Our Color-Coded Forest -- v2023

Happy Thanksgiving to readers of Princeton Nature Notes, now 17 years old--the blog, that is, and maybe even some of the readers. I will be leading a nature walk this Sunday, Nov. 26, from 1-3pm, open to all. Meet at the main parking lot for Herrontown Woods, off Snowden Lane. I had hoped to show off what I call the color-coded forest, but a storm of heavy wind and rain stripped most shrubs of their remaining leaves. It will still be good to have a hike, though, and you can see in this post what area woodlands looked like until just a few days ago.

November is when woodlands turn into one of those paintings where you match the color to the number. It's a time when you can gaze into the distance and identify every woody plant by its color. For instance, in this photo of a woodland overlooking the canal in Kingston, check out the yellow in the upper right. That's what's left of the Norway maple leaves, which turn color later than the native maples, and seem to know no other color than yellow in the fall. And the green in the understory? That is bush honeysuckle--what I call the "second forest." It's still green because it evolved on a different continent with a different climate, and so its timing is different from the native flora in spring and fall.

Seen this past week from the cliff in Herrontown Woods, the color coding was much more complex, with non-native Photinia, winged euonymus, and bush honeysuckle mixing with native species.  

Here's a glorious dogwood along the red trail. 

Up on the ridge, the maple-leaved Viburnums develop subtle shadings.

In our "cultural zone" between the Barden and Veblen House, young white oaks turned a rich burgundy earlier in the month. I tell people it's called a white oak because it turns red in the fall. Red oaks mostly turn orange. Naturalists have been doing Stop Making Sense tours long before David Byrne got around to it.

And then there's Photinia villosa, which is both beautiful and concerning, given how densely it has come to dominate in areas across town in Mountain Lakes and the Institute Woods. A few specimens turn bright orange, while

most turn bright yellow, even when growing side by side. You won't see a Norway maple going rogue with orange in the fall.

Another shrub, related to Photinia but just starting to show up in our woods, is a mystery. I discovered it across town fifteen years ago in Rogers Refuge, and even crack botanists have yet to put a name on it. 

Here you can see Photinia (yellow), American holly (evergreen), and in the foreground some sweetgum leaves (red). You can see how empowering the color coded forest is for distinguishing one species from another. 

Barberry is beautiful as well. If only wildlife could feast on beauty, we'd be all set.

Bush honeysuckle--here photographed mid-month with a background of pink winged euonymus--keeps its leaves longer than other nonnatives. Even after all that wind and rain, it could still be easily spotted, clinging to its leaves. 

A less common nonnative called jetbead (Rhodotypos scandens) has found its way into one area of Herrontown Woods near the little red barn. Like bush honeysuckle, it keeps its leaves late into the fall. Having blended in all summer, it suddenly becomes exposed this time of year, thanks to the color-coding.

Small patches of this unusual native grass, found thus far only in a couple spots along the ridge, are easily spotted now as well. 

You can see the long awn on the seed that gives this grass an attractive look, as if it has fancied itself up with long eyelashes. The coppery background leaf is beech, which will keep its leaves far into the winter, a reminder of November's color-coded artistry.

Past posts about the color-coded forest. 

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.

The Color-Coded Forest, 2010 Edition

This past Saturday, on a classic fall day, I led a walk through Community Park North and Mountain Lakes. This is the time of year when trees and shrubs emerge from their green camouflage to announce their identity in bright colors. Scanning a hillside, one can quickly inventory the woody constituencies it serves. I keep thinking the leaves should have numbers on them--1 for yellow, 2 for orange, 3 for persistent green, etc.

The first photo shows spicebush in yellow, competing with the persistent green of honeysuckle shrubs.

Orange this time of year at Mountain Lakes typically means Asian photinia. It was easier to appreciate their beautiful fall color before it became apparent they were taking over large areas of the park.

This closeup shows the Asian Photinia's obovate leaf (wider towards the tip).

Viburnum dilitatum, which unfortunately is also an invasive, has its own color scheme.

Catalpa, with its big oval leaves, pops up in the forest as it does in people's backyards.

The native hazelnut (note catkins on the left that emerge this time of year) numbers only three or four individuals at Mountain Lakes. We're trying to get more of them growing.

Towards the end of the walk, we stopped by the eponymous lakes, where repair of the dams is coming along nicely.

Several days later, I stopped by to find tree stumps dropped in a heap in the upper lake. These, saved from a small patch of woods that had to be cleared for the contractor's staging area, will be secured to the lake bottom as fish habitat.

