Sunday, September 17, 2023

Last Chance to Pull Stiltgrass

This week and maybe next are your last chance this year to pull stiltgrass (Microstegium vimineum). This mega-invasive is an annual, so the logic of countering its spread is to pull it before it can produce and drop seed. If the seeds haven't loosened yet at the end of the stalk, you can still pull it. Throw it in the trash, or if there's a lot, make a big pile of it so that any seeds that sprout the next year will all be in one place and easily covered or pulled. Definitely don't put it in your compost if its seeds are forming. If stiltgrass is just starting to invade your yard, pulling as completely as possible now will greatly limit its seedbank for next spring. Another strategy for large stands is to let the stiltgrass grow, then just as it begins to flower mow it short and hope its feeble roots don't have enough energy to grow another flowering stalk. 

For those fuzzy on identification, google lots of images, and look for the silver line running down the middle of the leaf. Stiltgrass can grow in the shade or sun, climb up to four feet, or thrive in a miniature state while ducking below your mower in the lawn. It's incredible survival skills include being incredibly inedible for wildlife. Stiltgrass gives nothing back to the habitats it increasingly dominates.

More on Stiltgrass, and a Success Story

Walking in the local woods, you've probably seen this kind of scene--what looks like a grassy meadow extending through the forest. In the filtered light of the understory, its simplicity and lushness may have some visual appeal. And yet, in some ways what you are looking at is the ecological equivalent of an urban food desert. 

Stiltgrass is an introduced plant that could be called a pervasive invasive, able to thrive most anywhere and dominate whole landscapes. Its success has come in part through being inedible. As wildlife selectively eat native vegetation, the stiltgrass expands, preventing the native plants from rebounding.

Unlike another nonnative annual weed that can look similar, crabgrass, stiltgrass becomes ubiquitous because it can thrive in sun or shade. That means the stiltgrass invading your lawn and flower beds can continue spreading ad nauseum into the nearby forest, or vice versa.

We used to call it bamboo grass--something in the shape of the leaves is reminiscent. The stiltgrass name refers to its angular growth, with each segment supporting the next as it climbs up and over fallen logs and other plants. Packing grass is another common name, referring to how it was once used to pack porcelain for shipment. That's probably how it first reached the U.S., in packing crates sent to Tennessee. 

When I first encountered it, growing on the bank of Ellerbe Creek in Durham, NC, I thought it graceful. Then came Hurricane Fran, bringing floods and fallen trees. In the aftermath of that massive disturbance, stiltgrass exploded in the landscape, expanding and ultimately choking forests with its vast, dense stands. New Jersey proved no different. 

Stiltgrass tends to establish itself along roadsides. Here it is growing in a green ribbon along Herrontown Road. Trails, too, provide an avenue for extending its reach, its tiny seeds carried on boots or the hooves of deer.

Though stiltgrass has covered large areas of woodland in the eastern U.S., we have found it worthwhile and even satisfying to counter its relentless incursions. Today in the Barden at Herrontown Woods, some volunteers pulled it out of a patch of native jewelweed along the edge of the parking lot. 

Nearby, on land where we have largely eliminated a massive clone of wisteria, stiltgrass was starting to move into the void. If nothing were done, this open woodland would have become a pasture of stiltgrass. But we have acted early enough to be able to remove all of this year's stiltgrass, dramatically reducing the seeds available for next year's crop. This photo shows the last patch before we pulled it. 

Interestingly, there are native grasses that look a little like stiltgrass, the main one being Virginia cutgrass (white grass), Leersia virginica. It has longer, narrower leaves that lack the silver stripe down the middle. As is a common ecological refrain, the native grasses "play well with others," not forming stiltgrass's massive, exclusionary stands. Some smartweeds like Lady's Thumb can also bear a resemblance. 

Saturday, September 16, 2023

Where Have All the Spotted Lanternflies Gone?

Well, it's happened, at least in our neck of the woods.

