Sweetgum: Embedded Mysteries of a Tree and Its Rare Paneling

A tree can be many things for many people: beautiful or a nuisance, its wood low-grade or its grain profound. A sweetgum tree is all these things for me. This post will give you a tour through sweetgum's beauties and annoyances, including its surprising use as high-end wood paneling in the 1920s and 30s.

First, regard the beauty. What other tree offers such a panoply of colors in the fall? Yellows, reds, purples, orange--sweetgum does it all. True, those powerful colors are only generated by trees that receive adequate sunlight, but there is some wonderful, creative chemistry going on there. Carotenes, xanthophylls, anthocyanins--these are the words that exercise the tongue while stirring curiosity about the possible purpose behind all that color.

There was a time in my life, during my extended undergraduate career, when I acquired a fascination with chemistry, specifically organic chemistry--the chemistry of carbon, the element upon which life is built. While premeds labored through the lectures with high anxiety for the grade they might receive, I was there with a love of subject and a hunger for knowledge.

In decades since, and not talking about premeds here, I've noticed that people who are disconnected from nature tend to be intimidated by nature's complexity. In order to feel comfortable, they surround themselves with a simplified, static nature of mowed lawn and trimmed shrubs. But for those of us who love nature, its complexity is appealing--a richness that rewards endless inquiry and exploration. I remember a bus ride through New England, probably in my 20s, looking out the window and thrilling at the thought of all the chemistry going on in the forested hillsides we were passing by. 

At the same time, it's hard not to be annoyed by the sweetgum's "gum balls" scattered on the ground, prickly and destabilizing underfoot. (Update: A friend says he collects them in winter to use for starting fires in the wood stove.)

Overabundance, too, can turn affection into surfeit. In the piedmont, stretching from central New Jersey down through North Carolina, sweetgum sprouts like a weed in areas we seek to maintain as meadows. Managing remnant piedmont prairies at Penny's Bend in Durham, NC, required mowing or prescribed burns to keep the rampant growth of sweetgum seedlings from smothering rare wildflowers. Grasslands in NJ often require similar intervention.

At least near water, one natural check on sweetgum's rampancy is beavers, who apparently love them for their inner bark laden with sweet gum--the liquid amber found in its latin name, Liquidambar styraciflua. This photo was taken during a walk at Plainsboro Preserve ten years ago. The beavers' preference was so strong, and the sweetgums so numerous, that we saw no other species of tree being chewed upon.

The vexing ubiquity in early succession that I've encountered in the eastern piedmont contrasts strikingly with my experience with sweetgum years prior in Ann Arbor, MI. Being a more southern species, the tree's native range doesn't extend into Michigan, so it's no surprise that a horticultural colleague at the University of Michigan proudly planted a sweetgum as something rare and wonderful, with its fall color and craggy winged stems. 

The sweetgum's wood, too, generates conflicting impressions. It rots quickly if left on the ground, is hard to split, and proves insubstantial as firewood. 

And yet, fifty years ago, my family moved into a beautiful house in Ann Arbor that was paneled in the most appealing way with sweetgum. The wood had a rich, warm glow--clearly a winner for paneling, but I have not knowingly encountered it since.

Then in 2023, we discovered a piece of wood from a packing crate bearing the name Demarest and Co on a wall inside the Veblen House. While researching the Demarest name, I came across an article about American Gumwood. In 1926, the Bureau of the Hardwood Manufacturer's Institute in Memphis, TN was promoting its new booklet: Beautiful American Gumwood: A superb native hardwood for interior woodwork and furniture.  

It took awhile to figure out that they were talking about sweetgum, not another eastern native called black gum. As a friend pointed out, calling sweetgum "gumwood" also risks confusion with the eucalyptus native to Australia, sometimes called gum tree.

The pamphlet begins by describing America's great forests as being our destiny to harvest. I've included long quotes to get a sense of the rhapsodic language.