Invasive Shrub Color

In fall, the local woods become a color-coded forest, making it easy to tell at a glance what species are growing where. Trying to take at least some advantage of this, I headed out in a car to survey where Asian photinia has invaded our nature preserves. The combination of its yellowish orange color and customary growth form aid in identification from the road.

Here's a new invasion getting going up on Mt. Lucas.

Once Photinia has lost its leaves, the honeysuckles are still green, revealing just how extensive is their invasion of the woods. That they hold their leaves long after native woody plants have dropped theirs suggests that the exotic honeysuckles evolved in a climate with a longer growing season.

The Color-Coded Forest--Nature's Halloween

This time of year, the forest does its own inverted version of Halloween. Rather than obscuring their identity behind costumes, the trees and shrubs reveal their inner identity. As the chlorophyll fades away, the leaves show each species' true colors, which had been there all along, hiding behind the green facade. These bold declarations make it suddenly easy to identify every bush and tree in the forest, near or far. In this photo, a small sweetgum tree shows its yellow, with Photinia behind it tending more towards brown, and the still green bush honeysuckle rising farther back. Flowering dogwood pokes in some burgundy at the top center of the photo.

Some species are tricky, varying their color depending on location. In front of the Princeton Shopping Center (no photo here), the winged euonymus shrubs lining the old gas station site turn brilliant red in full sun. Given less sunlight, as here, growing at the edge of the woods, they turn a modest pink.

In deep shade, their leaves turn white in the fall.

The native euonymus--Hearts-a-Bustin, which is currently extremely rare locally--also can turn this uncanny, ghostly white.

Very dramatic has been the Japanese maples growing next to the Veblen cottage out at Herrontown Woods, whose condition makes it seem to some a haunted house out in the forest.

The color coding can be useful for surveying the extent of species that are proving to be invasive, like this wisteria that's gone rogue around the Veblen House,

as well as for finding rarely occurring natives like this hazelnut, standing out from the surrounding honeysuckles.

Hazelnuts are real loners. There are three scattered specimens at Mountain Lakes, and only two found thus far in Herrontown Woods and vicinity.

Paradox Lost, or, Less Irony in the Woodland Diet

The woodlands of Princeton have long held a paradox. Abundant food in the form of non-native species has gone begging while deer and other wildlife stubbornly maintain their preference for eating natives. The result is a continuing imbalance as the non-natives gain competitive advantage and dominate the understory, forming what is essentially an inedible landscape.

Here's the classic example--a native spicebush with one main trunk large enough to escape the deer, but with any new shoots from the base getting eaten down. Those stubs of new shoots--dense stunted growth reminiscent of witch's broom--are a sign of heavy deer browsing. I hadn't seen anything similar on the nonnative shrubs like winged euonymus, Linden viburnum, privet, and asian photinia.

Last week, though, I saw something that would suggest that the forests grip on paradox is loosening. Here's a typical winged euonymus, showing off its pink in autumn's color-coded forest. If it were in full sun, the fall color would be bright red--thus the common name burning bush. Its ability to successfully invade and dominate in our preserves owes much to its inedibility. The native Euonymus shrub (E. americana) by contrast is a favorite of the deer, and is browsed so thoroughly that it survives only as sprouts here and there on the forest floor, a few inches high.

But what's going on there in the photo, down near the ground, to the left of the trunk?

This nonnative Euonymus has sprouts that look a lot like the browsed sprouts of the native spicebush.

And this invasive Linden Viburnum, cut down by volunteers with the Friends of Herrontown Woods maintaining Autumn Hill Reservation's trails--the new sprouts from the stump are getting browsed by the deer.

These are heartening signs that the deer may be, with an emphasis on "may", expanding their diet to include more invasives. The question for land managers is whether we could help this process along. I recently heard a testimonial that the mint-flavored sprays used on hostas and other plants to discourage deer browsing are actually effective. Perhaps there's a spray that would attract deer to invasives, and begin training them to consume them more. Is food preference learned or instinctive? Does one generation steer the next towards particular foods?

In the meantime, we walk the trails cutting invasives here and there, deer-like, applying the sort of steady browsing pressure on exotics that deer have shown can be so transformative when applied to natives. Normally, without a little dab of glyphosate applied to the cut stump, the shrubs would simply resprout and need to be cut again the next year to keep the trail clear. But if the deer cooperate and browse the resprouts, then some progress towards shifting the balance towards native species could actually be made, even without the stump treatment. If this is over-optimistic, blame it on the uplifting nature of a brisk autumn walk in the woods.

