monthly maple review

Tapping & Timber: Monthly Maple REVIEW

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After a several months long hiatus from our REVIEW articles, we are going to dive back into a Quebec research 2’fer that examines the effects of tapping on sugar maple tree growth rate and timber accumulation.  The Ohio State Maple team hosted a day’s worth of Maple Madness as a stop along the Ohio Tour less than 48 hours ago.  While giving sugarbush tours, hands down the most frequent question I fielded was whether tapping hurts the trees.  While some research has attempted to answer this question over the past decade or so, 2 relatively new studies out of Quebec take aim on this subject.

The question “does tapping hurt a maple tree?” can be answered from multiple different perspectives.  You might respond by citing information about the small percentage of a maple tree’s overall sap that is harvested through the tapping process, even with a high vacuum system.  You might make an analogy that a taphole is similar to an insignificant injury and point out that healed tapholes are barely visible to the eye just a year or less later and the percentage of compartmentalized wood is miniscule.  You might have another way of replying to that question.  The article “Effect of tapping for syrup production on sugar maple tree growth in the Quebec Appalachians” and the paper “Assessing the effects of sugar maple tapping on lumber production” provide additional insights to this delicate topic.

Before we dive in, a few caveats:

  • Caveat #1 – this issue has been addressed by different studies through different research labs through time, I’m examining these 2 studies today because they are recent and both from the same geographic area, Quebec.  Perhaps we will address some of the other work conducted in this space in future REVIEW articles.
  • Caveat #2 – The studies are from Quebec.  Stated another way, these studies are not directly applicable to Ohio, but we can certainly learn from them regardless.
  • Caveat #3 – both studies are based on tapping recommendations that encourage tapping to begin when a tree is 7.5-9.1 inches in diameter.  This recommendation in comparison to more conservation guidelines that we teach locally of 10″ minimum before tapping layered in with the fact that growth productivity is higher in Ohio than Quebec, and we have additional reason to not assume 1 to 1 transferability of results.

The study that focuses on tree growth rates was conducted by a foursome of researchers (Ouimet et al.) back in 2021.  They examined tapped and untapped trees within 7 Quebec maple woods on vacuum tubing systems.  The normal stringent criteria were applied to ensure trees in each group were as similar as could be except for the main treatment variable: tapped or not tapped.  Ouimet and crew worked off a primary hypothesis that tapping sugar maple trees would remove enough of the non-structural carbohydrates (sugars) that tree growth rates would be higher in untapped trees versus tapped trees.  Restating their hypothesis another way, extracting sap from sugar maples is in direct competition with resources needed for tree growth.

What did they find?  In 6 of the 7 sugar bushes, there was no effect of tapping on tree growth rates.  In the 7th site however, tapped trees grew 33% slower over the tapped year period (10 years) than did the untapped trees.  A partial explanation seemed to be that soils in that particular forest were strongly Ca-deficient; however, similar decreases in tree growth rate were not observed in 2 other woods that also suffered from low Ca levels.  Truth to be told, the team was scratching their heads a bit over the inconsistent results stating the “relatively small NSC [non-structural carbohydrates] allocation to syrup production might explain why we did not find a consistent tree growth response to tapping.”  In the most elementary of terms, tapping did not seem to trouble the majority of trees in the study.

The second study coincidentally also featured a four-person research team, and the research utilized data from 17 different sites within Quebec’s public forests.  Forest stand management scenarios (how and when to harvest trees) and lumber yields were simulated using a model that gathered data from over 2 thousand individual trees.  If taphole-stained maple lumber does in fact have niche value in local and regional niche markets, I would quibble with blanket statements such as the one they provide in the Introduction citing the National Hardwood Lumber Association – “Tap holes are considered defects, and they diminish the manufacturing value of boards.”  But the purpose of the work is clear, does tapping affect traditional lumber value of sugar maple logs?


