Fall Colors Walk and Other Weekend Events at Herrontown Woods

The Friends of Herrontown Woods is hosting various events this weekend. I'll be leading a Fall Colors walk Sunday, Nov. 1 at 11, but before that will be May's Cafe--coffee, tea, and baked treats served in the Barden, 9-11:30am--and before that will be the last session of Gratitude Yoga for the year on Saturday, October 31, at 11am, next to Veblen House. 

Don't forget to "fall back" timewise on Sunday.

The Sunday walk will focus on the woody plants that turn color this time of year, be they trees, shrubs or vines. Please register on the FOHW website. Though the walk is full, you can sign up for "overflow" and we'll figure out how to accommodate everyone.

We'll start at the Barden (600 Snowden Lane) and head up the boardwalk to Veblen House and beyond. 

One shrub people love to see is Hearts a' Bustin, the native Euonymus with ornamental seeds. We have a bunch of them in the Barden. Deer love them, too, to eat, so we protect them until the shrubs grow beyond the reach of the deer and can show off their wonderful qualities.

Another big surprise this time of year is the flowers of witch hazel--a Herrontown Woods native that blooms in November.

The most common native shrub is the blackhaw Viburnum, named for its berries, aka "haws," which turn black when ripe.

Along the walk I am hanging plant labels on many of the 70 species of trees, shrubs, and vines--an astonishing diversity for just one corner of the woods. This preserve is such a special gift the Veblens gave Princeton back in 1957. The habitat restoration our nonprofit has been doing over the past thirteen years has steadily revealed the depth and beauty of that gift. Important as well has been Princeton's management of the deer population, which set the foundation for our restorative work and helped the native flora to rebound and flourish. 

Below, a flowering dogwood that gets enough sun in the summer to put on a big show in the fall.

Four Emerging Invasive Plant Species in Princeton, NJ

Some invasive species have been in Princeton for a century or more, while others are just now arriving. Kramer's 1960s ecological study of Herrontown Woods mentions only Japanese honeysuckle as being overly aggressive in the landscape. Since then, as deer numbers rose and the native flora became intensely browsed, many more nonnative plant species have spread into local preserves to fill the void. No ecological study of Princeton in the 21st century would be complete without mention of a multitude of additional invasive species that gradually, quietly became established and now present a tremendous challenge for any land manager or backyard gardener. Call them too much of a good thing, with some good features but rejected by native herbivores and overwhelming in their dominance. Privet, bush honeysuckle, winged euonymus, Photinia, multiflora rose, linden viburnum, porcelainberry--their deeply embedded presence represents a deferred maintenance of daunting proportions.

Though we often think of them as a generalized menace, each invasive species has its own story of where and how it was introduced to the continent, and the extent of its spread. Having lived in Michigan, North Carolina, and New Jersey, I've seen how an invasive plant deeply entrenched in one region has yet to spread to another. The stiltgrass and lesser celandine that smother large areas of Princeton are just now starting to show up in Michigan and Wisconsin. The garlic mustard long common in the northern U.S. is relatively new to North Carolina. Even within Princeton, invasions can be very localized, affecting one yard but not yet another.

Here, for instance, is one solitary invasive plant out standing in a field near Carnegie Lake. By its scraggly tilted shape, you can tell it is Chinese bushclover, Lespedeza cuneata, also called Sericea lespedeza. I first encountered it in North Carolina, where the DOT (Department of Transportation) planted it along new highways to hold the soil on steep slopes. While serving one environmental goal--reduced soil erosion--this non-native bushclover's tenacious grasp of the soil abetted its spread into nearby piedmont prairies. Promoters of the plant's use for erosion control claimed its seeds would feed wildlife, but the small seeds moved through the birds' guts undigested. I've seen how it can take over, displacing diverse native meadows to form monospecific stands. The tragedy of Chinese bushclover's spread now extends to what few original tallgrass prairies remain in the great plains.

For decades, Chinese bushclover has been spreading along the gas pipeline right of way in Princeton. It also began invading Princeton's Greenway Meadows preserve years ago, became entrenched before anyone took much interest, and now the municipality is having a very tough time combatting it. 

What a pleasure, then, to remove just one plant down near Carnegie Lake, and thereby protect a whole field in five minutes. That's the magic of "early detection, rapid response"--intervening before a new invasive species can become established. Many weed warriors savor a big battle, but for me, being able to declare victory after the tiniest of skirmishes brings the greatest reward.

