Saving Bicentennial Dogwoods at Princeton Battlefield

The big Princeton Battlefield/Sierra Club workday earlier this month didn't include attending to dogwoods along the field's edge, but the care we gave them in previous years to liberate them from porcelainberry and other aggressive vines is still serving them well. Some historical research revealed that they were planted by the Dogwood Garden Club for the country's bicentennial celebration 42 years ago.

Back in 1976, before the deer population exploded and aggressive invasive vines spread across the landscape, it was probably much easier to sustain plantings like this. The planting design was logical enough, with daffodils on the ground in front of the dogwoods, and white pine trees forming a nice evergreen backdrop behind.

But now, the daffodils are obscured by invasive shrubs and brambles, and the dogwoods find themselves growing in a sea of porcelainberry vine on the ground that, if not controlled, will quickly rise into the dogwoods to smother them. Meanwhile, the pine trees that now loom large behind the dogwoods drop big branches during ice storms. It's a one-two-three punch that takes concerted effort to counteract, and the state agency in charge of maintenance tends only to the lawn, with little or no on-the-ground knowledge of plantings that have any complexity beyond trees and turf. Volunteers can sometimes fill the gap. Last year's workday was particularly spirited. We cut vines and competing woody growth away from fifteen dogwoods, so that they could continue to ornament the Battlefield and feed migratory birds in the fall.

But like Mr. Incredible says when interviewed at the beginning of The Incredibles movie, the world refuses to stay saved. Already, the porcelainberry is sending new shoots up into the dogwoods, and until some animal or disease comes along to limit the vine's rampant growth, people will need to intervene to sustain some sort of balance that allows the dogwoods to grow.

Meanwhile, out in the fields, delays in mowing have made it possible for the cuckoo flower (Cardamine pratensis) to bloom.

Rogers Refuge and the Importance of Stewardship

Looking out on this wetland, you would understandably think you aren't in Princeton anymore. But this broad and beautiful marsh, the centerpiece of Rogers Refuge, is just a short drive upstream from Alexander St, off West Drive.

The Friends of Rogers Refuge (FOHR), which has been quietly caring for this renowned bird sanctuary, turns 50 this year. Comprised mostly of devoted birders, the Friends group grew out of actions by the Princeton Environmental Commission in 1968 to halt filling of the marsh. A prominent ornithologist named Charles H. Rogers was among those who led the campaign.

A conservation easement renewed every ten years has helped to protect the wetland since, but no habitat is protected by a paper agreement alone. Though auspiciously located in the floodplain, between the Stonybrook and the Institute Woods, the habitat benefits from a collaborative effort of the landowner (NJ American Water) the town of Princeton, and the Friends group. For instance, though the wetland receives runoff and groundwater seepage from the Institute Woods, and occasional floodwater from the Stonybrook, the habitat benefits from a steady input of water pumped from the river during the summer months. The water company pays for the electricity to run the pump, the town helps with repairs, and the Friends keep an eye out to respond quickly to any breakdowns. The Washington Crossing Audubon Society not only leads walks there during bird migration in May, but has also funded much of the Friends' efforts to restore habitat and build observation towers. They also funded an ecological assessment and stewardship plan I did for the Friends in 2006.

Talk to members of the group and they will tell you excitedly about the kinds of birds they see at the Refuge. Since birds require habitat, much of the group's active stewardship centers around controlling invasive species. Though the native cattails can be a little aggressive, its the nonnative Phragmitis that poses the greatest threat to a balance of plant life in the marsh. In this photo, the cattails show as dark green, with wild rice appearing as light green in the distance. In the foreground and to the left is the browned remains of Phragmitis reed, killed with low-toxicity, wetland-safe herbicide. When a similar treatment was applied 12 years ago, the void left by the Phragmitis was quickly filled with a great diversity of native wetland species.

The same can be expected this time. Hopefully, another such large scale treatment will not be necessary if there's sufficient followup to prevent the few remnants of Phragmitis from rebounding. It's human nature to shift attention elsewhere when a threat has been greatly diminished, but when dealing with invasive species, that's when vigilance is most needed.

Another example is chocolate vine, which I discovered growing next to the small parking area at Rogers Refuge. This is the only location in Princeton where I've encountered chocolate vine, yet its behavior suggests it could quickly become a problem if left to grow.

