Trouble For Princeton's Trees

To inoculate you for the news carried in this post, I'd like to point out that wishful thinking is not the same as hope. In fact, to the extent that it postpones action, wishful thinking can be thought of as the enemy of hope. Bad news is much more easily accepted if we feel confident in our capacity to work together as a community to respond.

Princeton has a real challenge ahead if it is to keep its protective canopy of trees in coming decades. There are the losses in recent years due to storms like Hurricane Sandy, the ongoing attrition as some pin oaks and red oaks succumb to Bacterial Leaf Scorch, and then there is the gathering storm just to our west of the emerald ash borer. Through a recently completed tree inventory, Princeton can now look at the numbers, and they don't add up--the number of trees likely to be lost dwarfs the number of trees being planted.

Doing the Math

Here are the numbers, rounded off for easier math, as presented by Bob Wells of Morris Arboretum, who directed the inventory and integrated it with an earlier survey of borough trees done by Jim Consolloy. These are only the trees growing in the street right of ways. Trees in parks, preserves, and on private property are not included. Of Princeton's 19,000 street trees, 3000 are in poor condition--unlikely to live beyond the next five years. Another 6000 are in fair condition, with an estimated life expectancy of 5-15 years. Even those trees in good condition are threatened by a growing collection of invading insects and diseases, along with the increasing weather extremes associated with climate change. For instance, some of Princeton's 1400 pin oaks and red oaks will continue to be lost to Bacterial Leaf Scorch.

Compare those numbers with the current replacement rate. Princeton purchases and plants about 60 trees each year along the streets. Its tree crew takes down about 250 trees each year in parks and along streets. The numbers offered up by the tree inventory estimates the annual loss of street trees to be a minimum of 600. By this math, we will be losing ten trees for every one being planted. And this doesn't even take into account the imminent arrival of the Emerald Ash Borer.

http://www.tinleypark.org/index.aspx?nid=648

Emerald = Less Green

Perhaps most worrisome is the looming threat to Princeton's most common tree, the ash. We can expect to lose most of our 2200 white and green ash trees along the streets in coming years, plus the tens of thousands in our woodlands. The culprit is the emerald ash borer (EAB), an insect that hitch-hiked to southeastern Michigan in wooden packing crates from China, then proliferated to kill 50,000 trees before anyone knew what it was. Since its identification in 2002, EAB has been radiating out across the midwest, killing tens of millions of trees, including a relentless spread eastward through Ohio and Pennsylvania to the border with New Jersey. A map at this link shows New Jersey essentially surrounded by infestations in bordering states.

As chance would have it, the original EAB infestation occurred just north of Ann Arbor, MI, where I used to live. The city of 100,000 had to spend $5.8 million removing 10,000 trees. Interestingly, ash continue to sprout in the woodlands there, and can grow to 6 inch diameter, but the chances of their growing to maturity are slim.

Princeton has dealt with threats to trees in the past. A bacterium called Bacillus thuringiensis (BT) has been used to reduce the impact of gypsy moths. According to Greg O'Neil, Princeton's arborist, the wooly adelgid's attack on our eastern hemlocks was slowed down by pesticide, after which the pest appears to have "cycled through", allowing many hemlocks to survive.

There is, however, no known control for emerald ash borer other than individually treating each tree, and even then the results are mixed. As an added complication, Imidacloprid, the most frequently mentioned systemic insecticide for protecting ash trees, may be contributing to the decline of honey bees.

What To Do

The sooner we acknowledge the depths of the challenge we face, the more proactive we can be, and the better the prognosis for Princeton's tree canopy. There are a number of actions that can be taken. Treatment for ash trees that are particularly cherished is best undertaken before the emerald ash borer arrives. To better spread the work of removal over a number of years, some of the younger or less healthy ash trees can be taken down and replaced with another species before the invasion hits. The municipality should at least be planning for the extra staff needs and the seven figure expense coming down the pike.

The big question is how to replace so many trees with a limited budget. The more gaps in the street canopy, the more pavement is exposed to the sun, which through the "heat island effect" causes the town to be hotter than it need be in the summer. At $200 a piece, new trees aren't cheap, and then there's the planting and followup care to insure they survive.

One approach I'm exploring, as a member of the Princeton Shade Tree Commission, is transplanting "volunteer" trees that sprout in people's yards. Some species are more appropriate than others, and determining where to plant them along the street requires some guidance. Perhaps we can come up with a guide, and motivated neighbors could take initiative in their neighborhood to identify gaps and work with willing homeowners to get trees planted in an optimal place and manner along the street. Given the infinite reasons that can be summoned for inaction, such an approach will only work if people see how their own needs can be met by participating in the collective endeavor of shading our streets.

For me, the hope lies in the growth force and the natural affinity people have for trees. It's remarkable how quickly the red oak in this photo, which sprouted on its own in my next door neighbor's yard not that many years ago, has grown large enough to cast much-needed shade on our driveway.

Neighbors a couple doors down have transplanted volunteer trees to key spots in their yard--to shade the house, provide habitat for birds, and provide buffer from the street. After just a few years, they are robust young trees--a white oak, pin oak, American elm and tulip poplar. Another friend is growing a pawpaw and a fig in a sunny spot in their backyard--going for food rather than shade.

Each kind of tree has its strengths and potential drawbacks and vulnerabilities, but after years in which Princeton's landscape was dominated by mature trees, it's refreshing to see young ones coming on the scene, filling the voids, reaching for the sun.

Related to this, the opening reception for an art exhibit entitled "The Fallen and Unfallen: Trees in Peril" is Nov. 1 at the DR Greenway, 5:30 to 7:30. More info here. With paintings and photographs, it celebrates trees while also identifying some of the threats they face, in little snippets of info like this one.

Emerald Ash Borer in Princeton

Here's a stock photo of the recently arrived insect that will kill (there must be a better word) Princeton's most numerous tree species over the next decade. White ash, green ash, and the much less common black ash--all are vulnerable. The photo shows an ash tree with characteristic "D"-shaped exit holes. It will take a lot more than a penny to deal with the consequences of this diminutive beetle's appetite. I'll expand below, but I sent the quick read version out in a mass email that was then quoted in an informative article in the Town Topics:

"Emerald Ash Borer (EAB) was found in a trap set by the town arborist out along River Road. This small green insect, accidentally introduced to our continent from Asia, probably in wooden packing crates, has been spreading outward from its original introduction in the Detroit area, killing 100s of millions of ash trees. The insect will spread across Princeton over the next few years, eventually affecting all ash trees that haven't been treated. Highly valued ashes can be injected in springtime with an insecticide. The treatment can provide protection for several years. Of the various chemicals available, I've heard the most praise go to Arbor Mectin. Tree-Age has a similar formulation."

