Reading the Landscape Along the Towpath -- Early Spring

One place that gets a lot more interesting if you know plants is the towpath along the Delaware and Raritan Canal. For those into reading the landscape, the section just upstream of Harrison Street in Princeton makes for a good read, packed with history, beauty, poignancy, and the drama of invasion. 

First, there's the water, here with branches of elderberry reaching out over the canal in the foreground. Elderberry characteristically sprouts leaves earlier than other native shrubs. Water teaches the richness that reflection can bring to life. 

Along this stretch of towpath, the strip of land between the canal and Carnegie Lake widens, making enough room for a nature trail loop that for nearly 20 years has given hikers and joggers relief from the linearity of the towpath. Part of my life has been dedicated to making interesting destinations along very long trails, whether in Durham, NC or in Princeton. With a hardwired devotion to things, I've been an advocate for this little nature trail, and the unique, savanna-like habitat it winds through, since it was created nearly 20 years ago. Periodically stopping by to check that the trail hasn't been blocked by fallen trees, reading the landscape as I go, I always come away with a mix of joy, gratitude, and grief. 

Some flowers encountered during this walk are native, like this red maple reaching out over the trail.

Then there are some non-native species that fortunately aren't invasive, and speak to past intention. These photos were taken a week ago, when the ornamental cherries were just starting to pop. 

These really old ornamental cherry trees are reminiscent of those planted along the Potomac River in Washington, D.C. long ago. The cherry trees and the yellow spray of forsythia off in the distance show that this seemingly wild stretch of the towpath is actually populated with botanical remnants of another era, back when the university installed these plantings as an ornamental entryway to the campus. 

Adding to the evidence of past caretaking is a derelict row of winter honeysuckle (Lonicera fragrantissima), with very small, very early, and very fragrant flowers. Though it's included on invasive species lists, I've never seen it spread. 

If you're an environmental advocate at a local level, a walk can become a review of past successes and failures. For years, the DR Canal State Park, of which this ribbon of land is a part, would keep this nature loop mowed, but then their maintenance budgets started getting cut. Around the time one of their longtime mowing crew members died, they decided to turn mowing over to the landowners--Princeton University. That handoff happened at an administrative level, but not on the ground. After trying in vain to get the university to take care of the trail loop, I finally contacted Shana Weber at the PU sustainability office. Thankfully, she was able to reach the right people, and the trail is now being kept open. 

But one bit of mowing that the state parks people used to do has yet to be picked up by the university. And here's where the landscape's story shifts from joy and gratitude to grief. The nature trail loop winds through what for many years has been a savanna-like landscape of scattered trees and fields. Scattered trees allow enough sunlight to reach the ground to power a rich understory of wildflowers and shrubs. But due to a lack of annual mowing, that special landscape of forest openings, seldom found elsewhere, is being lost. Here is a forest opening that has become a layer cake of invasive plants, with multiflora rose blanketed by a web of super-aggressive porcelainberry vine. 

Other invasive vines also run rampant, like this Japanese honeysuckle smothering a branch.

Why is no one cutting the oriental bittersweet at the base of this tree, the wild gardener in me asks.

Many of the trees were planted, then ultimately abandoned, leaving a kind of derelict arboretum.

Some trees have succumbed altogether to introduced insects or disease, most commonly Emerald ash borer or bacterial leaf scorch. 

On the ground, the uber-invasive lesser celandine is laying a claim that will surely expand. 

Without annual mowing to sustain the forest openings, a tortured form of succession is underway, with sweetgum saplings being mobbed by the invasive vines. Annual mowing would sustain the special forest openings and reduce the smothering invasives.

A couple places where the native species are doing well are, not surprisingly, in standing water. Here's a rosette of a very healthy rose mallow hibiscus (Hibiscus moscheutos), its feet very much in water.

Here's a shrub that also flourishes in standing water, buttonbush (Cephalanthus occidentalis). 

There are lots of native plants that can thrive in floodplain habitats along the canal. If the university ever gets interested in habitat restoration, this would be a great place to start. It would be a high-visibility demonstration, to be witnessed by all the hikers, bicyclists, and joggers passing by, who currently see not the history and the ecological drama but just another stretch of green.

