The Art of Pulling Garlic Mustard

Each spring in Herrontown Woods, from April through May, we take part in the Great Garlic Mustard Pull. That's the effort, replicated in yards and nature preserves throughout the eastern U.S., to pull garlic mustard (Alliaria petiolata) out of the ground before it goes to seed. This post explores the logic, toils and unexpected pleasures, as well as the strategies that can make this annual gardening task easier each year.

We pull this nonnative invasive plant, with its aroma of garlic and mustard, because the alternative is too much to bear. Left unchecked, garlic mustard can take over a woodland or garden, altering soil chemistry and smothering native species.

People pulling the flower stems are surprised to learn that other, lower-growing plants coating the ground are also garlic mustard. Two very different forms of the plant are present at the same time. Unlike most herbaceous plants that are either annuals or perennials, garlic mustard is a biennial. That means it grows a rosette the first year, storing energy in its roots--energy that will be used the second year to send up seed-bearing stalks. After the stalk blooms and the blooms turn to seed, the plant dies, leaving copious seed for future generations.

Gardeners are often fooled at first into leaving garlic mustard be. The flowers are modestly attractive, and as they fade and turn into siliques packed with seeds, the plant too fades politely into the background. But wait a month or two, and the flowering stems turn into brown, skeletal remains that haunt the summer garden. By the time the gardener notices this blight, the seeds have already dispersed.

Much is made of the plant being edible. Young leaves can be used to make pesto and other dishes. Our friend Kirsten used it to make delicious deviled eggs. But in most situations, the plant's powers of proliferation quickly overwhelm people's appetites.

And so we pull, and pull. That's Herrontown neighbor Philip Smit in the photo. The aim is to get every last one, to ultimately exhaust the soil's supply of seed. Only with zero tolerance will the task get easier year to year. Here is where technique and timing come into play. If you pull hastily, or when the soil is dry, you may get the stem but not the root. This is an incomplete victory. That root will sprout new seedstalks that then too must be pulled. So we "grab low and pull slow", ideally pulling after rain has softened the soil, and hope to get at least most of the roots. Either way, it's important to return a week or two later to check for any resprouts.

And what to do with the pulled stems, whose seeds could still potentially mature? Bagging them is a lot of work and wastes energy to have them hauled away. This year, we've been putting them in trash bins, then rolling them to a pile. In case any of the seeds mature, the pile is located where the seeds won't wash down the hill, so any seedlings will all be in one spot.

I've heard stories of gardeners who pulled year after year, and yet the garlic mustard continued to sprout anew. Where would the seed come from? We speculated that erosion from heavy rains, or the diggings of squirrels, could expose long buried seed. 

But another cause could be these miniature plants I've been finding. We pull the bigger plants and think our work done, but no. A second and even a third pass is needed over the course of weeks, with an eye out for these tiny plants. 

There can be pleasure in the task. These two visitors to the preserve joined in one day. Kids, too, take to the pulling, seeking out the white blooms as if it were an Easter egg hunt.

We're grateful that some students from Princeton University's Outdoor Action--Will Aepli, Quest Starkey, and Zach Duscorsky--worked with FOHW board member Ben Schaffer and me to clear garlic mustard from the Veblen House grounds and the Barden. Inge Regan, Moss Gordon, Ninfa and Andrew have helped with a larger patch in another woodland we're restoring, behind Windy Top. 

Invasive species can seem an impossible challenge, but if the invasion is caught early, and the garlic mustard is completely removed year after year, the work we do to protect 230 acres of public open space at Herrontown Woods and Autumn Hill Reservation becomes a little easier, with some satisfaction and even pleasure in the task.

Related Post:

A Garlic Mustard Success Story From Michigan

The Mystery Tree Found in Autumn Hill Reservation

Not everyone gets to discover and report on a new invasive species in one's adopted home town. Though there were a couple kinds of invasive plants that I caught early enough to hopefully keep from spreading through town--thorny mile-a-minute and more recently the dreaded common buckthorn--this particular discovery is different, in that people have yet to agree on what it is. How strange it can feel, in a time when the internet can instantly tell you everything about everything, to find a plant to which no one can with certainty give a name.