The Next Fifteen Years

So, what happens now, and what can we do about it? Princeton's arborist, Lorraine Konopka, sees this slowly evolving catastrophe following a fifteen year arc. In the first five years, EAB will spread around town, building up its numbers with each new generation. Symptoms are slow to manifest, but in various ash trees we'll start seeing dieback starting at the top of the crown and working its way down. Many ash trees are already suffering from ash decline, notably a disease called ash yellows, making it even harder to know for certain when EAB has invaded a particular tree. Homeowners will be forced to choose between spending hundreds of dollars every few years to treat favorite ash trees with systemic insecticide, or spending thousands of dollars later on to remove their dying ash trees before they become brittle and dangerous. The five years that follow will be marked by radical dieoff, both in town and in our nature preserves. Some woodlands where ash trees dominate will be decimated. We'll see otherwise green hillsides dotted with skeletonized remains of ashes. The five years after that, more or less, will see the last untreated ash trees succumb. The population of EAB will drop dramatically, but protected trees will continue needing new injections of insecticide, though potentially less frequently. Ash trees will still be found in nature preserves, but likely get attacked as they grow towards maturity. More on the aftermath at this post, written after a visit to Ann Arbor, MI.

Life Cycle

According to an EmeraldAshBorer.info webpage, the Emerald Ash Borer hatches into an adult in May and June (coincidentally, emergence is said to begin around the time that black locusts bloom), flies to new areas and mates in June and July, then lays its eggs in August. The larvae feed just inside the bark in the fall, then overwinter as pre-pupae before hatching into a new generation of adults the next spring.

So it's not surprising that the first confirmed sighting of an emerald ash borer in Princeton happened in late July, when one was found in a trap placed near River Road by the town arborist. Previous documentations in the area were in Bridgewater, West Windsor and other towns.

Treatment to Protect Ash Trees

Homeowners will need to decide, over the next year or two, which if any ash trees they wish to treat. The expense of recurrent treatments, and the ongoing benefits of the tree, need to be weighed against the cost of removal. This definitive article recommends treatment of trees if EAB has been found within 10-15 miles, which is now the case for Princeton. Treatment is most effective in the spring, between mid-May and mid-June, just after the tree leafs out. The article confirms the superior performance of emamectin benzoate, the active ingredient in Arbor Mectin and TreeAge. This insecticide may be more expensive than others like imidichloprid, but lasts longer and has a higher success rate. For more on my research on this issue, scroll down at this link to "How to save specimen ash trees".

Natural Predators of EAB

Woodpeckers are said to eat 80% of the EAB, but that's not enough to stop it. There are native parasitic wasps that also prey on EAB, but not in sufficient numbers. Some parasitic wasps species from the EAB's native range in Asia are being introduced (hopefully with a great deal of prior testing to show they won't prey on our native insect species), but I doubt they will influence the arc of Princeton's infestation over the next decade.

An article in the NY Times discusses techniques to stimulate the defense systems of ash trees so that the tree itself will manufacture sufficient chemical defenses to ward off EAB, but again, any practical use is highly speculative.

What's a Dead Ash Good For?

Strangely, there seems to have been no planning at any governmental level to at least put the coming surge in dead wood to use. Talk of sustainability and the opposition to fracking and natural gas pipelines are weakened if we ignore local sources of renewable energy. Lacking wind, we need to turn to sunlight. Solar panels, now essentially free to install, are an obvious option, but for some reason wood is being ignored. Europe has clean incinerators that generate energy from wood chips. Ann Arbor trucked its ash trees to an energy-generating facility in Flint. Unlike the carbon from fossil fuels, carbon from trees comes from the atmosphere, not from underground, so there is no net increase in above-ground carbon when wood is burned. Composting requires considerable fossil fuel for turning and transporting the compost, and decomposition releases as much carbon as burning.

In addition, the EAB invasion is coming just as Princeton's collection of loose yardwaste is being expanded. There is no effective incentive yet in place for homeowners to trim their dependence on this costly program, and the addition of 1000s of ash trees to this already over-burdened collection service could overwhelm the capacities of the public works department and local composting sites.

Possibly relevant, the state compiled this list of "Forest Industry Professionals Accepting Ash Trees".

Previous Posts

The Emerald Ash Borer's arrival in Princeton had been long anticipated. Some fifteen posts on this blog mention it, dating back to April, 2010, when I wrote,

"In Princeton, we will over the next decade likely witness a dieoff approaching the scale of the chestnut and elm dieoffs of the 20th century, as the emerald ash borer, which hitch-hiked to Michigan from Asia in wooden packing crates, continues its spread eastward. There will, in other words, be a lot of gaps in the canopy for the chestnut to claim, if its return is successful." 

That last part, about a resurgent American chestnut filling the gaps as we lose our ashes to the Emerald Ash Borer (EAB), as the previous post about chestnuts shows, was a nice concept but overly optimistic. Here's a particularly extensive post on EAB, in which I included notes from a phone call with the division chief of Forest Pest Management in Pennsylvania, where they've been dealing with EAB for years.

Emerald Ash Borer Informational Meeting Tonight

Below is information from the Princeton Shade Tree Commission website about the meeting tonight at town hall.

I've written from many different angles on the subject of Emerald Ash Borer (EAB) in recent years, such as this one. Type "emerald" into this website's searchbox and various posts will come up. The photo shows the size of the insect, and the "D"-shaped exit holes.

A very experienced arborist I spoke to this week told me that he is injecting emamectin benzoate--the active ingredient in Arbor Mectin and TreeAge--for individual or specimen trees, and using imidachloprid where there are dense stands of ash that the homeowner wishes to save. Emamectin benzoate is more expensive but is more effective and lasts longer.

There are no easy answers as to whether to try to save an ash, take it down now, or keep it until it succumbs. All have a financial cost. With 2000 ash trees in Princeton's public right of ways, and many thousands more in parks, preserves and public lands, this little insect introduced from Asia via shipping crates will have an ecological impact on our open space lands and cost Princeton and its residents millions of dollars. Due to the transport of species from one continent to another, all the free ecological, aesthetic, and cooling services ash trees have provided through history will now have a price tag.

Info on the meeting below:

IMPORTANT MEETING ON THE EMERALD ASH BORER: PRINCETON WILL HOST AN INFORMATIONAL SESSION ON PRINCETON'S ASH TREES AND THE EMERALD ASH BORER, THURSDAY, JUNE 23, 7 PM, AT THE PRINCETON MUNICIPAL COMPLEX, 400 WITHERSPOON STREET. EVERYONE IS WELCOME.

More on Emerald Ash Borer

While in Chicago recently for a family reunion, I stepped out on the back patio of my niece's apartment in Hyde Park, looked up, and saw that a neighbor's tree was dying. The thick, opposite twigs suggested ash, and the loss of most of the crown, with only a few lower branches still green, suggested that Emerald Ash Borer (EAB) has made it to Chicago.

In a nearby Chicago park, I found the characteristic D-shaped exit hole (the native ash borers make a round exit hole).

New Jersey had been exceptional in being free of emerald ash borer, until last year when it was spotted in Somerset, then later in Mercer County. This year, at the May meeting of the Princeton Shade Tree Commission, council member Bernie Miller sounded reasonably sure he had seen one in his yard.