Random Spring Weed Identification

Most gardeners will have encountered a small weed this spring with tiny white flowers that have already bloomed. The thick circle of basal leaves suggests it's the non-native Hairy Bittercress, rather than the native Pennsylvania Bittercress.

The plants produce seeds that will fly up at you as you try to pull the plants out. That's how you know you have, yet again, procrastinated too long before weeding them out of the garden. I was moved to pull many of them from my yard in time this year, but only because I was expecting company. There's a lesson in there somewhere.

Another non-native is Veronica (probably V. persica), which forms low clumps in the lawn with many tiny blue flowers. Lovely flowers when viewed up close. It shows up in lawns, but I haven't seen it being as aggressive as some weeds. Update, spring, 2022: Veronica is spreading like crazy across my lawn. As with so many yard weeds, this is way too much of a good thing.

Japanese knotweed pops up like asparagus from among last year's dried stalks. It is a common non-native invasive along rivers, forming dense, exclusionary clones. This one's part of a patch just upstream of Pettoranello Pond.

An increasingly common weed in lawns and gardens is lesser celandine, mentioned in a previous post.

It spreads quickly to form dense masses that are pretty for a couple weeks but don't leave much room for other wildflowers to grow. If wildlife don't like the taste of it, and as far as I know none of them do, they have to seek food elsewhere. This is a big reason why even a beautiful exotic flower can be a concern, because it doesn't support a foodchain of diverse organisms, i.e.  is slowly making the landscape inedible.

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This is an aquatic plant at Pettoranello Gardens that I first noticed showing up last year, most likely called pond water starwort (Callitriche sp.).

From Europe and northern Africa, it's considered an exotic invasive in Connecticut.

It might be mistaken for the native duckweed, but a clump of duckweed consists of thousands of individual plants, each with a pair of leaves.

(Thanks to Chris Doyle for help with identification)

SOME OTHER POSTS ON WEEDS:

An Explosion of Spring Weeds

Weeds That Launch an Underground Insurgency

Collecting Live Stakes for Propagation

Some species have already sprouted, as many people discovered when branches packed with the flowers of silver maples fell to the ground under the weight of this week's snow. Their blooms are so discreet and elevated that, if not for the jumble of branches littering people's yards, no one might have noticed.

One branch, falling 50 feet from a tulip poplar, scored a direct hit on an old kiosk at Herrontown Woods that hadn't been used for twenty years.

People may not be feeling much affection for branches right now, but here are some stems, collected before the storm, that hold great promise. Called "live stakes," they can be pushed into soft ground to make new shrubs from old.

Elderberry is one of a select few native shrubs that will sprout roots and leaves after a cut section is stuck in the ground. In the wild, they grow in sunny spots in floodplains, and have big plates of white flowers in the summer. The berries are delicious in jellies and pies, and their abundance can overwhelm even the appetite of the catbird that otherwise steals all our backyard fruit crop.

Another is silky dogwood, related to flowering dogwood but less ornamental. It, too, grows along the canal, and can be selectively pruned so as to leave the original shrub intact but yield some nice live stakes for planting elsewhere. This stub was left not by us but by a hungry beaver living in Carnegie Lake.

Buttonbush, with its golfball sized blooms that are eagerly bumbled over by bumblebees in summer, is another super-easy shrub to propagate in this manner. These we'll harvest not from wild populations but from specimens that were planted as live stakes years ago in raingardens around town.

Encountered in the process were some blooms of skunk cabbage. The small, roundish green leaves are the first emergings of lesser celandine, also called fig buttercup, which is a nonnative plant poisonous to wildlife that invades valleys and yards, seducing with its pretty yellow flower before completely taking over.

A nice find, though not for live staking, was the swamp rose (Rosa palustris)--a native rose with larger hips and less vicious thorns than the ubiquitous multiflora rose. It needs more stable hydrology than the nonnative multiflora rose. Given historical draining of swamps, eroding of streams, compacting of ground, and other factors that have reduced infiltration and lowered the water table, the swamp rose is now found in only a few places in Princeton. Its species name, "palustris", is used to name many species found growing in marshy ground.