Its rapid expansion at Rogers Refuge, up trees and over bushes, should make any homeowner think twice about growing this nonnative species, lest the birds carry its seeds to a nearby nature preserve.

Porcelainberry is another invasive plant that has shown up at the Refuge in recent years, and has quickly begun dominating woodland edges. A look behind the Clark House at the nearby Princeton Battlefield shows how dominating this vine can become if left unmanaged.

Further evidence that a wildlife refuge doesn't take care of itself came a few years ago, when I discovered a third nonnative vine with highly invasive behavior, appropriately named Mile-a-Minute, growing along the driveway that leads to Rogers Refuge. A thorny annual with a distinctive triangular leaf, it too has proven extremely aggressive elsewhere in NJ. We've been fortunate to catch it early in Princeton, and respond quickly before it produces seed and spreads around town.

Heavy browsing from deer has been a problem in past years, but the town's investment in deer culling, since 2000, has not only dramatically reduced car accidents in town but also greatly benefitted habitat at the Refuge and elsewhere. The birders report that the return of a healthy understory of spicebush, previously almost eliminated by the overcrowded deer, has brought back ovenbirds that depend on the shrubs for nesting habitat.

Another challenge that the Friends of Rogers Refuge has faced, as have other Friends groups in Princeton, is vandalism. Again, it's the generosity of volunteers in the community who respond by repairing what is broken, as in this email sent to the Friends:

"I am pleased to report that the informational signs at the Refuge, ripped from their frames on the main platform by vandals a year ago, have been restored. Many thanks to the hard work and generosity of Charles Magee, who remounted them with a more secure system. Visitors can again find pictures and descriptions of some of our most attractive birds close at hand. Thank you, Charles!"

Erich Fromm best captured the ongoing struggle between vandalism and repair in his book, Escape from Freedom:

“The more the drive toward life is thwarted, the stronger is the drive toward destruction; the more life is realized, the less is the strength of destructiveness. Destructiveness is the outcome of unlived life.”

Leading the group in recent years has been Fred Spar (left), with particularly active support from his wife Winnie and Lee Varian (right). Fred reported to me that there was a particularly good spring bird migration this year, perhaps the best they've ever had, due in part to winds that shifted migration routes eastward. From the observation tower can be seen a purple martin house erected in the middle of the marsh by the Friends. It was alive with the comings and goings of the purple martins earlier this summer.

If you stop by this hidden gem, wish a happy 50th to the group that through quiet persistence and dedication has kept Rogers Refuge well cared for.

Champion Brearley Oak in its Glory

There's a magnificent black oak growing, growing, growing in an unlikely place along Princeton Pike. Like the Mercer Oak, Jr. just up the road at the Princeton Battlefield, this oak too is of such distinction that it has its own corral. Driving by recently, I couldn't resist pulling over into the new Bristol-Myers Squibb parking lot and walking down to take a closer look at how it's doing. This champion tree--so-called because it's by far the largest in the state--is thriving, standing like royalty, master of its domain, with full access to sunlight all around and the soil all below.

The crown overflows its 100 foot diameter corral. Each of its millions of leaves is glossy and beautifully sculpted, the acorns small, as if this giant tree were compensating for the lone osage orange tree up the way about half a mile, barely a quarter of the black oak's height but with softball-sized fruits.

You can see the location of the Brearley Oak marked on this map, just above the hyphen in Bristol-Myers Squibb, close to Princeton Pike. The tree stands at the southernmost point in the Lawrenceville Hopewell Trail--a trail large enough to have its own nonprofit and website.

Nearby, to the east and north, is Brearley House and a park named after a great meadow from colonial and Indian times, and which the oak may have been witness to. That meadow was likely natural in part, but also managed at first by American Indians, who tended to burn the landscape, the better to attract game with the nutrient-rich growth that sprouted in the fire's aftermath.

There was a time when an oak this massive, with 20+ foot circumference, and perhaps 80 feet tall, would have been the rule, not the exception, when much of America was managed by American Indians, with the help of fire. The oaks have fire resistant bark and decay-resistant leaves adapted to remain on the ground as fuel. Then, when a low, mild fire started by lightning or people comes along, the leaves carry the fire across the ground, which in turn kills the oak's thin-barked competitors but not the oak.