Our town arborist, Lorraine Konopka, has placed two traps on the east and west side of town--one at Valley Road, the other at Marquand Park. The traps contain a pheromone that will attract the insect if it happens to be nearby. Whether or not the traps catch any insects, it's best to assume that EAB has made its way to Princeton, and begin considering which ash trees to treat. It would be nice to think that some ash trees will resist attack on their own, but that hasn't been the experience elsewhere, as far as I know.

Below is info on treatment options from a previous post, along with some related links:

HOW TO SAVE SPECIMEN ASH TREES
It's important for those who have ash trees in their yards to know that those trees can be protected with systemic pesticides. Not all the available pesticides are equally effective, however. Though imidicloprid is being frequently recommended locally, the experts in other states that I've spoken to have all recommended emamectin benzoate (brand name Tree-Age, or Arbor-Mectin). 

Page 15 of this document is very informative, and says the emamectin is the most effective and longer lasting, while warning against use of imidicloprid on larger trees. Dave says that the EAB expert Deborah McCullough recommends emamectin, which is supported by this article about communities in Minnesota. The article is very optimistic about saving some ash trees, and offers this interesting approach:
"Burnsville is so sold on that idea of saving trees, rather than cutting them down, that it plans to encourage residents to treat their trees by extending to them the rates the city receives for pesticide injection. " 

Curtis Helm, a former Princetonian and currently an urban forester in Philadelphia's Parks and Rec department, advises against using imidicloprid on trees larger than 16" diameter. He says Philadelphia is treating 1000 ash with Tree-Age. 

In a previous post on the subject, I included notes from an extended conversation with Donald A. Eggen, Division Chief of Forest Pest Management Division of Pennsylvania. He, too, strongly recommended Tree-Age rather than products that use imidicloprid.
The emamectin benzoate, last time I checked, was more expensive, which may explain the local preference for imidicloprid, but that cost differential is reduced when the frequency of application is considered. 

Note: The Arbor-Mectin formulation is said to be absorbed into the tree more quickly than Tree-age, and therefore can be less expensive to apply. Both use the same active ingredient. 

Links to news stories about emerald ash borer being found in Mercer County are here and here.

There's also evidence from Yellow Springs, Ohio, that another native related to ash trees, the fringe tree, can be attacked by emerald ash borers. I've only seen fringe tree once in the wild, in a nature preserve I helped create in Durham, NC, though it is becoming more common as a beautiful ornamental shrub/tree.

The Emerald Ash Borer Quietly Changes Princeton's Skyline

Scan any skyline in Princeton and you're likely to see dieback in the trees. This happens to be the view from the front step of Veblen House in Herrontown Woods, but the same can be seen in the woods surrounding Princeton Battlefield, and most everywhere else in town. 

We're losing thousands of trees in Princeton, some quickly, some slowly. As described in past writings on this blog, dating back to 2010, the Emerald Ash Borer is proving every bit as destructive as predicted, killing all species of ash tree. And many red and pin oaks are succumbing to an introduced disease called bacterial leaf scorch. 

Many of the trees lost to introduced insects and pathogens in the past century or so--first the American chestnut, then the American elm, and now the ashes--had been dominant trees in our forests. Until the Emerald Ash Borer arrived, sweeping east from its point of introduction (hitchhiking in packing crates from Asia) in southeastern Michigan, the ash had been Princeton's most common tree. The physical gaps, if not the ecological ones, get filled by one thing or another. At Herrontown Woods, tulip trees, red maples, hickories, and sweetgums grow into the voids. 

These radical changes in the forest canopy present challenges for those of us who manage Princeton's woodlands. Dead ash trees become brittle over time. Branches and sometimes whole trees fall across trails, requiring removal. Though the town arborist and his crew have been helping, oftentimes it's volunteers who carry chainsaws deep into the preserves to reopen a trail. 

At Rogers Refuge, Princeton's birding mecca just downhill from the Institute Woods, it is avid birders who work on the trails. Lee and Melinda Varian have been particularly active. Melinda recently sent an email to the Friends of Rogers Refuge group, of which I'm a part, to report that "Lee and I just went out with our chainsaws for the third time this week to
clear fallen Ash trees from the Red Trail. It’s really heartbreaking."

She sent us these photos of a 50 year old ash tree that had fallen across a trail. Another volunteer at Rogers Refuge, Winifred Spar, wrote about how the history of the refuge is embedded in each tree's growth rings.  

In this section of trunk, where the bark has fallen away, you can see how the Emerald Ash Borer larvae consume the tree's cambium. Like the earth's total dependence on a thin surrounding layer of atmosphere (which of course our machines' invisible emissions are radically altering), a tree's vascular system depends on a thin layer of tissue surrounding the trunk, just below the bark. Lacking any evolved defense against the introduced ash borers, the native ash trees quickly become girdled and die. 

Though other tree species like oak and elm may be considered more statuesque, I have been surprised on occasion by just how gloriously big an ash can become. Two examples stood along the oval drive leading to George Washington's home at Mount Vernon. Another stood at the top of the bank of the Delaware in Lambertville. I was in awe at the thickness of their trunks. Surely the one in Lambertville has been lost, but might those at Mt. Vernon have been saved through chemical injections?

As tens of thousands of ash trees die in Princeton, requiring a vast expenditure to remove, has anyone actually seen an Emerald Ash Borer? I have seen a grand total of one, and that was a decade ago in Ann Arbor, MI, close to where they first were discovered in the U.S. By contrast, everyone has seen, and squashed, a Spotted Lanternfly, yet compare the harm done by the these two introduced insects and it's clear the largely unseen ash borer has been far more devastating in its impact. Our senses largely fail us for discerning the greatest threats to our world, be they an elusive insect or, far more devastating still, too much carbon dioxide in the atmosphere. To coin a phrase, call it "quiet radicalism."

By allowing light to reach the understory, the gaps in the canopy created by so many dying trees present a mix of problems and opportunity for managing our preserves. What shrubs will take advantage of the extra solar power, previously harvested by the trees but now reaching the forest understory? Native understory species like blackhaw Viburnum, highbush blueberry, and spicebush can now flourish and produce more fruit. If the deer didn't eat them, rarer native species like shadbush, pinxter azalea, and hearts 'a bustin' could make a comeback. But oftentimes, it is nonnative invasive shrubs that have colonized our woodlands--Photinia, honeysuckle, linden viburnum, winged euonymus, multiflora rose, and privet. Left uneaten by wildlife, the nonnative shrubs have a competitive advantage that could render our woodlands clogged with foliage inedible for local herbivores. 

Changes in the understory can affect whether wildlife thrive. Winifred, a keen observer of bird life in Princeton, wonders "if the gaps in the canopy and increased invasive understory may already be having an effect on birds in the Institute Woods. It might explain why there were noticeably fewer Ovenbirds this past summer; they are ground nesters." 

The ash tree won't disappear altogether. One old post, from 2014, entitled After Emerald Ash Borer, What Will Princeton Look Like, describes a visit to Ann Arbor, where the ash borer had already swept through. We still found young ash trees. My best guess back then remains my best guess now:

I would speculate that, once the native and introduced parasitic wasps become widespread, they in combination with woodpeckers could allow ash trees to persist in Princeton, though perhaps few would grow to maturity unless regularly treated with systemic pesticide.

