Porcelainberry: the Vine that Ate Princeton

Here it's Friday of National Invasive Species Awareness Week, and nary a post about invasive species!

First, readers should be aware that there are contrarians out there, writing books, articles and opeds, trying to deny that invasive species are a big problem. It's fascinating to analyze their mental gymnastics and deceptions, which are similar to those used to deny the reality and danger of climate change. I've picked apart their faulty logic in posts that can be found at this link.

Now, on to our porcelainberry tour of Princeton. You won't find it in shady areas, where other invasives like stiltgrass, garlic mustard and winged euonymus thrive. Rather, porcelainberry threatens to smother all of those sunny openings and edges that shade-intolerant plants depend on for survival. Porcelainberry is related to our wild grape, but much more aggressive. Your first impression will be, "What lovely multicolored berries!"

Your second impression, as it climbs up the stems of your shrubs, like this elderberry, might be, "Oh, a little rambunctious, but those berries are so pretty!"

Your third impression, as it turns your yard or park into a monocultural topiary, will be more along the lines of, "OMG! HELP!" No, this is not kudzu growing along a freeway down south. This is porcelainberry winning a modern day Battle of Princeton, with stealth and persistence far beyond anything we distracted humans might muster.

This is what a nearby patch looks like in December, just down the road from the Princeton Battlefield, along Quaker Rd between Mercer and 206. Invasive vines and shrubs can seem less overwhelming in winter, which is actually a good time to remove them. In spring and summer, though, all that growth energy can be intimidating.

And this is what porcelainberry is doing to the sunnier portions of our lovely nature trail off the DR Canal Towpath near Harrison Street. The blackbirds may say hello to the berries, but it's bye bye to the diversity of native wildflowers underneath that foliar blanket.

Turns out porcelainberry's a soccer fan. Here it is in the cheap seats at Princeton University's Roberts Stadium, at one end of the field,

and at the other.

Here it is (light blue and pink berries) in that "second impression" stage, climbing over a honeysuckle shrub (red berries) at Quarry Park. Give it a few years and it may reach the "OMG" stage.

I haven't seen much of it in eastern Princeton yet, but we'd be smart to keep an eye out and remove it before the berries mature.

Otherwise, sunny edges everywhere will look like these hapless flowering dogwoods, planted at Princeton Battlefield in 1976 for the nation's bicentenial, and now struggling to survive beneath a spreading blanket of porcelainberry.

Note: You can help liberate the dogwoods from the porcelainberry and other vines on Saturday, April 1 at 1pm. I've been collaborating with the Princeton Battlefield Society on invasive species work for the past several years, and will be leading a group to preserve the dogwoods that line the field on the north side of Mercer Street.

Another group of volunteers will be continuing the multi-year effort to reduce the bamboo clones near the Clark House, which we're actually having considerable success without herbicide. 

For purposes of identification, here are a couple closeups of porcelainberry. The berries are distinctive, with different shades of blue, red and white.

The leaves are easily confused with wild grape. This photo shows how variable is the shape.

I hope everyone's having a happy National Invasive Species Awareness Week. We'll end with a short Q and A:

• Are all nonnative plants invasive? No. Nonnative refers to origin. Invasive refers to behavior.
• Why are invasive plants invasive? Oftentimes, it's because the native insects/deer, etc don't eat them, giving them a competitive advantage. To regain the balance we lost by introducing species that evolved elsewhere, people end up having to be the herbivores, wielding saws and loppers.
• One nice thing about invasives? They get us out in the woods for workdays. 

Winter Aconite and Fig Buttercup (lesser celandine)--Related Flowers, Contrasting Behaviors

Both of these non-native wildflowers are in the family Ranunculaceae. Both bloom early and have pretty yellow flowers. While one appears to be modest and highly local in its spread, the other spreads so quickly across yards and into neighbors' yards and floodplains as to pose a threat to gardens and natural areas alike.

Here's winter aconite (Eranthis hyemalis) opening up a week ago in my garden, a legacy from the previous owner. Its modest spread is easily contained. I've never seen it spreading into nature preserves. Note the leaf shape, which distinguishes it from the related wildflower below.