The story of American gum wood dates back many centuries. Nature requires many years of favorable growth to produce a masterpiece, and in the vast stretches of our southland forests, extending from the Atlantic to the Mississippi valley and beyond, the quiet work of building cell and fibre was going on long before DeSoto and his valiant men first beheld in wonder the mighty "Father of Waters." What a marvel of creation, when from soil, moisture, and sunshine this fine wood came into being, now to be transformed by the hand of man into products that contribute to his well being and enjoyment.

By the mid-1920s, apparently, that enthusiastic harvest had led to more preferred species growing scarce:

Lumbermen have long known gumwood, yet vast tracts have been left standing while other interspersed hardwoods of widely varying species which happened to be wanted at the time, have been cut out. 

Overlooked in the past, sweetgum now stood ripe for the taking.

The tree itself, as it displays its lofty and graceful symmetry, is one of the glories of our native forests. Its sturdy proportions are enhanced by masses of scarlet, orange, and yellow leaves, which change, as the summer wanes. In size, it is heroic; one hundred feet to one hundred fifty feet in height, with a diameter of four or five feet, is not unusual. And some idea of the extent of growth of this important tree may be gained from the fact that with the exception of the oaks, gumwood exceeds all other hardwoods.

If sweetgums could read, they might have felt deeply flattered, but also be wondering if their tombstones were being readied and inscribed. And yet, one cannot be fully dismissive towards tree harvest--we who live in wooden houses and keep ourselves warm through the winter with fossil fuels rather than renewable energy from wood. 

This photo in the pamphlet looks reminiscent of the warm glow of the paneling I experienced fifty years ago, but doesn't capture the complexity and variety of mysteriously generated grains that sweetgum is capable of.

As the pamphlet explains:

Now no wood has more wonderfully interesting patterns than figured gumwood, but it is one of Nature's riddles to account for them. The pattern is not produced in the usual manner by quarter-sawing, although this process will improve any figure if it is already there. All one can say is that some trees have pronounced figured wood, others varying degrees of pattern, and many which show but slight indications of it. Undoubtedly the condition of the soil and the location of the individual tree affect in some mysterious way the structure of the wood. Only when the tree is felled, does the grain show itself as plain or figured. That is what makes the gumwood tree so interesting; it is like finding a }ewel, the value of which depends upon hidden qualities brought out by cutting and polishing.

The quizzled, tangled grain that makes sweetgum hard to split can bedazzle when milled. As with fall leaf color, the sweetgum's grain will vary tree to tree.

The figure ramifies through the wood at random, obeying no known laws. Gumwood logs will each display differing patterns, some subdued, some intricate and ornate.

Go forth, then, dear readers, and if you happen upon a sweetgum along a trail at Herrontown Woods or elsewhere in Princeton, slowly reaching for the dimensions the pamphlet describes, know that you are gazing upon a mystery of creation, whose creative chemistry is not yet fully understood, and whose sometimes plain, sometimes profound grain is impossible to predict from one tree to another.

There's one more passage in the pamphlet that helped me understand why my family home in Ann Arbor was paneled with sweetgum. The 1926 pamphlet may have influenced the couple, Walter and Martha Colby, who built the house in 1933, but they may also have encountered the paneling during their many travels in Europe. The pamphlet explains:

Europe has long recognized the exquisite beauty and texture of American gumwood. In fact, England, France, Italy, Spain, and other countries were first to recognize its fine working qualities. In America, however, its light was for a time hid under a bushel, so far as public acquaintance with its true worth is concerned. But now, due to growing appreciation of its merit, the valuable products of the gumwood tree stand forth proudly as "American gumwood,'* nothing else -so named, and so prized. The old adage, "a prophet is not without honor, save in his own country," no longer applies, if we may adjust this metaphor to a tree.

Here's a career move that musicians know well--a wood that needed to cultivate an audience abroad before it could be valued at home.

Encounters With Old-Growth Forest

Ever since attending the induction of Rutgers' Meckler Woods into the Old-Growth Forest Network, I've wondered whether any woodlands closer by could be rightfully considered old-growth. Rare is the woods that was never logged. The forests we typically encounter are of more recent vintage, having mostly grown up from abandoned farm fields. There's a valley at Herrontown Woods with giant tulip trees whose massive roots have lifted the ground around them, as if perched on a pedestal of their own making. Might these and the nearby big oaks and hickories meet the standard? And what exactly is the standard for deciding? Below is an account of encounters with old-growth, old stuff, and different forms of timelessness during recent travels.