The red dots on the map below, from Charles Mann's 1491, indicate areas managed by American Indians with fire. There are lots of dots shown in what is now NJ.

Red dots are areas managed by American Indians with fire (from the book, 1491)

In colonial and pre-colonial times, an oak like this would have had a rich understory of wildflowers and grasses, adapted to the ever shifting patterns of sun and shade.

One of the limbs is so long that it's  supported by a post.

And a lightning rod is attached on either side.

I'd love to go there sometime with a group of people. We'd recline on lawnchairs and gaze upward, tracing with our eyes the limbs' ascent towards the sky. A tree is like a city, with thoroughfares and sidestreets and cul de sacs of leaves. It is a solid built of air, some of which it breathed in before we were a nation.

Ignoring busy Princeton Pike and the sterile corporate lawns that surround it, this black oak soaks up the sun, drinks deeply from below, dreaming green dreams of mighty landscapes past.

Photos From a Spirited Cleanup Day at the Princeton Battlefield

Each year, the Princeton Battlefield Society teams up with the local Sierra Club to host a spring cleanup day at the Battlefield. My role the past couple years has been to lead some of the volunteers on work to clear vines and brush around some dogwood trees planted in 1976--the year of the nation's bicentennial. They line the edge of the lawn on the north (column) side of Mercer Street. As with any planting, some followup is necessary, and the state limits its maintenance to lawn mowing. Many of the dogwoods have had to withstand the smothering embrace of aggressive vines like porcelainberry, and bombardments of branches as towering pines lose their lower limbs in snow storms, making our yearly interventions feel like a rescue operation.

The cleanup days always begin with a group photo in front of the Clark House that adds a wonderful sense of place to all the open space around it. This year, while assembling for the shot, we momentarily lost focus when someone spotted a red-tailed hawk flying to a nearby tree, carrying a small snake. Nature and culture in close proximity--that's one of the charms of Princeton, though the snake might disagree.

It was the first nice spring day of the season, which added to our spirited work of lopping, sawing and dragging. There were a lot of good trees to rescue from the vines: cherries, oaks, and of course the bicentennial dogwoods.

A lot of learning happens at these workdays, as volunteers become familiar with some of the plants being saved or removed. Here are the flower buds of the flowering dogwoods, still dormant but poised to open. Their blooms in turn will form nutritional berries for migrating birds in the fall.

Hopefully the state crews will chip up the brushpiles we made.

This boy was very proud of having opened up a pathway that had been blocked by a young tree bent low by a burden of aggressive vines.

An invasive shrub (Honeysuckle) was smothered in invasive vines (porcelainberry). The easiest way to extract it was by cutting it at the base and "rolling" it out of the sea of vines.

Clearing the field's edge of brush uncovered some daffodils that had been planted long ago. We left the wineberries and blackberries in hopes of a crop during the summer.

We finished the afternoon encouraged, by progress that built on last year's progress, by each other's good company, and by the feeling of participation in caring for hallowed ground. Here's our merry crew.

Princeton Battlefield Clean-up -- March 31

Each year, the Princeton Battlefield Society and the local chapter of the Sierra Club team up to have a volunteer workday at the Battlefield. Though the Battlefield is a state park, the state limits its maintenance of the grounds to lawn mowing, leaving the rest of the park's greenery to grow as it may. Two very aggressive introduced species, bamboo and porcelainberry, have run rampant, impinging on trails and overwhelming some historic plantings such as the dogwoods planted in 1976 to celebrate the nation's bicentennial. As part of the Friends of Herrontown Woods' outreach, I'll be leading volunteers interested in sustaining the dogwoods planted around the perimeter of the park on the Colonnade side.

Anyone who'd like to join in, check out the flier below, and rsvp at https://www.theprincetonbattlefieldsociety.org/. If you can, bring workgloves, loppers, and handsaws. Here's a writeup on last year's spirited event, with our state senator Kip Bateman in attendance.