Photo: Firth Hardwood Export Logs

What did they find?  Unsurprisingly, the answer is yes.  Of course tapping reduces net lumber volume in sugar maples, and tapping reduces the probability of an individual tree yielding a 10 foot saw log.  The details are what I found especially interesting.  Trees in the study were binned into 4 different health categories.  Trees with fungal infections, rot, or noticeable crown dieback were impacted by tapping more than trees that were healthy by visual measures.  While this too is unsurprising, I was most impressed by the findings that tapped sugar maples have a 85-90% chance of still yielding a 10′ saw log.  However, net lumber volume is still markedly reduced by tapping as the vertical segment of the trunk sectioned by the lowest and highest tapholes (or “butt log”) is defect.  Guillemette et al. concede in the very first paragraph of the Discussion that their results do not account for “craftspeople sometimes use these butt logs to produce boards with specific features resulting from tap holes or stain.”  I appreciated this admission.  Even so under a more traditional notion of what is valuable maple lumber, a notable rule of thumb emerges from their Implications for Management.  “Tapping reduces the net standing volume of sugar maple timber by approximately 40% and reduces the harvestable volume after the first 30-year cycle by approximately 40%.”  Economic modelling of one-time profits due to timbering need to be compared to the year-over-year return on investment from sugaring a maple woods, but the study does provide some interesting ways to frame and think about our original question – does tapping hurt a maple tree?

More Benefits of Maple: Monthly Maple REVIEW

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September’s REVIEW piece bangs the same exact drum as our August post.  Put simply, the benefits of maple syrup are VAST, and this article by Faez Mohammed and team expand the discussion beyond nutritional to also include pharmacological and sensory attributes.  how do big trees make baby trees and what factors promote or inhibit that process.  In case you are interested in reading the full article which was published just over a month ago, “Nutritional, pharmacological, and sensory properties of maple syrup: A comprehensive review” is available here.

While this article is not presenting new research, the authors are doing the hard work of sampling the existing literature and drawing together a synthetic summary of what many many others have discovered in the past.  95 total research articles factor into this particular review.  Here are some interesting facts and tidbits that I found interesting as I read through the paper.

1) A major reason that maple syrup has a long list of nutritional benefits and something like white granulated sugar has a long list of known negative impacts is that maple syrup is NOT processed by humans as a refined sugar, instead maple syrup is processed as a source of carbohydrates.

2) Maple syrup is often compared to other natural sweetener alternatives.  Maple syrup contains 60.5 grams sugar per 100 total g.  This is less sugar than honey (68 g), molasses (74.7 g), and of course high fructose corn syrup (75.7 g).

3) When we say something is an antioxidant, we are referring to a substance that reduces free radicals that are loose like a “bull in the china shop” wreaking havoc on cells and cell membranes.  For something to arrest and capture free radicals is to possess antioxidant properties.  Maple syrup is known to have antioxidant properties that come primarily from 2 types of compounds.  Without getting overly technical and going into specifics, early season syrup has anti-oxidizing properties due to 1 set of compounds, and syrup made from sap harvested from the second half of the season relies on a different type of compound to chase down and capture free radicals.  That is cool!!

4) When we say something has antiproliferative properties, we are referring to a substance that keep cancer cells from multiplying quickly and without impediment.  It turns out maple syrup has these properties too!  But some maple syrup is better at slowing the growth rates of cancer cells than others.  Past research has found darker color maple syrup has a greater ability to slow harmful cell production than lighter grades of syrup.  Certain phenolic compounds register higher in darker colored syrup, and it is believed these substances are the active agents at play in antiproliferative defenses.

5) If you can get your hands on this article, it is absolutely a great resource.  I could list a number of additional points that reflect the general tenor of #3 and #4, but suffice it to say this post would grow real long real fast.  Again, here is a link to the abstract and research article in full.