When we headed north from Princeton to attend the wedding of a young couple in upstate NY, we had no idea that the theme of the trip would turn out to be old stuff and old growth. On the way up, we stayed overnight with friends whose house is filled with old furniture--a grandfather clock, of course, but also what may as well be called grandfather chairs that had been inherited or adopted from the curb, valued for their uniqueness and style regardless of how practical they might be. Each chair around the dining room table, each lamp, vase, and bureau, had a story behind it. A crank telephone perched on the wall in the kitchen, ready to call up the whisperings of distant ancestors. I found great comfort in this approach to stocking a house, even if a chair's quirky ergonomics didn't conform to modern expectations.

The next morning, we walked through Borden's Pond, a second growth woods whose scattered "wolf" trees and sedge meadows also have a story to tell. When the area was logged long ago to make pasture, farmers left a few scattered trees as shade for the livestock. Those trees, lacking any competition, with sun all around, grew thick lateral branches, so different in shape from the straight, younger trees--the "second growth"-- that grew up after the pasture was abandoned. This can't be called old-growth, I suppose, but it certainly has individual trees that go way way back.

Conveniently, the route to the wedding took us by Landis Arboretum, which too had some craggy old trees, standing next to the farmhouse. In the woods beyond, though, was an area declared to be old-growth, with a series of signs explaining how to distinguish old-growth from the second growth forest all around.

Don't expect big trees only, but a few big trees lingering in a mixed age stand. Around six old trees per acre is typical. In this photo, only one of the trees can be considered old growth, in this case a hemlock extending back 250 years. 

Really old trees lose their symmetry, with thick upper limbs and tops broken off by storms endured over the centuries, creating what's called a "stag-headed top." Look for mounds and pits on the forest floor--undulations caused by the lifting up of root balls as trees fall. And look for coarse woody debris on the forest floor in different stages of decay, where stable conditions and slow decay have allowed opulent growth of moss and fungi. One of the interpretive signs offered a clever way to judge a tree's age, not by its diameter or height--since some trees grow much faster than others--but by how far the moss has managed to grow up the trunk. 

One week later, I was in Durham, NC, where I started a watershed association 26 years ago, creating a string of preserves before moving to Princeton. I always get together with my botanizing buddies when I visit, and this time Perry Sugg, Cynthie Kulstad and I decided to stop by the 82 acre Glennstone preserve I had worked with a developer to create. We were walking down a sewerline right of way, with no particular destination in mind, when I thought of a special place to visit.

Just down the hill from the remains of a summer cottage, next to a rocky creek, are the remains of a spring where the owners of the cottage must have gotten their water. A small pipe sticks out of this half circle of stone, near the bottom. The ground there is consistently wet, but I've never seen water actually flowing out of the pipe. Last time I'd been there, I'd found a robust patch of JoePyeWeed, a tall wildflower found nowhere else in the preserve. This was also the only place I've seen smooth alders in the area. Apparently, the stable water source allowed the plants to survive droughts.

On this visit, armed with awareness gained at Landis Arboretum in upstate NY, I was able to focus in more on what sorts of trees were growing nearby. Past logging had left only narrow corridors of the original forest intact. Buffer regulations had forbidden harvest of trees within fifty feet of the stream. One tree in particular caught my eye, a towering shortleaf pine. 

The rough bark at its base brought to mind the Landis Arboretum signage:

"The bark changes on most species when the trees are over 150 years old, looking very different from the bark of younger trees.

Excellent signs include balding bark, shaggy bark (separating or curling strips), craggy bark (deeply grooved, fissured bark), and platy bark."

On this particular shortleaf pine, the bark changed dramatically about 20 feet up, from shaggy to smoother, platy bark extending to the top. That would suggest the tree is well over 150 years old.

The bark at the base was deeply grooved. 