Billed as a major calamity, the spotted lanterfly invasion has gone "poof" this year. Yes, the spotted nymphs could still be found clinging to the stems of Ailanthus sprouts at our Barden in Herrontown Woods. 
And a few adults were later seen perched on the rachis of Ailanthus leaves. We pulled the sprouts out of the ground to deprive them of this haven. Hard to say where they went after that.

Writing a post about lanternflies three years ago, I learned that numbers of the invasive insect had dropped in some areas of Pennsylvania five years after first being seen. Lanternflies first showed up in Princeton in 2018, and here we are five years later, with what appears to be a dramatic drop in numbers.
It's true that people gave themselves over to squashing the pesky bugs--leafhoppers, actually--in spirited ways. (This photo shows one of the more creative approaches.) Some think the unusual weather has had an effect. Insect numbers overall have been down, be it the pollinators on backyard flowers, the odorous house ants that used to invade our kitchen, or spotted lanternflies. But my guess is that it has been the full-time predators, feathered or with eight legs or six, that are to be most congratulated for stemming the explosion of spotted lanternflies. 
Just follow the trail of colorful wings that brightened a walk up towards Veblen House one day.

The most powerful contrast for me is between the invasions of emerald ash borer and spotted lanternfly. Since the emerald ashborer arrived, about ten years ago, I have yet to see a single adult ash borer in Princeton, and yet the devastation they have brought to the ash tree is all around us. The lanterfly, on the other hand, has been seen everywhere, and yet I can't point to a single plant that has died due to their appetites. We humans are visually oriented, but it's the invisible threats--be they an invasive insect or even more significantly an overdose of carbon dioxide--that most endanger our world.

Thursday, September 14, 2023

Yew Berries and Dewberries


I've passed by this yew hedge on busy North Harrison Street thousands of times, and usually pay it no mind.  

But a couple days ago, I happened to be looking down at the sidewalk rather than the gazillion cars and trucks driving by, and saw something that caught my eye.

Yew berries! They look like small, bright red pitted olives, but the pit is definitely still there. Fifty years ago, in botany class, I learned that the juicy red part is edible, but the hard central pit is most definitely not. The side of a busy street is probably not the best place to be harvesting edibles, but I picked a few, ate the flesh and spit out the pit--an unexpected treat along a sidewalk in Princeton 

Technically, the yew berry is not a berry at all, but
an aril. All students of botany will vividly remember the moment in class when they learned that, as one website states, "in contrast to a berry, which develops from the ovary, an aril is an outgrowth of the ovule, or of the funicle which attaches it to the placenta." Botany is full of surprises.

The yew we sometimes see planted around houses is one of the few conifers native to England, according to the Kew Gardens website. America has a native yew, Taxus canadensis, which shows up on a 1960s plant inventory for Herrontown Woods, but I've never encountered it. 


One thing I discovered this year is that we have dewberries growing in the Barden at Herrontown Woods. I had thought we had three types of brambles in the Barden: blackberries, black raspberries, and the nonnative wineberries. But some of the blackberry-like plants were crawling along the ground rather than arching upwards, as brambles are more normally wont to do. These we decided were dewberries. They still have thorns, but you could say they lack spine. The whole concept of a dewberry was likable, from its less intimidating presence to the promise of fruit. They are very adventurous in some areas of the Barden, however, crawling long distances. We may need to curb their travels, even though the berries, ripening in mid-August, are pretty tasty.

Thursday, September 07, 2023

Pilewort--A Native Weed With Hidden Flowers and Showy Seeds

Some plants have it all backward. Flowers are supposed to provide the show; the seeds, not so much. 

But with pilewort, its the seeds that catch the eye, clustered in raggedy bunches that look like cotton. 

The plant sets up great expectations as it grows and grows, fleshy like a large thistle, but soft and approachable, 

with a pleasant scent when you crush the leaves. What fabulous flowers will crown all this vertical ambition? 

Something looking like a flower bud appears, but it never generates anything resembling a flower with petals. Pollinators visit nonetheless, even though the flowers look like duds. 