By these whitish flowers you can see how many seeds that one Chinese bushclover could have produced.

There are native bushclovers. One with pink flowers is called slender lespedeza (L. virginica). Another is roundhead bushclover (L. capitata). Typical of native species, they "play well with others," integrating into a plant community rather than taking over. I fought to save a stand of these from encroachment and takeover by Chinese bushclover in a preserve I helped create in Durham, NC, but wasn't able to devote enough time to succeed. Thus the preference for catching invasions very early, before the work becomes overwhelming.

Another invasive species knocking ever more loudly at Princeton's door is a prickly vine that grows so quickly it's called Mile-a-Minute. This patch is growing on a bluff overlooking the canal, just off Alexander Road. Having seen how the vine can smother vegetation in rural areas outside Princeton, I've snuffed out small patches I have found growing in town along roadsides and field edges, lest the seed be eaten and spread by birds. Keep an eye out for its distinctive triangular leaf. It's a very prickly annual, so wear gloves and pull its vines out before their berries can ripen.

This past summer, you may have noticed some yellow in your lawn that wasn't dandelion. Chances are it was a legume called birdsfoot trefoil. Farmers often include it in the seedmix for pastures. The way it's spreading across lawns at the high school, and here along the gas pipeline right of way in Princeton Community Village, it could easily come to dominate untreated lawns in coming years. 

Some will be aghast at the thought of calling Queen Anne's lace an invasive species. The flower is one of the most beautiful creations, and it's the wild version of the carrots we eat, Daucus carota. Highly likeable! But see how it is beginning to take over the upper detention basin at Princeton High School. 

I'm not surprised by this behavior because years ago I saw how aggressive Queen Anne's lace could be in prairies and along roadsides in the midwest. Seeing it begin to spread in New Jersey, I had hoped that it would behave more tamely here. Apparently not.

As managers of the detention basin vegetation at Princeton High School, our Friends of Herrontown Woods crew let them bloom, then pulled every last one before the seeds could mature. Here is a pile of hundreds of plants. I estimated that just one robust plant could produce 5000 seeds. 

Wild carrot is a biennial, producing leaves the first year, flowers the next before dying. Though we removed hundreds of thousands of seeds, there are plenty of first year plants remaining that will produce flowers next year for people to admire and, in an act of romance without finance, maybe cut to share with a loved one. 

There are many other emerging invasive species in Princeton, such as Japanese angelica tree and black jetbead. Each year, the municipality hires the NJ Invasive Species Strike Team to make a first strike at some patches of these. With followup by local nonprofits, the goal is to avoid the mistakes of earlier decades, when invasive species were allowed to spread undeterred.

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. 

Fall Colors Nature Walk, Sunday in Herrontown Woods

Early November, and it's time for a nature walk through the color-coded forest of Herrontown Woods. Color-coded because each tree and shrub is showing distinctive coloration that can make it a snap to identify, even from great distance. 

The walk will head out at 11am this Sunday, Nov. 2, from the gazebo at the Botanical Art Garden (Barden), next to the main parking lot, 600 Snowden Lane. The walk is free, but donations to the Friends of Herrontown Woods are welcomed.

Come early and enjoy coffee and baked treats at May's Pop-up Cafe in the Barden from 9-11, and with all the fall colors, take part in an art project called the Community Collage. 

Along with colorful leaves--still on branches or lying in a colorful collective on the ground--we'll see the bright berries of Hearts 'a Bustin'. If you look closely, you'll even see witch hazel in full bloom. 

Here are four native shrubs that have shown particularly bright fall color: blackhaw Viburnum ("blackhaw" means black berry),

a highbush blueberry along the Veblen House driveway,

winged sumac (a "volunteer" that popped up at the Barden),

and a particularly showy Hearts 'a Bustin' in my backyard.

Buckthorn--A New Highly Invasive Shrub Found in Princeton

For years, I've traveled between Michigan and New Jersey and noted how some invasive plant species that have run rampant in the eastern U.S. have yet to show up in the midwest. That is changing. Last year, I encountered a dramatic example of stiltgrass spreading down a hillside in Michigan, and there are reports of lesser celandine gaining a foothold there as well. Similarly, Princeton had remained free of the common buckthorn--the most invasive shrub clogging midwestern forests. That, too, is changing.