Other large trees with distinctive, eccentric bark rose from the creekbanks. I doubt that this narrow band of mature trees along a stream would fit the definition of old-growth forest, even if the trees were old enough. The Network prefers stands of at least 20 acres. If there had been time, we could have followed this narrow band of old trees downstream, to better dream of what this woods had been before the logging. 

Late afternoon light caught the tops of these towering remnant trees rooted in a distant time yet still growing towards the sun. The experience of being there in that charmed hollow was not unlike the sense of timelessness felt while staying in our friends' house with furniture firmly rooted in the past. 

Keeping with the theme of old stuff, the young couple's wedding reception took place in the Hotel Utica, dating back to 1912, with massive, ornate chandeliers and tree-like columns. The groom's father was happy his son had chosen a place so steeped in history, but mourned that the glorious woodwork had been painted over during a recent renovation. 

It was the groom's father's idea to include an antique phone booth at the reception, where wedding guests could leave a message for the newlyweds, using an old dial phone. 

Click on "read more", below, for text from the Landis Arboretum's interpretive signage, describing in more detail the qualities to look for in old-growth forest.

 

Seeking "Lingering Trees"--Some Hope for Ash and Beech Trees

Most people attentive to nature are aware that Princeton has lost nearly all of its native ash trees over the past decade, and is now poised to lose its native beech trees as well. These are only the most recent losses due to assorted introduced insects, nematodes, and diseases against which our native trees had not evolved resistance. Also gone from the canopy over the past century are American chestnuts and American elms, with bacterial leaf scorch also taking a toll on red and pin oaks. As additional organisms enter the country due to an appalling lack of biosecurity, other species are threatened. 

What is there to do other than mourn, and mourn again, with each new wave of devastation? 

One answer to that question may be: Keep an eye out for "lingering" trees. It would be easy to assume that all our native ash, not having co-evolved with the Emerald ash borer (EAB), would be equally defenseless as the introduced larvae eat through the cambrium, cutting off the tree's circulatory system. But an initiative in Ohio has shown this not to be entirely true. Jennifer Koch, a research biologist with the USDA Forest Service, has been leading an effort to find "lingering ash", that is, mature ash that survive while others all around them succumb. Some ash that she and others have found have natural defenses that kill 20-45% of the larvae that bore into them. A very few trees kill 100% of the invading larvae. 

A very watchable video features Jennifer Koch, and also Holden Arboretum's Rachel Kappler, telling the 
story of ash lost, lingering ash found, and the effort to increase resistance among lingering ash through research and breeding programs.

One particularly impressive slide in the presentation showed how the resistant trees are able to stop the invading larvae before they do damage to the tree. 

 
Here are some of my notes from the video:

• Ash wood is/was used for bats and guitars
• Native ash species in our area: White, green, black, pumpkin
• 300 million acres of black ash-dominated forest in Minnesota could be lost (apparently no other tree species can survive in those wet areas)
• green ash is an important riparian buffer species in the plains states, hard to replace
• The lingering ash are found individually or in clusters, e.g Swan Creek, Oak Openings Park, near Toledo, 108 out of 11,000 had healthy canopies. Two specimens had no evidence of attack. Most resistance is partial, but resistance can be increased through breeding
• greenhouse tests can reduce the amount of land/labor needed for field tests
• resistance is inherited, though uneven

A central point these researchers make is how very limited is the area they have surveyed for lingering ash--only a small area near the Ohio/Michigan border. They call for similar initiatives in other parts of the country. 

That's where we come in, as keen or at least intermittently keen observers of the landscape through which we walk. It's important that any tree we believe to be lingering be a mature, wild tree--not a cultivar in a planted landscape--and that it be a tree that has weathered the massive wave of EAB over the past ten years, remaining green while others nearby have succumbed. Photos of lingering ash, and one story of their discovery, can be found at this link. 

A brief mention of the various species of ash: I associate white ash with higher ground and grander specimens found or once found around town. Green ash are less statuesque and more associated with wetter ground. Black ash I think of as growing, or having grown, in swamps, such as at Rogers Refuge in Princeton. The Ohio initiative is apparently finding most success with resistant green ash, though the video mentions lingering white, green, and black ash having been found in NY state.

