Climate

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!

Another Topsy Turvy 2023 Maple Season

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Our 2023 maple season was yet another sub-par year subjected to early and frequent warm spells.  2023 marks the 3rd consecutive year that our first run of the season ended not because temperatures took a prolonged dive below freezing but because temperatures spiked into the upper 50’s or low 60’s.  Three years in a row!  Crappie fishing weather to end the first run of the season!  Starting off a season with a warm temperature spike sets the table for sanitation issues, and those challenges were forefront to yet another Ohio maple season.  For all practical purposes, our production season at the Ohio State Maple woods was over by March 1st.

Early tappers were rewarded this year making the most out of a tough season.  A few producers up north are holding out for a final run or two before also switching to post-season tear down and cleaning duties.  How the entire state fares is yet to be determined, but the individual producers I have spoken with are not ecstatic over the year’s production totals.  The bottom line is that Ohio appears poised to enter, heck we might already be in, a new normal.  Though spring is temporarily stalled with the current slight cool down, spring invaded winter like a unexpected marauding army.  To get an idea of just how early 2023’s spring has been, check out the time-lapse map from the National Phenology Network.

Regardless of whether you are a producer up north with a few more days of boiling on your horizon or if the season is a memory at this point, be sure to check out Future Generations University’s webinar next Thursday evening.  On March 16th at 7 PM, the Out of the Woods semianr series will focus on post-season sanitation.  Mike Rechlin and Kate Fotos are going to share best practice guidelines on keeping your sugarhouse and your sugarbush spic and span headed into the off-season.  You can watch the webinar on Youtube or get your own registration link through Zoom here.

Climate Change & Maple: Who Cares?! 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.

“A Changing Climate in the Maple Syrup Industry: Variation in Canadian and U.S.A. Producers’ Climate Risk Perceptions and Willingness to Adapt Across Scales of Production” by Anna Caughron and colleagues.  This article was published in 2021 in the journal Small-scale Forestry.

The maple syrup industry is on an undeniable collision course with changing climatic regimes – shifting tree composition, more unpredictable and earlier sap seasons, and potential reductions in yield are all staring back when we look into the future.  This list represents just the tip of the looming iceberg, and more southerly producers anticipate an even rockier path forward as evidenced by some impacts that we can already talk about in the present tense.

Anna and her co-authors are not the first team to survey climate-related issues amongst producers, and perhaps we will review other similar papers down the road.  But one interesting angle, beyond the normal suite of factors like age or education or political affiliation, that this study examined was producer scale.  Does producer scale impact willingness and ability to adopt climate-adaptation practices in maple production?  Let’s first clarify what a climate-adaptation practice is.  Consider the effects of shifting tree composition in Ohio.  That shift will likely lead to increased dominance by red maples.  Adapting to that effect would be to tap a diversity of maple species, not just sugar maples.  Failing to adapt to shifting tree composition could lead to reduced tap quantity because of unwillingness to tap anything except a sugar maple.

With that point clarified, two over-arching findings stuck out to me.  First, nearly 90% of all surveyed producers agreed that maple syrup production is closely linked to climate, and only 15% of small producers (<2,000 taps) believed climate-induced impacts would be a net positive to their operation.  How often does that lop-sided a percentage of folks agree on something?  Not often.  Second, larger producers are more willing to adopt more climate-smart adaptation practices than medium or small producers.  And guess what, political affiliation had nothing to do with any of the above.  Yes, you read that correct – climate and maple is apolitical.

Before we dive into the specifics, know that it took 10,000+ taps to be categorized as a large-scale producer in this study.  Quite frankly, most US producers in this study were small or medium, and most Ohio producers would certainly be “small.”  A final caveat, before we dive into a few specifics, is that among the 354 survey respondents in the study, only 12 hailed from the Buckeye State.

Canadian producers, which are also more likely to be the “large” producers, are more apt to fertilize their sugarbushes and practice intensive silviculture, but significantly less likely to increase the number of trees they are tapping.  I can see the practice of fertilization.  Personally, I believe all maple producers – regardless of scale, should practice active silviculture in their maple woods.  The goal of active silviculture after all should be healthy maples!  The last point about tap quantity is a hard one to understand…until you discover that rules enforced by the Federation of Quebec Maple Syrup Producers prohibits most producers from increasing their tap count.  Given that most large producers are also Canadian, the pattern of stubbornly maintaining tap count then makes some sense.  I certainly learned something new with that fact pointed out to me.