I first encountered a single specimen of the mystery tree while conducting a plant inventory in Roger's Refuge in 2007. Only in the past few years have I found it proliferating in Herrontown Woods and Autumn Hill Reservation. 

Some call it a shrub, though when it grows to 30 feet, maybe it's time we start calling it a tree. There's agreement that it is in the genus Pourthiaea--a name that people will struggle to spell and pronounce (my attempt at a pronunciation is "pore-THEE-uh"). In a discussion on iNaturalist, the citizen science site for reporting and identifying species, some try to call it asian photinia (Pourthiaea villosa)--a nonnative shrub that likely escaped from Princeton-based nurseries long ago.

They are surely wrong, as the leaf shape and fall color of asian photinia are clearly distinct. This bright golden yellow is increasingly prettifying and clogging Princeton's greenspaces, from the Institute Woods in the west to Autumn Hill in the east, creating dense, exclusionary stands as it spreads beyond Princeton to proliferate across New Jersey. 

John L. Clark, a Princeton-based botanist frequently posting on instagram from the forests of Equador, has done a great deal of research into our mystery tree. Since the Pourthiaea genus originated in China, John tracked down a couple Chinese botanists to seek their insights. 

One, D.Y. Hong, responded that he was too old to take on the challenge of identifying the tree.

Another, Bin-Bin Liu, was also apparently unable to assist. John laments that botanists now trained in phylogenomics can identify gene sequences but not the actual physical plants themselves. 

There have been various species names thrown at the mystery tree--lurida, lucida, arguta--but none clearly stick thus far. Through Mike Van Clef, I learned of Jean Epiphan, a northern NJ plant expert at Rutgers, who had arrived at the species name "parvifolia", and even came up with a common name, "littleleaf photinia." Originally introduced in 1908 at the Arnold Arboretum," it's popping up in Morris County and, according to Jean, matches our mystery tree in Princeton. She has not seen it being sold in nurseries, and speculates that it is spreading from specimens in old estates. She sent a couple links (here and here) with descriptions, and a mention of it in Dirr's encyclopedic Manual of Landscape Plants.

Some sticking points, though, are that the link she sent to a photo has now gone dead, and the description is of a shrub less than ten feet high. A photo sent by Pat Coleman from Bowman's Hill Wildflower Preserve also matched our mystery tree in Princeton, but no word as yet whether they've come up with a name.

One thing to call the mystery tree is pretty, as are many invasive shrubs, both when they bloom and in the fall. This fall in particular, Autumn Hill Reservation was a jubilant jumble of colorful invasive shrubs, led by the bright red of winged euonymus, joined by the rich colorations of Linden viburnum and the golden yellows of the asian photinia Even the lowly privet got into the color game with an appealing dark bronze. 

When surrounded by such a dazzling visual display, it takes work to remind oneself that something important is being lost as these introduced species gain dominance in the understory. Their success and dominance is enabled in part through being rejected by deer, which prefer a diet of native plants. Thus, our eyes are well fed while the wildlife find themselves living in an increasingly inedible forest. 

As we lose many of the native trees dominating the canopy--chestnut, elm, ash, and now the beloved beech--the extra light reaching the understory drives the extravagant growth of nonnative shrubs. Surrounded by such a thorough invasion of nonnative growth, it is extraordinarily intimidating to contemplate the work involved to shift the balance back to the spicebush, blackhaw viburnums, blueberries, hollies, sumacs, and other natives currently getting smothered beneath the rising tide.

Native shrubs and trees don't exactly lack color. Here's a dogwood that was mixed in and easily confused with the mystery invasive. Note the way the leaves are paired rather than arising one at a time along the stem. 

All the invasive shrubs currently dominating were at one time, long ago, in a similar state, just starting to pop up here and there. Clearly there was no one back then able to see the future and take early action. In our era, the consequences of inaction are readily apparent. What is special about this moment in the history of Autumn Hill Reservation is that the mystery tree is still early enough in its invasion, and easy enough to spot in fall, that it can be stopped.  

