dr. Tim pointed out the greatest impact is from extended drought that lasts more than a few months or even multiple years.  What the producer is looking at is an above and below ground response to the drought.  During a drought the air temperatures increase, and winds also often increase.  This accelerates evapo-transpiration through the leaves, causing the leaves to dry out.  At the root level, the fibrous hairs on the roots are lost thereby reducing the amount of water flowing through the roots into the tree and up to the leaves.  One of the first things a producer will notice is the leaves drying out and in some cases dropping early.  This can also trigger dieback in the canopy, but many things can cause maple dieback.  In the first year of drought, this is normal and not a major concern.  If the event prolongs however, producers might want to cut back on tapping in multi-year droughts.  This could be nothing more than restricting tapping to one tap per tree, or in extreme cases, the producer might want to skip tapping a sugarbush in the spring of a drought’s second year.  An additional concern during any drought is heightened fire hazard risk.

In the near term, should producers consider not tapping a sugarbush that has been through some of the state’s most severe drought?  This will depend on how long the dry condition lasts and what the soil moisture looks like as we go into spring.  A lot can happen between now and the tapping season.  Heavy rains could change everything, and everything depends on the next several months’ weather going into next season.  One thing to consider is that our maple seasons are coming earlier than the historic norm; another earlier season will cut down on the amount of time the trees will have to recover from this most recent drought – if and when it breaks.  At this point, it is likely a wait and see situation.

Glad to See It Come, Glad to See It Go

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Thanks for Les’ contribution last Monday in his post – Is February the New March?  This is a more Mansfield-centric take on the 2024 season with a more in-depth analysis of statewide Growing Degree Days to compliment last week’s content.

What a season!  That sums it up in all the best and worst ways.  I stand by the words I typed in my 2/19 post – I believe we nailed our tapping date just about perfect.  The first run to follow was a marathon of 7 or 8 straight days, and the second run of the year culminated in our making syrup off the new OSU teaching evaporator for the first time ever.  Though many producers’ woods performed below average in terms of sap sugar, our Brix registered consistently at 2.0.  Talk about some highs.

We knew better.  The weather folks are not infallible, but there was no denying the forecast that lurked.  Warm, warm, and more warm.  But unexpectedly, February 21st was the death blow for our season.  While we were over at Malabar Farms helping out with an NRCS workshop on maple, our pump decided to quit working.  Without vacuum, the productive days of our season were over.  With a full season, we would likely have stayed tapped in until March 4th and posted one of our better season totals.  As it turned out in reality, the 2024 season ended on a low.

Looking more broadly around the state, the progression of Growing Degree Days (GDDs) was alarmingly early yet again.  If there any producers still resistant to the idea of tapping earlier than more traditional dates, then I don’t know what it will take to change minds.

Observe – Click Play for an animation of GDDs from 2021 (below).  Pay attention to 2 data points in particular.  First, the GDDs accumulated through March.  Second, the scale of GDDs on the legend.

Now, you don’t even need to see a similar video of 2024’s GDDs to know we covered lots more ground in fewer days than the previous year’s example.  Long story short, earlier AND hotter.  Hello sap season double whammy, goodbye sanitation!  I don’t believe many producers will be heard pining – “Boy! What I wouldn’t give for another season like 2024!”  And if you did hear such a remark today, then you probably also heard them quip – April Fool’s!!

Is February the New March?

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Remember when Les said he would come back at the season’s conclusion to tell you in 20/20 hindsight exactly what you may already suspect, he’s back to make some sense of the 2024 sugaring season!  Enjoy.

The Ohio maple syrup season ended on the first weekend in March.  This comes less than a week after President’s Day, the traditional starting date for the season in Ohio.  Of course, not this year as many Ohio producers started the 2024 season in January.  If you are a maple producer, you must wonder if the climatologist and everything we have been hearing about our climate is right.  Is February becoming the new March?  

Let’s analyze what we have seen and experienced in 2024.  OSU Climatologist Dr. Aaron Wilson has been telling us that the winters will get milder, and Spring will come earlier.  Once again, I refer to historical weather data to make a point using Weather Underground weather history maps.  Dating back to 2021, here is what I consider a relatively normal March (below).

Here is February of this year, 2024 (below).