“Medium” producers were more likely to tap earlier, implement rigorous sanitation practices, and stay up to date on latest research finding than “small” producers.  Multiple factors could be play as “large” and “medium” producers increasingly differentiate from “small” producers.  I’ll quickly highlight just one factor as I grapple with the study’s findings.  Some “small” producers are undoubtedly hobby producers.  Making syrup is fun and as soon as it seems like work, well…where’s the fun?  I can easily see why an individual producer with 100 or 2 taps would decide not to invest in high vacuum efficiencies.

Putting aside scale of producer and applying the lens of producer age, we learn that tapping red maples and using high vacuum systems are less likely among older producers.  Only focusing on the practice of tapping red maples, this fits within the pattern of a traditional no-no generationally passed down.  Not until more recently has University research been dedicated to documenting production potential in alternative maple species.  What’s that saying about “old dogs?”

I’ll wrap this review up by pointing a finger back at myself – a maple educators.  This sentence from the study speaks for itself, “Only 20.9% of producers…thought that information on climate change impacts on the maple industry was easy to access.”  Yikes, that is a huge wake-up call and harsh criticism for the University community.  Hopefully this site can help address these knowledge gaps for Ohio maple producers, and this Monthly Maple Review series is part of the solution.

Borers, Feeders, and Galls Oh My!

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Ohio Maple Days 2022 did not disappoint.  The food was fantastic, the vendor room crowded, and the presenters shared a wealth of knowledge of expertise across a wide range of subjects. Dr. Curtis Young, Entomologist, Extension Educator, and Associate Professor, expanded our knowledge regarding maple pests.  Many that most of us were already aware of, spotted lanternfly or Asian long-horned beetle for instance, and lots of lesser known pests.  Before we get into a few highlights, be sure to mark your calendars for next year’s conference December 8th and 9th!

Any attempt to summarize Dr. Young’s talk would fail due to the sheer amount of information that he is able to share in such a short amount of time.  And no notes!  Truly a wealth of knowledge.  Rather than attempt a synopsis, this is a great opportunity to share some general resources and up-to-date information for some of the more alarming maple pests we face here in Ohio.

University of Kentucky Extension has a great webpage that quickly catalogs a wide range of known pests across 4 general categories – leaf feeders, sap feeders, borers, and galls.  While most maple pests are just that – pests, similar to how most of us view the average mosquito, a few present a real and present danger.  That said, if your maple trees are stressed already, a relatively harmless pest can be the proverbial straw that breaks a camel’s back.  Moral of that last sentence, practice healthy silviculture and sugarbush management to ensure your trees are healthy and vigorous.

Asian long-horned beetle are always mentioned in these presentations.  Thankfully, in Ohio at least, control and eradication of Asian long-horned beetle is a success story that we seldom get to herald in the fight against invasive species.  While we keep our eyes out for future infestations, spotted lanternfly has rapidly expanded its range and our state records now show several counties with positive detections.

An excellent website to stay abreast of issues facing plant, shrub, and tree health is Buckeye Yard & Garden onLine where Dr. Curtis Young and many other experts from Ohio State University Extension provide “timely information about Ohio growing conditions, pest, disease, and cultural problems.”

Upcoming Webinars – Weather & Worms

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Two webinars are coming quickly on the calendar.  And yes, you read the post’s title correctly…

First, a perennial favorite speaker is coming to Future Generations University “Out of the Woods” seminar series next Thursday, January 19th.  None other than Aaron Wilson from Ohio State’s Byrd Polar and Climate Research Center will be discussing the weather and how it impacts your sugarbush.  If this talk is anything like usual, he delivers excellent information about general effects and then dials it in to the prognostications that seem to be developing for the current and upcoming sap season.  Click here to register – next Thursday night at 7 PM. 

And second – Wednesday, January 25th at 3:00 PM, Penn State Extension will be offering a webinar called “Stressors of Maple: Dieback and Mortality.”  The webinar will be recorded and sent to everyone that is registered.  The webinar will host speakers from Michigan Technological University and will cover what maple decline is, what is driving maple decline, how earthworms impact maples and native forests, and how to respond if you have maple decline.  For more information and to register for this January 25th webinar, click here.