In addition to the info below, there's also anecdata.org--a platform where citizen scientists can set up reporting initiatives.

This keeping an eye out for "lingering" ash can also be applied to other imperiled species in our area. The Ohio researchers request that people report lingering American beech, hemlock, and American elm as well. 

Related posts:

Emerald Ash Borer in Princeton

Beech Leaf Disease Sweeps Across Princeton

Holden Arboretum Studies Resistant Beech and Ash Trees

Finding Pawpaws in Paw Paw, Michigan

When the Lunar Octet, a latin/jazz band I've been in for 40 years, performed this past weekend in PawPaw, MI, a jazz naturalist like me was naturally curious about whether there are any pawpaws growing there. 

The town, named after the PawPaw River, which in turn was named by the indigenous people after the pawpaw trees that grew along it, has a population of about 3500.  Though the downtown preserves some historic feel, the town has not exactly embraced its namesake. Grapes ornament the town logo on the water tower and elsewhere, not pawpaws. 

Upon arrival, I asked my phone where I might find a pawpaw in Paw Paw, and was directed to the post office, where I navigated past redbuds and callery pears before finding this pawpaw tucked around the side. 

The tree had fruit, but none ripe as yet. I asked around, at the sandwich shop and down along the beautiful lake where we performed. Most people were unfamiliar with this native tree. The post office worker I ran into said he didn't know anything about pawpaw trees in PawPaw, except that he doesn't like the taste. 

The flavor of a pawpaw, a rich, creamy combination of mango, banana and pineapple is appealing to some but not everyone. Our host was more generous with her knowledge and assessment, mentioning a couple places the pawpaw grows in town, including at one of the schools.

The town of Pawpaw sprouted along the Territorial Road, one of the three main east-west routes of pioneer days. That history is documented next to the lake, but the native tree remains largely unknown and uncelebrated in a town that bears its name. 

My theory is that, since Asimina triloba primarily grows in floodplains, the pawpaw trees were lost when the river was dammed to make Maple Lake. Its fruit, with fragile skin and a taste less universally appreciated than other tropical-tasting fruits, resisted mass marketing. That, and the general drift away from plant knowledge, consigned the pawpaw to obscurity. 

Still, it remains a singular fruit, the only member of the tropical custard apple family, Annonaceae, to adapt to northern climates. And some of us still remember the song: "Way down yonder in the pawpaw patch"--a pawpaw patch that, in PawPaw, Michigan, became a lake with a lovely breeze to carry our music. 

Update: Turns out that, if you live in PawPaw Michigan, you'd have to drive to southern Indiana or Ohio to find a festival celebrating the pawpaw. PawPaw's festival celebrates grapes.

A Followup on Beech and other Threatened Native Trees

Having grown despondent about the devastating toll beech leaf disease will likely take on Princeton's beech trees, I was surprised and somewhat heartened by what I found on the Princeton University campus. 

A friend from childhood was visiting me for the first time, and as I showed him and his wife around campus, I began to feel as if we had somehow been transported back to an era before introduced pathogens and insects had marginalized many of our native trees.

An American white ash towered over us, healthy as can be. American elms, too, grew as if Dutch elm disease had never arrived.

Unlike the ailing beech trees up along the Princeton ridge, the beeches on campus appeared unfazed by beech leaf disease.

I looked for signs that these trees had been injected with chemicals to ward off invasion, but found none. Surely, though, this improbable survival depends heavily on medicinal intervention.

Since I first alerting the community to the presence of beech leaf disease in Princeton in a blog post and letter to the editor, some articles have been written in the local press--one in TapInto Princeton and one in Town Topics. 

Both mention phosphites as the primary treatment available thus far. Applied to the soil, phosphites are a biostimulant that improves the tree's immune system response. I was skeptical that this could make much of a difference, but the University appears to be having good results. Grounds supervisor EJ May said they started seeing signs of beech leaf disease two years ago. Speaking generally about efforts to save native trees, he acknowledged some losses but some success as well.  