Update:

Where found thus far:

• Rogers Refuge, Herrontown Woods, and Autumn Hill in Princeton
• Possible sighting in the Institute Woods in Princeton
• Bowman's Hill Wildflower Preserve
• Jockey Hollow and the NJ Brigade Area in Morris County
• Tourne Park, in Boonton

Update: A big thank you to "anonymous" in the comment section, who provided a species name and links to herbarium photos:

"Thanks for alerting us to this newly naturalized species. One of the best resources for documentation of plants on a global scale is GBIF. Reviewing the gallery of specimens online, the name leaves to appear to bear a resemblance to Photinia parviflora. https://www.gbif.org/occurrence/gallery?taxon_key=5363981"

Each photo at the link bears the name C.K. Schneid. Look at the wikipedia page for Camillo Karl Schneider and you'll find that he was a German botanist who traveled to China in 1913 to collect plants and seeds. His next stop was the Arnold Arboretum in Boston, where the species is said to have been introduced five years earlier by Wilson in 1908.

Each photo shows that the now accepted species name is not parvifolia but instead parviflora. 

Applied name Photinia parvifolia (Pritz.) C.K.Schneid.
Accepted name Pourthiaea parviflora (Cardot) Iketani & H.Ohashi

That puts into question the common name "little leaf photinia", since "parviflora" means little flower. 

So, we're not really there yet. 

A Bear Visits Riverside Elementary

As reported in TapInto Princeton, a black bear stopped by Riverside Elementary School during school hours this past Wednesday, May 28. The school was in "lock down" mode for two hours until the bear had moved out of the neighborhood. (Photo by Syth Devoe) The school, whose mascot is the River Bear, was reportedly last visited by a real bear in August of 2022. 

This PrincetonNatureNotes website serves as a diary of sorts for bear visits to Princeton. A common cause of bear visits is young males seeking new territory. For previous posts, you can do a keyword search for "bear," but "latte" works pretty well, too. "Duck in for a latte" is part of a comic but accurate description I wrote in 2012 about how a Princetonian should behave when encountering a black bear. 

Some background info on black bears in NJ can be found in a MyBergen article. 

Update: Carolyn Jones' writeup in TapInto Princeton, "Hey, Princeton, Time To Be 'Bear Aware' -- American Black Bears Are Increasingly Common," gives a good overview, including an extensive interview with animal control officer, Jim Ferry. 

Maintenance Will Determine the Fate of the Betsey Stockton Garden

When I look at a plant, a garden, a meadow, a forest, I can see the future. It's a form of extrapolation, defined in the Oxford Dictionary as "the action of estimating or concluding something by assuming that existing trends will continue." I only realize now, writing this, that not everyone exercises such powers. Not everyone has been a gardener of landscapes for fifty some years, accumulating memories of myriad plant species and observing their behaviors. I've seen thriving raingardens and neglected ones, healthy meadows and forests, and degraded ones. I've observed how various invasive weeds spread and come to dominate, each in its own manner and at its own pace. These are the accumulated data points used to predict the future.

One very satisfying thing about extrapolation is that I can see, in my mind, the flower a bud will become. But with that same power to see a garden blooming while still in bud, I can look at a garden in what for others is glorious bloom and see the "seeds" of ruin--the scattered pockets of invasive mugwort, nutsedge, stiltgrass or lesser celandine, crown vetch or Chinese bushclover that without early intervention will quickly expand and ultimately prevail. 

My interventions--a broad mix of successes and failures--have taught me above all that early intervention can make the difference between hope and despair. 

One special garden in town that I stop by to check up on, like an old friend, is the Betsey Stockton Garden planted atop the Firestone Library at Princeton University. This is a complex native planting, containing 35 native grassland species. The person or crew maintaining the garden needs to be able to recognize and identify all 35 intended species, plus all the weeds that could potentially cause problems, not only when they're blooming but at all stages of development. 

That deep knowledge is a tall order. Knowing how little respect maintenance often gets, I worry about this meadow garden in the longterm. Will it receive the knowledgeable, strategic attention it needs to thrive? This photo of wild bergamot blooming with lots of clumping goldenrods suggests things are going well. 

Here, some black-eyed susans lend color, but the pink blooms of quickly spreading non-native crown vetch spell trouble.

New to me is a weed called rabbits foot clover, which may have hitchhiked in from whatever distant nursery the intended plants came from. This, too, was not caught early, and now poses a significant challenge.

Thankfully, there's only one small patch of the fearsome mugwort, but that could quickly expand if not dealt with quickly. Getting as close to zero tolerance for invasives as possible makes maintenance much easier. 

