As part of our Tree Campus Higher Education Certification, we’re asked as an institution to summarize our year and activities managing our urban forest. 2023 has been, frankly, a year.
Our numbers for tree removals and plantings might seem a little off this past year, and are. The story is one echoed throughout the state, one of extreme weather events. I’d estimate in my 18 years here I’ve responded to 10-12 extreme storm events impacting our urban forest-ice, rain, wind, heavy snow, and the ilk. Of those 10 or so, 4 of them were last year, or more accurately in our reporting year, which starts roughly mid-December, when the information is due. Fortunately, we have a beautiful campus with a mostly healthy tree population, so while we lost some trees, we’re not panicking yet.
Trees do everything relatively slowly-germinate, grow, live, even die slowly, sometimes taking decades. Arborists speak of a ‘mortality spiral’-when a tree suffers a series of compounding minor injustices and slowly declines until it’s eventual, and often undramatic, death. Owing to this tree time, in arboriculture there are very few red flag moments, those ‘drop everything and deal with this problem’ panics. Most of mine tend to be trees that have fallen across roads or fire lanes. Recently, we removed the Holiday lighted tree from the center of the main quad, having found a major red flag.
The Lighted tree was a Norway spruce, located next to Storrs Walk on the way up to the Chapel. There are only a couple of spruce left, but in past years they had formed a line on either side of the quad north of the McCullough Gymnasium, making a border and windbreak to what was athletic fields and are now our quad.
Norway spruce is a widely planted fast growing tree, native to northern and central Europe. They tend to live about 300-400 years in their native range and grow 60-80’ tall. The branches rise and ascend at the upper levels of the tree canopy, but gracefully swoop and hang down at lower levels. This is thought to aid in shedding snow in northern climes, but also lend a grace and beauty to the tree. Their fast growth and evergreen status make them a very popular landscape tree, and the wood is prized for its excellent tone in stringed instruments. We have many large specimens scattered on all corners of our campus.
This tree has had lights on it since forever. It’s a pretty good slug of work yearly to keep lit, as the squirrels on campus seem to love chewing the wires. One of our landscape workers was doing a safety check of the tree before replacing some of the lights when he noticed holes in the ground at the base of the tree. He called me over to inspect, and I ambled over.
We keep a close eye on all our trees, but some more than others. Probably 20-30 are on a list of ‘risk’ trees that we inspect yearly, most often older specimens in prominent locations. The lighted tree was not on this list. It has been in poor health for the last 15 years I’ve been here, in part due to location. Much of the root system near the base of the tree is covered in concrete sidewalk. Looking at the crown of the tree the poor growth rate was evident-little new shoot activity and a thin crown with few branches. But not all trees have to be perfect, just safe.
The holes around the root flare were indeed concerning, there were multiple locations where clearly a chipmunk or something had burrowed underneath the root flare. This was not the red flag, though. The excavation did not seem to be recent, and was not accompanied by mounds and mounds of dirt around the holes. I took a small tool and tapped on the trunk, usually my next step after inspecting the root flare.
As I suspected, it sounded hollow, a low thunky sound that’s hard to describe. Healthy wood has a solid ringing sound, like it’s proud of its strength, a low muted thump is usually the sign of rotten wood, a loud drum beat means it’s hollow. Taking a drill with a long but very narrow drill bit I probed several locations on the trunk. The drill enters live wood slow and needs quite a bit of pressure to do down into the trunk, but on soft, rotten wood encounters no resistance at all. I discovered about 1” of live wood before drilling through what was clearly rot. I drilled up about 5’ and found it was a column of decay from the base right up through the main part of the trunk. Probing and drilling around the root flare didn’t seem to indicate decay.
This is called a heart rot-the heartwood of the tree being attacked and decomposed by fungi, in this case probably Phellinus pini.Not the red flag though! Picture an old brick building, it’s interior walls long gone, but the solid outer walls holding strong for years. A tree can be hollow and still be strong, or at least strong enough to stay upright. Heart rot breaks down lignin, the structural cell component that makes wood strong and able to bear weight. Of more concern are usually sap rots, fungal species that break down cellulose in cell walls and compromises the flexibility of trees.