It has been reported over the last several months that we ended 2023 with almost record-breaking high temperatures for November and December.  In fact, the climatological winter (December, January, and February) was the third warmest on record.  The 2nd warmest occurred in 1931.  The warm weather sent a warning to many maple producers, alerting them that something unusual was about to happen.  In Ohio, those that tapped in mid-January got it right.  Those tapping right after the first of the year were rewarded with 6 to 8 weeks of maple producing weather.  Many recorded over 14 boils before the first of March.  This year undoubtedly sets a new benchmark for early tapping.  Why did this happen and what can we learn from the experience.

The winter of 2023/24 followed the long-range forecast’s prediction.  With the exception of the invasion of a cold air mass in mid-January, the mild temperatures came back and continued throughout February.  This set up some extraordinarily good runs throughout the state.  However, a troubling and confounding factor was the overall lack of moisture.  I would say that many parts of Ohio were below average on moisture during this period.  Dryness in the woods is not good for maple production.  It is much preferred to have 4 to 8 inches of slowly melting snow, at the very least, lots of rainy days interspersed through the season.  I have seen woods that face north where the snowpack will last almost to the end of March.  These woods have produced good runs all the way to the end of March and even into April.  Not this year.

Here is the graph (above) showing the high, low, and average temperatures for the first two weeks in March.  The important thing to look at here is the minimum and maximum temperatures that clearly show we not only had daytime temperatures in the first two weeks March above 50 degrees F, but also had nighttime temperatures that approached and even hit 50 degrees.  This totally wiped out the freeze/thaw cycle, and we all know you cannot make syrup without a freeze/thaw cycle.  Sustained temperatures above freezing will undoubtedly be a recurring problem into the future.  Warm temperatures also accelerates the accumulation of Growing Degree Days, pushing the trees toward budding.  However, buddy sap did not end the season in much of Ohio.  It was the acceleration of microbial growth resulting from an abundance of unseasonably warm temperatures causing the sap to warm and foul systems.  It is almost impossible to make quality syrup under these conditions.  During the Ohio Maple Tour, I tasted multiple samples of syrup made in early March.  Just about all had that sharp taste of syrup made from sour sap.

Now comes the real challenge!  How do we prevent the possibility of this very marginal syrup from entering the market?  Especially in a year when many producers in states like Ohio had a poor year and now have syrup of questionable quality to sell.  Do you bottle the syrup and hope no one notices?  After all, it may have good color somewhere between Amber and Dark Robust.  The rationale in the past has been that most customers will not pick up on the off flavor; after all, they are used to high fructose corn syrup imitations.  The question now turns becomes, how much high-quality syrup will be made in the Northeast and in Canada this year?  Will the syrup they sell to the big box stores have better quality than what our customers can buy locally?  We already know it will most likely be less expensive.

In the end what have we learn? We added one more year to the string of abnormally warm maple seasons that we have experienced over the last 5 years.  For Ohio producers tapped in January, many experienced a near normal season.  Operations made some very good syrup that did not have quality issues.  Their markets are covered.  This also means that in 2025 when New Years Day rolls around, those producers who gambled right in 2024 will again be ready to tap trees at the first signal of good sugaring weather.  Unfortunately for many Ohio producers tapping later in the calendar, this year will be a hard lesson.  Those that tapped after mid-February found out that you cannot trust Mother Nature, because she does not read the Calendar.

A Little Science behind Maple Sugaring Weather

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Hands down, the number one question that comes up this time of year is “When should I tap?”

Due to the warmest December on record, I have heard a few Ohioans even asking “Should I have tapped in December?”.  When you look back over the years, the trend has been toward earlier tapping dates, but hoping that you can keep taps open for 3+ months is a bit of a stretch.  There is no way that will happen on a gravity system, and you will need more than a little luck even on high vacuum.

The scientific approach to planning involves studying climatological data and developing a plan based on that data. The maps below are long range weather predictions for the next three months. You can clearly see that all indications point to above normal temperatures for the next three months. For sugar makers what does this mean?

To quote a good friend and fellow maple researcher, “when you look at forecasts you need to look at it from the big producer / small producer perspective.”  Because most small producers tap everything at one time, they need to consider the value of a good short-term, 30-day forecast.  In most cases, especially if you are on a gravity system, you need to find the best 30-day window that will allow you to make the most syrup.  Once you tap, you are on the clock and that clock runs out shortly after 30 days.  On the other hand, if you are a large producer or even a medium producer on vacuum, you need to study yearly trends.  Trends will disclose what has happened over the last 3 to 5 years.  What we have seen is a trend to earlier tapping just about every year.  In most cases, early tapping has paid off in Ohio.  A major reason is that newer technology lends itself to pushing the envelope when it comes to tapping.  You have the advantage of running a semi-closed vacuum system utilizing 24/7 operation.  This lengthens your season considerably.