Maintenance is not given its due in part because success is often invisible. In a house, we note dirt's presence, not its absence. A well-run government agency doesn't make it into the news. The bass player who provides the harmonic foundation for a band often goes unnoticed until he plays a wrong note. In medicine, catching problems early doesn't pay as well as dramatically rescuing someone whose problem has grown into an emergency. Extrapolation can help with this. It allows us to see large consequence in small acts, to appreciate how big a problem has been avoided by digging up a small, isolated patch of mugwort.

I found a few relevant local writings. One was an opinion piece in the Daily Princetonian by an undergrad, calling for more native plantings on campus. Planting is a good start, but what goes unmentioned in the opinion piece is that maintenance determines any planting's fate. 

One strategy being used in newer native plantings on campus is to plant gardens with only three or four species, with lots of mulch inbetween plants. This reduces the amount of training required for maintenance. 

Other local writing specifically about the Betsey Stockton Garden can be found in the Princeton Magazine. It includes the list of intended plants (below), and describes the garden as low-maintenance, but that assumes the invasive weeds will be caught early and removed before they can spread.

The Betsey Stockton Garden was planted in 2018, two years after the demise of another campus native planting, around the Neuroscience Institute. Hopefully some lessons are being learned, and the University will bring the necessary expertise and strategic timing for maintenance to bear on this lovely, botanically complex planting. 

Native Plants Featured in the Betsey Stockton Garden
(Some are used on the High Line as well.)

Grasses: Carex comosa, Appalachian Sedge Carex pensylvanica, Pennsylvania Sedge Festuca ovina, Sheep’s Fescue Festuca rubra, Creeping Red Fescue Sporobolus heterolepis, Prarie Dropseed Elymus virginicus, Virginia Wild Rye Schizachyrium scoparium, Little Bluestem Tridens flavus, Purple Top Shade Plants: Aqueligia canadensis, Wild Columbine Aster laevis, Smooth Blue Aster Blephilia ciliata, Downy Wood Mint Erigeron puchellus, Robin’s Plantain Eurybia divaricata, White Wood Aster Polemonium reptans, Jacob’s Ladder Sisyrinchium angustifolium, Narrow Leafed Blue-Eyed Grass Solidago caesia, Blue-stem Goldenrod Solidago flexicaulis, Zig-Zag Goldenrod

Full-Sun Plants: Asclepias tuberosa, Butterfly Milkweed Aster laevis, Smooth Blue Aster Aster pilosus, Heath Aster Baptisia alba, White Wild Indigo Baptisia perfoliata, Catbells Centaurea cyanus, Cornflower Chamacaesta fasciculata, Partridge Pea Coreopsis lancelota, Lanceleaf CoreopsisEchinacea pallida, Pale Purple Coneflower Echinacea purpurea, Purple Coneflower Monarda fistulosa, Wild Bergamot Penstemon digitalis, Beard Tongue Rudbeckia hirta, Blackeyed Susan Solidago juncea, Early Goldenrod

Beech Leaf Disease Sweeps Across Princeton

Princeton is losing its beech trees.

We were feeling celebratory, having just completed a successful corporate workday in Herrontown Woods, when I happened to pass by this small branch of a beech tree along the red trail. The leaves were strangely contorted, with dark green stripes. I had heard distant rumblings about a disease of beech trees, but had managed to keep my head in the sand until that moment. 

Back home, diagnosis was but a google's search away. Similar images popped up on the screen, along with the name: Beech Leaf Disease. Tree maladies typically come with an acronym. Emerald ash borer is EAB. The dreaded asian longhorned beetle, which they've had some success keeping from spreading across the eastern U.S., is ALB. The Bacterial Leaf Scorch that afflicts pin and red oaks is BLS. Now there was a new one: BLD. 

For those unfamiliar with the American beech (Fagus grandifolia), it's a native tree related to oaks and chestnuts, with beautiful smooth gray bark. They can get very big and live for centuries. Thousands of them grow in Princeton, in the preserved forests along the Princeton ridge and on slopes above the Stony Brook. 