Update: For comparison, here is one of the first blooms of lesser celandine in 2021, on March 30. Note the shape of the leaves, which are "entire" rather than lobed. Just to confuse things, lesser celandine is also called fig buttercup, and its latin name Ranunculus ficaria has apparently changed to Ficaria verna. 

People think lesser celandine is pretty, transplant it to their gardens, then begin having regrets as it spreads uncontrollably to dominate their gardens and yards. If you are one of the distraught gardeners wishing you didn't have this flower, and not wanting to impose its spread on the rest of the neighborhood, late winter is the time to deal with it. 

Other posts on this subject can be found on this website by typing "celandine" into the search box. A post called "Will the real lesser celandine please stand up--a confusion of yellows" helps with identification.

Though I'm no fan of herbicide, that tends to be the only workable option in the majority of cases. I'm no expert on herbicides, but have been told that for lawns, a broadleaf herbicide like Weed Be Gone is effective. For flower beds, a 2% formulation of glyphosate (Roundup or equivalent) works well. Monsanto doesn't hold the patent any longer on glyphosate, so it's possible to buy if from other companies on the internet. I use a wetland-safe formulation, but for most yards, away from wetlands, some spot spraying with Roundup or equivalent should be okay. The plant itself is poisonous to wildlife. 

There have been other proposed means of killing the plant: 

Mulch

If you blanket the whole infestation thoroughly with mulch, e.g. a layer of cardboard covered leaves or hay or woodchips, it might kill the lesser celandine if you mulch as soon as the plants leaf out in late winter. Chances are, you won't cover it soon enough, or you'll miss some spots, and the lesser celandine will benefit next year from the fertilizer in the mulch. 

Vinegar/salts/detergent

This concoction has shown up on the internet: 1 gal white vinegar, 2 cups Epsom salts, 1/4 cup Dawn dishwashing detergent in a hand held 2 gal pump sprayer. Spray in bright sun on a windless day.

But I couldn't find evidence that it has been carefully tested, nor that it would kill the roots. If the roots survive, the plant will be back next year. The concoction contains an acid, and the salts are made of magnesium and sulphates. These may or may not be harmful to the soil if used to excess. 

Norway Maples, and Seeing the Future

One purpose of this blog is to help people to look at nature now and see where it's headed. Every gardener imagines the harvest while planting the seeds. In science, one extrapolates from past and current trends to predict the future. With practice, one can look at a woodland and see not only the present but past and future as well. As a land manager, one envisions two futures--one without intervention, one with. Because we've altered local habitats so much--through altered hydrology, past farming, introduced species, banishment of important forces like fire and predators like mountain lions and wolves--intervention can help restore functionality that no longer happens naturally.

Autumn is the easiest time to divine a woods' future, because each species shows its colors, making trends easy to spot. For instance, learn the Norway maple's brand of yellow this time of year, and you'll start seeing them all over town. Unpalatable to deer, they rise unnoticed until they become full-sized trees, mostly along backyard fencelines.

That's what's happening on a larger scale in the hidden valley between the Princeton University chemistry building and Washington Road. That mix of yellow and lingering green indicates that the Norway Maples are taking over the top of the valley,

and extending downstream. This is the perfect time of year to see the extensive invasion by this nonnative tree. Why have I on multiple occasions urged the university grounds staff to cut or girdle these trees, despite their attractive yellow in autumn?

The problem is an ecological one. This forest, one of Princeton's oldest, is steadily shifting from native trees that feed local wildlife to nonnative vegetation that does not. As the shade-tolerant Norway Maples push up into the native canopy above, their competition for water and nutrients weakens the giant oaks and black gums, hastening their decline and increasing their susceptibility to wind storms. Young native trees--preferred by deer and less shade tolerant--can't compete with the Norway Maples, which grow quickly, green up sooner in spring and drop their leaves later in the fall. This photo shows a 1-2 centuries old oak with a sea of Norway maples rising underneath.

Fortunately, most Princeton woodlands have not been invaded by Norway maple, though it would be worth it for land managers to take a walk through the woods to see if they are starting to get established elsewhere in Princeton's open space.