Wanted: A Few Good Herbivores

If you encounter a book or article that claims that, surprise!, invasive species aren't such a big problem after all (a few were written over the past decade), you'll probably find no mention of herbivory. They'll say that invasive plants are being falsely maligned, because actually they do wonderful things, like provide berries and nectar for wildlife. But it's to the plant's advantage to have its flowers visited and its berries consumed. What the plant doesn't "want" is to be eaten, and therein lies the problem with plants that become invasive. For whatever reason, be it an invasive's chemical defenses or ingrained dietary habits, the wildlife tend not to eat them.

Nature depends on consumption to keep things in balance. We love nature for its beauty and variety, but behind the scenes there's a whole lot of mastication going on. Take away predators and the deer population explodes. Introduce a new plant that the wildlife won't eat, and there's potential for that species to make habitat less and less edible as it displaces the natives. To fill this void in consumption, people have had to play the role of herbivores. What we do at Herrontown Woods, as we cut down dense groves of winged euonymus and other nonnative invasive shrubs, is to play the role of the missing herbivores, using our loppers for teeth.

There's some pleasure in the work--pleasing vistas created, serendipitous discoveries. But all things being equal, it would really be nice if the resident wildlife could show some flexibility in food preferences and fill the void in consumption. Invasives, after all, represent a huge, untapped food source for any animal willing and able to broaden its palette.

Given how much work it would be for humans to play the role of herbivores in the forest, any evidence of wildlife gaining an appetite for invasive plants stirs some hopefulness.

For instance, an invasive honeysuckle shrub was recently found stripped of its leaves. A closer look revealed something had been hard at work, its mandibles outshining our loppers: the caterpillar of a snowberry clearwing moth, also known as the "hummingbird moth" or "flying lobster", for its capacity to hover in front of flowers as it sips their nectar. Maybe if we had more summer wildflowers for the adult moths to feed from, their caterpillars would help control the populations of bush honeysuckle in Princeton's preserves. Nice to think, anyway.

And what's this orange plant growing on a dense expanse of invasive mugwort that grows as a monoculture along the gas pipeline right of way in Herrontown Woods? Dodder is a parasitic plant with little capacity to gather energy from the sun. Instead, it wraps itself around other plants and sucks out their juices.

Usually, its impact is small, but this must have been a particularly good year, because a sizeable patch of mugwort was sucked dry.

If only we could get the dodder (genus Cuscate) to preferentially neutralize the mugwort all along the right of way, some diversity might return. Again, a nice thought and tall order.

A new invasive trying to gain a foothold in Princeton is mile-a-minute vine, with a distinctive triangular leaf, a prickly stem, and a growth habit to match its name. Another post shows how invasive this annual vine can be , on farms just outside of town. Fortunately, after weeding out a small population back in 2007, I know of only two patches currently growing in Princeton, still small enough to control and hopefully eliminate altogether.

One's at the Princeton Battlefield. This year's growth was pulled out in early summer, and when checked in late August, the patch had only managed to produce a few leaves, all of which were being very effectively munched on by a weevil intentionally introduced to the U.S. to bring this rampant new species under control.

Ah, I concluded, to control mile-a-minute vine, simply reduce the patch in early summer, leaving enough for the weevils to sustain their population on. Their appetites appeared to be sufficient to prevent any flowering or fruiting that could lead to the patch spreading elsewhere.

Nice concept, but it wasn't working at the other site, down along the driveway into Rogers Refuge, where the vine had sprung back up, flowered and fruited, undeterred by the minor nibblings of the weevil. That patch had to again be pulled out by hand.

Another discovery was the work of the Ailanthus webworm moth, which had completely defoliated a young tree of heaven near the parking lot of Herrontown Woods. The moth, like the tree, is an introduced species.

If you have flowers like boneset growing in your backyard, you may be helping the adult moths to prosper.

Here again, though, the larvae have thus far been seen only on very young trees, with larger ones largely left untouched.

These are glimmers of hope, sprinkled across Princeton. It will take some concerted mastication by as yet unnamed herbivores to stem the tide of rapidly spreading species like porcelainberry, callery pear and stiltgrass--a giant uneaten salad that grows by the year. A little salt and pepper, perhaps?

Hicans and Other Useful Trees at Princeton Battlefield

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

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

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

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

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

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

Chinese chestnuts, too, are having a banner year.

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

It, too, is laden with chestnuts.

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

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

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

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

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

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

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