The "grandifolia" in the latin name refers to the leaves, which are larger than the leaves of European beeches. This photo shows some healthy leaves (on top) and the curled, darker green leaves that have been contorted by nematodes overwintering in the buds. Beech leaf disease is caused by these nematodes--tiny worms spread by birds or the wind. 

Viewed from beneath, the infected leaves show a curious striping of dark and light green. 

During a subsequent hike in Autumn Hill Reservation, I was astonished to find nearly all the beech trees affected--their leaves contorted, their crowns beginning to thin. Beech in Rogers Refuge are showing symptoms, and Mountain Lakes preserve is reportedly also affected. According to online sources, essentially all of our beech trees will be dead within ten years. The news comes exactly ten years after the first emerald ash borer was found in New Jersey, with the skeletons of ash trees still haunting our woodlands.

According to this map, on the Holden Arboretum website, the disease was first spotted near that arboretum in Ohio in 2012, and has spread in all directions, most rapidly eastward.

According to the Maryland Extension website, the microbe causing the disease is Litylenchus crenatae mccannii, a subspecies of a nematode found in Japan. As one would expect, the only beeches resistant to this particular nematode are those that coevolved with it in Japan. 

The Holden Arboretum website mentions a chemical treatment that is being tested. It is a compound that is sprayed on the tree in the fall just as the nematodes are moving from the leaves down into next year's buds. Unfortunately it is highly toxic. The snail's pace of tree research compared to the rapid development of Covid vaccines caused one friend to ask, "Where is science when we need it?" 

The loss of a tree species from the canopy has all sorts of impacts on wildlife. Ash, elm, and maples bear abundant seeds early in the season to feed on. Two of those three have been largely lost. Nut-bearing trees provide food in fall and winter. Gone from wildlife diets are chestnuts, bacterial leaf scorch is reducing oak production of acorns, and it now looks like beech nuts will become very rare. Websites detail the ecological web of connection and dependence that is unraveled by the loss of a tree species. 

A post last year by the Brandywine Conservancy in Pennsylvania provides a particularly chilling description of what is in store for eastern forests:

"As the disease progresses, leaves will become smaller in subsequent years, and it will seem like autumn in the summer as infected leaves brown and fall from the tree, resulting in thinned crowns and branch dieback. Eventually, BLD will cause beech trees to abort their buds, leading to the death of the tree. Young beech tree saplings die within 2–5 years of infection, while mature trees live a bit longer. Death from BLD is likely accelerated in beech trees stressed by drought or Beech Bark Disease, which is a different infection that involves scale insects and fungi."

Here's a writeup I found on beech bark disease, which also poses a mortal threat. 

I encourage people to visit favorite beech forests in the area sooner rather than later, to appreciate the now threatened beauty of this singular tree. Over the next few years, if you are fortunate enough to find one that remains healthy while others around it succumb, you should let people know. The Holden Arboretum site provides someone to contact.

Yesterday evening, I visited the fabulous congregation of European beech off of Elm Lane on Constitution Hill in western Princeton. The many trunks appear to all come from the original massive trunk in the middle. 

Seen from a distance, they appear to be separate trees, but more likely were either branches that touched the ground and took root, or sprouts from the original tree's massive root system.

You can see how some of the trunks still have a sort of navel, where the original branch from the "mother tree" was cut off.

Its leaves, smaller than those of the native beech, were  showing early signs of the disease.

Some of Princeton's most spectacular native beech trees grow in the Institute Woods. That will be my next stop--that and a hidden valley between the Princeton University chemistry building and Washington Road, where I found a mixed forest of 200 year old trees, part of the great American forest cathedral that, in unspeakable sadness, loses its towering pillars, one by one.

Here is how I concluded a recent letter to the editor in the Town Topics: 

Outrage is often triggered by the intentional cutting of trees. The highly visible spotted lanternfly caused a stir, yet has proven relatively innocuous. The biggest threats we face are neither visible nor intentional. The emerald ash borer is hidden behind bark. Nematodes are microscopic. Our machines’ climate-radicalizing carbon dioxide? Unintended and invisible.

There is so much joy still to experience, for me particularly in Herrontown Woods, and yet in the larger workings of the world, so much to grieve.