Except in that Washington Rd. gorge woods, they have proven invasive only in people's yards, showing highly localized invasiveness much like Japanese maples and Rose of Sharon. This photo, taken along North Harrison Street, shows the classic problem with ignoring the silent ascent of Norway maples, in this case under a powerline. Chances are they grew unnoticed by the homeowner, and now will require repeated pruning to keep them from threatening the wires.

At least the half of the tree closer to the street shades the pavement in the summer,

but another annoying aspect of the species--their dense shade and aggressive roots that leave little sun or water for the lawn--has made it impossible to grow grass on the steep slope.

Like climate change and the nonpoint pollution of our waterways, the Norway maple silently transforms the world, undermining food chains and biodiversity, while our attention is elsewhere.

What a Little Dew Can Do

Here's a bit of serendipity. Shadows play upon the grounds of Princeton Battlefield, charmed with dew on a Saturday morning.

Ever the resident tourist, a shadow selfie with Mercer Oak II. Had no luck getting the shadow to smile.

Sorry, but you can't look at any screen--TV or computer--without at least one obligatory car commercial popping up. The sound track runs something like, "If George Washington were alive today, ...", though he might eschew fossil fuel altogether and stick with a horse. Those founding fathers thought about long term consequence. What ever happened to that kind of thinking?

The original motivation for stopping during a drive by of the Battlefield was documentation, not aesthetics: to photograph the invasive porcelainberry overgrowing flowering dogwoods planted as part of the nation's bicentennial celebrations in 1976.

One of my recurrent cause celebres is to save the Dogwood Garden Club's dogwood legacy from the aggressive vine growth. From the green/yellow of the porcelainberry vines crawling over the red leaves of the dogwoods, you can see who won this year's skirmish. The Dogwood Garden Club doesn't know who I am, and for all I know they've forgotten that they ever planted these trees along the field's edge in the first place.

There was also an obligatory photo of the great disappearing bamboo patch. Two years ago, this was a thick clone of bamboo growing out over the path down to the Quaker Meeting House, but a series of well-timed cuttings with magic loppers over the past couple years have sapped vigor from the bamboo's giant root system. The decisive strategic intervention came this past June, when Kip Cherry and I cut down the regrowth from a cutting in the spring. It was some inconvenient toil, but deprived of any payback from that big investment in regrowth--two years in a row--the bamboo has nearly given up. A visit next spring should be light work, followed by a refreshing beverage on the Clark House porch.

Dew was also working some magic on the vista on Quaker Road near the towpath. Scattered pin oaks in a field of goldenrods.

Thanks goes to my daughter Anna for getting me out that way early on a Saturday, to drop her off for a busride to Philadelphia to do some canvassing. Otherwise, that encounter with morning dew would have never happened. Finally, a reason to be thankful for this election season.

Alert: Monitoring for Lesser Celandine

Memory was finally jogged that this is the time of year to be scouting Princeton's natural areas for the dreaded Ficaria verna, a.k.a. fig buttercup, or lesser celandine. Dreaded because it has an alluring yellow flower that makes one want to leave it be when it starts showing up in the yard or local preserves, but then quietly takes over, paving whole valleys. Pettoranello Gardens is carpeted with the plant. In Durham, NC, I once tracked an infestation upstream to a homeowner's yard. He was greatly relieved to find out what plant had taken over his garden, and proceeded over the next several years to completely eliminate it. Unfortunately, by then the plant had spread far downstream and would transform a whole watershed, from one small infestation in someone's yard. He was, however, able to remove some he had put in his son's yard elsewhere in town, before it had a chance to spread downstream. This is why it's so important to get the word out about these highly deceptive species.

When I was working at Mountain Lakes, I'd walk the valley leading down from Stuart School, searching for any small patches that could be eradicated before they expanded beyond remedy. It's satisfying to be able to nip invasions in the bud. Now that my focus is Herrontown Woods, the spring ritual is playing out there. Yesterday's walk yielded no sightings until the very end, when I checked the pawpaw patch we planted New Year's weekend, and headed back through the woods towards the parking lot. There, right where the groundwater seeps out of the ground in what originally may have been a primitive septic system, was a patch of lesser celandine. Already, it has spread down the ditch about fifty feet, but is still of a size that we can eradicate it before it spreads down the valley, beyond control.