Carolyn Edelman, a poet and nature enthusiast, recently posted a quote of Adlai Stevenson, II, dating back to a speech he gave in 1952. Its sentiment is part of a vein of American thought that views love of the American landscape as deeply connected to the love of freedom. For me, it is not coincidence that we live in a time when both nature and democracy are being undermined.  Read the quote through today's filter of gender equality and inclusion to find its relevance.

It was always accounted a virtue in a man to love his country. With us it is now something more than a virtue. It is a necessity. When an American says that he loves his country, he means not only that he loves the New England hills, the prairies glistening in the sun, the wide and rising plains, the great mountains, and the sea. He means that he loves an inner air, an inner light in which freedom lives and in which a man can draw the breath of self-respect. Men who have offered their lives for their country know that patriotism is not the fear of something; it is the love of something.

A great tree species passes from the landscape, but the love remains, and in that love reside both grief and possibilities.

Princeton Expected to Lose Its Ash Trees

This is a towering white ash tree, one of thousands in Princeton, and for as long as anyone can remember, it has grown "real good for free", as Joni Mitchell might say. As with the clarinet player in her song, playing for free on a street corner, people pass it by without a thought, while it quietly supplies beauty and abundant ecological services--shade, cooling, habitat, oxygen, carbon sequestration--all rendered at no cost.

That's about to change. Four years ago, I wrote on this blog:

"In Princeton, we will over the next decade likely witness a dieoff approaching the scale of the chestnut and elm dieoffs of the 20th century, as the emerald ash borer, which hitch-hiked to Michigan from Asia in wooden packing crates, continues its spread eastward." 

It doesn't take any great clairvoyance on my part to see the future. I had once lived in Ann Arbor, MI, which had to cut down 10,000 ash trees at a cost of $5.8 million.

Living in Princeton, then, is like having traveled back in time. Knowing what's in store, what's been sweeping eastward from the midwest, makes me appreciate more what we still have. I pause more than I might otherwise at the sight of an ash, particularly in the fall when they change color. The halcyon moment for me with ash trees will always be the time, long before the emerald ash borer came on the scene, when I drove north in Michigan to play for a wedding that was perfectly timed with the fall colors. Sugar maples dominated with their radiant orange and gold. Sumac made horizontal strokes of brilliant red. And the uncanny mix of yellow and purple in the ash trees was so strong it seemed to vibrate. We were paid for our time, but they let us play the jazz tunes we love, outdoors, overlooking a glorious valley of color. Our singer's rendition of Make Someone Happy was so full of buoyancy and conviction we knew we had found the meaning of life. If a composer like Scriabin can see color in music, then surely there was music in the colors of the north woods that day, the trees playing an ancient symphony freely given, filling us with enough color to last us through the long Michigan winter

This spring, the emerald ash borer, known unaffectionately by its acronym, EAB, was finally found in NJ, 25 miles north of Princeton, in a parking lot next to Patriot Stadium in Bridgewater. Though those of us who knew it was coming have a head start on grief, the official announcement on May 21st still had an emotional impact. This link used to show New Jersey as free of EAB, but essentially surrounded by infestations in bordering states. Now NJ has been added to those with EAB. It may have flown in on its own, from NY or Pennsylvania, or it may have been transported in firewood. None have shown up in traps set in Princeton, but the traps are an imperfect test of their presence.

Princeton's battle with the beetle will be expensive. The strategy cannot realistically be to win, but to cushion the blow to canopy and pocketbook. Any view more optimistic than that veers into wishful thinking. In the twelve years since it was first identified in Michigan, neither white nor green ash has shown resistance to the insect, and no controls are poised to save the day. We may save some of our ash trees with systemic insecticides, at considerable expense, but far more will be lost to a diminutive beetle that no one noticed in Michigan until it had become to entrenched to eradicate. And Princeton has a lot of ash to lose, it being our most numerous tree. Arborist Bob Wells' recent inventory identified 2200 white and green ash trees along the streets, plus the uncounted thousands in our parks and woodlands. 

The strategy for dealing with the invasion, which could arrive in Princeton in a year or two, or could already be here but undetected, will likely involve chemical treatment to protect the finest specimens, and beginning to cut down other ash even before they show symptoms.

There are chemicals that can be used to save individual trees. As a proactive measure, Princeton University began treating its most valuable ash trees two years ago. Choosing which insecticide to use involves tradeoffs. Imidicloprid is less expensive, but is injected into the soil around it rather than directly into the tree. Because the compound is toxic to pollinators, it should not be injected where flowers are growing beneath the tree. The herbaceous plants will absorb the chemical and transfer it to the pollen in their flowers, where the pollinators will be exposed. Other options can be found in the extensive notes below.

Two things are particularly upsetting about the arrival of the emerald ash borer. Of course first and foremost is the loss of a tree species and all the beauty and services it has been providing for free. The other is New Jersey's incredible lack of preparedness. Composting centers are already overwhelmed. Trees make an excellent fuel--one of the few ethical forms of energy we currently have available to us, since wood's carbon comes from the air rather than from underground sources. The technology is available to cleanly run cogeneration plants with wood for fuel. If the state actually is preparing for what one arborist called "ten years of mayhem", it's being done very quietly. Chances are, New Jersey will only start reacting once the devastation begins, even though it had ten years to prepare.

The recurring lesson is of the abundant services and beauty nature gives, every day, none of which are entered into our economic calculations, and the increasing vigilance and stewardship required to guard those gifts as global trade increases the pace of change. Below are my collected notes on the coming invasion, including an extensive phone conversation with Donald Eggen, division chief for Forest Pest Management in Pennsylvania. 

Notes from a conversation with Donald A. Eggen, Division Chief of Forest Pest Management Division. (These notes were rapidly written, but are my best rendering of what Eggen said.)

EAB attacks trees as small as 1" in diameter.
The insects start at the top of the tree and work down.

Expansion of EAB into new areas
In 2013, PA documented EAB in 16 new counties without even looking very hard
The Louisville Slugger baseball bats are made out of ash harvested in northern PA. EAB is now moving into that area.
Traps for detecting EAB in an area don't work very well. Their odor imitates a stressed tree.

In a given area:
EAB doubles each year. If 16% of trees affected, the next year there will be 32, then 64, then all. It can sweep through a town in five years. (sources on web suggest more like ten years--perhaps it takes a few years to get to 16%, and then a couple years to kill those that are last to be attacked).

Assessment of a tree
Take DBH (DBH (diameter at breast height) is a poor measure. Bigger trees need more juice.)
If 70% of crown looks good, then tree could be saved
If it dies, it becomes a hazard tree
Don't treat if more than 30% in decline. Insect damage can't be repaired. Most ash in decline, even without EAB, due to winter storms, wet weather, all of which, if it's a street tree, brings out root ball problems left over from improper planting. Kill the roots, kill the tree.

Strategies
Options are to treat, to remove, or to remove and replace.
Don't delay on treatment. Do most critical trees in first year. Spread the cost out.

