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.

A Curious Paucity of Ticks--Pushing Back On a Scary NY Times Article

I'd like to push back on an Aug. 20 article in the NY Times magazine about a rising tide of ticks. The article surely scared the bejesus out of anyone who ventured into its hellscape of graphic descriptions and imagery. One quote in the article recommends "staying out of the woods" to reduce the risk of tick bites and the panoply of diseases they can carry, yet it warns that even urbanites can no longer be assured "that glass, steel and pavement are a moat against woodsy threats." While deer ticks wait passively for a warm-blooded meal to come along, lone star ticks "can sense a target up to 15 yards away and aggressively pursue their prey." I try to imagine the logistics of verifying that claim of "up to 15 yards." 

The article's title, "The Summer the Ticks Took Over," stirs visions of hapless humanity reduced to cowering in a corner of the living room, scanning the perimeter for incoming ticks while clutching a can of bug spray. 

My experience, living in Princeton and spending long hours in the woods, on the trail and off, tells a much different story. The idea that good bugs, in particular the pollinators, are in decline while pests are on the rise seems only half true. Pollinators are noticeably declining, but in my experience so are ticks, house ants and spotted lantern flies. I work in woodlands and fields without much precaution and without apparent consequence. Tick checks come up empty. Similarly, the odorous house ants stopped invading our house several years ago. Spotted lantern flies, the oft-mentioned invader of recent years, have grown scarce in my part of town. 

The curious paucity of ticks goes beyond one perambulating land manager's observations. Others who work at Herrontown Woods report few if any ticks this year. One day I met two women who had driven from Long Island to Princeton's Herrontown Woods to take a walk in the woods. Their reason? Fewer encounters with ticks, which are way too numerous on Long Island. 

Does this good fortune extend to Princeton generally? I reached out to Jeff Grosser of the Municipality of Princeton Health Department, who offered the following supportive evidence in an email:

"Here are 2025 and 2026 stats so far for confirmed cases of tick-borne disease in Princeton. No confirmed alpha-gal in Princeton last year. In general, numbers in Princeton and our region are lower this year than previous years. We are also working through a trend analysis year over year that we will certainly share once it is compiled."

2025	PRINCETON	BABESIOSIS	<5
2025	PRINCETON	BRUCELLOSIS	<5
2025	PRINCETON	LYME DISEASE	63

 

2026	PRINCETON	ALPHA-GAL SYNDROME	<5
2026	PRINCETON	BABESIOSIS	<5
2026	PRINCETON	LYME DISEASE	41

 

If ticks are in fact causing fewer cases of Lyme in Princeton, it likely arises out of factors both intended and serendipitous. Beginning in 2001, then Mayor Marchand and other courageous leaders instituted a combination of bow hunting and professional culling to significantly reduce the deer herd. The backlash from animal rights advocates made it into the NY Times, but failed to overcome broad community concern about the high incidence of collisions with deer on the roadways. After using emotion-laden words like "slaughter," "devastation," and "massacre" to describe the culling of deer, the Aug. 20 tick article quietly acknowledges that the venison goes to food pantries. Fewer deer also means more native plants surviving in the woods.

In addition, local predators have upped their game. Foxes are particularly adept at reducing the number of mice that serve as a reservoir for the Lyme disease microbe. 

The article on ticks focuses on the bad news, particularly about lone star ticks that can give some people alpha-gal syndrome--an allergy to red meat. Much of the good news in the article is hidden in parenthetical and prepositional phrases: "(It’s worth noting that an alpha-gal allergy can, in many cases, eventually fade, if a victim steers clear of meat for a while.)" and "while Lyme is “basically treatable” in 95 percent of cases..." More overt is a robust discussion of vaccines and other deterrents working their way through research labs and trials. 

The curious paucity of ticks prompted reflection on other scarcities and abundances in local nature. My experience in the field in recent years is stirring an ever more complex mixture of gratitude and grief. Below are a couple examples.

Butterflies were particularly scarce in early summer, making the sighting of 8 tiger swallowtails feasting together on the nectar of a buttonbush in front of Veblen House at Herrontown Woods a cause for at least a brief celebration. I've been seeing more monarch butterflies this summer, mostly solitary but two at the same time recently at a detention basin wet meadow we created in Smoyer Park. 

Also in that meadow, there's now a surprising abundance of a favorite native wildflower, partridge pea. Keep the invasive species at bay, and native abundance can happen. And I haven't noticed a single tick on me after periodic work sessions there to remove invasives.

While scary articles boldly grab our sleeves and demand to be read, the good news, resigned to its parenthetical status, approaches from behind and taps us softly on the shoulder. "By the way," it says, "did you notice?"

Note: Thanks to Jeffrey Grosser of the Municipality of Princeton Health Department for this additional info on vector borne diseases that may be of interest to readers.