Control options can be found at this link. A comparison of lesser celandine with other yellow spring flowers, such as marsh marigold and celandine poppy, can be found here. If possible, avoid hiking through an area with lesser celandine--there's a risk of inadvertently spreading it into new areas in the treads of your shoes.

Callery Pear and Deceptive Appearances

Callery pear, widely known by one of its cultivars, Bradford Pear, is a good example of how appearances can deceive. People crave blooms after a long winter, and callery pear comes through with its masses of radiant white flowers that look like someone turned on a giant 100 watt lightbulb in the landscape. Though it originally was thought not to spread, callery pear has been popping up along roadsides across the U.S., looking as if someone strung masses of Christmas tree lights along the highways. The visual effect is pleasing at a time of year when most of the native species are just coming out of dormancy and the landscape still looks otherwise drab.

At that superficial level, which is how most people see the landscape, the callery pear seems an unmitigated blessing. People who plant it would seem to be doing everyone a favor, as the tree's beauty spreads far beyond the original planting. The specimens on Witherspoon Street in Princeton lift the spirits of passersby, and are celebrated as harbingers of spring by the local newspapers.

At a deeper level--if you take a look underneath the ecological "hood", peak behind the visual soundbyte--you'll find the story is the complete opposite. The rapidly proliferating callery pear poses a profound threat to America's landscape. Across the country, callery pear is spreading rapidly into forests and fields, displacing native species and steadily imposing a monotonous conformity. It was originally imported from China specifically for its adaptability to a wide variety of soil types and moisture and light levels, produces abundant fruit that starlings spread across the land, and so can quickly invade a broad spectrum of habitats. The website naturalbiodiversity.org calls it a "bio-bully". A county in Indiana suffering from an advanced stage of invasion calls the callery pear "a bad, bad plant with pretty flowers." This lovely flowering tree is like the celebrated town figure who, unbeknownst to the local citizenry, has been running a seedy operation on the outskirts of town.

Just to be clear, aspersions are not being cast on all non-native plants. Whatever you think of the exotic forsythia (this imposing hedgerow runs parallel to the American elms along the Washington Road entry into Princeton), it has not become a menace to woodlands and fields. It may offer little to wildlife other than cover, but it stays where its planted.

Callery pear, then, is a symbol of the time in which we live, when the present is in deep conflict with the future. This is a time when that which is much loved and enjoyed, and which appears on the surface to be completely benign, is quietly working beyond most people's awareness to dismantle our cherished inheritance. How does one convey this to people without seeming to be a killjoy? Such knowledge, by threatening our enjoyment of the world we've made, poses an emotional challenge that people are left largely unprepared to handle. Is there a way to still experience the simple pleasure of a callery pear's beauty while at the same time understanding that they collectively pose an extraordinary danger? The same challenge awaits anytime one climbs into an automobile, needing to get somewhere yet knowing that collectively the use of cars is destabilizing our climate. Some means of handling cognitive dissonance, preferably not complete denial, is necessary just to get through the day.

Only by making these connections, and coping with the responsibility they imply, can towns like Princeton step out of a pleasant bubble and begin to question the way we unwittingly contribute to massive changes underway beyond our borders.

As we collectively remake the world, there are other impediments to our understanding these connections between individual acts and collective impact. One is the notion that nature is in control, that if I plant an invasive species, anything it does after I plant it--spread into the neighbor's yard, or into the local preserves--is in nature's domain and not my fault. There is also the belief that nature will eventually mend itself--a capacity being severely tested. Perhaps the most interesting impediment is a skewed notion of what constitutes freedom. The increase in one freedom can lead to a precipitous drop in another. For instance, the freedom to buy and plant highly invasive species like callery pear essentially consigns the larger landscape to the tyranny of invasion, and deprives future generations of the freedom to enjoy the beauty of a diverse native woodland or field, and the wildlife that needs a diverse food supply to thrive. On a small scale, many of us are forced to deal with ongoing invasions of english ivy or bamboo from neighboring yards. What are the property rights of those being invaded?