Tent Caterpillars and the History of Black Cherry Trees in Herrontown Woods

Black cherry trees draw attention in early spring because of the "tents" that tent caterpillars weave on them. I was surprised to find out that these tents are sometimes mistaken for gypsy moth infestations. There's also some disagreement as to how damaging tent caterpillars are to the trees they feast upon, so I decided to do some investigation. 

First, some distinctions between tent caterpillars and gypsy moths. Tent caterpillars are native, feed primarily on cherry trees, build conspicuous tents, and do their feeding on the fresh, tender leaves just beginning to emerge in April. Gypsy moths are a nonnative species imported from Europe, start feeding in May on a very wide spectrum of hardwoods and even some conifers, and do not build tents. 

Gypsy Moths

The story of gypsy moths in our area is most easily grasped by looking at how many articles about them have been archived in the Papers of Princeton through the decades. Outbreaks of gypsy moths remained minor in New Jersey until the 60s, then grew into massive defoliations of forests in the 1970s. By the early 1980s, gypsy moth populations were beginning to drop, thanks to a natural virus, introduced parasites, and aerial sprayings. A naturally occurring bacteria called Btk proved safe and effective when sprayed on trees where gypsy moths were feeding. There was a recurrence from 2007-8, but numbers have dropped off since then. Though the forests largely healed, the trauma of past gypsy moth infestations lives on in people's memories. 

Tent Caterpillars

What we have this spring, and springs extending back through millenia, are native tent caterpillars making their tents. 

Some sources on the web suggest that tent caterpillars, despite the powerful visual of the tents and defoliated branches, don't do enough damage to a tree to worry about. I'd really like to believe that, but this young black cherry tree, now bearing eleven tents from which the caterpillars make forays, is almost completely defoliated. 

They say a tree can survive one complete defoliation, but if defoliated several years in a row, it becomes increasingly susceptible to disease and insect attack.

Meanwhile, our very hungry tent caterpillars have even followed a branch over to a neighboring pin oak, which now, too, is getting chowed down upon.

We pause to note a couple recurring themes in nature. One is that the tent caterpillars will shift to a less desirable food source (a pin oak tree) if their favored cherry tree leaves run out. Deer, too, will begin eating less desirable foliage if they run out of their favorites. Thus, an overabundance of deer in the 1990s almost wiped out spicebush in our Princeton woodlands, despite it being low on the list of deer's preferred foods.

The other example of a recurring theme in nature is that the tent caterpillar eats only one crop of leaves, then is done for the year, allowing the tree to recover. The worst thing a predator could do is be so effective as to eliminate its prey. 

The introduction of a new insect, though, could throw off this balance of predator and prey. If another insect, say, a gypsy moth, came along and defoliated the same tree yet again in the same growing season, that tree would be in big trouble, having twice committed energy to manufacturing a whole crop of leaves, only to have them eaten. One question is whether the gypsy moth outbreaks in the '70s and '80s killed more of one tree species than another, causing changes in forest composition still noticeable today.

There's a lot of caterpillar behavior whose purpose is not immediately obvious. A week ago, caterpillars were crawling about on the outside of the tent, turning this way and that. My best guess was that they were expanding the tent by adding another layer of silk, but no strands could be seen coming from their bodies as they moved about. 

And why are these caterpillars clustered on the side of the tree, outside of their protective tents? Wouldn't they be easy picking for the birds that are said to consume them? 

As their spring residency has continued at the Barden in Herrontown Woods, the tent caterpillars have spun not only isolated tents but also enveloped the trunk and limbs in a silken web reminiscent of the webbing people drape on their shrubs for Halloween. A closer look reveals that the caterpillars have spun silken highways upon which they commute from tent to the "pasture" of the canopy. These highways are only one lane wide, requiring a caterpillar to temporarily step aside if it meets another coming the opposite direction. Some silken highways are suspended in air, like overpasses--a great way to smooth out the rough terrain of a black cherry tree's "black potato chip" bark. 

A tree colonized by tent caterpillars, then, has elements of occupancy, transport, and exploitation not unlike the human footprint on the land, with our homes, highways, and farm fields. A big difference being that the tent caterpillar's settlement is seasonal--more like the impact of nomadic tribes than our permanent villages--giving the tree a chance to recover.