During our monthly nature walk at Herrontown Woods this past Sunday, I was grateful that one of the participants pointed out some other activity around the pilewort flowers. A common local ant species was busy tending to a flock of aphids sucking juice from the stems. The ants harvest the aphids' honeydew. 

Pilewort (good luck with the latin name, Erechtites hieraciifolius) is what I call a native weed. They pop up in large numbers in areas that have been disturbed, rising 8 feet high in what looks like a fleshy forest dusted with snow. 

Maybe the name comes from the piles of seeds it deposits all around. Another common name for it is fireweed, because it sprouts abundantly after a fire has swept through.

You might think this plant a menace that will take over. The nonnative lambsquarters, also an annual, can give this impression too, growing densely and tall the first year after a disturbance. But I've learned not to be concerned over their dominant presence. The first year's show of abundance fades in subsequent years until you can hardly find a one. Other plants move in, and pilewort awaits the next disturbance. 

Tuesday, September 05, 2023

Obedient Plant: Big Pink in a Season of Yellows

Among sun-loving native flowers of summer, the so-called obedient plant shows up all fresh and fulgent just as the party is starting to wind down. Each year it catches me by surprise with its pink when so many other flowers--sunflowers, cutleaf coneflowers, Silphiums, Heleniums--go with yellow. 

Obedient plant (Physostegia virginiana) is also off my radar because it is risky to plant. Its tubular flowers may obediently remain sideways if you push them, but the plant itself spreads aggressively underground. Not surprisingly, it's in the mint family, known for roots that spread hither and yon.

That's why this gardener on Grover Ave was so smart to plant it between a sidewalk and the road, where its capacity to spread is limited.

A similar strategy to curb its spread was used in front of Jay's Bike Shop. 

Obedient plant also pops up in several spots in Herrontown Woods each summer. Hard to say if it was planted or part of the indigenous flora. Interestingly, it doesn't seem to spread much when in an open woodland rather than a garden. Many other species that seem modest, even rare in the wild--various native sunflowers, groundnut, virgin's bower, fringed loosestrife--also turn rampant when planted in the comparatively tame environs of a garden. 

Wednesday, August 16, 2023

Princeton's Fuel Tank Raingarden Threatened By Lack of Early Intervention

A couple years ago, the town planted this raingarden next to the fuel tank on Witherspoon Street. They put in some pretty cultivars of showy native species like black-eyed susan, purple coneflower, and St. Johnswort, then mulched it all carefully. Everything looked under control, as gardens do when they are first planted.

Even this summer, with flowers blazing, it looks like a success. 

But I can see that the seeds of its ultimate demise have already sprouted. This botanical drama has played out many times before--raingardens that failed for lack of strategic intervention when aggressive weeds started to move in.

Most deadly is the mugwort that has become established and is quickly spreading. That one invasive species alone could obliterate the intended plants in a few years.

Nutsedge, too, spreads rapidly.

Along with foxtail grass, 

and barnyard grass, the nutsedge is obscuring a nice stand of soft rush the town planted two years ago. 

More easily dealt with are the ragweed--a native weed with allergenic green flowers--
a flamboyant patch of crabgrass, 
and what looks like a patch of black medic. The mulch laid down two years ago surely helped, but its capacity to stifle weed growth clearly didn't last.

And what's this vine, crawling out over the other plants? Ivyleaf morning glory is a new one for me. 

Back in late April, when this photo showed the mugwort looking tamable, pullable, sprayable, I alerted the town that early detection and rapid response is what's needed to keep the weeds from taking over. The response was that a public works crew weeds the garden once or twice per year. That's not how a raingarden works. I know from long experience. Catch the aggressive weeds early, and the raingarden will ultimately become very easy to maintain. 

Vikki Caines, a longtime member of the Recreation Department who recently retired, kept beautiful gardens growing in areas near the community pool. But that was a labor of love, done in her spare time. It's love, of a parental variety, that leads one to acquire plant knowledge in the first place, and then to grow a garden and anticipate its needs, and check for weeds, much more than once or twice per year. 