This is the less than lovely backstory on a lovely display of flowers on Witherspoon Street in April.

Note #1: For alternatives, google "native alternatives to callery pear".

Note #2: A quick and fascinating primer on callery pear can be found at this link. There is also a very informative webinar that just came out, combining an appreciation of the callery pear's beauty with an objective discussion of how it is spreading, and why. Below are instructions on how to navigate to the presentation by researcher Theresa Culley:

"Last week, the Midwest Invasive Plant Network held our first webinar on Invasive Plants in Trade.  We had some technical difficulties at the beginning of the presentation, but we did manage to record Theresa Culley’s talk on Callery pear.  The recording is now available at the following link: https://gomeet.itap.purdue.edu/p67o689ypt4/. After the first minute, the recording goes silent.  Skip ahead to minute 15, and you’ll be able to hear the full presentation.  Make sure your computer’s speakers are turned on to hear the audio portion."

The "Second Forest"

This is a good time to see the "second forest"--the layer of exotic shrubs underlying the native tree canopy. Honeysuckle, multiflora rose and privet, having evolved on other continents and under different climate constraints, all leaf out earlier than the native species.

Historically, an eastern forest would have been carpeted with spring ephemeral wildflowers of great variety, flowering and collecting another year's energy stores before the trees leaf out and grab all the sunlight. The exotic shrubs throw a wrench into the works, leafing out early and shading the native wildflowers before they have a chance to store enough solar energy for the next year.

Lesser Celandine Blooming, But Mostly Spreading

 I wish I could go back to the first time I saw this flower and could appreciate its beauty without being worried it would take over all of Princeton. At Pettoranello Gardens it grows like green pavement next to the paths, blooms beautifully, but is radically invasive. Since becoming established at Pettoranello Gardens, it has spread downstream and has now become established in floodplains at Mountain Lakes Preserve. It displaces native plants, is apparently inedible to wildlife, and though it's pretty for a couple weeks, the rest of the time it's busy making natural areas less supportive of plant diversity and wildlife.

 In a suburban yard, it first appears as a couple plants, with small, roundish, shiny leaves.

It displaces the grass over time, then dies back in late spring to leave bare spots in the lawn. Its many underground bulbules make it hard to eradicate by pulling.

Lesser Celandine has started to show up in my former home of Durham, NC, where I've been trying to help eradicate small populations before they spread downstream.

Repairing the Towpath and Nature Along the D-R Canal

For years, the towpath was a given, a high quality crushed-stone pedestrian and bicycle thoroughfare stretching more miles than most anyone has time to explore, up and down the DR Canal. That changed last August as the unprecedented flooding of Hurricane Irene--tearful after having been downgraded to a tropical storm--deposited a thick layer of silt over the trail. The gift of fertility, reminiscent of the ancient Nile, would have been more welcome if the valley's investment was in agriculture rather than transport.

I inquired last fall and was surprised to hear that there were no funds available for repair, and if and when they become available, the northern portion's washouts, up towards New Brunswick, would get the first attention. Some repair in the Princeton area, by the water authority rather than state parks, has taken place. The photo shows a patch job just up from Turning Basin Park.

I called Stephanie Fox at DR Canal State Park today, and was told that more extensive repairs are waiting on FEMA money from the federal government. In addition to trail damage, some of the park's historic buildings were also damaged in the flood. Though the crushed stone surface is still intact in most places underneath the mud, repair will involve bringing in additional stone. Cost for repairing just one mile of minimally damaged trail could run $10,000, so overall cost will likely be very high.

Near Harrison Street, where the nature trail branches off, the towpath is in relatively good shape, at least when it is dry. The trail loop was built by parks personnel after I "discovered" the meadow there where the land between Carnegie Lake and the towpath broadens out. At the time, the park crews were mowing the meadow weekly during the summer. When I pointed out that they were mowing not grass but a field of beautiful native wildflowers, they agreed to limit mowing to once a year in late winter. Everyone was a winner with this arrangement: less work, more habitat, more flowers.

In winter, at the trailhead, the switchgrass leaves are an attractive legacy of last year's growth.

Word is that the bluebirds have hung around all winter, it being so mild.