Another big difference between tent caterpillars and other builders of shelters--bees, ants, birds, mice, people--is that the caterpillars don't seem to bring anything back to the shelter other than their bigger, well-fed selves. They aren't adults bringing food back to the young. The caterpillars, like super resourceful children, work collectively to raise themselves, then leave the tree on their own to pupate and turn into adult moths. 

A nice writeup about tent caterpillars (Malacosoma americanum) found at ThoughtCo.com states that the broad side of the tents faces the sun, and that the caterpillars make three forays per day, returning to their tents inbetween. That will be something to check out next spring.

Surprisingly, the subject of wild cherry trees in what is now the Barden (formerly a pine plantation) came up more than 50 years ago, in Richard J. Kramer's book about Herrontown Woods. 

"Wild black cherry, which grows to magnificent size in the Allegheny Mountains, is a poorly formed tree in Herrontown Woods, occurring mostly in areas which were recently open fields. Its best growth has been in the pine plantation, where specimens are 30 to 40 feet tall and possibly may develop into good-sized trees. Apparently these black cherries were able to develop along with the young pines after these were planted in the open field. Although the birds do bring seeds of the cherry into the forest, the many seedlings and the few saplings that occur there grow poorly and remain shrub-like."

Gone now are most of the pine trees in the pine plantation, and those larger cherry trees are nowhere to be found. Our 12 little black cherry trees in the Barden, all saddled with tent caterpillars, must be the descendants of the larger cherry trees Kramer describes. Only one large black cherry tree is known to exist now in Herrontown Woods, almost completely free of tent caterpillars, growing next to Veblen House. Have tent caterpillars contributed to keeping the black cherry trees of Herrontown Woods from achieving full size, in the past as well as in the present?

If we wanted to relieve the cherry trees of the spring burden of hungry caterpillars, we could remove the tents and remember to crush the egg masses laid by adult moths on small branches in late summer, as suggested in this useful post about the insect. 

But as insect numbers continue to decline, the role of trees as food for native insects grows in importance. And if the cherry trees remain small, that will allow more sunlight to reach the many wildflowers growing in the Barden. Leaving the tent caterpillars to grow undisturbed can serve as an experiment, to see if they continue to flourish year after year, or if nature's array of predators, pathogens, and parasitoids finally up their game and reduce the burden these trees now bear.

The Lost Forest of Rogers Refuge

This past November, I received a request to look at a lost forest in Princeton. 

The request came from what may be the oldest open space organization in town--the Friends of Rogers Refuge. Dating back to 1967, FORR has been working with the town, and the water company that owns the land just down from the Institute Woods, to sustain the refuge's role as premier habitat for a tremendous diversity of birds.

Over the years, I've been able to witness and collaborate with a progression of leaders who have overseen stewardship--the Southerlands, Tom Poole, the Spars, the Varians, and most recently David Padulo. 

At annual meetings, discussions have tended to focus on the refuge's central feature, the surprisingly extensive marsh--how to keep it wet enough and protect it from the super-aggressive Phragmitis.

But this year, concern now extends to the floodplain woodlands surrounding the marsh--also vital bird habitat. One of these woodlands, thriving four years ago, has lost its trees.

This was not a forest classically lost to logging. The trees were not cut down but rather strangled over the course of several years, then left standing, each tree a monument to its past life. 

Few have seen the now ubiquitous strangler, the Emerald Ash Borer accidentally introduced to the U.S. from Asia. It's larvae work quietly under cover of bark, feasting on the ash trees' circulatory tissues. 

That a whole forest could die speaks to how common ash trees once were. The most numerous tree in Princeton up until just a few years ago, comprising more than 10% of the tree cover, the ash tree's skeletons can be found throughout the canopy of residential and open space lands. Ash were particularly good at colonizing abandoned fields, to the point of dominating one area of what is now Rogers Refuge. 

As the botanist in an organization of birders, I was asked what the longterm prognosis for this lost forest might be. Winnie Spar, Joe Melton, and I walked the red trail to have a look.

One striking feature is what I call "poison ivy trees." These are dead trees, still standing, that have been scaled by poison ivy vines, with their classic "hairy is scary" stems. In order to bloom, poison ivy must climb a tree, sending out lateral flowering shoots along the way. The branch-like laterals give the tree the look of still being alive, even though all the leaves are now poison ivy. The flowers produce berries that, birders will enthusiastically tell you, serve as important food for birds.