I want wrap up this REVIEW by focusing on a small subsection within the larger article titled “Effect of maple syrup production processes on its nutritional value and component bioactivity.”  In other words, what should the maple syrup production process look like to enhance and bolster the nutritional and medical benefits of finished maple syrup product?  Here are a couple quick takeaways in closing.  Antimutagenic (preserving DNA integrity) properties seem to be highest in the earliest lightest color syrup made in the season.  Darker syrup grades are better equipped to fight cancer cells.  Drying syrup (making some value-added products) reduces total phenolic content (the agents responsible for antiproliferative defense) and antioxidant capacities.  This is my own two cents, but I get the growing sense that investigating the intricate and minute details of maple syrup in terms of its chemical structure, molecular compounds, and different properties, traits, and characteristics is like a medical explorer penetrating the deepest and darkest most remote corners of the tropics where previously undiscovered plant species may hold the spark to the next game-changing pharmacological revolution.  Remarkable stuff!!

 

 

Maple Nutrition: Maple Monthly REVIEW

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You might have spent some of the last month or so under a rock if you have not caught at least a glimpse of month’s REVIEW article, actually presentation.  Much ado has been made of the research presented at the 2023 American Society for Nutrition conference, “Substituting refined sugars with maple syrup decreases key cardiometabolic risk factors in individuals with mild metabolic alterations, a randomized, double-blind, controlled crossover trial.”  The hubbub surrounding the research has landed the work across major news outlets, morning talk shows, health blogs and podcasts, and of course, the Maple Syrup Digest.

Do some searches for Dr. Andre Marette and Dr. Marie-Claude Vohl’s recent research trial or open the latest issue of the Maple Syrup Digest, and you will have tons of information at your fingertips.  Here’s the skinny on the research.  You or I would recognize the study participants as normal-looking, average Americans – not fitness models, but certainly not too unhealthy either.  Everybody in the trial participated in both sides of the experiment, but participants did not know when they participated in each half.  The beauty of this design is that each participant serves as his or her own control for optimal comparability.  In one half of the experiment, participants supplemented their daily nutrition intake with a flavored sucrose syrup, and then participants flip-flopped to consuming a couple tablespoons of the real McCoy – maple syrup.

Here are the key takeaways put as simply as possible:

1) Maple syrup helped participants manage their blood sugar levels, which has obvious implications for diabetes-related risk.

2) Maple syrup consumers had a lower blood pressure, which reduces risk for cardiovascular disease.

3) Maple syrup slowed the accumulation of android fat, a double whammy health benefit.

In short, this new research trial is some of the clearest and most irrefutable evidence for maple syrup health benefits yet!  In a more wordy paragraph and excerpted from a 2022 review paper on maple syrup, here’s a great synopsis of the health benefits of maple.

Of the many natural sweeteners, maple syrup is recognized as a much superior alternative to refined sugar for not only its mineral content, but also for its high concentration of phenolic compounds with bioactivity properties, i.e., anti-mutagenic, anti-radical, antioxidant, and anti-cancer.  Compared to dextrose, corn syrup and brown rice syrup, maple syrup brings about lower glucose and insulin responses, which make it a healthier substitute for refined sugars in our diet.

Memorize that block quote to recite next time a potential customer is waffling at whether or not to pony up some hard-earned cash for your delicious maple syrup.

Maple Regeneration: Monthly Maple REVIEW

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July’s REVIEW piece lands on the subject of maple regeneration.  Put simply, how do big trees make baby trees and what factors promote or inhibit that process.  This review comes courtesy of a doozy of a 2021 titled paper “Complex drivers of sugar maple (Acer saccharum) regeneration reveal challenges to long-term sustainability of managed northern hardwood forests.”  The team of authors, all from the mitten-shaped state to the north, was led by Catherine Henry from Michigan State’s Department of Forestry.

It goes without saying that it requires a whole bunch of seeds to hit the forest floor in order for a single tree to reach maturity decades later.  But just how complex is the regeneration struggle for sugar maples?  After all, despite a lifespan of 300 years give or take a century, if mature sugar maples do not replace themselves with seedling, sapling, and teenager sugar maples, the ultimate goal of passing one’s genes on to the next generation will fail.  Henry et al. examined research plots in 141 different forest stands to dig into factors related to sugar maple regeneration throughout northern Michigan.  The study sites were all managed with single-tree selection silviculture for decades, a forestry practice that is commonly regarded to be a great tool for regenerating and recruiting sugar maple.  It is important to note potential geographic differences between the study’s region and Ohio; not everything will necessarily apply to our state, but we can learn from their findings as well.