The red flag appeared as I walked up to the tree right at the very beginning, although I wasn’t sure. It seemed to me like the tree developed a lean, about 3 degrees towards the east, now appearing to loom subtlety but menacingly over the north/south sidewalk. I wasn’t sure, though. Looking at the ground next to the trunk it appeared slightly heaved up on the west side, but not dramatically so.
A persistent tree myth concerns roots. Roots don’t go deep, certainly not as deep as the tree is tall, and very rarely do trees have a true taproot. Instead, most tree roots are found within the top foot of soil, extending out past the crown of the tree. Most trees will send sinker roots down from those lateral roots, driving about 2-3 feet down, like a tent stake. Norway spruce, however, don’t grow a lot of sinker roots, and as a species tend to be prone to tipping over, particularly in clay soils or high wind locations.
We have both here, high winds from the west coming downslope, and a heavy clay soil prone to seasonal moisture at the base of the ledge. Remember the soil was heaved on the west, and we also noticed a crack in the trunk. Clearly, something was moving around here. The technical, and scary sounding name is Root Plate Failure, and it’s a big deal. Trees can be hard to define, but I prefer the concept of them being a large woody plant that if it falls on you will kill you. Root plate failure means the tree has lost its support and can fall. Seeing ground heaved up next to the trunk means recent and dramatic failure, and for organisms that do everything slowly root plate failure is lightning speed in tree time.
Trees need three items to be considered a risk tree, here we have all three. One, a part that could fail (the roots), second, a mechanism for failure (wind, upcoming winter snow load), and three, most importantly, a target. The sidewalks, the fire pits, tent out in the quad, all this means many people walking around, a classic ‘target rich environment’.
It is, however, the lighted tree. All trees deserve thoughtful consideration before removal, but iconic trees in prominent locations up the ante. Giving it every chance we could, we did an old fashioned pull test. Sounds fancier than it is-tie a rope most the way up the tree on the trunk, stand way back, and have a couple people pull, simulating a windstorm. A couple people pulled towards Old Chapel, and I stood at the base of the tree and felt the trunk and ground. Sure enough, the ground beneath me moved, and the entire trunk flexed all the way to the base. This was enough of a red flag I started calling every manager/director/vice president I could reach while we had the rope in the tree, as this was best experienced live.
The International Society of Arboriculture certifies arborists in Tree Risk Assessment, and I usually run through the process before any removals. I feel like we owe it to the tree. Following standard Tree Risk Assessment protocols, with high consequences of failure and a somewhat likelihood of failure and impact I determined this tree presented moderate to high risk.
Mitigation options other than removal are non-existent. Tree based interventions, such as preventing wind throw by bracing or crown thinning are contraindicated in both the species and this tree, and there are no treatments for heart rot with such advanced decay. Given the high activity near the tree with the tent, fire pits, et.al, site-based interventions such as moving pedestrians or restricting access is not possible. Sadly, given the level of risk remaining, we felt like the tree should be removed. We waited until holiday break, to not make a lot of noise during final exams.
It’s not your imagination, the leaves are turning early this year. The reason will seem a little odd, but an understanding of a tree’s relation to time helps.
I feel for scientists that have trouble explaining the concept of time. We are lineal creatures, stuck watching time pass from one year to the next. As a horticulturist, my year goes from spring to spring. But anthropologists measure civilizations in centuries, not our ordinary years. How about geologists, counting back years by the billions. Most impressive, let’s talk about Astronomy. A light year-the time and distance it takes for a photon of light to travel. It’s called the speed of light for a reason.
Tree time moves differently. Trees do everything slowly-germinate, grow, mature, reproduce, even die. Some varieties live well within one of our short lifetimes, while others will live for generations. Time moves in fits and starts for a tree, on yearly cycles familiar to those in Agriculture. But they aren’t exactly lineal.
Remember last year? It was a growing season in a bitter drought, with no rain for most of the spring, all of summer, not breaking until late in the fall. It was hot, dry, and overall not very pleasant. I use our annual flowers we plant as a barometer, and the ones we planted around campus languished in the heat, and with the exception of some petunias none ever really amounted to much.