The live stakes will be pushed into the ground at a couple places where we've converted detention basins to native wet meadows, and also at Herrontown Woods next to the parking lot, where we are creating a place where people can see and learn to identify the native plants of Princeton.

Invasive Plant Species in Princeton

This Monday, May 22 at 7pm, the Princeton Public Library will host a presentation on invasive species in Princeton by Mike van Clef, of the NJ Invasive Species Strike Team. There will also be representatives of FOPOS and DR Greenway participating. Princeton municipality hired Mike to develop a report on invasive species in Princeton preserves, and in 2016 he and two interns worked through the summer on invasive species control. Because of the massiveness of the problem, they focused on emerging species--those whose populations are still small enough that a summer's worth of control would make a difference. 

We may look back on 2016 as a pivotal year, when the town began investing in invasive species management, much as 2000 marked the beginning of professional deer management in town. 

Although it may sound self-congratulatory, another important date in Princeton's history of invasive species management would be 2006, when the Friends of Princeton Open Space hired me as their first Natural Resources Manager. 

When I arrived in town in 2003 on the coattails of my wife's appointment to the Princeton University faculty, a couple things quickly became obvious. First, Princeton had done wonderful work preserving land for open space. Second, the open space itself needed a lot of work. Though the trees in Princeton's woodlands were mostly native, the understory vegetation was often dominated by nonnative, invasive plants. Stiltgrass, honeysuckle and privet, to name but a few, had filled the void created long ago when the diverse native understory had been plowed under, back in Princeton's agricultural era. In the decades since, the native trees had rebounded, but the understory had either not come back, or succumbed to heavy browsing pressure from deer.

Because wildlife tend not to eat the leaves of nonnative plants, their proliferation in preserves renders the habitat largely inedible. Yes, birds can eat the berries of nonnative shrubs like honeysuckle, but if the insects and other wildlife aren't eating the leaves, then much less of the solar energy captured in the plants can move up the food chain. 

I proceeded to make the case that Princeton could expand its effective acreage of open space through management for native species. As most readers know, I've been leading workdays and nature walks ever since, for six years as an employee of FOPOS, and more recently as president of the Friends of Herrontown Woods (FOHW). Highly motivated volunteers like Tim Patrick-Miller and Andrew Thornton, and more recently Kurt and Sally Tazelaar at Herrontown Woods, have had a positive impact over time. Meanwhile, FOPOS has sustained its Natural Resources Manager position--having just hired the fourth to hold that position--and continues to do invasive species removal at Mountain Lakes Preserve. After so many years of nonprofit, largely volunteer efforts, to finally get municipal support through Mike's crew this past summer was a real boost that we hope will continue.  

It's important to note that Mike van Clef's study of invasive species in Princeton is limited to parks and preserves owned or managed by the town. There are large expanses of open space owned by the state (Princeton Battlefield and DR Canal) and by the Institute for Advanced Study (the 600 acre Institute Woods). Portions of the Battlefield and the DR Canal are being overrun by porcelainberry (in photo), which barely registers in Mike's survey, and mile-a-minute vine is beginning to show up there as well. I've been trying to help fill a void in management, co-leading workdays at the Battlefield and, in the proactive "early detection, rapid response" tradition, dealing with two small infestations of Mile-a-Minute in town before they become unmanageable. Another nonnative plant that's spreading rapidly, both in people's yards and in nature preserves, is lesser celandine (a.k.a. fig buttercup). It can only be controlled in the spring, long before summer interns begin work. Ideally, a town-wide coordination to manage invasive species would be developed.

The town's investment in invasive species control comes at a critical time. With the emerald ash borer (another highly invasive introduced species) poised to decimate Princeton's most numerous native tree, large gaps will be created in our forest canopy, allowing light to penetrate to the understory. Princeton's long investment in deer culling has allowed native shrubs like spicebush to make a comeback, but in many woodlands, the understory is dominated by nonnative shrubs and stiltgrass. Wildlife have evolved over millenia to eat native species. It's a question of whether edible natives will capture that extra sunlight in the understory, or the privet, winged euonymus, honeysuckle, barberry and Photinia. The foodchain depends on our intervention.