The fateful day came on September 16, 2025. I was standing in a spot I'd passed by many times, near the entrance to the Herrontown Woods parking lot, when I happened to look down and saw that characteristic leaf of common buckthorn--the first sighting, by me and perhaps anyone, of this uber-invasive shrub in Princeton. 

The leaves of common buckthorn (Rhamnus cathartica) have arc-shaped veins, and are described as "sub-opposite," because they can appear to be paired on the twig but are slightly staggered.

Buckthorn gets its name from the two terminal buds, which make the shape of a buck's hoof, with a thorn-like protrusion between them.

This photo from upstate NY shows there can be thornlike protrusions along the trunk as well.

Shunned by deer, buckthorn's combination of massive seed production and shade tolerance allow it to clog forests and bury whole native plant communities under its dense growth. The richly diverse bur oak savannas of the midwest were nearly lost beneath a rising sea of buckthorn. Only botanical sleuthing and the hard work of clearing buckthorn, honeysuckle and other invasive plants from beneath the massive oaks, along with reseeding and prescribed burning, has brought back that plant community. 

The small cluster of young shrubs I spotted at Herrontown Woods has fortunately not yet produced seeds. But anyone who has lived in the midwest knows the potential of buckthorn to grow, seed and spread.

An email to the Stewardship Roundtable group of land managers in NJ yielded some responses. Duke Farms has it, as does the Watchung Reservation. The Friends of Great Swamp have an info sheet on their website, so I suspect it has established itself there as well. Mike van Clef, who deals with invasive plants all across New Jersey, writes: 

Duke Farms definitely stands out! From iNaturalist, there are 64 research grade observations, heavier toward northern NJ but all over the state. I often find it as single immature individuals, especially in northern NJ...which is always a head scratcher because I never seem to find a nearby large fruiting individual...

This photo shows the lingering green of buckthorn in upstate NY. Like many invasive shrubs that evolved in a different climate, buckthorn keeps its leaves longer that native species in the fall. 

Given New Jersey's already long list of invasive shrubs clogging our forests--among them multiflora rose, Photinia, privet, and Linden Viburnum--it's hard to imagine another having much of an impact. Having seen what buckthorn does in other areas of the country, all I can say is "Watch out!"

Early detection and rapid response are key to stopping biological invasions. This is true both of the immune systems protecting our bodies and of land managers caring for nature preserves. At Herrontown Woods, we've done very well with that creed of early detection and rapid response. Lesser celandine and garlic mustard--the bane of many a nature preserve--are now vanishingly rare. Vigilance each year in August has helped keep many areas free of stiltgrass, the most rapid spreading of all. People who care and take action can make a difference.

On a town-wide scale, some early interventions have helped keep the thorny Mile a Minute vine from spreading across Princeton. Though Princeton has hired contractors to help counter at least some invasions in their early stages, it's hard to get private residents--often disconnected from the yards they own--to act collectively to knock out new invasive species before they become a problem. Having fought the good fight, my advice about buckthorn is: be informed, be on the look out, and be proactive. There's also a super handy, targeted, and frugal way for homeowners and professionals to cut and treat buckthorn and other invasive shrubs. Appropriately enough, it's called a Buckthorn Blaster. 

Seven Native Shrubs Offer a Progression of White Blooms in Spring

Why do gardens and nature diversify over time?  Since most flowers last only a week or two, any gardener seeking a steady progression of blooms will naturally seek out new additions to fill the gaps. This spring, I noticed a different sort of steady progression: of blooming trees and shrubs in nature's garden at Herrontown Woods. No gardener put this steady progression together.

Flowering dogwood (Cornus florida) put on a show in late April.

Blackhaw viburnums (Viburnum prunifolium) dotted the understory with white pompoms for the first few days of May, their period of bloom shortened by the heat.

Alternate-leaved dogwood (Cornus alternifolia) followed in the second week of May, with scattered blooms in the shade,

and abundant blooms in the sun.

Arrowwood Viburnum (Viburnum dentatum) in the lowlands sustained flowers through cool days in the second half of May, 

along with maple-leaved Viburnum (Viburnum acerifolium) up on the ridge.

In the last week of May, abundant disks of elderberry (Sambucus canadensis) flowers began an extended residency.