Our tree canopy looked OK though, and we had a nice fall. But this year, not so much. Maples are turning early, losing their already smaller than normal leaves about 4 weeks too soon. Oaks have been thin all year, with many dead twigs and branches. But it was a great growing season this year, with all flowers blooming non-stop since commencement. But not in tree time.
Sugar Maple by Battel- August 30
Trees are about a year off, marking time in their own way. They leaf out and grow all season, but reach back to the previous year’s sugars and energy stored from the prior growing season. Last year’s food is this years energy. So the drought last year certainly affected the growth of trees, but on tree time it doesn’t show up until this year. Weakened roots and inadequate resources in twigs and stems are stunting growth this year, and trees are wearing out and starting to turn early. Trees live a dual year, growing in the previous year while stockpiling for the next.
Same Maple as Above- September 18
Ordinarily in the early fall there are always a couple of trees starting to turn, and the easy answer is that they are weakened, stressed trees, our canary in the coal mine showing us underlying problems we might not have seen. Usually the Black maples east of Old Chapel turn fall color early, a problem of not only age but poor soil and compaction from living in a college quad for 200 years. This year, though, it is many, many trees. Primarily sugar maples, and mostly middle-aged trees, I’d guess 40-75 years old. In tree time for a maple you can think of them as 30-year olds facing a mid-life crisis with all the associated baggage. Primarily we’ve seen trees turning this year as ones in poor soil, either on ledge, or heavy clay. Above my house on Snake Mountain I see the canopy turning color, the relatively young forest showing it’s stress.
Snake Mountain, first Week of September
Younger, less mature trees are probably more in balance, and also flaunt vigorous and resilient root systems, while old, mature veterans had the massive underground roots to weather the (lack of) storms. Neither are showing the stress or are turning early.
It’s too soon to say what the fall will bring for color, but I’d sure like to see a little more rain soon, and a break in this mini heat spell we’re having. I do predict an early season, though, maybe longer if the oaks in the lower elevations can hang in there.
Abnormal weather always has people worrying about their trees and shrubs in the yard, and this winter is anything but normal. It’s the warm temperatures that are troubling, and many people have come up to me asking if the trees are going to be OK, or if the warm temperatures mean they are going to start growing.
Surprisingly, it’s the opposite, but this winter is a long ways from being worrying.
All temperate climate plants go through a period called dormancy, a mandated winter rest. This is triggered in the fall by not only temperatures, but by day-length. As the days get shorter the plants go through chemical and physiological changes to prepare for below normal temperatures. Once dormant, the plant needs sustained cold (500-2000 hours below about 40 degrees) to break dormancy and get ready to grow again in the spring. So, if this winter were to have stayed above about 50 all winter long the plants wouldn’t have started to grow, but the opposite, would just sitting there doing nothing.
And this makes sense. I’m always amazed at how smart and resilient plants are. While this winter is fairly unusual in the sustained warmth, we do see warm spells most winters, and plants that would start to grow at the first blush of spring wouldn’t be around very long. Breaking dormancy requires not only warm temperatures, but increasing day-lengths, longer spells of sunshine to break their winter gloom.
What can hurt a plant is freezing temperatures once dormancy is overcome. In trees, this is seen as frost cracking, long vertical fissures in the bark caused by water freezing in the xylem after warming up and moving around in the daytime. (Look at the trunk of the Sycamore in the triangle in Wilson Terrace outside McCullough)
This adaption to day-length also explains why plants with a local background (called provenance) is best. Day-length varies by latitude, with greater variation seen in northern latitudes. Take a tree from Vermont, move it down to Georgia (poor thing), and it will stop growing mid summer, as the days are a northern fall-like short. What I see quite a bit more, though, is the opposite. Plants grown in a nursery down south and moved up north don’t know when to shut down and start dormancy, and are often growing late into the fall, with their leaves and twigs freezing, unprepared for winter.
And while I’ve got your attention, let me take care of one final question I’ve been getting. No, your lilacs aren’t ‘budding’. Many people are looking at their giant buds on the ends of the lilac twigs, and think they are swelling about ready to pop and start growing. They were actually that large this fall, you just were too busy looking at fall foliage. Fear not.
