sugar maple

Mini Maple Arboretum

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The new additions just keep coming at the OSU-Mansfield sugarbush.  12 trees were planted for a miniature arboretum right off the corner of the new maple pavilion.  With a collection of all the common maple species in Ohio, we are now better equipped than ever to teach tree identification workshops.  Sugar maple, boxelder, silver maple, black maple, red maple, “rilver” maple, Norway maple – single trees of some, multiple representatives of others.

A summer watering schedule, some mulch around their bases, and protection from the local deer herd should give these a great shot at surviving and playing a role in many maple workshops in the future.

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?

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.

 

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!