Some other observations during a beautiful fall day in Autumn Hill Reservation:

Slow-mo wrestling match. The bark of a dogwood trunk has completely enveloped a Japanese honeysuckle vine that had grown around it. The vine was squeezing the trunk, and now the trunk is squeezing the vine. I cut the vine at the bottom to improve the dogwood's prospects.

A lone hazelnut, with a lone female flower bud. Autumn color-coding in the forest makes it easier to discover the solitary hazelnut shrubs scattered across Princeton. I know of one in Autumn Hill Reservation, two in Herrontown Woods, and four at Mountain Lakes Preserve.

Photinia Spreading in Princeton's Woodlands

Asian Photinia (Photinia villosa) is a shrub that land managers in the Princeton area are targeting for removal from natural areas. It was sold by Princeton nurseries many decades ago, and has begun invading the local woodlands. Why are we so worried about this shrub that turns a pretty golden color in the fall, with bright red berries?

There are many reasons. For one, the shrub appears not to be edible for wildlife, and 2) the shrub has shown a capacity to out-compete the native shrubs and forbs wildlife do use for food. The spreading monoculture of Photinia in the forest understory is rendering the landscape less and less hospitable for the native diversity we seek to nurture.

An additional reason for focusing on Photinia is that it has yet to spread across New Jersey. Action now in the Princeton area could prevent Photinia from becoming a statewide pest.

This is a typical sight under berry-producing Photinias: a dense clustering of seedlings that leaves little or no room for native species to survive.

Photinia is very easy to spot this time of year. Nearly all native species have already dropped their leaves, making the woods a color coded picture of various invasive species. Honeysuckle shrub leaves are still bright green, Photinia's are golden yellow.

Here's what the woods looks like after a very dense patch of Photinia has been cut and stacked. Not as pretty, to be sure, but it's the first step in restoring a more edible native landscape for wildlife that will also be pleasing to the eye.

Homeowners are encouraged to identify and remove Photinia. Though it may be appealing from the standpoint of its deer resistance, the spread of the berries threatens the ecological balance far beyond the boundaries of one's backyard.

Nature Walk Sunday, Oct. 30, 1-3pm, Herrontown Woods

Fall colors beckon at Herrontown Woods. This Sunday, Oct. 30 at 1pm, I will lead a nature walk entitled "The Color-Coded Forest." This is the time of year when trees slip out of their green anonymity and reveal their identity through color and texture. Meet at the Herrontown Woods parking lot at 600 Snowden Lane, across Snowden from the Smoyer Park entrance. Sturdy shoes are a good idea. Maps at this link.

The Color-Coded Forest

Even this late in the fall, some shrubs and trees announce their identities by the colors of their leaves. They can appear as if a child carefully colored in a number-coded landscape-- oaks and blackhaw Viburnums bronze, the Asian photinia a golden yellow that turned to dark brown in the hard frost. Here is a photo of Pettoranello Gardens, with native oaks bronze above a shrub layer of still-green exotic honeysuckles.

The logic here is that the honeysuckles evolved in a milder climate on another continent, whereas plants native to America adapted to longer winters by dropping their leaves earlier.


Just upstream of Mountain Lakes, the extent of exotic invasive shrubs is especially revealed this time of year, as the vistas open up. The pink of winged Euonymus has just fallen, but the invasion of honeysuckle shrubs can easily be tracked by their persistent green.

Using Flowers To Read a Landscape

Flowers, like fall colors, create a color-coded landscape that can provide a snapshot of trends in plant populations. Blooms have seemed especially abundant this spring, with native dogwoods and Rhododendrons laden with flowers, and now the elderberries, Korean dogwoods and catalpas showing profusion. Catalpas have a knack for sprouting along edges, then spreading their branches of elephant ear leaves (front right in photo), tubular flowers and long seed pods up and over everything else. The branches take interesting, gnarly shapes. When catalpas are in flower, it's easy to notice how they have gained dominance in that prime front-row seating along the edge of this clearing, on waste ground near the Princeton Shopping Center. The opening itself is being taken over by Chinese bushclover, which also tends towards exclusionary dominance.

Nature Walk This Saturday, 10am-noon, Herrontown Woods

For all those who happen to be fancy free and wanting to get out tomorrow, I'll be leading a nature walk through the color-coded forest at Herrontown Woods in the morning. Meet at 10am at the preserve's parking lot, which is at the end of the deadend road opposite the Snowden Lane entrance to Smoyer Park. Included in the walk will be a visit to the grounds of the Veblen Farmstead, and a discussion of recent progress towards preserving and restoring the long-boarded up buildings there.