He mentioned Chris Sadoff at Purdue, and I later found this, which is one of many such documents on the web to help with decision making: http://extension.entm.purdue.edu/EAB/PDF/NABB_DecisionGuide.pdf

Treatment: Recommends Tree-age (Emamectin Benzoate), a play on the word "triage". Not available to homeowners, it's restricted use, and must be applied by professionals. It's more expensive than another treatment with various names such as Merit, but has advantages in that it is injected directly into the tree. The injection point is at the base of the tree, where it flares out just above the ground. This is where the sapwood is thickest. The product is made by Arbor Jet, and applicators should undergo training through Arbor Jet. There is reason to believe that it will last longer than two years, possible 4 or more.

Merit, as with other similar products whose active ingredient is imidicloprid, is injected into the soil around the tree. If the soil is compacted, the uptake could be slower. Something called Safari is sucked up faster by the tree than Merit, but doesn't last as long (?). Both Merit and Safari protect the leaves well. A product called Xytec has to be applied every year.

Timing
With Tree-age, treat late May through June. A cloudy day with a little breeze is best. (presumably when a tree is translocating upward most effectively).

Cost
Ash can be more costly to remove than to treat. If they die, they become brittle very quickly, which makes them more dangerous to work on. Some arborists refuse to go up in the trees if they have become brittle. An increase in accidents has been documented. The trees can also become weak at the roots and topple over at the base.

Chicago is treating tens of thousands of ash, at a cost of $1.4 million/year.
The plan is on the website. Westchester, PA has a 10 year plan that includes cost.

Other insects/diseases
Asian Longhorned Beetle (ALB) in Wooster, MA, big infestation. ALB has gotten into the woods, which is bad because it doesn't kill trees in the woods and therefore is hard to find. Not as good a flyer as EAB, so slower to expand territory.

Black walnut disease found in Bucks County, contained apparently.

(End of Eggen notes)

__________________________________________________

SYMPTOMS OF EMERALD ASH BORER (taken from the web)

1. D-shaped exit holes – 1/8” inch holes left after adults exit the tree

2. Bark splits – vertical splits in the bark

3. S-shaped feeding galleries – can only be seen when bark is scraped or in bark splits

4. Woodpecker damage – missing or discolored bark beginning at the top of the tree

5. Crown Dieback – foliage at the top of the tree may thin or discolor

6. Epicormic sprouting - shoots of leaves growing from the trunk

The New York Times ran an article on emerald ash borer, featured in a talk in Princeton by the Times science editor that same day.

Here's an article that claims that woodpeckers can play a role in controlling EAB. I'm skeptical.

I also found on the web a city that was paying $90/tree for treatment using Tree-age

Interestingly, ash continue to sprout in the woodlands in Ann Arbor, and can grow to 6 inch diameter, but the chances of their growing to maturity are slim.

Some sources on the web suggest that once EAB  passes through and attacks all the trees there are to attack, then ongoing treatment costs for those trees saved will come down somewhat.

Update: A short video on a parasitic wasp being introduced in Maryland to help control the EAB. Sounds like it could potentially help in the longterm, but is described as "a drop in the ocean", given the vast numbers of EAB compared to the few parasitic wasps released.

After Emerald Ash Borer, What Will Princeton Look Like?

Back in July, I took a trip to the future. Princeton still has a few years before the emerald ash borer is expected to decimate our ash trees (what a cheery sentence that is), but Ann Arbor, MI, has already weathered the EAB storm. The city is located less than an hour away from the original introduction of the insect, which went unnoticed in the Detroit area from the early 90s through to 2002 when it was finally identified. The introduction was likely via wooden shipping crates arriving in Detroit/Windsor from China.

Ann Arbor's tree removal lasted ten years and cost $5.8 million. What does this city of 110,000 look like now?

By chance, my trip to Ann Arbor coincided with a visit by college friend and early EAB researcher Dave Cappaert. We visited County Farm Park, one of the sites where he and fellow entomologists did the dirty work of cutting open some 10,000 ash trees to study the behavior of the emerald ash borer and search for parasites that might help control its numbers.

While immersed in research on EAB, Dave discovered a formerly unknown braconid wasp that parasitizes EAB larvae, and now bears his name: Atanycolus cappaerti. Other useful parasites have also been discovered, here and in China, and they could play a role in reducing the number of emerald ash borers that continue to affect ash trees after the first mega-wave of ash borers passes through an area. There's a video that gives a brief history of EAB (complete with darkly evocative sound effects) and then describes three parasites of EAB that were found in China and are now being released in the U.S. after thorough testing.

There's a bit of good news. Valued ash trees along streets or in yards can be spared, for a price. And wild ash trees do not disappear altogether. We found 20 foot tall ash trees making a go of it, here and there. Dave says that 80% of the EAB larvae get eaten by woodpeckers. It's still a mystery how the woodpeckers are able to locate the larvae under the bark with such consistent precision.

Here's a young ash showing the outer symptoms of EAB attack. I would speculate that, once the native and introduced parasitic wasps become widespread, they in combination with woodpeckers could allow ash trees to persist in Princeton, though perhaps few would grow to maturity unless regularly treated with systemic pesticide.

While we were walking around, Dave found one of the signs he and other researchers had placed around the park years back to explain why they happened to be pulling the bark off of thousands of trees in a public park.

Click on the photo to make it more readable.

Here's an ash tree showing signs of dieback on the upper right--likely to be a common sight in Princeton in coming years.

HOW TO SAVE SPECIMEN ASH TREES

It's important for those who have ash trees in their yards to know that those trees can be protected with systemic pesticides. Not all the available pesticides are equally effective, however. Though imidicloprid is being frequently recommended locally, the experts in other states that I've spoken to have all recommended emamectin benzoate (brand name Tree-Age, or Arbor-Mectin).

Page 15 of this document is very informative, and says the emamectin is the most effective and longer lasting, while warning against use of imidicloprid on larger trees. Dave says that the EAB expert Deborah McCullough recommends emamectin, which is supported by this article about communities in Minnesota. The article is very optimistic about saving some ash trees, and offers this interesting approach:

"Burnsville is so sold on that idea of saving trees, rather than cutting them down, that it plans to encourage residents to treat their trees by extending to them the rates the city receives for pesticide injection. "

Curtis Helm, a former Princetonian and currently an urban forester in Philadelphia's Parks and Rec department, advises against using imidicloprid on trees larger than 16" diameter. He says Philadelphia is treating 1000 ash with Tree-Age.

In a previous post on the subject, I included notes from an extended conversation with Donald A. Eggen, Division Chief of Forest Pest Management Division of Pennsylvania. He, too, strongly recommended Tree-Age rather than products that use imidicloprid.

The emamectin benzoate, last time I checked, was more expensive, which may explain the local preference for imidicloprid, but that cost differential is reduced when the frequency of application is considered.
Note: The Arbor-Mectin formulation is said to be absorbed into the tree more quickly than Tree-age, and therefore can be less expensive to apply. Both use the same active ingredient.