Our barely green lawns across campus belie a hard fact this summer-it’s been dry. Very, very dry.
Funny, considering how wet it was in late spring, when it was almost too wet to do anything outside. The High Plains Regional Climate Center (kick ass website for weather geeks!) maps show we have 25% of the normal precipitation in the last two months, that’s a 6″ deficit of rainfall.
A general rule of thumb I can’t find a reference for but I always tell anyone is that Vermont plants need a 1/2″ of rainfall per week for optimum growth. We’ve had only about 1″ in all of August, and only 1″ in July. Most of that falling in one day, leaving our clay soils to dry out and become nearly resistant to small rainfalls.
The early leaves you see falling are signs of that. Trees in temperature zones such as ours develop wide, spreading root systems, not going too deep in search of water or nutrients. In fact, much of our campus is on ledge, with very little topsoil available, meaning plants need to go shallow and wide to root into the ground.
(My unsubstantiated theory is that Middlebury was founded where it is because of the ledge-poor soils make poor farmland, and why waste valuable agricultural soils and farmland on something as unimportant as a college? Farmland in 1825 was precious, hard earned space, so let the geeks have the hill, we’ve got crops to harvest)
These wide spreading root systems enable fast, efficient uptake of water and nutrients in poor soils and a short growing season. In ordinary years, this is ideal, but in dry years, this strategy can be costly. As you can imagine, the shallow soils dry quickly, and the plants don’t have the deep extensive root systems to find moisture in the lower soil profiles. Trees are gamblers, and they’ve got a losing hand this year.
Older Black maple in the Library quad showing drought stess in the upper canopy.
Flowers and other perennials show stress by wilting-the curling of the leaves cut down on the loss of water through the stomata (transpiration, if you want to flash back to high school biology). Trees react like that too, but also have the ability to shed leaves. We are seeing this now, and it may cause an early fall. The inner leaves on trees turn color and fall away, a survival mechanism. Inner leaves in the crown are not as efficient, they don’t photosynthesize as well, and therefore are not as “useful” to the tree as the outer, younger leaves. In desperation, the tree will shed the inefficient leaves ,brutally choosing the younger leaves to use the precious remaining water they have remaining.
Younger Red maple showing classic drought stress-note interior leaves browning with ends of branches still green
Closeup of foliage
We’ve had a little bit of rain this weekend, and more is coming, so luck it will come in time to prevent a wholesale dropping of leaves before your parents come up for fall family weekend. Snake Mountain above my house is starting to turn brown along the ledges, though, though, so lower expectations while you can.
Snake Mountain, early September. Note the brown stretches of foliage, probably on ledge.
Part of my absence from the blog would be teaching my winter term class “Trees and the Urban Forest” again this semester. It’s a great class, in a super rushed sort of way all winter term classes probably are.
As you may well be aware, the Emerald Ash Borer is a small exotic insect invading the country, and is poised to enter Vermont in the next couple of years. It has the potential to eliminate all the native Ash trees from the state. Just on the campus grounds itself we have over 200 large Ash trees that will need to be removed at great expense, and replanted. For a quick explaination, see http://www.vtinvasives.org/invaders/emerald-ash-borer .
Two years ago my winter term class took a draft of an emergency preparedness plan for the eventual arrival of the insect from the State Department of Forests, Parks, and Recreation and completed it for the Town of Middlebury. This winter term we are now drafting the plan for Middlebury College. This includes surveying all the Ash on campus, coming up with options for treatment or removal, giving replanting options, and running a computer model to calculate the lost benefits from these trees, including stormwater and pollution abatement, carbon sequestration, and energy savings.
We’d be honored if you could join us to present the plan to the College community on Wednesday, January 28th at noon, in The Orchard, room 103 in the Franklin Environmental Center. I understand it’s short notice (sorry!) and winter term is crazy in even a relaxing year. Please feel free to email me with questions, and if you know of someone else that would be interested, please let them know!
An extremely late spring-not warming up until mid May-left our landscape department short on time. We decided to postpone Arbor Day for a fall celebration, which we are holding next week.