"In terms of the larger, available data, please see below:

 

• This is a good map from the CDC that compiles several tickborne diseases on the county level (Rickettsiosis, ehrlichiosis, anaplasmosis, babesiosis, tularemia, Lyme): https://www.cdc.gov/ticks/data-research/facts-stats/geographic-distribution-of-tickborne-disease-cases.html

 

• NJSHAD has county-level Lyme data: https://www-doh.nj.gov/doh-shad/indicator/view/LymeDisease.County.html

 

• This is a vector borne disease data dashboard from NJDOH and includes a tab on tick activity: https://www.nj.gov/health/cd/topics/vector_borne_disease_data_dashboard.shtml

 

• If he wants to view vector-borne surveillance reports from NJDOH: https://www.nj.gov/health/cd/statistics/arboviral-stats/"

Looking for Hope With Stiltgrass

Often, we think of good as struggling against evil, but a lot of problems are caused by too much of a good thing. Too much carbon dioxide in the air is an obvious though invisible example--vital in small amounts, destabilizing if allowed to radically increase. Plastic sure is handy, but a problem as it builds up in the environment. Many species considered invasive or weedy would be welcomed in the garden, forest and field if they didn't have a proclivity for taking over. What to do, then, about Japanese stiltgrass, the uber-invasive that rises like a wave in late August, lifting itself up and over other plants, preparing to carpet the ground with a deluge of seeds that will surely expand its dominion the following year? If only animals ate it, to keep it in check, but the plant seems of value only to itself. Its one use to people--historically as "packing grass" to protect porcelain for shipment--was also its means of spreading across the planet. 

Keeping some areas stiltgrass-free involves a lot of effort in August--the month of opportunity before it goes to seed. If I were a biochemist, working in a lab rather than out in the field, I would dream of someday discovering a compound that would magically release the landscape from stiltgrass's smothering grasp.

The vexing irony of stiltgrass (Microstegium vimineum) is that it is both frail and indomitable. Weak roots make it easy to pull, yet the dense congregation of billions of plants will quickly overwhelm and exhaust the spirit. Nor have any herbivores found its wiry, flimsy frame worth eating.

One of stiltgrass's strengths is also one of its potential vulnerabilities The species uses something called C4 photosynthesis. There are two main biochemical pathways plants use to harvest energy from the sun, called C3 and C4. It has to do with how the process of photosynthesis is organized in the cells. The "C" stands for carbon, which is ever so conveniently supplied to the plants in the form of airborne carbon dioxide, so they can turn it into sugars and carbohydrates--the building blocks of growth. Plants using the C3 pathway tend to prosper in cooler months and languish in hot weather, while C4 plants grow more efficiently in the heat of the summer. (Note: Follow the link above to a short video that explains why.)

If you've ever wondered why crabgrass becomes a problem in yards in late summer, its because it is a "warm season" grass that uses C4 photosynthesis to outcompete the C3 "cool season" turfgrasses. Corn is another example of a warm season C4 plant that gets going later in the spring, then grows robustly through the hot summer months. What makes stiltgrass invasive in nature preserves, while crabgrass is not, is that stiltgrass is one of the few C4 plants that grows really well in the shade, allowing it to leapfrog over the C3 plants all around it during hot weather in late August. 

If someone could develop a compound that selectively kills C4 plants while not harming others, it would be really handy for spraying stiltgrass in the shady forest understory where it may be the only C4 species. So, every now and then I do an internet search, using a phrase like: herbicide specific to plants that use the c4 carbon pathway. AI actually comes up with some interesting results, which you can access by clicking on "see more" at the bottom of this post.

In the meantime, there's still reason to harbor a little bit of optimism about stiltgrass. I remember the first time I saw it, a graceful little plant growing on a streambank in Durham, NC. It seemed harmless until it later exploded across the landscape in the wake of Hurricane Fran's mass disturbance in 1996. A similar story can be told in New Jersey, but even now, thirty years later, it's hold on the landscape is hardly uniform, giving some reason for hope. In my August perambulations, I find it clogging floodplains and proliferating across moist slopes, but many other areas remain surprisingly stiltgrass-free. Your yard may be clogged with it, but many yards have yet to be invaded, or have only a few that can easily be pulled before it goes to seed. If you're one of the lucky ones, now is the time to inspect your yard and pull out every last one, even the annoyingly tiny ones.

Princeton University is a good example of a campus that has very little stiltgrass and could remain so with vigilance. I recently found a patch just up from their New South building. This could easily be sprayed using a highly targeted, minimalist approach.  Stiltgrass's weak roots mean the spray can be very dilute. Otherwise, seeds from this patch will spread downhill, with the problem growing year after year. I alerted the grounds staff at PU, and hope they are proactive.

Meanwhile, in the yard in this photo, the infestation was small enough that I was able to pull up every last stiltgrass before it could form seed, tossing them on the driveway to dry. Since they were already flowering, they needed to go in the trashcan, not the compost. Sometimes multiple followups several days apart are necessary, because one always misses a few. The payoff comes as the job gets easier each year. 

For an annual grass like stiltgrass, no seed means no future.

Related post: Stop Stiltgrass From Taking Over Your Yard

Black Bear Scat Spotted in Herrontown Woods?

Herrontown Woods neighbor Paul Schedl, a frequent hiker in the preserve, helps out by alerting me to any downed trees blocking the trails, but his email this week was about a sighting of a different sort. 