The primary argument for habitat management remains that, by improving the quality of habitat, Princeton effectively increases the functional acreage of open space. This is true not only for wildlife but also for people. Controlling invasive species also makes the human experience in preserves more rewarding. As we've cut down invasive shrubs at Herrontown Woods, we've not only made more sunlight, water and nutrients available for native species to prosper, but also have opened up pleasing vistas and made the woods more navigable. 

The problem of invasive plants may seem overwhelming, but we can take our inspiration from the deer, who transform landscapes through the cumulative impact of browsing here, there, and everywhere, one mouthful at a time. The pioneers, too, thought the continent too vast to ever tame. Though their goal wasn't exactly to increase native plant diversity, they showed how steady effort makes a difference over time. Ideally, professionals will complement existing volunteer efforts, and the locals who know the preserves best will help steer the professionals' interventions. 


At Monday's presentation, there will also be discussion of a list of invasive species that people are being discouraged from planting. It's a very long list, and I wish it could better reflect the broad spectrum of invasive behavior we see in the field. One reason the list is so long is that, though many of the species on the list may not be found spreading into Princeton's nature preserves, history shows that invasive behavior in nonnative species may not become manifest until many decades after they've been introduced. Chinese silver grass (Miscanthus sinensis) is a case in point. Though it has yet to spread to Princeton's Tusculum meadows, it is now posing a big problem for meadows at Duke Farms up in Hillsborough. The flyer for the library event includes a photo of butterfly bush, which I've never observed exhibiting invasive behavior. Monday's presentation may help put local observations in a broader context.

Update: Full house for the program! Good to see.

Murder Hornets and Princeton's Cicada Killer

The scary reports about murder hornets offer an opportunity to write about invasive species and insects generally. "Murder hornet" is a nickname, but the insect's real name, Asian giant hornet, is not very reassuring. There have been some scary videos making the rounds. The NY Times article was less sensationalistic, and captured well the potential threat along with the actions being taken to counter it. Rutgers hastened to clarify that the insect isn't found in the northeastern U.S.. And it's still not clear whether the AGH (Asian giant hornet) has established a population in the northwest, and if so whether the population is still small enough to be eradicated.

Big insects are scary. One nightmare remembered from childhood was of an ant about two feet long. I had a memorable bike ride home one day with a wasp having perched on my shoulder. I decided to just let it sit there, and eventually it flew off. The more I learn, though, the less scary most insects become. Late last summer, I waded out into a lawn full of blue-winged wasps flying about, knowing they were harmless. Knowledge can lead to a gentle response to something seemingly dangerous in nature. When the fishhook-shaped thorn of a multiflora rose bush pricks the skin, the best thing to do is relax, move towards the shrub rather than away, calmly cut the stem to which the thorn is attached, or rotate so the thorn has a chance to slip back out of your clothing.

Learning more about the Asian giant hornet can bring at least a little reassurance. Along with the uncertainty of its establishment in the U.S., I heard via an invasives listserve that "AGH does not attack people unless it feels threatened", and though they do pose a threat to honey bees, they only "attack and kill other bees in the late summer when developing males and future queens need extra protein to complete their life cycle."

The largest wasp in the Princeton area is the cicada killer, which looks much scarier than it actually is. Like dragonflies, they can tackle insects in midair. Ten years ago, there was a colony of cicada killers living near the Princeton Community Pool. Cicada killers are large wasps in Princeton that dive-bomb cicadas in mid-flight, then haul them back to their underground nests to use as food for their young. They pose little danger, but the colony was exterminated by the parks department because the wasps alarmed people walking by in their bathing suits. (Photo is a dramatization featuring our local cicada killer and an unknown actor.)

While pointing out that some threatening looking insects can be benign, I've also long advocated for action on invasive species. As introduced plants like lesser celandine and porcelainberry spread their smothering growth across Princeton's open space and lawns, there is an opportunity to keep them out of some areas through proactive action. It's been very hard to get people to think strategically, however.