One reward of exploring the nature trail this time of year is an encounter with fragrant honeysuckle (Lonicera fragrantissima), whose small white flowers live up to their name. This is the one exotic bush honeysuckle species that I've never seen spreading into wild areas. A line of the shrubs remains from maybe 40 years ago when that ribbon of land between the canal and Carnegie Lake was carefully tended as part of the grand entryway into the university.


Each year, with no assistance other than annual mowing, the meadows have become richer with wildflowers like joe-pye-weed, ironweed, tall meadowrue and cutleaf coneflower. It seemed time to relax, sit back and enjoy the fruits of less labor.

But a trained eye will see in this very plain-looking photo a web of vines. Porcelainberry, a grape-like exotic vine that has covered forest edges at Princeton Battlefield with stifling kudzu-like curtains of growth, has been spreading down the canal corridor. A light infestation noticed a few years ago is now exploding, threatening to permanently overwhelm the wildflower meadows.

Park crews are busy elsewhere along the canal, dealing with invasive Japanese knotweed and hops. We'll have to see if there's anything that can be done this year.

In the meantime, there are sweetgum balls serving as natural tree ornaments next to the trail,

the resident geese, and, if one can negotiate with the geese for access to the shore,

trout to be caught.

Invasive Plant Threatens Albatrosses

Strange how learning happens. Here's an unlikely string of events: 28,800 rubber duckies are lost overboard in the northern Pacific in 1992. A high school english teacher named Donovan Hohn eventually hears word of this and leaves his job to find out where the drifting duckies drifted to. He writes a book called Moby-Duck and travels to Princeton to make a presentation at the public library's 2011 Princeton Environmental Film Festival.

One of the images he showed is of a baby albatross that died, apparently due to a stomach full of the notorious plastic bits that currents concentrate in that part of the Pacific. But he explains afterward that the photo of the 200+ bits of plastic in the albatross's gut tells only part of the story. Also making life difficult for the albatross is global warming, which he says is making its nesting grounds too warm, and an exotic plant called Golden Crownbeard.

Native to the U.S., Golden Crownbeard is, according to my internet research, the most invasive of hundreds of exotic plants on the Midway Islands. Chances are, it hitchhiked to the islands in topsoil--a notorious means by which plants travel to new locales. The plant displaces low-growing native vegetation, making tall dense stands unsuitable for building nests, sometimes growing so fast that the adult birds lose track of their young. Managers of the refuge are hoping to eradicate the plant from the islands.

A rubber ducky spill in the north Pacific, then, ended up bringing to Princeton a very familiar story of the impact of plant invasions on native wildlife, and the human efforts going on around the world to restore ecological balance.

Ivy's Deadly Embrace

This picture tells the story of a neighbor's Kentucky Coffee Tree  laid low by English Ivy's long embrace. The smaller trunks are the ivy, which had climbed far up into the canopy of the tree. During the freak snowstorm earlier this fall, the snow clung to all that extra surface area created by the ivy, the extra weight of which toppled the tree. The fallen tree blocked the street for a week.

My backyard, too, is in an uncomfortable embrace of English ivy, in that the vine is invading from the neighbor's yard to the north,

cascading in over the ramparts facing the park to the east,

and creeping over, under and through the fence to the south. If a neighbor's runoff is flowing into my yard, I can change the contour of the ground to direct it away from the house, and consider the problem largely solved. But the flow of ivy in from neighbor's yards cannot be diverted, and instead creates a perennial chore.

The moral of this story? Never plant english ivy anywhere that its potential to spread is not blocked on all sides by lawn, pavement or foundation. Cut english ivy off of any tree you wish to live. Better yet, never plant english ivy, and remove as much as you can from your yard.

One approach to getting rid of it without working too terribly hard can be found at http://princetonnaturenotes.blogspot.com/2007/11/ivy-control-part-2.html.  Other related posts can be found by typing the words english ivy in the search box at the upper left corner of this blog.

Big Changes Come to a Hidden Valley

 There's a hidden valley in Princeton that everyone drives by but no one sees. Just over this ridge is Washington Rd, with athletic fields beyond. Down to the left is Faculty Road and Carnegie Lake.