Sugar maples are generally considered to be shade tolerant tree species, and that is a fine way to categorize them from a 30,000 feet above the surface of the earth perspective.  Zoomed in up close however, a simple shade tolerant descriptor is insufficient.  Sugar maple regenerate best under conditions of intermediate canopy openings, and successful production of seedlings and saplings is optimized in larger single-tree gaps that are maintained or increased through time.  The truth is that while maple seedlings are technically shade tolerant, more light is required as regeneration grows into sapling sizes and beyond.  Prolonged deep shading stunts out maple regeneration, and it is important to remember that shade doesn’t just come from overstory trees; ferns, dense midstories of beech, and invasive plant infestations can all starve a cohort of seedlings of the light they require to become saplings and ultimately larger trees.  In addition to growing space, variables of deer browsing pressure, site quality (related to soils), and competing vegetation were considered.

The very first line of the study’s Results section reads as follows: “Stand-level sugar maple regeneration was highly variable within and among size classes.”  It goes without saying that nature contains tremendous variation, and this statement reinforces that idea.  Examining one forest stand and anticipating the next forest to behave identically is foolish, and taking one study and assuming that it directly applies to a novel new region is equally foolish.  All that said, there are absolutely some lessons to be learned.

Maple regeneration was most successful at intermediate basal area levels and at sites with intermediate quality.  Imagine an upside-down U where the peak is in the middle and the start of the curve and end of the curve are low, that’s essentially what the graph would look like.  This plays well with the Goldilocks analogy that we like to use for sugar maples – sugar maples favor conditions that aren’t too _______ but also aren’t too ________, just like Goldilocks didn’t dive straight into a bowl of scalding hot or freezing cold porridge.  The study had some educated guesses as to why this may be.  Excessive basal area (a forest stand that is overstocked) and too many sugar maples in the overstory casts deep shade that even the shade tolerant maple babies can’t survive.  Too few mature maples in the overstory may be limited by seed availability and more easily overwhelmed by deer browse pressure (see photo above).  Low quality sites for sugar maple, duh, did not have a lot of vigorous healthy sugar maples.  But high quality sites were often associated with higher deer densities that likely led to overbrowsing of seedlings and smaller saplings.  An additional explanation is that overstory maples grow so quickly on high quality sites that canopy gaps quickly close thus reducing understory recruitment.

https://oregonforests.org/field_collection_item/485

The study is published in the journal Forest Ecology and Management, and authors are encouraged to write a rather in-depth closing section called “Implications for management.”  In these parting paragraphs, Catherine Henry and her colleagues boldly comment that single-tree selection silviculture – a system that ought “to produce ample sugar maple regeneration” – is failing.  While the study’s results were highly variable, factors of deer overbrowsing, site quality, light limitation, and seed availability confounded attempts to successfully recruit sugar maples to the sapling size class in nearly 70% of plots.  The solution is not easy or obvious.  While the authors point to silvicultural harvest methods that open more growing space and release more light into the understory – namely uneven-aged group selection and even-aged shelterwood harvests – they acknowledge a different approach may exacerbate other problems (denser shrub densities, higher success of undesirable species).  Regardless of harvest method, a parting recommendation was that managers take deer population management seriously through increased hunting take or use of exclusion practices, such as wire fencing or natural slash walls.

Bringing this review home to Ohio, what are the over-arching takeaways.  While there are undoubtedly more to consider, I’ll quickly point to 3 recommendations.  #1 – Deer can destroy even the best laid plans, our state mammal HAS TO BE managed.  The best possible silvicultural plan can quickly unravel with too many deer.  #2 – Cutting a single tree here and a single tree there is not likely to recruit your next generation of syrup-making trees.  #3 – Work with a state or credentialed forester to develop a management plan for your woods.  They will understand the complexities and caveats to navigate a timber harvest and help you balance your objectives against the impacts of the past, the conditions of the present, and the goals for the future.