Another lead I had checked out was a kind of beech mentioned in a list of special campus trees.  Called a fern-leaved beech (Fagus sylvatica 'Asplenifolia')--a variety of European beech with unusual foliage--the university had gone to great lengths to save this extraordinary specimen during construction of the new chemistry building. The tree's described online as having "no serious insect or disease problems." Was the text written before beech leaf disease was discovered in 2012, or might this variety have some sort of natural immunity? I stopped by to take a look, and could find no visible symptoms. 

There remains, too, an uncertainty as to the origin of the nematode that causes beech leaf disease. It is most similar to a species found in Japan, but differs in some ways. 

Beech Leaf Disease Sweeps Across Princeton

Princeton is losing its beech trees.

We were feeling celebratory, having just completed a successful corporate workday in Herrontown Woods, when I happened to pass by this small branch of a beech tree along the red trail. The leaves were strangely contorted, with dark green stripes. I had heard distant rumblings about a disease of beech trees, but had managed to keep my head in the sand until that moment. 

Back home, diagnosis was but a google's search away. Similar images popped up on the screen, along with the name: Beech Leaf Disease. Tree maladies typically come with an acronym. Emerald ash borer is EAB. The dreaded asian longhorned beetle, which they've had some success keeping from spreading across the eastern U.S., is ALB. The Bacterial Leaf Scorch that afflicts pin and red oaks is BLS. Now there was a new one: BLD. 

For those unfamiliar with the American beech (Fagus grandifolia), it's a native tree related to oaks and chestnuts, with beautiful smooth gray bark. They can get very big and live for centuries. Thousands of them grow in Princeton, in the preserved forests along the Princeton ridge and on slopes above the Stony Brook. 

The "grandifolia" in the latin name refers to the leaves, which are larger than the leaves of European beeches. This photo shows some healthy leaves (on top) and the curled, darker green leaves that have been contorted by nematodes overwintering in the buds. Beech leaf disease is caused by these nematodes--tiny worms spread by birds or the wind. 

Viewed from beneath, the infected leaves show a curious striping of dark and light green. 

During a subsequent hike in Autumn Hill Reservation, I was astonished to find nearly all the beech trees affected--their leaves contorted, their crowns beginning to thin. Beech in Rogers Refuge are showing symptoms, and Mountain Lakes preserve is reportedly also affected. According to online sources, essentially all of our beech trees will be dead within ten years. The news comes exactly ten years after the first emerald ash borer was found in New Jersey, with the skeletons of ash trees still haunting our woodlands.

According to this map, on the Holden Arboretum website, the disease was first spotted near that arboretum in Ohio in 2012, and has spread in all directions, most rapidly eastward.

According to the Maryland Extension website, the microbe causing the disease is Litylenchus crenatae mccannii, a subspecies of a nematode found in Japan. As one would expect, the only beeches resistant to this particular nematode are those that coevolved with it in Japan. 

The Holden Arboretum website mentions a chemical treatment that is being tested. It is a compound that is sprayed on the tree in the fall just as the nematodes are moving from the leaves down into next year's buds. Unfortunately it is highly toxic. The snail's pace of tree research compared to the rapid development of Covid vaccines caused one friend to ask, "Where is science when we need it?" 

The loss of a tree species from the canopy has all sorts of impacts on wildlife. Ash, elm, and maples bear abundant seeds early in the season to feed on. Two of those three have been largely lost. Nut-bearing trees provide food in fall and winter. Gone from wildlife diets are chestnuts, bacterial leaf scorch is reducing oak production of acorns, and it now looks like beech nuts will become very rare. Websites detail the ecological web of connection and dependence that is unraveled by the loss of a tree species. 

A post last year by the Brandywine Conservancy in Pennsylvania provides a particularly chilling description of what is in store for eastern forests:

"As the disease progresses, leaves will become smaller in subsequent years, and it will seem like autumn in the summer as infected leaves brown and fall from the tree, resulting in thinned crowns and branch dieback. Eventually, BLD will cause beech trees to abort their buds, leading to the death of the tree. Young beech tree saplings die within 2–5 years of infection, while mature trees live a bit longer. Death from BLD is likely accelerated in beech trees stressed by drought or Beech Bark Disease, which is a different infection that involves scale insects and fungi."