Still to come is silky dogwood (Cornus amomum), 

which will look remarkably like its predecessors when it blooms.

There are many examples of how native plants that have co-evolved behave in an egalitarian way. Though there are exceptions, they tend to "play well with others," sharing the ground rather than bullying their way to dominance. Might this sharing have a collective advantage that benefits them all?

People trying to understand why invasive species can be detrimental will rightly point out that many invasive plants provide abundant flowers for pollinators. But if one species comes to dominate, its week or two of blooms will be preceded and followed by precious few flowers, leaving pollinators little to sustain them through the season.

An interesting experiment would be to monitor what sorts of insects pollinate the progression of blooms generated by native dogwoods and Viburnums. Have their visually similar blooms evolved to attract the same sorts of pollinators? If so, they could be thought of as a sort of tag team, collectively sustaining the needed pollinators through the season. 

Native Fall Color and Berries in Herrontown Woods

One vision being gradually realized at Herrontown Woods through the power of incrementalism is the transformation of the long boardwalk into a native plant corridor that will be especially attractive in spring and fall. The boardwalk, given the V-ful nickname of Voulevarde because it was built by chainsaw virtuoso Victorino and leads from the main parking lot up to Veblen House, was intentionally routed past some mature examples of native shrubs.

Arrowwood Viburnum has toothed leaves (thus the latin name Viburnum dentatum) and can turn a brilliant reddish color in fall. 

We're managing the corridor for an open woodland, so that enough sunlight can reach the understory to power abundant berry making by the native shrubs. The many Blackhaw Viburnums, named after their black berries ("haw" means berry, as in hawthorn), are a dramatic example. 

The preserve's largest winterberry shrub--a holly called Ilex verticillata--greets you along a bend in the Voulevarde with abundant red berries this time of year.  

One of the preserve's large highbush blueberry bushes--they tend to be loners persisting here and there in the preserve--also grows along the route, with bright orange fall color.

The largest native swamp rose (Rosa palustris) in the preserve is also near the trail, its single pink flowers emanating a heavenly fragrance on hot summer days. Its rose hips are bigger than those of the nonnative multiflora rose. While the invasive multiflora rose is ubiquitous in the preserve, there are only two native swamp roses found thus far across 150 acres, mostly because the swamp rose needs more consistently wet conditions to compete. We've started planting more of them, in wet spots that get some sun, to see if we can increase their numbers over time. Again, the battle cry: "Incrementalism!"

Beyond the boardwalk, up towards Veblen House, is a good example of a rare native shrub, variously called Hearts a' Bustin' or strawberry bush. The deer love it so much that we needed to cage it until it was tall enough to escape their browsing. Located in a partial forest clearing, it receives enough sun to develop abundant berries.

In the fall, its leaves turn white. Hearts a' Bustin' is a native euonymus (Euonymus americanus), rarely seen due to deer browsing, while the nonnative euonymus, burning bush, is ubiquitous in the preserve and largely shunned by the deer. Notice a recurring story?

Up at the horserun near Veblen House, these look like shrubs or small trees, their fall color backlit by late afternoon sun. They are in fact trumpet vines growing on some sort of structure placed there decades ago. 

A different angle shows the trumpet vine with the bright red of Virginia creeper in the foreground. Both are native vines that can be a little aggressive, but sufficient shade deprives them of the energy to be obnoxious, allowing us to enjoy their best traits without any need to keep them in line.

Virginia creeper has five leaflets to poison ivy's three. These leaves look like they've donated some of themselves to the insect world. 

The boulders in Herrontown Woods, bedecked by mosses and lichens, are reminiscent of whales whose gray skin has collected barnacles. Sweetgum leaves are particularly creative and varied with their fall color.

Also generous with fall color is the native winged sumac, which has started to pop up in areas where we remove invasives. They seem to be part of the soil's memory of past eras when the forest was younger, before the canopy closed and shrouded the ground in deep shade. 

Another source of beauty, noticed while removing dead ash trees near the Veblen House driveway, is the combination of the old evergreen cedar trees with the deep burgundy of young white oaks rising to ultimately fill the space left by the ash.

The loss of ash trees to the emerald ash borer is a profound tragedy, but if we can take advantage of the new openings in the canopy to reawaken a diversity of native shrubs and trees, there is at least some recompense.