How can your typical institution--where staff lack plant knowledge, motivation, and the flexibility in routine needed to catch problems early--successfully tend to a botanically complex raingarden planting? For the past 30 years, I've watched as many native raingardens and meadows planted by towns or universities have incrementally failed for lack of early and ongoing intervention by a knowledgeable caretaker. Maintenance requires more knowledge than installation, because the caretaker must know not only the intended plants but also the many species of weeds that inevitably try to move in. Yet we see over and over that money is invested in design and installation, while maintenance is deprived of funding and respect. We have doctors and nurses to care for people, but precious few plant doctors to care for landscapes. 

A bit of good news: Last year, I wrote a google review of the Betsey Stockton Garden planted on top of the Princeton University's Firestone Library, pointing out that white clover and other weeds were invading the flower beds. Whether the review had an impact, I can't say, but the university is taking better care of the meadow planting this year.

Related Posts:

Followed two years later by:

Cindy Taylor, Princeton's First Open Space Manager, Moves On

It was a brief but extraordinary tenure for Princeton's first Open Space Manager, Cindy Taylor. Her hard work and accomplishments made abundantly clear the importance of the open space manager position in town government, validating the view of all of us who fought long to have the position created, and the wisdom of the current council in funding it.

Cindy served as primary contact within town government for the nonprofits that take care of Princeton's open space at Marquand Park, Mountain Lakes and Herrontown Woods. Among her many activities, she compiled an inventory of open space in Princeton, worked with the Environmental Commission on updating the Environmental Resource Inventory, and helped apply for habitat restoration grants. In my many communications with her, I would have to say she was impeccable, sending us detailed notes from meetings, and attending quickly to our various requests. 

After a year and a half on the job, she is leaving for a job in Mercer County open space. We thank her for setting such a high standard of public service.

(Photo plucked by TapInto Princeton from a zoom video of a council meeting)

Friday, August 11, 2023

The Invasive Grass Fueling Wildfires in Hawaii

Hawaii didn't used to get pummeled by highly destructive wildfires. What has changed? A big part of the answer lies in the interaction between climate change and invasive species. 

Begin with a couple paragraphs buried in a NY Times article:

The area burned annually by wildfires in Hawaii has quadrupled in recent decades. Declining rainfall and rising temperatures have left the islands more susceptible to blazes, climatologists say.

Invasive grasses that are highly flammable have crowded out native vegetation in some areas, and climate change has exacerbated dry and hot conditions in the state, allowing wildfires to spread more quickly.

But what invasive species? A University of Hawaii website points to one that has been particularly destructive:
Guinea grass (Megathyrsus maximus), a nonnative invasive grass in Hawaii, forms dense stands that outcompete native plants and has very high fine fuel loads that greatly increase fire potential, spread, and severity.

Wikipedia describes guinea grass as a tough customer, growing ten feet tall. Though it can thrive in full sun, it can also tolerate shade, allowing it to invade native woodlands and thereby increase their vulnerability to fire during droughts. Native to Africa, the grass was introduced not only to Hawaii but also to south Texas.

How did guinea grass get to Hawaii (also spelled Hawai'i)? Wired provides an answer:

When Europeans arrived in the late 18th century and established plantations for growing sugarcane and pineapple, they also brought invasive grasses. Now the economics have changed, and those fields lie fallow. But the grasses have spread like a plague. “Those fire-prone invasive species fill in any gaps anywhere else—roadsides, in between communities, in between people’s homes, all over the place,” says Pickett. “At this point, 26 percent of our state is covered in these fire-prone grasses.”

This stuff is highly sensitive to short-term fluctuations in rainfall. The grass will grow like crazy when the rains come, then quickly desiccate when the landscape dries. “When we get these events like we’re seeing these past few days—when the relative humidity really drops low—all those fine fuels become very explosive,” says fire ecologist Clay Trauernicht of the University of Hawaiʻi at Mānoa.
An article in ABC News explains how the more intense and frequent fires affect the soil and human health: 
Elizabeth Pickett, co-executive director of the Hawaii Wildfire Management Organization, a nonprofit working with communities to prevent and mitigate fires, lamented the changes wrought by fire.