 

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!

 

Talking with the Trees: Monthly Maple REVIEW

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A brief introduction to this relatively new feature – Monthly Maple Review, which is now in its third month.  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.

After a more technical and heavy academic discussion of factors influencing bud break in sugar maples during our March review, I decided to explore a peer-reviewed article that draws from a much different perspective.  Biosemiotics is the study of signs and meaning in living organisms and systems (as defined by Springer Publishing – Springer has curated a quarterly journal dedicated to this topic for 15 years).  Biosemiotics, put more simply, asserts that life is based on signs and codes – a statement that straddles the line between science and philosophy.  “Food, Care and Sugar Maple Stand” by Jonathan Hope was published in 2021 in the journal Biosemiotics.  This article does not present any experimental research or new study, but rather challenges us to think about maple trees and our relationship with maple trees in a different light.

When we anthropomorphize, we assign human-like attributes to non-human objects or organisms.  For instance, a talking candlestick or feather duster imparted with human emotions in the movie Beauty and the Beast is a great example of anthropomorphizing.  In recent years, popular books such as The Hidden Life of Trees have popularized the idea that trees may have the ability to communicate and respond to one another through local and more extended networks.  This progressive notion certainly challenges a more narrow view of trees that relegates them simply to living cells constituting trunks, roots, leaves, and an annual cycle of growth.  Sugarmakers certainly hold trees in higher esteem than just such a rudimentary and crude description, it is after all maple trees that we put on a pedestal to admire, cherish, and prize them!  But trees communicating?  In the more human sense, that might still be a stretch for many of us.

The maple producer who understands the multitude and complexity of factors that impact a maple tree’s growth, health, vigor, and day-to-day performance through a sugaring season is keenly aware of just how responsive maple trees are to stimulus.  Jonathan Hope – the article’s paper – proposes that this keen ability to respond to changing signals and environments is a testament to the mindfulness of maples.  Enjoy the following passage.

“Running a sugar shack requires that producers learn how the biological engine of the trees works, or more precisely, that they understand the behavior of the trees…Understanding how maples groves function also requires that the sugarmaker learns, or becomes familiar with, what [Aldo] Leopold calls the ‘language’ of wildlife – through ‘semiosis’…this language could refer to many types of sign relations.  In other words, learning the language of trees depends on one’s readiness to admit that meaningful things happen to/in them.”

When we view trees as having and responding to a unique set of signals and languages, we also begin realizing that trees are connected to the soil, are dependent on and connected to the subsurface and surface water cycles, are potentially harmed and injured by non-native pests, are life providers and habitat for many native organisms, are intimately linked not just to the seasons but also to minute changes in weather and climatic conditions, …  What are those intimate links, those connection points – of course, these are the essence of ecology.  Everything is linked to everything else.  Are humans interwoven and part of that web and outside and distant from that web of connections?  I’ll let you answer that.

If we anthropomorphize and grant trees the ability to communicate, to respond to external stimuli, and to profoundly influence organisms in their sphere of influence, then perhaps it’s not a stretch to take the following quote serious.  “Humans can take care of each other, of other animals, of plants and natural environments; and inversely environments, plants and animals take care of themselves, and sometimes, take care of humans.”  I don’t believe this way of thinking is a big stretch for many maple producers.  We absolutely love our trees, and we understand that we are profoundly and deep rooted to our maple woods.

Here’s one final line from the article – certainly a far departure from a technical and verbose experimental study.

“So many relations interlace in a can of maple syrup…Maple sugar producers intervene on the forests and tinker with their semiosis, harnessing, and participating with the ‘energy pathways’…of food and care.  Eating and caring have always been marked by commensality.  Maple sugaring shows once more that this togetherness extends far beyond the limits of the human.”

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!

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.