Any decision about how Princeton should proceed with pesticide applications (some homeowners have already begun applications, given that EAB has been discovered 25 miles north of here), should weigh heavily the input of those in Michigan, Pennsylvania and elsewhere who have benefited from years of experience.

A Mysterious Hitchhiker From Argentina

Back in early September, walking down a hallway in our house, I happened to look up and saw a strange insect on the wall near the ceiling. My impulse is not to squash such things but to take a closer look. It had very long antennae and white spots on a black body. Preoccupied, I took a photo and thought nothing more of it.

A month or so later, I happened to move a wooden bowl on the wooden table that holds the TV. Beneath the bowl were miniature piles of sawdust, and two small holes where something had started to bore into the table. I guess we should dust more often, but who expects a miniature drilling operation to begin underneath a pretty souvenir?

We had bought the bowl in August at a tourist spot called Aripuca, in northern Argentina near Iguazu Falls. The site has a grassy open space surrounded by remarkable buildings built of wood.

This description of the main building is from Lonely Planet:

"Designed to 'capture the conscience of man' (an aripuca is a trap used by the Guaraní to catch small animals) this interesting structure is made entirely from the timber of 29 different endangered native tree species. While this might sound contradictory, the timber is all salvaged..."

A guide at the site showed us how the trap, whose shape the building imitates, is set by Guarani indians.

Scavenged wood from the forest is used to make all sorts of benches and tables, all of which are too big to bring home in a suitcase.

The store offered more portable objects hewn from the local wood. The Aripuca site has a strong emphasis on ecological stewardship of forests--something much needed since most of the Misiones forest has been destroyed. The famous Iguazu Falls is one of the few protected remnants.

Our selection, as mentioned, was the bowl with the attractive grain and markings. A week later, we carried it obliviously through U.S. customs, not knowing it was a Trojan Horse with little hitchhikers, a few of which would gnaw their way out the following month.

They emerged as adults, some in better shape than others. This inadvertent insect-smuggling can be a potential menace. Consider the Emerald Ash Borer, which has killed "tens of millions" of ash trees in the U.S. and Canada since it hitchhiked to the U.S. from Asia in wooden packing crates.

The long antennae on the beetles emerging from our bowl suggest it is, surprise, a longhorned beetle. The most notorious hitchhiker in this category is the Asian Longhorned Beetle. Nicknamed ALB, it should strike fear into even those who lack any fear of bugs. Readers may be unaware that the U.S. has been at war since the late 1990s with the ALB, which could decimate our forests if it spreads. Its favorite tree species are maples, which gives you a sense of what's at stake. The ALB, like the Emerald Ash Borer, comes from a climate similar to our own, so has been able to survive our winters.

Because ALB is slower to spread than the Emerald Ash Borer, there's been some success in eradicating it, but at considerable expense and sacrifice. All maple trees and some other species need to be removed in the vicinity of an infestation, which means many non-infested trees are destroyed to prevent spread. Current infestations are in Ohio, New York and Connecticut. Late 1990s infestations in Chicago and NJ were reportedly eradicated, though it's hard to be completely sure.

The longhorned beetles sprouting in our house had markings unlike the ALBs. There were just a few of them, and coming from a tropical area, they likely wouldn't be adapted to survive a NJ winter. Still, I wondered about the sawdust marks on the firewood in the living room.

And what was this substantial pile of sawdust, made visible as I burned the last of the logs? Probably the work of native insects that hitchhiked indoors from the backyard woodpile.

One morning in mid-December, we were greeted to the sight of two more emerging, as if the bowl was playing the role of Sigourney Weaver in Aliens. They didn't make it out, though, apparently stillborn in dry indoor conditions.

I've emailed Aripuca about the situation. A tourist from a climate similar to tropical northern Argentina could potentially spread the insects to new locales where they could escape and become established.

The biggest problem is the wooden pallets and shipping crates used in global commerce. Regulations now require fumigation of shipping crates. One has to wonder, though, what the automatic, indiscriminate budget cuts put in place by the sequester are doing to the nation's ability to adequately inspect shipments and continue to do battle with the infestations.

I'm the sort who, long aware of the threat invasives pose, will inspect my shoes before traveling out of NJ to make sure I'm not carrying seeds of Japanese stiltgrass or garlic mustard. So there's some irony in being an accidental vector for alien insects. The bowl is probably free of the beetles by this point, but we'll continue to keep an eye on it, and be more leery of bringing home interestingly marked wooden souvenirs in the future. 

Requiem for an Elm

The lovely, spreading American elm at the corner of Harrison St and Hamilton Ave. has finally succumbed to Dutch elm disease. Not that many people will have noticed. Thousands of cars pass through this busy intersection every day, their drivers seeing only a blur of green. And there are many trees in the neighborhood that even those of us who walk will find conspicuous only in their absence, when we encounter a stump and a large gap in the canopy and wonder what was there.

This elm is one of the trees I noticed, so well matched to the space it was given, its long limbs spreading the gift of shade. And though I grieve its passing, it has lived a longer life than any American elm could be expected to live. Coming to New Jersey from Michigan and North Carolina, I had largely conceded the elm to fringe status, its glorious, towering vase-like form living only in memory. But in Princeton, American elms are more than a memory. They may sometimes be downed by the disease, but are not out. Nine years ago, the famous elm in Princeton Cemetery finally succumbed, but not before making the front page of the New York Times and spawning a generation of disease resistant elms, some of which were chosen to grace Pennsylvania Avenue in Washington, D.C.

By chance, I happened to be walking by the elm at Harrison and Hamilton recently when a man was standing beneath it with a clipboard. It was Arborist Joe Christopher, who oversees treecare at the housing development there. He said the tree has to come down, and recalled stories of how, when Dutch Elm disease swept across America, chain saws could be heard all day.

We agreed that Princeton is on the cusp of a similar era. Christopher predicts "a decade of mayhem", beginning when the emerald ash borer sweeps into Princeton as it has all over the midwest and now in the east, killing any ash tree that hasn't been inoculated against it. Over the years, Princetonians have rallied to protect this or that beloved tree from being taken down by developers. But there's a much bigger battle going on, one that has to be fought by government agencies, regulators and inspectors, to protect America from the radical change that comes when a pest like emerald ash borer is introduced.

Other tree species are also threatened. Thousand cankers disease, a major threat to black walnuts, was found recently in Bucks County. The Asian longhorned beetle, another accidentally import that threatens many hardwood species, particularly maples, has been found again on Long Island, and is proving hard to eradicate in Massachusetts.

We're in for a rough patch with our trees, and all the myriad kinds of insects and other wildlife that depend upon them, which is why the loss of our elm at the corner is by comparison a positive story. It lived a good and fairly long life, despite considerable odds. Efforts are underway in town to bring back the American chestnut and the butternut. Ash may still persist as small individuals in the woods after the emerald ash borer sweeps through. But the beauty and diversity that was once ours for free is now having to be worked at. What we're losing, species by species, is that easy grandeur that has long defined America.

Native Trees of Princeton

An attentive reader commented that the page for "Native Trees of Princeton", which I thought I had added along the top of the homepage, does not exist. Funny, I clicked on the "publish" button but the list of trees refused to publish, nor did it magically publish itself during the ensuing weeks when my mind was on other things. Maybe Googles ever more sophisticated software detected that it still needed work, which is to say it was a bit "drafty".