Invasive and fire-prone grass species have moved in over time and during a fire they can burn into native forests, which means the forests are replaced by more grass, Pickett said. The soil burns and sloughs off, leading to massive post-fire erosion that smothers coral, impacts fisheries and reduces the quality of the ocean water, she said.

The state is windy and the dust blows for years, harming human health, she added.

“When you lose your soil, it’s really hard to restore and replant. And then the only thing that can really handle living there in many cases are more of those invasive species,” Pickett said. “It’s systemic. Air, land and water are all impacted.”
A Philosophical Footnote
It's important to note that both climate change and the spread of invasive species are largely unintentional. Our world is threatened by excess carbon dioxide and other planet-heating gasses--lowly biproducts of our economy and lifestyles. We are used to thinking of collateral damage as minor and incidental, and tend not to judge people by what they do unintentionally. In fact, the cumulative impact of unintentional acts is the central threat we face. We live our days trapped in a predicament in which humanity, largely well-meaning, is allowed to collectively and unintentionally create problems, but not allowed to collectively and intentionally solve them. 

Additional reading: Thanks to a comment (see the critical comment and my response below), I found a couple more interesting articles about guinea grass. One gives a good overview of guinea grass as both an excellent, deeply rooted forage grass for cattle, and a weed that has disrupted ecosystems and croplands around the world. The other invests the grass with cultural connotations.

Other Invasive Grasses Fueling Fires in Hawaii

My friend Fairfax sent a link to another informative article that mentions three other introduced grass species fueling fires in Hawaii: fountain grass, buffel grass, and molasses grass. It also stresses that these and other highly flammable introduced grasses are altering fire ecology in the mainland U.S. as well.

What Guinea Grass Has in Common With Japanese Stiltgrass

Some people aren't aware the extent to which grasses affect our lives, for better and for worse. Corn is a grass, as are sugar cane, bamboo, and sorghum. In Princeton and up and down the east coast, the most dominant invasive grass is Japanese stiltgrass, which like guinea grass can grow in sun or shade, and uses what's called C4 photosynthesis to fix carbon from the atmosphere. Plants that use the C4 process--corn also being an example--are more efficient than other plants that use C3. Stiltgrass has invaded most areas of Princeton, growing from a zillion seeds each spring to blanket large expanses of woods. Wildlife don't eat it, so as it takes over, the landscape becomes increasingly inedible. I've long wished that someone would come up with a highly selective herbicide that would impact only C4 plants. If stiltgrass's impact on eastern habitats hasn't been sufficient to stimulate research, maybe the fire hazard in Hawaii will get researches to take a look.

Friday, August 04, 2023

Four Kinds of Honey Bees in Northern Thailand

These bee hives look like something Winnie-the-Pooh might stick his paw into. The hives are made of hollowed out sections of tree trunk. The photo was taken by my daughter Anna, who was traveling this summer in southeast Asia. 

To escape the heat, she and her boyfriend headed up into a mountainous region in northern Thailand called Chang Rai, where the residents drink three kinds of tea and grow four kinds of honey. She was surprised to learn that the black, green, and white teas all come from the same plant--the same species of tea. But the four kinds of honey are not made by the same kind of bee. This is four kinds of honey made by four species of bees. Thailand, it is claimed, has the greatest bee diversity in the world, including half the world's species of honey bees, and in this tiny village the various honeys they produce are an important part of the diet. 

There's the honey we're familiar with, and then there's another one that tastes like apricot jam. A third, produced by the stingless bee, has a fermented fruity flavor like Kambucha. 

Another species, the asian giant honey bee (Apis dorsata), can't be kept in a hive, so villagers climb trees to reach the honey. Wooden footholds are placed in the tree trunk to expedite the climb. The giant honey bees don't stick around all year, but instead migrate up to 200 kilometers, returning to the same branch six months later.

