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

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.

Update on Native Butternuts and Chestnuts in Princeton

There's a lot of gratitude being expressed towards trees these days. The gratitude tends to be towards trees in general, but this fall, I'm especially grateful for three trees in particular. 

All three, growing at the TRI property, are among many that have been planted over the years by local nut tree expert Bill Sachs and me as part of an effort to bring back two marginalized native tree species. One is an American chestnut. The other two are butternuts. Both of these species have been laid low by introduced diseases, and I feel fortunate to be part of an effort to make them numerous once again in Princeton. 

The two butternuts at TRI bore a bumper crop this year, some 200 nuts--the first sizable harvest since the parents to these two trees were lost 14 years ago. One fell in a storm; the other ironically was cut down as part of an environmental remediation. It's Bill who played the role of Noah, growing new seedlings from the seeds we collected from the two trees before they were lost.

We planted other members of this new generation of locally sourced native butternut trees at Harrison Street Park, Herrontown Woods, Mountain Lakes, and Stone Hill Church. Bill in particular did a lot of the followup work, checking the cages that protected them from the deer, and serving as a one man bucket brigade to sustain the trees through droughts in their first couple years.

Bill also did a great deal of work to re-establish native chestnut trees in Princeton. That project began in 2010, when chestnut researcher Sandra Anagnostakis, of the Connecticut Agricultural Experiment Station came to town to give a talk. She brought along 20 chestnut seedlings for us to plant in local parks. The seedlings were 15/16th native, 1/16th Japanese chestnut. Of all of those that Bill planted, at the Princeton Battlefield, TRI, Herrontown Woods, and Harrison Street Park, only the one tree at TRI has borne fruit. Many of the hybrid trees have died, despite the effort to breed in resistance. 

There have been some other efforts to get the American chestnut growing again in Princeton, by the Friends of Princeton Open Space at Mountain Lakes and also by arborist Bob Wells at Greenway Meadows. The best bet for repopulating our world with the American chestnut may well lie in research that led to inserting a gene from wheat into the American chestnut genome that confers resistance. This seems a much more dependable and faster way to embed resistance to the fungus, and bring back this spectacularly useful native tree. 

In the meantime, we can celebrate the hard-won harvest we're getting from this new generation of native nut trees, and after letting them cure a bit will even get to find out what a butternut tastes like.

Related posts

From 2021: Butternut Redux--A New Generation Bears its First Crop

From 2010: The American Chestnut Returns to Princeton

Hicans and Other Useful Trees at Princeton Battlefield

When people think of trees at the Battlefield, the first and perhaps only tree that comes to mind is the Mercer Oak, which these days is Mercer Oak II, an offspring of the original, donated by Louise Morse, a remarkable woman who spent much of her long life advocating for good causes. She was wife of Marston Morse, one of the first generation of mathematics faculty at the Institute for Advanced Study.

The Mercer Oak plays an ambassadorial role for the Battlefield, a star, positioned near the road while other less heralded trees serve more prosaic functions further back.

The young oak, a teenager or perhaps a young adult at this point, is flourishing after donating much of its foliage to the insect world two years ago.

It's appropriate that the oak came from Mrs. Morse, because she herself was extraordinarily long lived, reaching 105, and, like an oak that gives of its foliage to 100s of species of insects, gave generously of her time to such causes as Stuart School and civil rights.

Closer to the house are less known but more edible trees. Beneath this one is a bumper crop of pecans, but the tree is not fully a pecan tree.

It is, instead, a hican. Like a mythical beast whose body doesn't match the head, it has the base of a hickory and the top of a pecan. You can see the change in bark from rough to smooth about six feet up on the trunk.

Chinese chestnuts, too, are having a banner year.

In front of the house, a native chestnut we planted (15/16th American), is hanging in there, though its trunk is nearly girdled by the blight.

It, too, is laden with chestnuts.

Another native chestnut on the other side of Mercer Street had looked to be flourishing, but succumbed suddenly this year. The disease does not kill the root, however, so multiple sprouts rise from the base, to be browsed on by deer.

Undeterred, Bill Sachs and I added protection to some more recently planted native chestnuts that were getting beat up by the mowers. Such a perilous world these trees enter into.

Along the field edge, the bicentennial dogwoods planted in 1976 are benefitting from the work volunteers did this spring to keep the porcelainberry vines off of them.

This shot from underneath the trees shows the wave of porcelainberry that wasn't quite able to reach the lower branches of the dogwoods.

The less shading from the vines, the more berries the dogwoods can produce to fuel the fall bird migration.

This would be the fate of the dogwoods if we didn't help them out--completely enveloped by the porcelainberry.

Two of the classic inedible trees to be found around historic homes are horsechestnuts and black locust. Clark House lacks the horsechestnut but has several grand black locusts. Black locusts provided extraordinarily rot-resistant wood for fenceposts, abundant flowers for honey, and some say they help steer lightning strikes away from the house.

With Trees, Looks Can Be Deceiving

Here's a tree that looks dead, but is probably okay. It's a horse chestnut--a species long associated with historic houses, and like many horse chestnuts lost its leaves early, perhaps due to a leaf blotch fungus. Though planted in front of a newer home, its history is connected to the 18th century house around the corner, once lived in by Joseph Stockton and, reportedly, an occasional sleeping pad for Thomas Jefferson.