Here it is, nonetheless, published as a post rather than one of those enduring "pages" at the top of the blog. It was created as a step towards fleshing out, or foliating, a rather bare tree list we have on the Princeton Shade Tree Commission website.

My apologies to any native tree species not included here. Please speak up. Catalpas, we'll talk.

ATTRIBUTES OF SOME NATIVE TREES IN PRINCETON 

This is an extensive but informal list of native trees you may encounter in the wild or in your yard, with some description, based on ten years of observation. 

Acer negundo (box elder)--Grows wild. Not commonly planted. It's soft wood can provide good habitat for birds. Considered messy and not very well formed.

Acer rubrum (red maple)--A durable, very commonly planted street tree. Also common in the wild.

Acer saccharinum (silver maple)--Common in yards and in the wild. Not often intentionally planted. Has a reputation for dropping limbs, but performs well in many yards, providing an attractive, open shade.

Acer saccharum (sugar maple)--Less common, but a sturdy, attractive native.

Amelanchier canadensis (shadblow, shadbush, serviceberry, Juneberry)--A very small tree or large bush. White flowers early in spring, supposedly when the shad are surging up the Delaware. Berries edible, but frequently attacked by cedar apple rust, so don't get your hopes up. Even our resident catbirds were disappointed.

Asimina triloba (pawpaw)--Small tree, up to thirty feet. I heard there's a wild stand behind someone's house down across Carnegie Lake, and a substantial patch in a park over in Cranbury. Plant more than one to increase prospects for the often elusive fruit. They clone, so best planted where there's a little room to expand.

Betula lenta (cherry birch)--Grows wild along the Princeton ridge. Not commonly planted in yards.

Betula nigra (river birch)--Beautiful bark and form, frequently sold with three trunks.

Betula (paper and grey birches)--These species are more characteristic further north.

Carpinus caroliniana (blue beech, hornbeam, musclewood)--Common along the Princeton ridge. Not often intentionally planted.

Carya alba (mockernut hickory)

Carya cordiformis (bitternut, swamp hickory)

Carya ovata (shagbark hickory)--Hickories are common in the wild, but not frequently planted.

Castanea dentata (American chestnut)--Devastated by the imported chestnut blight in the early 20th century. Only a few small specimens persist in the wild. The disease does not kill the root, which then resprouts. Backcrossing has developed resistant native varieties with a small percentage of asian genes, e.g. 1/16th Chinese. Some of these 15/16th native trees have been planted in parks and preserves in Princeton in an effort to reestablish the species. A few chestnuts grow along streets in Princeton, but are either Chinese or Japanese. The nut husks are very large and prickly.

Celtis occidentalis (hackberry, sugarberry)--Sturdy native, infrequently seen in the wild, underutilized in planted landscapes. They line Walnut Street across from JW Middleschool.

Chionanthus virginicus (fringe tree)--Very attractive flowers. Small tree/large shrub. Some evidence in Ohio that it can be attacked by emerald ash borer, but more evidence is needed before deciding not to plant.

Cornus florida (flowering dogwood)--Attractive small tree, commonly planted, with berries that provide important nourishment for birds migrating south in the fall. Fairly common in the wild, but an imported fungus has cut back on its numbers. It can be harder to establish that the Korean dogwood, whose fruit are eaten by monkeys in its native Asia.

Crataegus crus-galli (cockspur hawthorn)--Attractive small tree. Rarely found in the wild. Underutilized in planted landscapes, perhaps because of thorns.

Diospyros virginiana (persimmon)--Attractive mid-sized tree. Females bear fruit, which may be appreciated or viewed as messy.

Fagus grandifolia var. caroliniana (beech)

Fagus grandifolia var. grandifolia (beech)--Beech trees are common in the wild along the Princeton ridge, but are seldom if ever planted.

Fraxinus americana (white ash)--Princeton's most common tree, soon to be decimated by the arrival of Emerald ash borer. Though typically encountered in second growth forest, it can grow to a towering height, with a few extraordinary specimens to be found on campus and in older neighborhoods. Planting ash is discouraged, since all ash species will soon be dependent on chemical injections for survival. Anyone owning an ash they wish to keep should get it treated, with emamectin being the most frequently recommended insecticide to inject into the trunk.

Fraxinus pennsylvanica (green ash)--Usually found in wetter conditions, and less attractively shaped, than the white ash. Same susceptibility to emerald ash borer.

Gleditsia triacanthos (honey locust)--The wild variety has thorns and is rarely encountered, perhaps because it was spread by now extinct megafauna. The unripe seed pods have a sweet, edible inner lining. One large specimen can be found near the old gas station at Princeton Shopping Center. Planted varieties, such as those at the new Dinky station and Hinds Plaza, have no thorns, and provide a pleasant, open shade. The tiny leaflets conveniently disappear back into the lawn in the fall.

Gymnocladus dioicus (Kentucky coffee tree)--A remarkable tree, rarely found in the wild, for reasons similar to honey locust. Its very large compound leaves emerge late in spring, and drop early in fall, making the tree ideal for planting on the south side of passive solar houses. They were used in the landscaping for the Dinky parking lot.

Hamamelis virginiana (witch hazel)--Attractive small tree/large shrub. The native species flowers in late autumn, while asian species flower in the spring.

Juglans cinerea (butternut)--Rarely seen. Some are hybrids. The native species has suffered from the introduction of a fungal disease. Efforts are underway to bring back the butternut in Princeton, in parks and nature preserves.

Juglans nigra (black walnut)--Common in some wild areas, and in some backyards. Rarely planted, due to large nuts and the juglone compound emitted by the roots, which can suppress growth of tomatoes and other plants.

Liquidambar styraciflua (sweet gum)--Sturdy, large tree, common in the wild and sometimes planted intentionally. The "gum balls" it drops can be a drawback for some.

Liriodendron tulipifera (tulip tree)--Fast growing, long-lived tree that can reach great size. Flowers tulip-like and attractive, but usually too high up to appreciate. Common in the wild, but not typically planted intentionally.

Magnolia virginiana (sweetbay, swampbay)--Small tree. Can have attractive flowers. Not typically planted along streets.

Morus rubra (red mulberry)--The white mulberry (M. alba, nonnative) is also found in Princeton. A small tree. Bears abundant, edible berries similar in appearance to blackberries. The berries can be messy, and the tree lacks an attractive form. Very tasty berries, though, if you can reach them.

Nyssa sylvatica (black gum, tupelo)--Beautiful fall color. Sporadically encountered in the wild. Long-lived, sturdy. Is becoming more frequently planted along streets.

Ostrya virginiana (ironwood, hophornbeam)--Small tree. Not common in the wild, nor in the landscape trade.

Oxydendrum arboreum (sourwood)--Small tree with bright red fall foliage. Craggy form. Underutilized; may not be well adapted for the nursery trade. More common in the wild further south. Several specimens in Princeton, including one next to the church across from the high school.