Here's a writeup I found on beech bark disease, which also poses a mortal threat. 

I encourage people to visit favorite beech forests in the area sooner rather than later, to appreciate the now threatened beauty of this singular tree. Over the next few years, if you are fortunate enough to find one that remains healthy while others around it succumb, you should let people know. The Holden Arboretum site provides someone to contact.

Yesterday evening, I visited the fabulous congregation of European beech off of Elm Lane on Constitution Hill in western Princeton. The many trunks appear to all come from the original massive trunk in the middle. 

Seen from a distance, they appear to be separate trees, but more likely were either branches that touched the ground and took root, or sprouts from the original tree's massive root system.

You can see how some of the trunks still have a sort of navel, where the original branch from the "mother tree" was cut off.

Its leaves, smaller than those of the native beech, were  showing early signs of the disease.

Some of Princeton's most spectacular native beech trees grow in the Institute Woods. That will be my next stop--that and a hidden valley between the Princeton University chemistry building and Washington Road, where I found a mixed forest of 200 year old trees, part of the great American forest cathedral that, in unspeakable sadness, loses its towering pillars, one by one.

Here is how I concluded a recent letter to the editor in the Town Topics: 

Outrage is often triggered by the intentional cutting of trees. The highly visible spotted lanternfly caused a stir, yet has proven relatively innocuous. The biggest threats we face are neither visible nor intentional. The emerald ash borer is hidden behind bark. Nematodes are microscopic. Our machines’ climate-radicalizing carbon dioxide? Unintended and invisible.

There is so much joy still to experience, for me particularly in Herrontown Woods, and yet in the larger workings of the world, so much to grieve.

Tent Caterpillars and the History of Black Cherry Trees in Herrontown Woods

Black cherry trees draw attention in early spring because of the "tents" that tent caterpillars weave on them. I was surprised to find out that these tents are sometimes mistaken for gypsy moth infestations. There's also some disagreement as to how damaging tent caterpillars are to the trees they feast upon, so I decided to do some investigation. 

First, some distinctions between tent caterpillars and gypsy moths. Tent caterpillars are native, feed primarily on cherry trees, build conspicuous tents, and do their feeding on the fresh, tender leaves just beginning to emerge in April. Gypsy moths are a nonnative species imported from Europe, start feeding in May on a very wide spectrum of hardwoods and even some conifers, and do not build tents. 

Gypsy Moths

The story of gypsy moths in our area is most easily grasped by looking at how many articles about them have been archived in the Papers of Princeton through the decades. Outbreaks of gypsy moths remained minor in New Jersey until the 60s, then grew into massive defoliations of forests in the 1970s. By the early 1980s, gypsy moth populations were beginning to drop, thanks to a natural virus, introduced parasites, and aerial sprayings. A naturally occurring bacteria called Btk proved safe and effective when sprayed on trees where gypsy moths were feeding. There was a recurrence from 2007-8, but numbers have dropped off since then. Though the forests largely healed, the trauma of past gypsy moth infestations lives on in people's memories. 

Tent Caterpillars

What we have this spring, and springs extending back through millenia, are native tent caterpillars making their tents. 

Some sources on the web suggest that tent caterpillars, despite the powerful visual of the tents and defoliated branches, don't do enough damage to a tree to worry about. I'd really like to believe that, but this young black cherry tree, now bearing eleven tents from which the caterpillars make forays, is almost completely defoliated. 

They say a tree can survive one complete defoliation, but if defoliated several years in a row, it becomes increasingly susceptible to disease and insect attack.

Meanwhile, our very hungry tent caterpillars have even followed a branch over to a neighboring pin oak, which now, too, is getting chowed down upon.

We pause to note a couple recurring themes in nature. One is that the tent caterpillars will shift to a less desirable food source (a pin oak tree) if their favored cherry tree leaves run out. Deer, too, will begin eating less desirable foliage if they run out of their favorites. Thus, an overabundance of deer in the 1990s almost wiped out spicebush in our Princeton woodlands, despite it being low on the list of deer's preferred foods.