Friday, October 10th, starting at 3:00.
We’ll start with a tree tour, this time focusing on the 10 (12) oldest trees on campus, but of course looking at more than that. We’ll start at the plaza at the Mahaney Center for the Arts, and walk through campus, eventually ending up at-
The west side of Battell-the corner of Battell Beach. After looking at the oldest trees on campus, at 4:30 we’ll plant what will be the youngest trees on campus. This is an area that saw a lot of tree vandalism (since cured! no damage this year). We’ll plant a half dozen or so trees on this corner of the beach, forming a little grove of color.
We’ll bring the food, and pre-dig the holes (oh, hydraulics and backhoe, my mistresses in crime), so all you’ll need to bring is a willingness to get your hands and knees a little dirty. Rumor has it there will be ice cream, cider donuts, and cider.
Come for the tree tour, or come for the planting, or join us partway after your classes. I’ve never done a tree tour during foliage season, so if you’ve gone on one before this one will have new stories.
Oh, and someone bring a frisbee. My 14 year old daughter just joined the high school frisbee team, and needs some practice.
Middlebury Magazine asked me to help with a story a month or so ago-they were looking for the 10 oldest trees on campus. Naturally, I gave them 12. There were a couple I just couldn’t leave off, and I walk around and still see a couple more I should have added.
Our campus features many spectacular trees, but surprisingly none of them are very old. Charles Baker Wright, Professor Emeritus of Rhetoric and English Literature , in the Middlebury College News Letter of 1931 talks of the story of campus trees, and how early in the history of the college was an old time notion that “trees wouldn’t grow on that hillside”, and how finally in about the 1830’s trees were planted wholesale, so thick that 70 years later Old Stone Row was a ‘veritable thicket’. Other areas of campus were likewise barren of trees, but didn’t have the donations to plant like near the Row. (as always, click on the picture for larger version) (especially to see the guys in the top hats)
Painter Hall in 1879
Painter Hall 2014 Note large Sugar Maple in picture, smaller in picture above
Some of the more dramatic pictures were taken along the back of Old Stone Row, on the road that was called Waldo Avenue.
Starr Hall 1890
Starr Hall 2014
Old Chapel 1875
Old Chapel 1895
Old Chapel 2014
Another sad chapter in the arboreal history of Middlebury is Dutch elm disease, which you can read much more about on other pages in this blog. Many areas presently bare of canopy from shade trees are previous Elm locations. This is not all bad-views from Old Chapel Road to Mead Chapel are greatly enhanced by the clear lines of sight.
A football game in 1900. Note the large elms along the west side of Painter Hall.
Same view 2014
The Spring issue of the Middlebury newsletter in 1981. Those are elm trees lining Mead Chapel walkway behind the May pole (which Facilities still has stored somewhere!)
2014-no May pole, and sadly no costumes.
Mead Chapel 1942
Mead Chapel 2014
Trees have a lifespan, like us, and it may be useful to think about tree years the way many people think about Dog years, but with no set figure to multiply. A redwood is ancient at 2000 years old, Bristlecone Pines date to 3500 years old, while a Poplar tree is old at 40. I’d venture to say an old tree for Vermont is 300, with precious few of them remaining.
A great grandma of all the trees on the Middlebury campus is a spectacular Bur Oak on the north side of the Mahaney Center for the Arts. Fellow horticulturists have estimated an age of easily 250 years old. Even in tree years, this one’s sitting on the porch rocker being waited on hand and foot. Trees like this, particularly oaks, were often left as boundary markers for property, and would be referenced in deeds and other legal documents. Aerial photographs of the area show this tree sitting next to Porter Fields, the combination baseball/soccer fields for years. It was there long before Baseball. I’ve written about this tree before.
Bur Oak at the Mahaney Center for the Arts
Paper Birch is, like all birch, an early successional tree, born to live fast, set seed, and die young. This tree isn’t very old in human years (I’m guessing about 85-90), but a mature birch is only 45-50. Proof that the right tree in the right spot will do wonderful things. This tree would be a grandparent too, one of those impatient ones yelling at the grandkids to keep off the lawn. It is safe to assume this birch was planted by the former owners of the house (the McKinley’s, I think, as that is what we call the house). Paper birch is an extremely popular landscape tree, but prone to many diseases which shorten the lifespan.
