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.

September Nature Vignettes

 Encounters with nature and sustainability around Princeton in September.

One of my favorite corners in Princeton is near the middle school, at Guyot and Ewing. It's a small enclave, a triangle of sense, where the yards and the roofs of houses actually perform work, growing food and gathering energy. On one side is a small house with a small yard that the owner has turned into an orchard and vineyard, as might be more often encountered in Italy. 

Nearby is a house whose south-facing roof has been completely covered with solar panels for 20 years. 

When a house was torn down recently at the corner, I feared it would be replaced with something huge and unattractive, 

but instead, a one-story house with extra thick insulated walls and solar panels and interesting design is taking form. It was a real surprise to see a one-story house being replaced with another one-story house that is sensitive to the history of the site and seeking to fit in, while showing off a modern design that seeks to minimize energy consumption.

They even have a sign on the fence describing the project and what was there back in Princeton's agrarian era. 

Blooming along the fenceline next to the house are sunflowers and autumn clematis vine. Gorgeous as they are, thankfully generating color at a time when most flowers are spent, they are best not planted in a garden unless where the spread of their roots is limited by a house or pavement. Otherwise, given abundant sun to power their aggressively spreading roots, they will take over your garden.

Another common encounter in September is with late-flowering thoroughwort, which spreads not by roots but by seed. It can be weedy but also lovely and even elegant at times, and is great for pollinators. I couldn't get myself to pull this one out in our backyard, even though it has completely taken over a garden path.

At the Barden in Herrontown Woods, they are so plentiful that we don't feel too bad pulling out the ones that lean over the pathways.

The fight against invasive species has the side benefit of taking me to areas of a nature preserve where I wouldn't otherwise go. Recently, it led me to a patch of native diversity in Herrotown Woods that I hadn't noticed before.

Here is obedient plant, 

New York ironweed, 

and the post-flowering look of water hemlock. 

One of my favorite garden plants this time of year is stonecrop "Autumn Joy." 

A sedum, its disks of flowers go through a gradual enrichment of color from green to pink to deepening shades of red, then finally chocolate. Nonnative but noninvasive, it has the added benefit of being popular with pollinators. 

Pawpaw trees are becoming more common in Princeton. The patches planted in Herrontown Woods have yet to bear, but this one in my backyard reflects a growing interest in this unusual species native to the north yet with a tropical taste.

Native persimmons, likely once common in Princeton but often shaded out by larger trees in recent decades, are an attractive smaller tree that might actually bear edible fruit if you happen to get a female and harvest it just at the right time.

If the drought hasn't made the berries too dry, these blackhaw berries could make for some good picking after they darken. Blackhaw viburnum, Viburnum prunifolium, is the most common native viburnum in our woodlands.

Less generating of anticipation are the fruits of a female ginkgo tree, encountered growing near the Princeton Junction train station. The fruits have such an unappealing smell that people try to avoid planting female trees. 

Among inedible fruits, I call this the incredible shrinking pokeweed, because it initially grew to be seven feet tall--way too big to grow along a busy street. So I cut it down midsummer and thought that was that, only to have it sprout back as a smaller version of itself. You could try this technique with a number of perennial native wildflowers that get too tall for people's taste. Cut them down partway through the summer, then let them grow back in a miniature form. 

Though it dies down to the ground each year like a perennial wildflower, pokeweed looks more like a miniature tree, and in fact it has a close relative in Argentina. The ombu grows to the size of a large tree, yet lacks xylem. 

This shrub, too, needs to be cut back. It's an oak-leafed hydrangea I planted long ago in a little raingarden at the front of the Whole Earth Center. The landlord the store leases from must have a new landscape firm taking care of the grounds, because I stopped by recently to find that my native shrubs have been trimmed to look like bowling balls. Funny to see a native shrub and wildflower planting getting the bowling ball treatment. I'll have to take some loppers to restore light to the window next time I stop by to buy some beets or delicious bread.

Sometimes, frequently in fact, I find myself wishing I wasn't right. Take this ash tree for instance, planted by the people who landscaped the new parking lot that Westminster Choir College built about ten years ago. I told them they needed to remove the ash trees they had just planted. The emerald ash borers are coming, and the trees won't survive. They left the trees in. The trees survived longer than I expected, but are finally succumbing. 