Upcoming Maple Events

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There is a flurry of upcoming maple programming and events to consider.

Of course, the International Maple Conference just concluded up in Lacrosse, Wisconsin held over the latter part of last week and weekend.

Next weekend, the Ohio Maple Producers Association are convening for a great line-up of food, fellowship, tours, and syrup contests.  Dates are Nov 4-5 and additional details can be found here.

Just a few days after, Seldom Seen Farm will host a Woodland Wednesday program from 4:00-7:00 PM on November 9th.  In collaboration with Geauga Soil and Water Conservation District, Geauga County Farm Bureau, NRCS, and host Seldom Seen Farm, speakers will discuss the relationship between modern forestry and the maple industry.  Specific topics will include thinning, tree crown development, soil conditions, and maple tubing in the sugarbush.  All are welcome to this free outdoor event that will benefit the landowner and woodsman alike.  Please RSVP to Kevin Holy at 440-596-9717 or via email (kevin@seldomseenmaple.com).

Lake Erie Maple Expo, the following weekend of November 11 and 12, will host its usual showcase of vendors, talks, and all and everything else maple.

Completing the first half of November flurry, Penn State Extension Educator Brian Walsh will discuss what is known about the spotted lanternfly and observations about maple trees that provide insight as to the impact the insect could have on the industry.  Pennsylvania has endured a longer stint of spotted lanternfly infestation than Ohio, and we can learn more about what to potentially expect by seeing what has been learned by our neighbors to the east.  Register for the November 16 – 10:00 AM webinar here.

How to Combat Buddy & Sour Sap – The Path to QUALITY Syrup (Part 4)

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Prevention of sour sap is all about sanitation. Here are a few things to consider when developing a sanitation plan for your maple operation. As soon as the previous season ends, producers using tubing need to clean and sanitize their lines. There are many ways to do this, but the most important thing is to make sure it gets done. As the new season approaches, inspect your lines for sanitation problems, consider replacing not only the spouts but the drops and tees if needed. As the new season begins, producers using high vacuum should consider running your vacuum 24/7 to keep your lines clean, clear, and cool.  During the season, make sure you wash your holding tanks often to prevent microbial scum buildup.

Where sap is held for a long period of time, avoid using plastic tanks for long term sap storage. Plastic is porous and retains bacterial inoculum that will quickly generate bacterial growth. These plastic tanks are often referred to as commercializers, named after the old commercial grade of syrup that nobody wanted. Once a plastic tank becomes contaminated, they are almost impossible to clean and should be replaced.

In the sugarhouse, making quality maple syrup starts with your reverse osmosis (RO) unit. Concentrate must be evaporated as soon as it comes off the RO. Bacteria multiply quickly in concentrated sap. This is the result of a higher percentage of sugar in the concentrate. There is also an increase in the sap temperature as it moves through the RO. It may enter the RO at 40 degrees F or less, but when it comes out, it will be closer to 50 degrees F. High Brix concentrate, elevated sap temperatures, and a warm sugarhouse are the perfect recipe for taking good sap and turning it into a microbial cesspool if not careful. This is one of the reasons many producers are now considering using refrigerated milk bulk tanks to store concentrate. This cools the concentrate and allows more time to manage the boiling process.

Producers often accept the fact that concentrate left on the evaporator overnight will produce a darker grade syrup, at least until fresh sap is introduced.  This does not have to happen if managed properly.  Small evaporators should be drained if possible. Larger evaporators can be equipped with a wash system that allow the entire evaporator to be cleaned and drained. Once the syrup leaves the evaporator, the process of sanitation continues. Syrup should be filtered and placed in a stainless-steel drum after being reheated to at least 180 degrees F. There is an inherent risk when you attempt to drum syrup at lower temperatures. Spoilage happens when barrels are packed at low temperatures. The hot syrup and cold barrel causes condensation (H2O) which combines with the remaining air in the barrel ultimately resulting in mold and fermentation.  It is best practice to place filled barrels in a cool place like a basement or a barn that does not heat up. Another practice worth looking into, is to build a cool room by equipping  a small insulated room with an air conditioner.