Despite being sandwiched between a busy road and Jadwin Gym, the valley's rich soil sustains old oaks, tupelo, beech and ash that reach improbable heights.

This year, big changes have come to this long-hidden valley. Approached from Faculty Road, stacks of boulders and heavy equipment suggest some sort of road construction.

 A pile of stumps looks less than auspicious.

Further up the valley, more boulders, bales of hay, and orange fencing.

Giant trees, some a yard thick, have been cut down. How could this be anything but bad news? But wait, this post is getting depressing, so let's start from the top of the valley and work our way down.

The valley, which is to say the remnant of valley that was never developed as campus, begins at the new bridge over Washington Road. In the distance is the new chemistry building and the football stadium.

Looking downhill from the bridge, a lovely little stream meanders peacefully down the valley.

Starting farther up towards Nassau Street, the stream runs underground through campus, then emerges (or "daylights") from a big pipe just below the bridge.

The water immediately encounters what looks like an olympic luge track, attractively armored with stones.

 Further down, the narrow channel flows through a broad floodplain.

All of this--the pleasing meanders, the floodplain for stormwater to spread out into, the series of riffles and little waterfalls over stones--is manmade.

Why would anyone want to remake a stream? After a hundred or two years of flash floods caused by all the impervious surface on campus, the stream channel had eroded the ground around it, and was threatening to undercut Washington Road (beyond the green fence on the right) if nothing was done.

Here's a portion of the old streambed, broad and ill-defined. More photos of the old streambed can be found in a post one year ago when members of the Princeton Environmental Commission were given a tour of the proposed project.

A group from Rutgers developed the plans. In this photo, you can see the hoses used for pumping water around the section of stream being worked on. The "V" of stones at the left is called a "cross-vein". Water flowing over the rocks converges to scour out a pool just below them. Pools, riffles, and a narrow stream bed to focus flow are all characteristics of a healthy stream.

The stacks of boulders, then, are materials used to direct water in such a way that the streambank will survive the flash flooding coming from the hardened landscape of campus.

Lots of digging is required to form an adequate floodplain to accommodate the massive infusions of water during storms. The disturbed areas will be restocked with native plants, and though they had to take down some large trees, many were spared.

So that gets us back to the downed trees. This section of white ash is 36 inches in diameter. I counted roughly 200 annual rings, which are caused by the alternation of light-colored fast spring growth followed by a darker band of slower growth later in the season. The tree, and others in the valley, standing or cut, could well date back to the Revolutionary War. Visitors to Mount Vernon may remember the giant white ash trees in the circular drive approaching the house.

 About 160 years back, this ash began to grow very slowly, as can be seen from the very narrow rings on the left. Perhaps it was shaded heavily by another tree, which apparently fell 120 years ago when the rings began to spread out again.

It is unsettling that such old trees have been cut down, and all the more remarkable that few even know about it in a town that loves and protects its trees. But there are extenuating circumstances, tradeoffs made, factors that mitigate, at least partially, the loss. Erosion from campus has been undermining some of the majestic trees, and this project is meant to reduce that erosion.

Time will tell if the trees that were saved will survive all the disturbance around them. Tree roots are very sensitive. And the carefully designed channel is not necessarily immune from the powerful erosive forces of repeated floods.

One useful pursuit at this point would be to study the rings of the fallen trees to see what they might tell us of Princeton's past.

I had recommended a pre-construction rescue of rare native plants like horsebalm, but the idea probably got lost in the mix. Not everyone has learned to make a distinction between rare wildflowers that have survived for centuries in a valley, and whatever natives one can buy in pots at a nursery.

I had also encouraged them to remove the Norway Maples (mottled green/yellow in this photo and next) that have invaded the valley, since the invasive maples are competing with the old growth natives, and their dense shade will threaten the newly planted natives over time.

Overall, though, there's reason to believe this stream restoration--rare in New Jersey--will validate its good intentions. The project leader spoke excitedly last year during the tour about how he hopes students will find the valley an attractive place to visit, rather than merely serving as a traditional shortcut for athletes heading to practice.

This long-sheltered space, with so many stories to tell of past centuries, is beginning a new chapter worth reading.