Another feature of a lost forest is the shrub growth that now thrives on the infusion of sunlight previously claimed by the tree canopy. Much of this shrub growth, unfortunately, is nonnative and inedible to wildlife, like this Asian Photinia. At least it can be said that the invasive shrubs are not as thick at Rogers Refuge as they are at the Institute Woods just up the hill.

A few other native tree species fill a small portion of the void. In early November, the occasional silver maple and pin oak still had many of their leaves. Mixed in were a couple elms, and a red maple. 

Used to the numerous red maples at Herrontown Woods on the other side of town, I was surprised to find instead an abundance of box elder of every size growing in this broad floodplain of the Refuge. Related to maples, box elder are not the most statuesque of trees, but their soft wood can make good bird habitat. They now stand as the main hope for rebound in this patch of former forest. 

The walk being with such knowledgeable birders, attention never strayed far from bird life. We saw a couple pileated woodpeckers, a coopers hawk and a couple other larger hawks. Winnie kept up a running monologue about the status of this or that bird. Mockingbirds have been around for a long time, but the catbirds keep them out of their territories when they are present. While a warming climate is causing many birds to extend their ranges northward, ravens, surprisingly, are moving south. She's seen some in the Refuge. Warblers love something about the spicebush flowers, whether it's the flowers themselves or an insect in them. Blue gray knatcatchers were mentioned, along with many other bird names that didn't register in my botanical brain.

There's a lot of concern that last year's fires in Canada have been very hard on migrating birds that nest up there. A woman who catches and tags migrant birds had been having very few birds coming back down from Canada, but her catch/tag/release activity, conducted on Sundays, was hampered by rains every weekend this fall. One day she got only ten birds, total. 

But then Winnie is quick to add that she saw Cape May Warblers in the Refuge for the first time, several in fact, with immatures, and they too nest in Canada. Winnie is one to accent the positive, while acknowledging that migrant bird numbers are down 50-90%. 

This lost forest, the decline in bird numbers, accelerating changes in climate, democracy under threat--in many ways, America is losing its memory of what it once was. The soil, for its part, holds memory through the seeds that remain dormant within it. Back when the seed bank--this stockpile of seeds yet to sprout--was dominated by the seeds of native species, succession as an ecological phenomenon featured an orderly and predictable progression of species, from grassland to shrubland to mature forest. But the soil under our feet has lost its memory, whether by plow, development, intense browsing, or displacement of native species. Invasive lesser celandine, poisonous to wildlife, coats the ground in the spring, followed by inedible stiltgrass and its billions of seeds in late summer. Invasive shrubs and deer combine to limit native species and thwart the once timeless process of succession. Though the tree canopy is still dominated by natives, these are under increasing attack from introduced insects and disease.

Even healthy trees can be overwhelmed by vines of porcelainberry and wisteria.

Given the circumstances, it's fair to ask what sense there is in persevering. What I find is that the native growth force, if often smothered and badly abused, remains intact. When given a chance to prosper, native plants and wildlife still can thrive. In Rogers Refuge, we've seen a tremendous rebound of spicebush since the town began culling deer to reduce browsing pressure. That in turn has improved habitat for birds. FORR has paid contractors to successfully set back the Phragmitis and porcelainberry. 

Through periodic interventions over a number of years, the Varians have virtually eliminated the one patch of invasive Japanese knotweed at Rogers Refuge. 

We pick our spots, time our interventions strategically to have the most impact for the least amount of effort, and look for opportunities. Despite the tragedy of losing ash trees, the new openings in the canopy could potentially allow native shrubs to grow, flower and bear in ways they haven't since being shaded out decades ago. 

Our inherited environmental mindset is that nature, if protected from intentional depredations like logging and draining, will heal itself. As FORR's webmaster Laurie Larson points out, "when Charles H. Rogers and the Southerlands started birding the “Water Company” in the 60s and 70s it was a landfill." The initial fight was to put an end to dumping. But now, at Rogers Refuge and many other places, the main depredations (invasive species, climate change) are unintentional, and the healing must be helped along by intentional effort. That effort could seem a sacrifice, but the primary feeling is one of gratitude, for the chance to work with nature--the greatest and most generously creative collaborator of all.