When you re-open a barrel of syrup, you should have syrup that is ready to bottle. When you bottle your syrup bring the syrup back up to 185 degrees for packing. Syrup packed below 185 F is subject to spoilage and reduced shelf life. Going above 190 also creates several problems. And if the syrup peaks above 200 F, the syrup will start to foam, and niter will start precipitate. The only solution for this scenario is to filter the syrup again. You will also overheat your jugs causing them to contract and suck in if they are not 100% filled. Plastic jugs should always be filled within a half inch of the top and laid on their side to kill any bacterial that may have found its way in the jug.  If you pack in glass bottles, make sure you put your bottles in the oven at 200 degrees for a few minutes. Hot glass will not condensate moisture and you can eliminate most problems with this simple step. It is always good to pack several times over the course of the year to maintain the highest quality in your syrup.

Many years ago, there was a use for commercial outlet for sub-standard syrup. The majority was sold to the tobacco industry. It was used to sweeten chewing tobacco. That outlet for the most part no longer exists. There are places where substandard syrup could be used but its objectionable flavor drastically lowers its value. For this reason, there is now a movement to prevent this type of syrup from getting into the market. Bulk buyers no longer want to handle sub-standard syrup and if they buy it they are not going to pay very much for the product. In addition, there is a currently an effort by the International Maple Syrup Institute and others to promote educational programing to raise producer awareness about ways to avoid producing this kind of syrup. The reality is that there is very little economic return from sub-standard syrup production. With rising costs of equipment and inputs the production of anything less than top quality saleable syrup in today’s high demand market is foolish.

There you have it – a 4-part series starting with a lesson on phenology and how to track growing degree days, relating growing degree days to tree bud development, appreciating the differences between buddy sap and sour sap, taking sanitation seriously at every single phase, and PRESTO! viola! alakazam (if only it were that easy!!) – you are making QUALITY maple syrup!

Off-Tasting Syrup: Understanding the Culprits (Part 3)

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Now that we have talked about tree phenology and maple buds and growing degree days, let’s the talk more about the main prize of every sugarmaker’s dream – QUALITY syrup!  As we get ready to embark on a new maple season, let’s go over some of the things that will help you to improve the quality of your syrup in 2022. We all know that paying attention to detail in the woods will pay off with big rewards; however, the place where paying attention to detail is most important is when the sap or concentrate is on the evaporator. The finishing process can make or break your operation. Maple production is becoming a very competitive business, and the producers making the highest quality syrup will rise to the top.

Here is an oversimplification of what happens during the syrup-making process.  Once bacteria are introduced into the sap, a conversion of sugars takes place. A portion of the maple sap, which is almost 100 percent sucrose, is converted into glucose and fructose. This portion of the sugar content makes up the invert sugars present in syrup. When the sap is heated (The Maillard Reaction – something you can read more about here) the color of the syrup and the flavor of the syrup is formed, largely based on the amount of glucose and fructose sugars and other factors happening at the same time.  Thus, the level of microbial interaction plays a vital role in determining the color, grade, and corresponding flavor profile of the syrup produced. So, as you can see not all microbes are bad, in fact they are essential to everything we love about maple syrup!

Sap flowing from the maple tree is sterile, so where do the microbes come from?

Microbial activity begins as soon as sap is exposed to the outside environment. Early in the season microbial development is slow due to the normally cold temperatures, but once warm weather arrives (above 50 degrees F), more and other strains of microbes begin to multiply in the sap. As the microbes interact with the sap, the syrup produced darkens and develops an increasingly bold and pronounced maple flavor. Microbe colonies continue to expand eventually resulting in very dark and viscous syrup with an unpalatable strong flavor. Because this degradation of the sap is more likely to occur at the end of the season, low quality syrup is often associated with tree budding which happens at approximately the same time.

If you did a taste comparison, you would notice is a definite difference between buddy syrup and sour sap syrup. Buddy syrup has a chocolate flavor akin to what a Tootsie Roll tastes like while sour sap syrup has a bitter sometimes fermented taste that stays in your mouth. If you boil buddy sap, it will produce a pungent unforgettable smell. Sour Sap thickens to the point where it cannot be evaporated and will be difficult to draw off the evaporator. In extreme cases, you can pour a stream out and it will suspend in midair. This is referred to as “ropey syrup”. Sour sap is a result of intense microbial activity that builds anytime during the season when environmental conditions are right for bacterial growth. Buddy syrup comes from sap collected when the buds emerge naturally from the tree. This is a normal physiological growth stage that occurs every year.