Paper Birch at the McKinley House
Nearby there is an elm along Route 30 next to the field house. I often wonder about all the construction it’s been watching over the years. Our guess is about 175-200 years old, an old survivor from when elms were transplanted from the woods to line the rudimentary roads of the new country. Old photographs show elms lining both Route 30 and 125, and we work hard to save the few that remain. This one’s middle aged in tree years, elms can go for many decades more than this one has been around.
American Elm at Field House
Norway Spruce grow fast when young, and get leisurely in their middle age. The massive Norway spruce north of McCullough was planted as part of a windbreak to protect the athletic fields next to the gym. Photographs from 1890 show already mature trees next to the baseball field, making this spruce easily over 150 years old. This tree is unusual for a Norway spruce in that the main stems are going through reiteration-the bottom stems forming entirely new trees, so looking up from the base into the canopy of this tree one would see multiple trees sharing a single trunk. This is much more common in Redwoods, but clearly this spruce dreams big.
Norway Spruce
Old Stone Row and the Main Quad in 1890-the large Norway spruce is in the closer row
Old Stone Row and the Main Quad 2014
Another perspective on the spruce row-1892
Same perspective as above 2014
Hepburn Hall in 1929
Hepburn Hall 2014
Up the hill from the spruce is a Black Walnut, probably 80-100 years old. It’s a middle aged tree as well, but was part of the extensive gardens of Maude Mason planted to the south of Hepburn. Most walnuts live to about 150 years old, but in the right location (which I hope this spot is) can go over 400.
Black Walnut at Hepburn
This walnut was probably planted as part of extensive gardens to the south of Hepburn at the beginning of the century. There was an old cottage nearby as well. The only remnants left of this landscape is a small garden with a plaque on the top of Stewart Hill dedicated to Maude Owen Mason, ‘who planned and planted and tended it from 1916 till 1937’. The garden has since been overcome by Mugo pine, a great example of breaking Tim’s first rule of landscaping-‘If it looks good when it goes in, it’s too crowded’.
Hepburn Hall Gardens in 1937
Hepburn Hall 2014
The former Battell Cottage, now known as Adirondack House, has two very large Austrian Pines in the front yard facing Route 125. A picture from 1929 shows one of them fully mature, making these an impressive 150 years old or more. In tree years, very old.
Austrian Pines at Adirondack House
Adirondack House-1929 Austrian Pine on right side
Adirondack House 2014
3 Black Maples, a close relative of Sugar Maple, remain in a row along Storrs Walk next to Old Chapel. This is the area of campus heavily planted in the 1830’s, and these are the only remaining trees left. At 185 years old they are reaching the end of their typical lifespan, but we are actively preserving them, and hopefully will be around much longer. I’ve written of Black maples in the past.
Black Maples at Old Chapel
Old Chapel -1895
Old Chapel 2014
Old Chapel 1900
Old Chapel 2014
Old Stone Row 1910-Black Maples in center background of picture
Old Stone Row 2014-Black Maple in center left of picture
A photograph from 1947 shows a couple of Sycamore trees planted alongside the road across from the Student Union Building, where Proctor is now. The trees were reaching maturity then, so they are only 85 years old, but one is massively large, once again the right tree in the right spot. So much for trees not growing on that hillside.
Sycamore near Proctor
Old Student Union Building-(where Proctor is now) -1947 Sycamore tree in center of photo
Same view 2014
Another view 2014
Near the Gravity monument by Warner science is a Littleleaf Linden, a tree the British call Lime trees. This one sets the state record for size, with an estimate of age of over 100 years. Its growth rate has slowed considerably; she’s reaching old age gracefully now.
Littleleaf Linden at Warner Science
Aerial photographs from 1942 show the Pin Oak to the south of FIC gracing the front yard of a house there, with Chateau in the back yard. We estimate this tree at about 125 years old, a teenager for an oak.
