The Mystery Tree Found in Autumn Hill Reservation

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Update:

Where found thus far:

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

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

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

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

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

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

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

So, we're not really there yet. 

Leaves -- A Love Story

Leaves are easiest to love during their "fifteen days of fame" in the fall. But though a true love of leaves may first take hold in the fall, maybe in a particularly colorful leaf picked up by a child on the way to school, it ultimately deepens and matures to include the less showy times that leaves go through, from an obscurity of green up above to an obscurity of brown underfoot, to a slow return to the air and ground from which they came. A love of leaves is so richly rewarded, by the oxygen they give in abundance, the shade, the transpirational, transformational cooling in the summer, the remembered exhilaration of raking and leaping into leafpiles, and the fabulous pulse of surface area and food leaves give to the ground each fall to insulate and feed the life of the soil that in turn sustains all life. Such abundant gratitude they show for the ongoing gift we give without even thinking, "a breath to build a leaf on." Leaves, after all, are built to a great extent from the carbon that we and other animals exhale.

Here are some photos collected this fall:

A sweetgum tree on Princeton University campus across from McCarter Theater. Of course, you expect leaves in such a setting to be above average,

but even the wild ones can put on something of a show, as in this field of sweetgum seedlings in a field next to Snowden Lane,

and even rival the cultivateds. This photo was taken only with the intent of showing variation in size of leaves that fell near Veblen House. The car's hatchback windshield was the closest horizontal surface. Only when looking at the photo later on did I see that nature, ever the artist, was composing the photo as much as I.

This photo of a native witchhazel planted next to a house on Linden Lane led to the unceremonious end of a phone conversation, as my cellphone battery died moments later.

In Herrontown Woods, witch hazels were more the color of these backyard pawpaw leaves. Shade can mute the brilliance of color, and sometimes alter the color itself.

The leaves of mapleleaf Viburnum vary year to year and place to place along the Princeton Ridge.

Wasn't expecting a musclewood to be so colorful. This is a lovely understory tree of Princeton's forests, but my neighbor has one flourishing in her front yard, close to a busy street. (Carpinus caroliniana)

Virginia creeper hanging from a blackhaw Viburnum. Lots of sun, lots of color.

The oakleaf hydrangia and stonecrop "autumn joy" can be a fine combo, their colors slowly shifting through the fall. The stonecrop isn't native, but stays where it's planted, and gives pollinators a fine late-summer dinner plate of nectar.

And lastly, another form of autumn joy--my older daughter when she was discovering the pleasure of leaves while growing up in Durham, NC. The child within us can make that love and delight last a lifetime.

Woody Plants With a Farmer's Tan

A couple photos to post before fall slips entirely away:

The leaves of winged burning bush (Euonymus alatus) turn bright red in full sun, or white in full shade. This photo shows the gradation on a single bush.

Please, by the way, don't plant this species, and if you have it, consider replacing it with some less invasive colorful shrub. It can be pretty, but winged burning bush has proven highly invasive in local woodlands, outcompeting native shrubs and shading out spring wildflowers.

This maple on Aiken may have gotten a farmer's tan on the top because the lower half is shaded by the tree across the street, and thus is slower to change color.

Coralberry: Late-Bloomer in the Whole Earth Center Raingarden

The narrow little raingarden in front of the Whole Earth Center, along the Nassau Street sidewalk, is a bit of an anomaly. It flourishes beyond all expectation and despite several factors that could easily work against it. Portions of it are covered by a canopy, which means those areas receive no rain. And though I weed it periodically, do some thinning and trimming, and clean up any trash that blows in, there are others who take care of it as well. A professional landscape crew comes in each spring and lays down fresh mulch. I see signs now and then that someone on staff is also paying it some attention. That none of us communicate or coordinate would normally lead to problems, and yet it all works out.

There are, too, a few plants in the raingarden that wouldn't normally be considered ornamental. Fringed sedge and deertongue grass are wild natives, and yet provide a look of surprisingly attractive grassy opulence along the sidewalk's edge. And the native coralberry in these photos, taken a few weeks ago, makes a nice mound at the building's corner.

Bees, I discovered one day walking by, take an interest in coralberry deep into the fall.

A closer look was rewarded by this scene. Turns out the coralberry has its own brand of commerce--a sort of roadside stand set up in front of the Whole Earth Center, serving organic nectar to honeybees.