Both processes require and progress with seasonal warming. In a normal season, the two tend to occur simultaneously and accelerate at the end of the season. Though the two are correlated, it is important for producers to understand the differences if you want to avoid the problems associated with each.

 

Maple Buds and the Story They Tell (Part 2)

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We have all heard it (or said it) – once the maple trees ‘bud out’ the sap collection season is done.  “Done” meaning the sap has become buddy and making syrup for the season is over.  Our eyes see it and we know to expect it, but we all hold out for just one more day of collection before the tide turns.  That day or the very next, the sweet smell of sap turns sour.

The good news is you don’t have to rely completely on your nose when boiling that last batch of sap.  Keep a close eye on how the tree buds develop as the season progresses.  When you start the season the buds are tight.  As the season progresses and the weather changes towards spring, the tree buds tell the story. We can use our eyes to track bud development as the season progresses, the weather warms, and making syrup draws to a close.  The good news is that this progression is somewhat predictable if one understands how something called growing degree days (GDDs for short) correlate.  Read Part 1 released last week to learn how you can start tracking GDDs and incorporate them into your season planning.

Using a 60-power spotting scope we took pictures of our trees on March 17th, 23rd and 27th during the 2021 sap season.  The bud progression is for sugar maple and a red x silver native hybrid maple that are present at the Ohio State Mansfield sugarbush.  For reference, we deemed our sap no longer worth collecting on March 21st.

First the red x silver “mystery” maple – in the March 17th photos, the hybrid’s buds are noticeably swollen but the flowers have not burst forth yet.  In the branch I’m holding, you can see the flower buds cracking open with the leaf bud still tightly closed in the center (black arrow).  This is crucial to understand because trees have both flower buds and growth buds which break at different times and have different impacts on the sugaring season.

By March 23rd, despite the difficult lighting, the buds have clearly flowered.

This is even more apparent on March 27th when I took the last set of photographs.  Examine the leaf bud (in the black circle) which is protruding more but still closed surrounded by the bright red maple flowers.  Our operation’s sap edged towards being “buddy” in the last 2 days preceding the red maple buds popping completely out.

For the sugar maple photos, the differences are more subtle and the progression is slower – a timeline we talked about in Part 1 last week.  In the March 17th pictures, the buds were barely noticeable at the ends of the uppermost twigs of the trees; however, buds were more prominent 6 days later.

By March 27th and nearly a week after we had closed down the sugarbush, sugar maple buds were elongated and swollen and obviously scaled but not yet officially burst open.

All in all, this was a great exercise to watch how trees go through the season’s progression as the weather changes.  A set of binoculars is a handy tool for the sugar maker; pick some key trees in your woods and watch their buds next year.  Better yet, keep detailed notes and be a studious observer of 3 primary things: sap quality, tree bud development, and those GDDs we mentioned earlier.  Once you are familiar with what the bud progression looks like relative to your tree’s sap production, you will have information to align alongside GDDs for anticipating when the end of the season is near.

The Ohio State Phenology Calendar: Understanding Nature’s Biological Clock (Part 1)

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A special thanks to Denise Ellsworth from OSU’s Department of Entomology for contributing her phenology expertise that makes this article possible!

Phenology, sometimes referred to as the world’s oldest science, is the study of recurring biological events and their relationship to weather and climate. Examples of phenological events include bird migration, flowering of plants, and the seasonal appearance of insects. Because the growth and development of plants depend on temperatures, phenological events of plants, such as bud swelling or flowering time, may be useful for monitoring short-term weather patterns. Likewise, scientists can detect long-term changes due to climate change by tracking the pattern of phenological events over many years.