The other example of a recurring theme in nature is that the tent caterpillar eats only one crop of leaves, then is done for the year, allowing the tree to recover. The worst thing a predator could do is be so effective as to eliminate its prey. 

The introduction of a new insect, though, could throw off this balance of predator and prey. If another insect, say, a gypsy moth, came along and defoliated the same tree yet again in the same growing season, that tree would be in big trouble, having twice committed energy to manufacturing a whole crop of leaves, only to have them eaten. One question is whether the gypsy moth outbreaks in the '70s and '80s killed more of one tree species than another, causing changes in forest composition still noticeable today.

There's a lot of caterpillar behavior whose purpose is not immediately obvious. A week ago, caterpillars were crawling about on the outside of the tent, turning this way and that. My best guess was that they were expanding the tent by adding another layer of silk, but no strands could be seen coming from their bodies as they moved about. 

And why are these caterpillars clustered on the side of the tree, outside of their protective tents? Wouldn't they be easy picking for the birds that are said to consume them? 

As their spring residency has continued at the Barden in Herrontown Woods, the tent caterpillars have spun not only isolated tents but also enveloped the trunk and limbs in a silken web reminiscent of the webbing people drape on their shrubs for Halloween. A closer look reveals that the caterpillars have spun silken highways upon which they commute from tent to the "pasture" of the canopy. These highways are only one lane wide, requiring a caterpillar to temporarily step aside if it meets another coming the opposite direction. Some silken highways are suspended in air, like overpasses--a great way to smooth out the rough terrain of a black cherry tree's "black potato chip" bark. 

A tree colonized by tent caterpillars, then, has elements of occupancy, transport, and exploitation not unlike the human footprint on the land, with our homes, highways, and farm fields. A big difference being that the tent caterpillar's settlement is seasonal--more like the impact of nomadic tribes than our permanent villages--giving the tree a chance to recover.

Another big difference between tent caterpillars and other builders of shelters--bees, ants, birds, mice, people--is that the caterpillars don't seem to bring anything back to the shelter other than their bigger, well-fed selves. They aren't adults bringing food back to the young. The caterpillars, like super resourceful children, work collectively to raise themselves, then leave the tree on their own to pupate and turn into adult moths. 

A nice writeup about tent caterpillars (Malacosoma americanum) found at ThoughtCo.com states that the broad side of the tents faces the sun, and that the caterpillars make three forays per day, returning to their tents inbetween. That will be something to check out next spring.

Surprisingly, the subject of wild cherry trees in what is now the Barden (formerly a pine plantation) came up more than 50 years ago, in Richard J. Kramer's book about Herrontown Woods. 

"Wild black cherry, which grows to magnificent size in the Allegheny Mountains, is a poorly formed tree in Herrontown Woods, occurring mostly in areas which were recently open fields. Its best growth has been in the pine plantation, where specimens are 30 to 40 feet tall and possibly may develop into good-sized trees. Apparently these black cherries were able to develop along with the young pines after these were planted in the open field. Although the birds do bring seeds of the cherry into the forest, the many seedlings and the few saplings that occur there grow poorly and remain shrub-like."

Gone now are most of the pine trees in the pine plantation, and those larger cherry trees are nowhere to be found. Our 12 little black cherry trees in the Barden, all saddled with tent caterpillars, must be the descendants of the larger cherry trees Kramer describes. Only one large black cherry tree is known to exist now in Herrontown Woods, almost completely free of tent caterpillars, growing next to Veblen House. Have tent caterpillars contributed to keeping the black cherry trees of Herrontown Woods from achieving full size, in the past as well as in the present?

If we wanted to relieve the cherry trees of the spring burden of hungry caterpillars, we could remove the tents and remember to crush the egg masses laid by adult moths on small branches in late summer, as suggested in this useful post about the insect. 

But as insect numbers continue to decline, the role of trees as food for native insects grows in importance. And if the cherry trees remain small, that will allow more sunlight to reach the many wildflowers growing in the Barden. Leaving the tent caterpillars to grow undisturbed can serve as an experiment, to see if they continue to flourish year after year, or if nature's array of predators, pathogens, and parasitoids finally up their game and reduce the burden these trees now bear.