The Asian giant hornet is at least being taken seriously. Quick action could prevent it from getting established in the northwestern U.S., though usually an introduced species is already established by the time anyone sees it in the wild.

As with COVID-19, there are questions as to how the hornet would adapt to climate in the U.S. The L.A. Times questioned whether the AGH would adapt to California's cool summers and warm winters.

Some introduced insects become enduring pests, like Asian tiger mosquitoes that bite annoyingly during the daytime, and the Emerald ash borer that has decimated ash trees. On the other hand, we hear little about the killer bees that were touted as such a big threat in the 1980s. The best news would be that the Asian giant hornet hasn't become established after all.

High School Ecolab Wetland--Spring Edition

A detention basin is a dug out area designed to collect rainwater from roofs and parking lots and hold it for awhile after storms. Usually they are designed without thought to their potential as wildlife habitat, and are planted with high-maintenance turf. When located at a high school, it sounds like a place where water is told to go when it's been bad.

This basin was converted to a wetland, planted with native species and informally stocked with native frogs, fish and possibly a turtle. It is fed by an eternal spring, which is the romantic name I'm giving to the sump pump that sends groundwater from the school basement into the wetland every twenty minutes or so, year-round, rain or shine. The steady water supply allows a greater variety of native wetland species to prosper.

After two years and some t.l.c. from teacher Tim Anderson, his students, myself and others, the native plants have become well established. An early bloomer is the marsh marigold. This showy native species is difficult or impossible to find growing in the wild in Princeton, but flourishes in this constructed wetland. (Frequently mistaken for marsh marigold is the bright yellow flower that has colonized many local floodplains--an invasive exotic plant called Lesser Celandine--see April 27, 2007 post.)

The blooms of a species of willow planted in the ecolab wetland were a pleasant surprise. Though native, willow tends to be an aggressive grower that may need to be controlled to allow other species to coexist.

This spring, a pair of mallards showed up, and seemed to give serious consideration to breeding there.

Spring Photos From Herrontown Woods

While I've been documenting the imperialist tendencies of nonnative lesser celandine in Princeton, ever vigilant, some friends have thankfully been sending photos of local nature that speak to beauty, stability and enduring diversity. 

Joanna Poniz sent some lovely photos of a wood frog in one of the vernal pools at Herrontown Woods, 

and skunk cabbage growing up against a boulder.

Oftentimes patches of trout lilies have lots of leaves and no flowers, so it's special to find one.

Here's a nice patch of spring beauties.

Local botanist Betty Horn also periodically sends photos, documenting the ongoing survival of hepaticas at Herrontown Woods, and an especially large patch of spring beauties on the trail to Council Rock in Woodfield Reservation. 

Joanna captured a threefer here, with trout lily, spring beauty, and bloodroot growing together. This is a good example of how native species have a tendency to intermingle, creating concentrated diversity.

Inge Regan captured this twofer, which looks like a onefer until you take a closer look and realize that the smaller flower isn't another bloodroot but instead a rue anemone.

Joanie Marr sent these photos of the many different kinds of daffodils growing around Veblen House and Cottage at Herrontown Woods. 

Someday I'll learn the names of all of these varieties. 

I was happy for Joanies' photo of the black vulture that hangs out at the Veblen Cottage this time of year. We got beyond viewing it as a bad omen, and now take pleasure in its annual return. Seeing it perched alone on a branch, I worry that something may have happened to its mate. They mate for life, and this pair has for many years raised young in the corncrib next to the red barn. Maybe it's just standing guard while its mate tends the nest. I'd check the corncrib to verify, but don't want to disturb.

No matter how endearing, it's still hard to end a blog post with a vulture, so back to Joanna's frog. 

Time To Pull and Pile Garlic Mustard

One of the most rewarding invasive plants to weed out is garlic mustard. Unlike lesser celandine, which must be either sprayed or dug out, garlic mustard is easy to pull and pile. It's also easy to identify, with a strong garlicky smell to the leaves. Early leaves in the spring can even be tasty, which may explain why it was brought to America from Europe, as early nourishment after a long winter. 