Insects emerge earlier in warmer years than in cooler years, and plants bloom earlier too. The critical assumption in the use of plant phenology to predict other biological events is that the phenological sequence (the order in which events occur) remains constant from year to year even when weather patterns differ greatly. It is no mystery, even to a novice sugar maker, why plant phenology matters in maple. The quality of maple syrup is at stake! Once the phenological calendar for a sequence is established, the biological calendar is easily monitored to anticipate when maple syrup quality drops. If phenology can be grasped, this can greatly simplify the logistics of planning and scheduling monitoring programs, post-season clean-up and sanitization, and other critical activities. And using phenological sequence is valuable to a whole host of applications beyond just maple—beekeepers, naturalists, and gardeners also use the predictable patterns of nature to predict plant bloom and other biological activity.

On The Ohio State University Phenology Calendar website, degree-day data and related plant bloom and pest emergence sequences are accessible for any location in Ohio.  A degree-day is a measure of the amount of heat that accumulates above a specified base temperature during a 24-hour period. A degree-day is also referred to as a growing degree-day (GDD), heat unit, or thermal unit. One GDD accumulates for each degree the average temperature remains above a specified base-temperature over those 24 hours. Several degree-days can accumulate during a 24-hour period.  However, it is important to understand that degree-days have meaning only in relation to the base temperature that has been specified. The Ohio State Phenology Calendar uses 50 degrees F as the base temperature. To provide an example, if the average temperature over a 24-hour period is only 47 degrees F with a base temperature of 50 F, no GDDs would accumulate. However, if the 24-hour average temperature was 55 degrees F, 5 GDDs would be added to the phenology calendar (more on degree day calculation here).

To inform The Ohio State Phenology Calendar, daily temperature data from 12 OARDC Research Stations and three USDA-ARS weather stations located throughout Ohio are used to calculate cumulative GDD in real-time.  Calculations for locations between weather stations are extrapolated from climatic isotherms for Ohio.  Upon entering a date and any Ohio zip code, degree-day accumulation for that location is calculated, and the user is directed to the appropriate spot on the phenology calendar to determine what plants are blooming and what pests are active in their locale.  By scrolling through the full phenological calendar, it is possible to see what blooming and pest events have already occurred, as well as what has yet to occur.  And by clicking on the Summary tab, you can get a year-by-year breakdown of GDD count for the same date and zip code location across the past 6 years.

It is important to define a couple terms as we launch into species-specific phenology.  First bloom is defined as the first flower opening to expose sexual parts. Full bloom is when just one out of twenty buds is still closed while all others are open to expose sexual parts.

Of particular interest to maple producers, silver maple is listed first with 34 GDD at first bloom. A bit further down the sequence, silver maple reappears with full bloom at 42 GDD.  Red maple first bloom follows at 44 GDD just after silver maple full bloom. Red maple full bloom averages 75 GDD.  Sugar maple is not currently listed on the GDD calendar; however, it is believed that sugar maple tracks very closely with black maple – another of the “hard” maples.  While there is some uncertainty about the exact GDD timing for sugar maples, they are definitely “late bloomers” as compared to their “soft” maple counterparts.

The consistency in phenological sequence from year to year demonstrates that even one year of observation is useful to expand the phenological sequence to other plants or insects not included on the OSU calendar. This means that users can readily create, expand, and customize their own biological calendars by observing plants in first or full bloom and taking note of the GDD for that date on the OSU calendar. Many observers use a journal or excel file to track plant and insect activity from year to year, adding in new plants or insects of interest. These calculations can even be made by referring to photographs that show first bloom or full bloom; the photo’s date and location can be entered on the OSU calendar to determine the GDD for that event. Insect observations should be of developmental stages, such as egg hatch or adult emergence.

For the maple producer, understanding the predictability of nature’s patterns is crucial for better anticipating the end of each maple season. For years and years, sugar maple bud break was the traditional visual signal to take down buckets and end the sap season. Unfortunately, lots of poor-quality sap was made waiting for those first buds to break. Now we know that physiological changes occur within the tree prior to actual bud break that bring seasons to a close earlier. And sanitation issues that result in “sour” sap (due to bacterial build-up) halt most sap seasons before “buddy” sap is rampant. While we are excited to continue tracking sugar maple performance relative to GDDs, keeping an eye on the 100 GDDs mark is a rough indicator for when things are winding down. Some woods will shut down earlier and others will stretch a bit later, but when the Forsythia approaches full bloom in your yard – which occurs right around 100 GDDs depending on variety – you can be sure the end of your sugaring season is nigh.