Platanus occidentalis (sycamore, plane-tree)--Can be confused with the London planetree, which is a hybrid between two species, one of which is P. occidentalis. Attractive, large tree, with highly ornamental bark. Its more susceptible to anthracnose than the hybrid.

Prunus pensylvanica (fire or pin cherry)

Prunus serotina (black cherry)--The native cherries are attractive mid-sized trees typically found in earlier successional forests. They nearly rival oaks in the diversity of insects they provide food for, and so are very important for food chains.

Quercus alba (white oak)--One of the most majestic trees. The white oak "family" (those with rounded lobes, such as white oak, swamp white oak, and willow oak) are less susceptible to bacterial leaf scorch than the red and pin oaks (pointed lobes).

Quercus bicolor (swamp white oak)--Sometimes planted along streets.

Quercus coccinea (scarlet oak)--Attractive, but less commonly planted.

Quercus palustris (pin oak)--Very common street tree in Princeton. Its lower branches characteristically angle downward and often die back. Many are being lost to bacterial leaf scorch, which causes gradual dieback.

Quercus phellos (willow oak)--More frequently planted than in the past. More common in states further south. Its narrow leaves can form an attractive mulch, somewhat like pine needles.

Quercus rubra (red oak)--Common tree in the wild and along streets. Susceptible to bacterial leaf scorch.

Quercus velutina (black oak)--Encountered in the wild. Less commonly planted than red oak.

Robinia pseudoacacia (black locust)--Native to the Appalachians. Widely planted and naturalized elsewhere. Its wood is resistant to decay, it has attractive flowers, and can achieve a very attractive form with dark, craggy limbs contrasting with the foliage. Can be invasive in some habitats, and can clone, sending up young shoots armed with thorns. But some specimens in Princeton front yards are beautifully formed and well behaved.

Salix nigra (black willow)--Fast growing. Sometimes planted in low areas in the belief that it will dry the soil out.

Sassafras albidum (sassafras)--Attractive tree, common in the wild. Can clone, which may be why it's not commonly planted.

Tilia americana (American linden, basswood)--Attractive. Underutilized. Sporadically encountered in the wild. Linden trees along streets are generally not the native species.

Ulmus americana (American elm)--Though the elm was hit hard across America by Dutch elm disease, Princeton varieties have shown considerable resistance, allowing specimens to perform well and provide shade for many years, even though they may eventually succumb.

Ulmus rubra (red elm, slippery elm)


Native Evergreen Trees:

Ilex opaca (American holly, Christmas holly)--Attractive native, sometimes used in yards. Can grow eventually to 30 feet or so.

Juniperus virginiana (eastern red cedar)--Small tree. Useful in some situations.

Pinus strobus (eastern white pine)--Not encountered in the wild unless in planted stands. Its native range is to the north of Princeton. Can get big, and tends to drop large branches during ice storms.

Where Have All the Spotted Lanternflies Gone?

Well, it's happened, at least in our neck of the woods.

Billed as a major calamity, the spotted lanterfly invasion has gone "poof" this year. Yes, the spotted nymphs could still be found clinging to the stems of Ailanthus sprouts at our Barden in Herrontown Woods. 

And a few adults were later seen perched on the rachis of Ailanthus leaves. We pulled the sprouts out of the ground to deprive them of this haven. Hard to say where they went after that.

Writing a post about lanternflies three years ago, I learned that numbers of the invasive insect had dropped in some areas of Pennsylvania five years after first being seen. Lanternflies first showed up in Princeton in 2018, and here we are five years later, with what appears to be a dramatic drop in numbers.

It's true that people gave themselves over to squashing the pesky bugs--leafhoppers, actually--in spirited ways. (This photo shows one of the more creative approaches.) Some think the unusual weather has had an effect. Insect numbers overall have been down, be it the pollinators on backyard flowers, the odorous house ants that used to invade our kitchen, or spotted lanternflies. But my guess is that it has been the full-time predators, feathered or with eight legs or six, that are to be most congratulated for stemming the explosion of spotted lanternflies. 

Just follow the trail of colorful wings that brightened a walk up towards Veblen House one day.

The most powerful contrast for me is between the invasions of emerald ash borer and spotted lanternfly. Since the emerald ashborer arrived, about ten years ago, I have yet to see a single adult ash borer in Princeton, and yet the devastation they have brought to the ash tree is all around us. The lanterfly, on the other hand, has been seen everywhere, and yet I can't point to a single plant that has died due to their appetites. We humans are visually oriented, but it's the invisible threats--be they an invasive insect or even more significantly an overdose of carbon dioxide--that most endanger our world.

The Viburnum Leaf Beetle's Gathering Harm

This fall, before the leaves fall off, check any Viburnum shrubs you know and love, whether in your yard or in your favorite nature preserve. Do the leaves look like this, pitted with holes, or even stripped down to the veins?

Most people have heard by now about the Emerald Ash Borer's rapidly multiplying demolition of our ash trees. Lest that devastation not be enough ecological and horticultural tragedy to absorb, there is another invasion underway in Princeton, by the Viburnum leaf beetle. This one--a European insect that first showed up in Canada before spreading to the U.S., is going after our understory, one Viburnum species at a time.

This and the above photo are of Viburnum dentatum, the arrowwood Viburnum, which grows here and there in our woodlands, preferring wetter soils. The light damage could have been done by a native insect, or by the first few Viburnum leaf beetles to show up, suggesting much greater damage the next year. Listed as "highly susceptible" on Cornell's website, the arrowwood Viburnum will be the first to succumb.

The maple leafed viburnum, frequently encountered along the Princeton ridge, is less susceptible and thus isn't showing any damage this year. As the Viburnum leaf beetle increases in numbers and exhausts the most susceptible species through complete defoliation, it will presumably begin attacking those that are less susceptible.

We are not completely helpless as yet another careless introduction to the continent wreaks slow motion havoc. This site offers some ways to prevent the beetles and their larvae from consuming your favorite specimens. As with all environmental damage done, the ecological and aesthetic services these shrubs were providing for free will now start coming with a price tag for human maintenance.

The Cornell site offers another ray of hope. An extension official in Rochester, NY asserts that even highly susceptible species may in the long term become viable again, as predatory insects and soil nematodes build up to prey on the Viburnum leaf beetles. Then, perhaps, the introduced species would come into some sort of ecological balance, doing some damage but not enough to kill the Viburnums.

It's a perfectly logical and reassuring scenario, and yet observation often brings into question the speed and effectiveness of nature's capacity to restore balance and sustain diversity. More often, invasive species remain dominant and destructive, be they Phragmitis, or Japanese stiltgrass, or porcelainberry. I called up the Frick Park Environmental Center in Pittsburgh, where I had first witnessed the devastating impact of Viburnum leaf beetle a decade ago. Asked whether they had seen any signs of balance being restored, they answered, "Not yet."

Related links:

The Pennsylvania extension service also has some useful information.

Past NatureNotes posts about the Viburnum leaf beetle, dating back to 2013, can be found here.

This post explores the likely aftermath of the Emerald Ash Borer invasion currently underway.