It's not coincidental that this native shrub looks reminiscent of the nonnative and frequently invasive honeysuckle shrubs. Both are in the family Caprifoliaceae. Grab your botanical latin books to find out the meaning buried in the scientific name, Symphoricarpos orbiculatus.

At the other end of the raingarden are the more mainstream native shrubs, favored for the showy flowers and bright fall colors that the coralberry doesn't deliver on. Fothergilla (witch alder) turns brilliant orange, contrasting with the purplish oak-leaved hydrangia behind it.

One nice trait of the corralberry for us lazy propagators is that it makes new plants when its branches touch the ground. Each can be dug and grown into a fullsize shrub. From old raingardens, new ones can be born.

Norway Maples, and Seeing the Future

One purpose of this blog is to help people to look at nature now and see where it's headed. Every gardener imagines the harvest while planting the seeds. In science, one extrapolates from past and current trends to predict the future. With practice, one can look at a woodland and see not only the present but past and future as well. As a land manager, one envisions two futures--one without intervention, one with. Because we've altered local habitats so much--through altered hydrology, past farming, introduced species, banishment of important forces like fire and predators like mountain lions and wolves--intervention can help restore functionality that no longer happens naturally.

Autumn is the easiest time to divine a woods' future, because each species shows its colors, making trends easy to spot. For instance, learn the Norway maple's brand of yellow this time of year, and you'll start seeing them all over town. Unpalatable to deer, they rise unnoticed until they become full-sized trees, mostly along backyard fencelines.

That's what's happening on a larger scale in the hidden valley between the Princeton University chemistry building and Washington Road. That mix of yellow and lingering green indicates that the Norway Maples are taking over the top of the valley,

and extending downstream. This is the perfect time of year to see the extensive invasion by this nonnative tree. Why have I on multiple occasions urged the university grounds staff to cut or girdle these trees, despite their attractive yellow in autumn?

The problem is an ecological one. This forest, one of Princeton's oldest, is steadily shifting from native trees that feed local wildlife to nonnative vegetation that does not. As the shade-tolerant Norway Maples push up into the native canopy above, their competition for water and nutrients weakens the giant oaks and black gums, hastening their decline and increasing their susceptibility to wind storms. Young native trees--preferred by deer and less shade tolerant--can't compete with the Norway Maples, which grow quickly, green up sooner in spring and drop their leaves later in the fall. This photo shows a 1-2 centuries old oak with a sea of Norway maples rising underneath.

Fortunately, most Princeton woodlands have not been invaded by Norway maple, though it would be worth it for land managers to take a walk through the woods to see if they are starting to get established elsewhere in Princeton's open space.

Except in that Washington Rd. gorge woods, they have proven invasive only in people's yards, showing highly localized invasiveness much like Japanese maples and Rose of Sharon. This photo, taken along North Harrison Street, shows the classic problem with ignoring the silent ascent of Norway maples, in this case under a powerline. Chances are they grew unnoticed by the homeowner, and now will require repeated pruning to keep them from threatening the wires.

At least the half of the tree closer to the street shades the pavement in the summer,

but another annoying aspect of the species--their dense shade and aggressive roots that leave little sun or water for the lawn--has made it impossible to grow grass on the steep slope.

Like climate change and the nonpoint pollution of our waterways, the Norway maple silently transforms the world, undermining food chains and biodiversity, while our attention is elsewhere.

How to Thank a Leaf

On this day of gratitude, I would like to thank leaves of all kinds for all they do, for all the CO2 they eat, and all the treats they make possible, with their patient translation of sun into sugar. As if that weren't enough, they close the summer's show by becoming candy for the eye, then fly and fall in a dance with gravity, to blanket and feed the earth upon which all depends, though we pretend otherwise. How do I thank them all, where they lay in humble anonymity, while we brag and boast and think ourselves the center of the world? And how do I thank the windblown leaves that raced along with my bicycle a week or two ago? The wind at our backs, they cheered me down the sidewalk like a tickertape parade, as if all the world were going my way.

Nature Walk at Herrontown Woods: the Color-Coded Forest, Sunday, Nov. 13, 1pm

Trees and shrubs are still showing their true colors up along the Princeton ridge this week, making it possible to tell at a glance what species surround us. We'll decode the forest, see what we can see, and find some solace in the woods. All welcome.

Meet this Sunday, Nov. 13, at 1pm at the Herrontown Woods parking lot, off Snowden Lane. Maps can be found at http://www.fohw.org/p/maps. html.

This photo of hazelnut is from a 2013 post on the color-coded forest at this link.