The asian honey bee (Apis cerana) produces less honey than our honey bee, but is much easier to take care of

A Brief Account of Life in a Mountain Village in Thailand

Their first night in the village, they were surprised to be awakened at 3:30am by the robust crowing of roosters, so raucous that the whole village has little choice but to rise and begin its day. Chickens run loose, apparently free of local predators that might consume them before people have a chance to. Once a year, a tiger passes through the area, apparently without raising much concern.

The town runs on solar energy, but lest one think this mountain village an idyllic integration of humanity into nature, daytime brings cooking fires and the burning of refuse. The villagers are conditioned to the resulting stew of smoke that can linger in the valley, but it registered as noxious and toxic to Anna. 

Some of the refuse is plastic, which we're all told releases toxins when burned. What plastics do the villagers have if they grow their own food and have few possessions? Though they cook delicious meals most days, there are times when villagers may not feel like cooking, and so pull out store-bought noodles and tomato sauce, the plastic wrappings from which end up getting burned in the refuse pile. 

This is not much different from my own experience growing up in a small village in Wisconsin in the 1960s. One of my chores was to burn the garbage, plastic and all. In autumn, we'd rake some leaves into piles to jump into, and others into piles to burn. We'd toss acorns into the glowing core of the fire and wait for the popcorn-like explosion. On brisk, sunny fall days, the whole village became suffused with what registered as a sweet and endearing aroma of burning leaves. Even after moving to a city, the 1930s house we moved into had an incinerator in the basement for burning trash. And in the 70s and 80s, when I played jazz gigs in smoke-filled bars, it was not until the next morning that I'd notice the wretched smell of stale smoke in the clothes I had worn. 

There have been efforts to promote cleaner air in remote mountain villages around the world. Some students, before entering Princeton University, sign up to spend a "bridge year" in a foreign country doing good deeds, one of which is helping build cleaner burning stoves for villagers in Peru and elsewhere. You'd think the villagers would be grateful for a home less choked with smoke, and maybe they are, but the capacity of the body to become conditioned to abuse is both impressive and exasperating.

Lots of interesting reading out there on bees. Here's some info about eight species of honey bees around the world.

Thursday, August 03, 2023

The Pleasures of American and European Elderberries

One of my favorite shrubs, the elderberry, took on new facets and dimensions this year. 

When I was a kid, we'd drive out to the countryside and harvest its berries, clustered on broad disks. What they lacked in size they made up for in numbers. Brought home in big brown paper grocery bags, they were soon on their way to becoming delicious jelly and pies. We made jelly out of wild grapes, too, but elderberries had a flavor all their own. It took a little time to strip all those small berries off the stalks, but the reward lasted all year.

How we managed to beat the birds to the berries back then is a mystery. Though we grow the shrub in our backyard in Princeton, the catbirds often make quick work of the berries.

Elder Flower Syrup

Fortunately, there's something amazing to be made of the flowers, and this year, we finally made it. One summer many years ago, a friend had served me an elder flower drink that was revelatory, but somehow I got the idea that only the flowers of the European species (Sambucus nigra) could be used. Searching today's internet, that distinction appears to have dissolved. The elderberry native to the eastern U.S., Sambucus canadensis, makes perfectly fine elder flower syrup. 

Our friend Joanna served as mentor and activator, directing us to pick the clusters when all the flowers were open but still fresh. For best flavor, one website suggests picking the flowers in mid to late morning. 

Some Caution

Some recipes are less concerned than others about including any fragments of the green stems, which are toxic. Only the flowers and the cooked ripe berries are edible. We stripped the petals off the stems by hand, which is time consuming but delivers good results. 

Making the Syrup

Recipes vary online, but all use lots of sugar and sliced lemons, which are added to the flowers along with some citric acid. Pour in boiling water and let it sit, covered, for most of a day, then pour through a cloth to get the syrup. We had to call around to supermarkets and hardware stores to track down some citric acid. 

Pour a little of the syrup in chilled water, white wine, or prosecco. It was a big hit at our Veblen Birthday Bash at Herrontown Woods. 