Pin Oak by FIC
Same aerial photograph-an apple planted next to what looks like gardens. This makes sense, as that entire area of campus has a proliferation of Pear trees similarly old we know nothing about. This tree is probably about the same age as the Pin Oak, but quite a bit older in Tree years.
Apple tree by Coffrin
The oldest tree (in tree years) on the campus is also one of the youngest in human years. Yellowwood is a pretty little tree with Beech like bark and pendulous white flowers in the early summer. The tree tends to branch low with multiple trunks, and falls apart after 50 years or so. Ours is probably 75, with multiple steel brace rods holding the trunks together.
Yellowwood tree by Hadley Milliken
Many thanks to the Digital Media archives, where I spent an enjoyable day in front of the woodstove on the laptop-any use of their pictures should go through them (I’m talking to you, Pinterest) All new pictures are my own.
Any kid will tell you maple syrup is special, but how special? Is tapping a maple tree like putting a spigot in the trunk? And why maple?
In a wonderful book I’ve written about before by Nalini M. Nadkarni called “Between Earth and Sky-Our Intimate Connection to Trees” she writes of how botanists and tree physiologists have been looking at how sap is produced within maple in the last couple of decades. Like many things, the wild world of maple syrup seems like a freak chance, a perfect random combination of physiology.
A tree’s goal, aside from reproduction, is to feed itself-it’s tough being an autotroph, and a whole lot of work. Photosynthesis takes place all summer long, making sugars for respiration, growth, reproduction, and a little extra. This extra, in a sugar maple, gets stored as starches within the sapwood of the tree. The sapwood, as the name sounds, is the area of the trunk and branches where water and sugars move around, located within the first couple rings of the wood.
As my winter term class hopefully remembers, Sugar maple is one of our “live slow, die old” species of trees. These trees are more shade tolerant, in life for the long haul, and have the foresight to save extra sugar for lean times, such as the introduction of shade or competition. Other tree species, such as Poplar, live fast and die young, and burn through all their sugar like a hyper 3 old, just as prone to growth spurts as an Aspen in the spring.
Early spring brings sun, a little higher in the sky, and better able to warm. Cats in our house know this, moving away from the woodstove and into little patches of sunlight on soft surfaces. Trees know this too, as the sun warms the bark and the wood. The air may be below freezing, but tree surfaces and interiors could be well above freezing. Once the wood gets to be above 40 degrees, enzymes turn these stored starches into sugars, mostly sucrose, and the sugar is now within the sap. This explains the magical sugaring temperature of 40, any warmer and this process stops.
The other freak chance miracle of maple is getting the sap flowing out of the tree. Not all trees can do this. Water is moved throughout the xylem of the tree by capillary action and transpiration, meaning the leaves need to be on the tree for water to move very effectively. That would ordinarily make for tough sugaring in March and April, except in Maple.
In maple trees the space around the wood fibers is filled with gas, not water like most plants. When the temperature drops, this gas contracts, making space for the sap laden with sugar in between the cells. So water can move upwards from the roots by capillary action without the benefit of transpiration from leaves. This water freezes at night between the cells.
The day brings warm temperatures, melting this ice and expanding the gas, forcing water down the branches into the stems and trunks of the tree. The taps put into tree trunks to collect sap pierce the xylem all this sap is moving through, and water flows down the tap into the bucket or plastic line.
Elms have that classic umbrella shape, but can vary from specimen to specimen. We are fortunate to have trees in a wide variety of sizes and shapes, from the low spreading type like the Dog Elm behind Munroe (yes, we’ve named some of them), to the spectacular high and arching Field House elm. We also have been planting disease resistant varieties, such as Accolade Elm.
I remember a conversation with one of our seasonal employees several years ago, and we were discussing the difference between botany and horticulture. He cited the elm as a good example. Botanically, we will always have elm trees. They don’t die from Dutch elm disease until past their reproductive years, so they will always set seed and produce more young. And looking at them from a geological time perspective, eventually they will develop resistance, although that may be many millennia. Horticulture, though, is as much art as science, and as horticulturists we preserve some of the grandeur of an old elm, and we remember the dignity of the old shade tree as it was, even as we work towards bringing them back.
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