Actually, if you were trying to make Princeton sustainable, you might want to "farm" Princeton with smaller, short-lived trees that provide shade but are less expensive to take down. The above ground portions could be periodically harvested as a local energy source, and the roots left in the ground would sequester carbon. Trees are a source of solar energy, since they draw their carbon not from underground but from the atmosphere all around them. Thus, no net increase in atmospheric carbon from their combustion.

The landscaping for the parking lot also called for a raingarden to be planted here in this hollow. After being planted, the young river birch trees soon began to wither for lack of water. I assumed they would die, and that the raingarden would be poorly maintained and ultimately be mowed down. I was only half right. The river birch trees survived.

Here's what looks like a bright white flower that isn't. The white is the puffy seeds that give the plant its name. The flower seems not to open but remain in what looks like a bud stage. It's pilewort, a native weed that can reach seven feet tall.

Finally, a grass encountered in fields and local rights of way. When its flowers open and display their golden anthers, this native member of the tallgrass prairies can be eye-catching. Indian grass, Sorghastrum nutans, reminds me of the midwest prairies I used to help manage, and a time long ago when prairie openings were common in the east as well.

The Unbearable Whiteness of Being in June

Note: The memorable title "The Unbearable Lightness of Being" may not be as fresh in people's minds as it was in the 1980s when the novel and subsequent movie came out. There's nothing unbearable about white flowers, but there sure are a lot of them this time of year.

It was on a recent walk along the green trail at Autumn Hill Reservation that I suddenly noticed I was surrounded by white. 

Mostly, it was invasive species: the white of multiflora rose

and Linden Viburnum. The prompt for the walk was to check the trails. The Friends of Herrontown Woods takes care of the trails at the adjacent Autumn Hill, and this spring's intervention was a boardwalk spanning a section that for years had been chronically muddy. The town's open space manager, Cindy Taylor, got the town crew to help out by removing some fallen trees, and I was checking to see if anything else was needed.

Though the nonnative shrubs were the dominant flowers, a few natives could be found, also with white flowers. A cluster of partridgeberry hugged the ground. The "repens" in its latin name, Mitchella ripens, refers to its crawling habit.

The mapleleaved Viburnums usually don't grow beyond a few feet. Their latin name is Viburnum acerifolium. The latin name for maples is Acer, so acerifolium is the latin way of saying maple foliage, or mapleleaved. 

Almost missed among all the whiteness was a beautiful specimen of Styrax, probably American snowbell, S. americanus. It's on the left as one pulls into the Autumn Hill parking lot. My guess is that it was planted. I've walked by it dozens of times, but only when it flowered did I take note. That makes a grand total of two of this species seen thus far in Princeton.

Back home, there was the mock orange-a once commonly planted landscape shrub that survives in my neighbor's yard, peeking over the fenceline.

More whiteness comes from the native elderberry, whose berries make delicious pies if you can beat the catbirds,

and the abundant spires of Virginia sweetspire.

The mountain laurel

and the Deutzia in our yard are refusing to grow beyond one foot high for some reason.

White clover can be benign in a lawn but mischievous if it invades a flowerbed.

Update: Ten days after initially posting about white flowers, and feeling like the title of the post, though playful, sounds more judgemental than it would have ten years ago, I've noticed a few more. The Korean dogwood, for instance.

and catalpas, whose flowers reward a closer look.

Japanese honeysuckle, which yield a drop of sweet liquid if pulled apart in the right way.

Some sort of hydrangia vine on our patio.

The flowers of a native swamp azalea. They look to be keeping their flowers downcast, as if to avoid eye contact. Too many zoom meetings.

A small patch of daisies in a preserved pasture near Veblen House.

A white cloud of daisy fleabanes in the foreground, with an oak-leaved hydrangia in the background. 

This oak-leaved hydrangia, native though I've never seen it growing in the wild, started as one plant, but over time it produced stems that could be dug without disturbing the original plant. We now have a whole grove of them.

The oak-leaved hydrangia is one of three classic native shrubs that sustain white in the garden through June, as Virginia sweetspire (above) segues into oak-leaved hydrangia,

which segues into the bottlebrush-shaped spires of bottlebrush buckeye. 

Why so much white? My curiosity did not sustain me very far into an internet search. Perhaps white takes less energy for plants to produce than other colors. White reflects the most light, which could help insects find it. And then there's the research that shows that pollinators don't actually see the flowers as white, and are picking up on aspects of the flower beyond human perception. 