One of the most valuable pieces of data you can use are temperature history graphs for your location.  Weather Underground has some of the best.  They plot the maximum, minimum, and average temperatures.  Plotting the maximum and minimum will give you a good idea on the number of freeze-thaw days to anticipate for a month.  As we all know, freeze-thaw cycles are very important and drive daily sap runs.  You can look at these cycles over a five or even ten year period.  Over time you begin to see how various weather patterns play out.

Keeping in mind these are zip code specific but we are talking at the broad scale of an entire state, here are three February graphs. You can clearly see we started February leaving a warm end to January on two out of the three graphs.  In all the graphs, conditions continued to warm up as February wore on.  In two out of the three, the temps dropped going into March.  This may be a hint for what could happen this year.  2020 and 2022 were almost normal.  In both cases, our records show average to above average production.  2021 was the outlier and production was down for that year as temperatures stayed warm through most of March.  The other two years highlight the fact that starting out February warm does not mean you will march into March warm.

Too much science?  Here is a more common sense approach that prioritizes the size of your operation.  If you are tapping thousands of taps, you must start early to get the job done.  For a moment, think about a huge 50,000-tap operation.  Should they consider tapping right after the first of the year?  Definitely!  One of their strategies is to tap 5,000 taps super early.  This results in the Facebook posts you may have seen bragging about syrup being made over Christmas.  Several big producers in the East did this in December.  Does that mean they tapped everything?  Most likely not.  A large commercial producer hedges their season by tapping some early and the rest over the month of January with everything in the tree and ready by February 1.  Small producers who are setup to boil early can also do this, the only difference is they may start tapping their early running trees shortly after New Year’s but plan to finish out in February.  This keeps fresh taps in the system and prevents you from putting all your eggs in one basket.  The best way to accomplish this is to keep very good records.

That brings us back to our initial question.  When should I tap this year?  All indications are that we are going to have a warmer than normal winter.  If you are in Southern Ohio, you might be tapped already.  North of I-70, you should probably hold back until the end of January.  This is where analyzing the 30-day forecast is critical.  Studying several long-range forecasts a little closer, I noticed that we may have some of the coldest weather of the winter on the last week of January and the first week of February.  While the forecast is showing a warming trend coming off several weeks of genuine cold weather, depending on your situation you may even want to hold off until the first week of February.

Of course, the joker in the deck is the El Nino weather event we are experiencing.  El Nino’s are known for extremes and all it takes is a bend in the jet stream and you could be looking at 10 more days of below average weather.  Once this happens, you usually go right back to the warmer than normal pattern.  In this case, cold weather is your friend.  What we do not want is 10 days straight above normal!

As for my prediction!  I will tell you what kind of season we had in 2024 on the first week in April.  May your sugar season be long and sweet.

Change Over a Century: Monthly Maple REVIEW

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Here is May’s edition of our feature Monthly Maple Review.  Once a month, we review a research article to spotlight key findings, investigate curiosities, and uncover important implications for Ohio’s maple producers.  Please comment below if you have thoughts, ideas, insights, or questions.  If you stumble on to a new maple article and want to see it highlighted in a Monthly Maple Review, please reach out to me via email – karns.36@osu.edu.

Phenology, put simply, is the study of nature’s timing.  A couple years back, we did a special article series on the use of growing degree days (GDDs) to monitor and predict the progression of trees and shrubs in Ohio.  Typically, sugarmakers are most keyed in and interested in whether maple trees are early, right on time, or late to produce the sap runs we convert into maple syrup.  But phenology gets at much more than just the time of year we make syrup.  Leaf out, dormancy, seed development, emergence of different insect pests, fall color change, and leaf drop are all elements of the annual cycle of plant phenology.  Phenology is a topic we keep coming back to you, but it’s interesting, it’s important, and it’s complicated – so we are back again!