And here's a recently planted ash tree a few blocks away at the Westminster parking lot, looking good but not long for the world, due to Princeton's ongoing Emerald Ash Borer invasion. When I saw that ash trees were planted as part of the parking lot expansion, I urged Westminster to get the designers to pay for replacements that would actually live long enough to shade the cars parked beneath them. Hoping I'm wrong about it all, but any followup photo a few years from now will likely show a gap where this tree now stands.

Starlings, Passenger Pigeons, and the Uneaten Acorns

Acorns, anyone? It's called "flooding the zone"--a technical term commonly used by botanists who grew up playing sports. Some people see it as a mess, and curse the trees. An alternative target for cursing, just to put it out there, would be the tree-phobic landscape of concrete and lawn that we impose beneath the trees. A forest floor is far more accommodating of arboreal excess. There, a tree can let it all hang out, let it all fall down--seeds of all sorts, leaves, branches--and the forest floor will shrug, take it all in, and turn it into wildflowers.

In town, the blanketing of acorns turns into a blanketing of oak seedlings, few if any of which have any prospects of reaching maturity. The seedlings seem to be saying, "Move me to an opening along the street where I could shade some asphalt", but it doesn't look like people are listening.

For some people, a love of trees is layered with deep resentment of this fecundity. For me, looking for logic in nature's ways, the question is not "What to do with it all?", but "What's missing?" Past posts about osage orange and honey locust ask the same question, and suggest a missing herbivore that would have consumed the abundance in the past. Botanical abundance has lost a once complementary zoological abundance.

A partial answer came this past Nov. 10, when masses of starlings swept through, congregating in the pin oaks behind our house. A closer look revealed they were gobbling down acorns. Minutes later, they were gone, having left our pin oaks a little lighter.

The starling is not native, though, so doesn't speak to what would have consumed the oaks' abundance historically. And starlings appear too small to deal with the larger acorns of other species such as red oak. Still, it's behavior suggests that the spectacular fecundity of oaks might once have fed a complementary fecundity in the avian world--some highly mobile species, large enough to deal with a broader range of acorn size, that could make quick wing across eastern North America, swooping in to feast and move on.

Enter Ectopistes migratorius, a.k.a. the passenger pigeon, a bird of spectacular mobility and historical numbers. The photos are from a wonderful NJ State Museum exhibit two years ago.

A fine writeup on the Smithsonian website says "the mainstays of the passenger pigeon's diet were beechnuts, acorns, chestnuts, seeds, and berries found in the forests." They may also have swept in to feast on the seeds of our native bamboo, Arundinaria, which at one time covered large areas in the southeast and, like other bamboos, typically bloomed only once every several decades.

It can be tempting to say that the starling is providing a service by partially filling the void left by the extinction of the passenger pigeon. A few books have come out in recent years that claim invasive species like starlings aren't a big problem after all. The books in turn embolden news editors to publish articles and opeds with a similarly seductive revisionism, showing the same willingness to cherry pick evidence and rush to conclusions. I've written detailed critiques of various of these, including one recent article that mentioned starlings.

It would be interesting to explore to what extent the massive numbers of starlings have filled the niche left empty by the extinction of the passenger pigeon. Though feeding habits may overlap somewhat, one big difference is likely to be nesting behavior. Starlings compete with native birds for nesting sites, while the passenger pigeons appear to have built nests on branches, where they would not have displaced birds seeking tree cavities.

Woody Plants With a Farmer's Tan

A couple photos to post before fall slips entirely away:

The leaves of winged burning bush (Euonymus alatus) turn bright red in full sun, or white in full shade. This photo shows the gradation on a single bush.

Please, by the way, don't plant this species, and if you have it, consider replacing it with some less invasive colorful shrub. It can be pretty, but winged burning bush has proven highly invasive in local woodlands, outcompeting native shrubs and shading out spring wildflowers.

This maple on Aiken may have gotten a farmer's tan on the top because the lower half is shaded by the tree across the street, and thus is slower to change color.

A Modern Times Moment With Persimmons

There's a scene in Modern Times where Charlie Chaplin's fantasy of domestic bliss includes reaching out the window to pluck some grapes. A cow comes to the back door to supply milk. Nature is cleverly tended to put its bounty within arm's reach.

I think of that scene every time I bicycle over Princeton University's graceful Streicker Bridge above Washington Road, ever since I noticed some native persimmon trees rising up alongside the bridge. They were planted intentionally, like Chaplin's grapes, and each year they've gotten higher, pressing their leaves and fruits closer to the fencing .

Posts from 2014 documenting the persimmon trees' rise can be found here and here, and a 2015 post is entitled "Close but no persimmon".

There's a catalpa growing within reach as well, but that's not as appetizing, somehow.

This year, the long awaited casual Chaplinesque reach was finally possible. Heading to a university soccer game, I'd check their progress.

The fencing is a real deterrent, though, as if Chaplin's dream of domestic bliss were set in a high-crime neighborhood where all the windows were barred.

At last, time and fruit seemed ripe. But wait, one problem. It's a persimmon. Can't they be astringent in the extreme? So much expectation, only to have a very pucker-mouthed ride home.

The soccer season passed less than gloriously into history, the leaves fell. A few persimmons remained on the tree, but out of reach.

Giving it one last try, I gave up on the fruits coming to me and went down below the bridge to see what lay on the ground. There, preserved on top of a leaf, was one ready to taste. It was sweet, without a hint of astringency, delicious beyond all expectation.

Sometimes dreams don't play out the way you imagined, but they can still come true.