Below is beardtongue having a good year in the Veblen Circle of wildflowers at the Barden in Herrontown Woods. 

Related post: The Unbearable Whiteness of Being in May

Shrubs and Vines to Cut Back Along Nature Trails

Without volunteers wielding clippers and loppers, most trails in Princeton would quickly become overgrown. Some preserves, like Mountain Lakes, Herrontown Woods and Autumn Hill Reservation, have more organized maintenance, but in some others it's catch as catch can. In May and June, that first flush of growth begins reaching out over trails, and so a pair of clippers is handy to keep in the back pocket during a hike. Cutting back anything that overhangs a trail is useful, but as a botanist I'm also identifying as I go along. Most of the shrubs that grow out into trails are invasive species that we'd want to cut wherever they are growing, but especially along trails. There are also some natives, but I'll start with the non-natives, which are so numerous mostly because the deer won't eat them. 

Privet -- A shrub that people plant as hedges, but which has spread into nature preserves, establishing dense stands. In low, wet, shaded areas, there can be thousands and thousands of these, claiming all the space. Most don't bloom because they are too shaded.

Here's a typical branch of privet growing out over a trail. 

Linden Viburnum has become highly invasive, forming dense stands. It has attractive flowers and fall color, but is just way too aggressive. It looks a lot like the native arrowwood Viburnum (V. dentatum), which is relatively rare and has more deeply toothed leaves. 

We commonly call this shrub Photinia, after its latin name. You can identify it by its distinctive obovate leaves, meaning the leaf is wider towards the tip. Names can get complicated in botany. The common name, which I just learned, is Christmas berry. The latin name was Photinia villosa, but that got changed to Pourthiaea villosa. Can you say "Pourthiaea"? Neither can I. In any case, it is another way-too aggressive nonnative shrub that we cut back or down.

This shrub, winged Euonymus, is super easy to identify. Just look for the "wings" on the stem (those brown ribs that run along the stem). It, too, is a nonnative that forms dense stands and often obscures what would otherwise be lovely vistas from the trail. If you see a nice vista from the trail, oftentimes it's because we've been cutting these shrubs down to open up the view. 

A common story about native plants in the wild: there's a native Euonymus, called Hearts-a-Bustin', but it's rarely seen because the deer love to eat it. We've nurtured a few specimens of it to show off at the Barden.

Bush honeysuckle -- Honeysuckle comes in the form of a vine (Japanese honeysuckle) and several species of shrub. it is frequently found along the edges of people's backyards--a sort of default vegetation that moves in on its own. It can also be numerous in some of Princeton's preserves.

Wineberry is an asian species of bramble with distinctively hairy reddish stems. It has tasty berries, but we often cut or pull it, given its lanky, thorny growth.

Autumn olive has a distinctive silver sheen on the underside of the leaves. While many invasive shrubs thrive in shade, autumn olive prefers sun, and so is infrequently encountered along our wooded trails.

Multiflora rose is an introduced species that has made many a forest impenetrable with its curved "fishhook" thorns. Multiflora means many flowers clustered together, as opposed to the single flowers that many roses have. We definitely cut this one back, or down to the ground, to keep hikers from getting snagged. 

Our native roses--at Herrontown Woods, that would be the very rarely encountered swamp rose--have single pink flowers, as opposed to the multiflora's clusters of white.

If you forgot your clippers, it's possible to avoid the thorns while carefully bending a young sprig like this one back on itself with your fingers until it snaps.

Two nonnative vines we pull out along trails are the Japanese honeysuckle 

and oriental bittersweet. Both are easily pulled out. For more success in pulling them out, grab low and pull slow. 

There are native versions of vine honeysuckle and bittersweet, but never encountered, as far as I know, in Herrontown Woods.

A common native along trails is sweetgum, which can grow into a statuesque tree but which we tend to cut or pull along trails, since its seedlings are so numerous.

The most common native shrub is blackhaw Viburnum, which has tasty berries in the fall. Sometimes it can be distinguished from other shrubs by its pairs of tiny leaves tucked in among the larger leaves, growing tight against the stems.

Another common native shrub is the spicebush, which has very fragrant, citrony leaves. 

Hickories are common as well. This is a photo of one leaf with five leaflets. 

I always feel some remorse while cutting native species back, but it has to be done if the trails are to remain clear.

Related post: Portrait of Sidewalk Neglect -- A post about plants that are growing over a neglected sidewalk.