If left unpulled, stands of garlic mustard will become denser year by year, releasing toxins into the soil that inhibit the growth of other plants (can you say "allelopathic"?). If you have a patch that feels overwhelming, here's a success story to inspire you. 

It's best of course to nip an early invasion in the bud. In any given year, you'll see two generations of garlic mustard. In the first year of growth, a biennial plant only produces leaves, gathering energy to launch a flowering stem in the second year. I just pull the second year plants, ideally when they first appear in the spring, but usually when they are in bloom and easiest to spot.

Pulling time is in April, extending into May. This first bloom, in the photo, was on April 10, but they're still blooming now. The clusters of white flowers can make weeding feel like an easter egg hunt. Last year, we had a girlscout troop pull garlic mustard that was growing along the edges of the Herrontown Woods parking lot. They got every last one!

That's the strategy, to pull every last one, before the seeds mature and scatter. If this is done year after year, the soil will run out of seeds to sprout. Each year there will be fewer and fewer plants, as the seedbank in the soil becomes exhausted. How many tasks do you know that get easier every time you do them? It's important to get every plant, every year, so the seed bank can't rebound.

Other gratifying aspects of weeding garlic mustard? Each plant is big enough that each pull provides a feeling of solid accomplishment. And the soil is often still soft in April, so the root comes out easily, especially after a heavy rain. I tell people to "grab low, and pull slow." 

What to do with them once they are pulled? Some people stuff them in plastic garbage bags and put them out with the trash, but though that gets rid of the seeds, it also makes more trash. My strategy is to make a pile. Word has it that even if you pull them in the flowering stage, they can still develop mature seeds. So don't just leave the stems scattered around the yard. If you concentrate them in one pile, it doesn't matter if any seeds mature, because the new plants will all be in one spot and easy to pull or smother. It's important to locate the pile where heavy rains won't wash the seeds away from the piles. 

We've been pulling garlic mustard and piling it like this for years around the Veblen House. This year, it took about an hour to get every last one and put them in this small pile, resting on a log, roots drying in the sun. That job's done for the year. It's a rare feeling for a gardener. I don't entirely trust it, and am going to go out again and check, just to make sure.

Losing Control of the Lawn

Most everyone has at least a little lawn, pleasant to walk upon, setting off the shrubs, or simply a default means of dealing with that rectangle of nature a homeowner inherits with the house. Collectively, lawns are a show of cultural unity in the form of a vast expression of control and uniformity, with growth kept within strict limits, each grass blade the same height. Oftentimes, the uniformity is enforced by noisy, machine-laden coiffeurs, akin to paramilitary outfits that land and deploy, then hasten away when the mission of growth-control has been achieved.

Early in spring, where chemicals aren't used, there can be small rebellions here and there in the lawn, instigated by the "early risers", e.g. assertive wild garlic, or star-of-bethlehem, forming an effect I call "lawn blotch". When the grass starts to catch up, there's a peaceful week or two of quiet conformity, the green spotted with the pleasant yellow of dandelion blossoms. And then, lulled by spring into reverie, proud of our environmental high road of chemical free lawn care, we wake up to the white, seedy roar of the dandelion, going rogue, letting its freak-flag fly, rocking the sea of green with its passion for propagation.

The photo, taken a week ago, is of my neighbor's lawn, a rental, but mine was "hearing the roar" as well. There may be approaches to organic lawn care that minimize the dandelions, but for most of us who do nothing beyond periodic mowing, the dandelions hold reign for a couple weeks each spring. The sense of losing control, though, is temporary, and though it may add to the number of dandelion seeds parachuting in to other yards, it has no ramifications for natural areas. Maybe the deer eat them, but for whatever reason, dandelions pose no threat to our stream corridors or nature preserves that I've noticed.

This contrasts with an introduced species like lesser celandine, whose rapid spread not only triggers feelings of having lost control of one's yard, but also threatens transformation of nearby preserved lands.