This month’s article, published in March of this very year, is titled “A Century of Climate Warming Results in Growing Season Extension: Delayed Autumn Leaf Phenology in North Central North America.”  Authors Kellen Calinger and Peter Curtis (both Ohio State University researchers in the Department of Evolution, Ecology, and Organismal Biology) published their study in an open-access journal called PLoS ONE.  Open-access meaning, if you want to read the full paper, you can access the article here.

The methodological approach for this research paper is particularly interesting and clever.  A farmer named Thomas Mikesell from Fulton County, OH, collected data from the years of 1883-1912, meticulously recording phenological and meteorological information that was preserved in a massive 700+ page publication that is still accessible today.  Kellen and Peter, the modern day researchers from Ohio State, used Mikesell’s observations as a baseline to compare data from 2010-2014, a full century later.

Among the tree species selected in their study (they chose 7 in all), no Acer maple species were chosen unfortunately.  However, the beauty in this study’s approach is the real focus on this month’s review.  It is both elegant and simple to think that someone’s observations over 100 years ago could serve as such a significant monument in time to understand how conditions shift and change through the decades, even centuries.  Sometimes science gets complicated, complex, to the point of absurdity it seems.  This is a pleasant reminder that there is profundity in the simple as well.  Write down your observations, allow time to pass, make more observations, and compare.  Simple.  Done.

I believe there is a lesson here for us all – take notes, jot down curiosities, record all the important dates from every sugaring season.  And most importantly – save those scribbles and notes in a place where not only you, but the next generation too, can find them and propel your own personal learning journey.  Just in case you don’t recognize the common name “white maple” – that’s silver maple.

If you’re from northwest Ohio, or even just from the upper quarter latitude of Ohio, I strongly suggest you peek at this table to see how your observations jive (or don’t jive!) with Mikesell’s observations back in the late 1800s.   What conclusions do you draw?  Are there big differences for each observational category – first fully formed leaf, in full leaf, in blossom, fruit ripe, and complete change of foliage?  Or are some categories different, but some phenomenon right on schedule and unchanged?  It is important to remember that phenology is driven by a host of factors (as we noted in our March Monthly Maple REVIEW) – shifting climate is one factor, but precipitation plays a role, active and recent weather events/trends, photoperiod (fancy name for day length), and more.  Observations that have not changed much on the calendar are likely responding to more static and unchanging factors such as photoperiod.  Observations that do differ, those are more likely triggered changing climate and other more dynamic factors.

If you’re not from that part of Ohio, dig up those old records that your dad’s dad kept back when he ran the sugarshack in years bygone.  Rifle through the old drawers of dusty old spiral-bound notebooks.  Flip over the back of black-and-white photographs to see if there is an inscription that reads “first boil, 1952.”  All those memories are also records, and we learn about the present when we look to the past.  So I guess this review is less of a review and more of an admonishment – bear witness to the power of data collection and long-term record keeping.  Participate in keeping notes.  If nothing else, those notes will be curiosities to be pondered years down the road.  At best, meticulous notes and records can help you make sense of the dynamic, cluttered, and information-dense world that we live!

 

What Triggers Bud Break? Monthly Maple REVIEW

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A brief introduction to this new feature – Monthly Maple Review – we review a research article once each month to spotlight key findings, investigate curiosities, and uncover important implications for Ohio’s maple producers.  Please comment below if you have thoughts, ideas, insights, or questions.  And if you stumble on to a new maple article and want to see it highlighted in a Monthly Maple Review, please reach out to me via email – karns.36@osu.edu.

“Bud Break in Sugar Maple Submitted to Changing Conditions Simulating a Northward Migration” by Ping Ren and colleagues.  This article was published in 2021 in the journal Canadian Journal of Forest Research.

In our first Monthly Maple Review, we looked at producer attitudes and behaviors regarding climate change and its projected impact on maple.  For this our second installment, we focus on how a simulation experiment predicts climate change will effect bud break in sugar maples.

As climate shifts and range-restricting thresholds follow, plants and animals must adapt and keep up with changes or risk being left behind.  Many organisms are well-suited, at least from a mobility standpoint, for keeping up – take birds and their gift of flight for instance.  Other species likely face serious challenges; the American pika is commonly pointed to as an example.  Pika are small, marmot- or groundhog-like creatures that live in treeless alpine habitat in the Rocky Mountains.  It is easy to imagine pika being literally stranded on mountain peaks above timberline unable to migrate and keep up with shifts in suitable range.  Many plants are also considered less adaptive to shifting conditions and may not be able to move into higher latitudes or elevations necessary to keep up with suitable growing conditions; sugar maples are no exception.