Elderberries Join a New Family

One bit of news from the turbulent, restless world of scientific nomenclature: the elderberry has been uprooted from its long-running membership in the Caprifoliaceae family and now rubs phylogenetic branches with Viburnums and a couple other genera in the Moschatel family, also known as the Adoxaceae

A Curious Variety of European Elderberry

On a recent roadtrip, I encountered a strange, purple shrub in a couple gardens. I was surprised that the botanist I now carry in my pocket, better known as an app called Seek, was calling it an elderberry. "Black tower" elderberry, perhaps--one of many bred varieties of the European elderberry. It's pretty, and different, but it's not something I personally would plant. Each gardener evolves differently, but for me, the sequence of interest across fifty years went from vegetables, to roadside weeds, to pretty ornamentals that were native or not (a black tower elderberry would be in this category), then to the community of native species that coevolved together over ions. It's a fidelity deeply rooted in a sense of place. 

Johnny Elderflower Strikes Again

If some combination of the abundant flowers and berries breeds in you a love of native elderberries, you can easily go forth and propagate them using 2' long cuttings from the dormant stems. The bushes are typically found in wet, edge habitat where there's some sun. Hopefully you'll emerge from your winter dormancy before the elderberry bushes, because they leaf out earlier than other native shrubs. Press the bottom end of the "live stake" as deeply as possible into soil to make roots, leaving a few buds above ground to make leaves. I've used this highly economical approach to propagation in many places over the years, most recently in a wet, open woodland area at Herrontown Woods. The act of planting is deliciously lazy, but followup is needed in the form of watering during droughts the first summer, and protecting them from deer browsing with wire cages. If things go well, in a few years the special flavors of elderberry will be all the easier to be had in Princeton.

Wednesday, July 19, 2023

Monarch Butterfly Update -- July, 2023

How many monarch butterflies are people seeing this year? I've seen a grand total of two thus far. Neither paused for a photograph, so this picture is from a past year. 

On July 11, I saw one flying crazily at the Barden. They are expert and often seemingly whimsical flyers, but this one's flight was unusually frenetic. At double the usual pace, it would approach flowers but not land on them, leading me to speculate that it was looking for a mate rather than nectar. A useful Q&A post at suggests that these episodes of particularly erratic flight are induced either by a predator's attack or by a male chasing a female. But the frenetic flight made me instead imagine what it is like for monarchs when their numbers are few, and the search for a mate consumes more and more of their energy. Might a fruitless search at some point become frantic?

A few days later, I saw a monarch in a pasture near Herrontown Woods, flying at a more measured pace. 

There were a few common milkweeds growing in the pasture, but I was particularly happy to discover a couple specimens of green comet milkweed (Asclepias viridiflora), growing there as well. It's a species I've only seen twice in Princeton, the other incidence being a few individuals in the Tusculum grasslands. 

It's common to think that monarchs gain all their sustenance from milkweeds, but in fact the adult butterflies obtain nectar from a broad range of flowers. Otherwise, they would starve after the milkweeds have finished blooming. The caterpillars, however, are highly particular, and will only eat the foliage of milkweeds. The milkweed foliage is around all season long for the munching, though a lot has to happen for the foliage to actually be put to use. A female needs to lay eggs, and those eggs need to elude predation long enough to hatch. I have not seen an actual caterpillar in years, nor much evidence of milkweeds being consumed, but clearly a few are surviving somewhere.

To get a more in-depth report on the status of monarchs, my go-to is the savant Chip Taylor, who blogs at MonarchWatch. In a June 14 post, writing about whether monarchs will be listed as threatened or endangered, Chip Taylor wrote openly about the eventual end of the great monarch butterfly migration. It's believed that the monarch itself is not likely to go extinct, but that the migration--involving the portion of monarchs that participate in the fantastic journey north from the mountains of Mexico up into the U.S. and Canada, then back to Canada in the fall--is increasingly vulnerable. According to Taylor,
"As applied in this case, extinction refers to the loss of the monarch migration and not the species per se. Given the link between the increase in greenhouse gas emissions and increasing temperatures and the world’s slow response to these changes, yes, the monarch migration will eventually be lost."