"Bear scat," he asked? I forwarded Paul's photos to Jim Ferry, Princeton's Animal Control Officer, who confirmed. "Very good chance yes! Sightings have come and gone this year but yes, we've had several sightings this summer. No issues, just sightings."

Typically, the occasional bear sightings in Princeton are of young males searching for new territory. Previous posts on this blog about black bears show them most commonly coming through in late spring or early summer, with mid-August being the latest documented here, until now. 

Since no aggressive bears have been reported in NJ, I'll continue walking in local preserves, but it's a good idea to review the info in the link below, and step a little more noisily while hiking, so the bear has plenty of time to scat, so to speak. Also, the sighting is an excuse to include below my comic instructions from 2012 on how a proper Princetonian should behave when encountering a black bear.

In a followup email, Jim Ferry added this:

"On a local level, we tell folks to be bear aware and bring in any possible food source. Also the NJ DEP website has good info. Hikers can carry bear spray if they want, but I have not heard of any aggressive bears in our part of the state. If there was, I'm sure it would make the news."

From a 2012 blogpost:

At the presentation last month on black bears, given by state officials in township hall, I was astonished to learn that, in the very rare case that a black bear attacks, the best tactic is to fight back. Princetonians have not been called upon to display such courage since 1777, when we all could conveniently claim we had yet to be born. 

To bridge this gap between experience and expectation, I herein provide a translation of the wildlife officials’ instructions, customized to fit the Princetonian lifestyle:

Black bears are near-sighted, so make noise to avoid surprising it. If the bear stands up on its hind legs, don’t worry. It’s just trying to see you better. Make sure the bear has an escape route. For instance, if it is following you out of the public library, hold the door open and give it plenty of room. If you encounter the bear in the woods, or on Nassau Street, you can back away slowly, but don't turn your back to the bear. In a calm, assertive voice, put the bear on notice that you are a Princetonian fully armed with opinions, and will not hesitate to express them. 

Avoid eye contact. If it doesn't run away right off, bang the pot you happen to be carrying with you, or download a "kitchenware noise" app on your cellphone. Bears hate to cook, which explains their interest in garbage. Otherwise, clap your hands, raise your arms over your head, wave a jacket, all of which should make you look large and impressive.

On rare occasions, the bear will do a bluff charge, at speeds up to 35 mph. If a cafe is close by, this is a good time to duck in for a double latte. If that option is not available, then you'll need to dig deep. Fleeing will only make you appear weak. Perhaps the stirring words of a high school football coach will come to mind. In any case, stand your ground, wave your arms and shout. Pretend you're in front of town council, venting your outrage over moving the Dinky. The bear should veer away from you at the last moment, providing a bigger thrill than any 3D movie at the mall. 

If the bear actually attacks, which is extremely rare, it's time to drop all remaining pretense of civility. Fight back. Don't worry about the bear's lack of access to dental care. Without asking permission, bop it on the nose. Bears' noses are 100 times more sensitive than ours. Use this sensitivity to your advantage, all the while reveling in what a great story this will make to tell the grandkids.

In case you surf the internet for more info, don't be confused by accounts of how to behave when encountering a grizzly bear out west, where the protocol is completely different and not nearly so gallant. - July, 2012

The municipal website mentions fruits and nuts in the bears' diet, and some of the seeds in the photo above look a lot like pawpaw seeds. The pawpaws are starting to drop to the ground in our two pawpaw patches near Veblen House. The dietary needs of bears were not on our minds when we planted them.

Planting Trees Strategically to Shade Playground Equipment

People talk about planting trees, but there are still a lot of parks in the world with play equipment that gets burning hot in the summer for lack of shade. Why, I often wondered as a parent of young kids, aren't shade trees planted strategically, where their shade will do the most good? It takes some imagination, to envision the full-sized tree a sapling will ultimately become, and some belief in the future, whether one's going to be around to see it or not.

In 2010, Rebecca Shell Kanarek, Princeton High School class of '99, contacted me with the desire to plant a tree in celebration of her and her husband's newborn son. Council woman Barbara Trelstad and I collaborated to choose a tree--an October Glory Red Maple--and arrange its planting. I suggested Potts Park, because it's playground equipment was roasting in the sun. My role was to decide where in the park to plant it. 

It can be surprisingly tricky to choose a good place to plant a tree. You have to imagine the sun's arc in summer and how the future tree will intercept it. At the same time, shade is not an unmitigated blessing. It's wanted some places and not others. In this case, I wanted to position the tree to ultimately shade both the climbing equipment and the swings, while keeping the tree's trunk out of the way of games and running kids. Planting it too close to other trees could slow its growth. And then there's the followup watering while it's getting established.

The spot chosen was a compromise, but sixteen years later, the tree is doing its job, cooling the play equipment in summer, then dropping its leaves to allow the sun to provide warmth in the winter. It's pretty straightforward. Trees grow, and the future comes.

And newborns grow up, too. 

(Thanks to Rebecca for the photo.)

Other posts about Potts Park and young trees