In emergency scenarios, assisted migration is a solution whereby humans literally help other organisms keep up with shifting climate conditions.  Already, experiments have been conducted with many plant species, including some trees such as the whitebark pine, to verify suitability of growing conditions beyond the current limits of the species distribution.  Will sugar maple or other maple species need a special assist from us?  No one knows for sure, but studying what factors drive bud break is a small step to understanding if they are likely to need our help in the future.

The essence of Ping Ren and team’s experiment was to examine bud break under controlled conditions while varying temperature and photoperiod (also known as day length).  The experiment’s most basic hypothesis was that “photoperiod outweights temperature in initiating bud break when the chilling requirement in unfulfilled.”

To understand the study’s results, we first need to wrap our minds around 3 main environmental factors, or signals – the variables we believe most plants are responding to when they wake from winter dormancy and start to stir towards bud break.  First, winter chilling – more intense and longer periods of cold during the heart of winter contribute to chilling.  This deep freeze is what resets the annual clock of trees and influences the trigger of growth reactivation.  Perhaps it is worthwhile to think of chilling as similar to a human experiencing a prolonged session of deep sleep.  Second, spring temperature – this is just what it sounds like.  In a simple system, cooler spring temperatures may wake plants from deep sleep more slowly than a rapidly warming and sudden onset of spring (check out a series we did in winter 2022 on growing degree days to better under the role of spring temperature).  And finally, photoperiod – more commonly known as day length.  The most important thing to note on this final factor is that while any given year might vary in terms of winter chilling or spring temperature, length of day is fixed and will always be fixed regardless of where climate change takes us.

While each factor in isolation is relatively easy to understand, it is the complicated interactions between winter chilling, spring temperature, and photoperiod that likely determine the actual timing of bud break in a species.  This study ran 2 experiments that essentially confirmed the hypothesis that sugar maple bud break is more determined by photoperiod than by spring temperature when the requirement for chilling is not met.  Let’s put that another way – during winters that do not put sugar maples into a deep sleep for long enough (winter chilling), day length has more of an effect on bud break timing than how cool or warm spring temperatures are.  In other words, the experiments confirmed the authors’ central hypothesis.

Let’s unpack that a bit more and talk about some take home messages.

Resetting a sugar maple’s internal clock is accomplished primarily by meeting the chilling requirement – being cold enough for long enough.  When that chilling requirement is not met, it takes additional and louder signals to wake up a tree from dormancy to initiate bud break.  While this might sound a bit counterintuitive, the fact is that waking up a tree from a deep sleep is easier and more predictable than trying to wake up a tree that has been tossing and turning in its winter bed.  Under changing climatic conditions, warmer winters may result in unmet chilling requirements that ultimately result in delayed bud break thereby shortening growing seasons.  But remember, winter chilling is just the first consideration.  What about spring temperatures?

At face value, most sugarmakers understand the effect of a warm spring – trees break bud faster.  In a cool spring, buds stay closed longer and the sap season might last a bit longer too.  In a worst case scenario, climate change wreaks complete havoc on winter weather not allowing sugar maples to adequately chill and temperatures jump back to springtime highs so quickly that any sap season is effectively crowded right off the calendar.  That’s where day length seems to play a crucial and important role.

Think of day length/photoperiod as a speed governor on a go-cart.  I hate so-called governors growing up.  I wanted to ride my go-cart at top and dangerous speeds, but my parents set the speed governor so that I could only drive certain speed limits.  When spring temperatures warm abruptly and it seems that the sugar maples might break bud extraordinarily early, length of day pumps the brakes and slows down that process regulating it closer to normal.  Essentially, photoperiod may be a crucial regulating factor to keep sugar maple bud phenology more on track than would be expected otherwise.  In the authors’ own words – “Because day length will not change under climate warming, photoperiod becomes ultimately limiting when bud break in sugar maple occurs too early.”

So where does that leave us?  Will sugar maple need our help in assisted migration as conditions change faster and faster into this and coming centuries?  Time will tell, but if this study teaches you nothing else – you can certainly walk away with 2 big takeaways.  First, trees are remarkably complex organisms.  And second, trees have a few tricks up their sleeves!