It's important to note that those who raise alarms about the climate crisis are the optimists. It is optimistic to face up to a grave risk, and call for action to save what will otherwise be lost. Denial and dismissiveness are rooted in pessimism. They take a gloomy view of 1) our capacity to recognize dangers and 2) our capacity to act collectively to prevent catastrophe. Taylor's recognition of the high likelihood that we will lose the migration raises an obvious question, which he hastens to answer.

"If the monarch migration will be lost eventually, why make great efforts to sustain it? Faith. We have to have faith that the world will come to its senses and work collaboratively toward the reduction of greenhouse gases to save the natural systems that sustain us. There is hope. The rate of increase in CO2ppm has declined in recent years."

Another answer is that, the longer the migration can be maintained, the longer humanity has to "come to its senses." 

It is stunning, knowing the extraordinary power of carbon dioxide to influence the earth's climate, that society has left it unregulated. As individuals, cities, and businesses, we remain free to pour as much of it as we please into the atmosphere. Until that giant hole in our regulatory protections is patched, the vast majority of people will not change their behavior. 

Tuesday, July 18, 2023

A New Invasive Plant at Princeton High School

Here's a story about how an invasive nonnative plant can be accidentally introduced and quietly transform an area. It also shows how invasion can be regional but also very localized.

This is a big picture of a little yellow flower called birdsfoot trefoil (Lotus corniculatus). The clusters of flowers and especially the subsequent seedpods resemble the shape of bird's feet, and the tiny leaves echo this shape to some extent.

I hadn't knowingly seen it much, and only learned the name a couple years ago, but this year, 
it has spread aggressively along the grassy extension along Walnut Street at Princeton High School. I'd noticed a few the year before, but now it is dominant along a stretch in front of the Performing Arts wing and the Ecolab wetland. 
This year also, it is coating areas of an old pasture next to Herrontown Woods. In the pasture, it was probably planted intentionally as forage for cattle, but at the school, it surely was introduced accidentally.

Should we be concerned about either example of this nonnative rampancy? I sent an inquiry to a couple listserves of land managers, and received a tepid response. Birdsfoot trefoil is mostly a roadside weed, was the sentiment. It only gets a couple feet high, so will likely just stay in the background rather than stifle native species. 

But I have a vivid memory of a prairie walk I went on last year at the Kishwauketoe nature preserve in my home town in Wisconsin. At one point, leading us through a gloriously restored prairie, the botanist spotted a birdsfoot trefoil and immediately went over and pulled it out. Was it merely a pet peeve, or was his determination rooted in past observations of dramatic consequences if birdsfoot trefoil is allowed to spread? 

This short video shows how birdsfoot trefoil can alter the appearance, if not necessarily the composition, of a meadow:

I did a quick survey of school grounds and the nearby neighborhood by bicycle, and discovered that the infestation is limited to grass next to the extra wide sidewalks that were installed along Walnut Street a couple years ago. It probably hitchiked in on machinery or soil used in construction of the sidewalk. Another possible vector was the planting of new street trees right where the birdsfoot trefoil growth is now the most dense. Rootballs, topsoil, tools, heavy equipment--all can carry weedseeds.

This is an invasion that's in the very early stages, and could be easily nipped in the bud. For instance, I found a grand total of three plants on the middle school grounds. Five minutes of spot spraying with a selective herbicide now is all it would take to stop an infestation that will otherwise become intractable.

Another reason to take action is that it is poised to invade the new native meadow planting in the detention basin next to the tennis courts. In this photo, a few plants of birdsfoot trefoil grow just across the parking lot from the new native planting. Does the school want a native meadow, or a meadow that is thick with a nonnative species that appears capable of outcompeting many of the native grassland plants? 

Now, while the extent of the spread is limited, would be the time to take proactive action.