A Pre-requiem for Viburnums

Ignorance, I suppose, is bliss. If one has never learned of the existence of Arrowwood Viburnums (V. dentatum), which flower along streambanks and in wet woods near the canal,

or the Mapleleaf Viburnums (V. acerifolium) common among the boulders along the Princeton Ridge, then their future absence will go unnoticed. So, is it better to maintain ignorance, or cultivate awareness so that these and other native Viburnums can at least be more consciously treasured during their remaining years in our woodlands?

The Viburnums look perfectly healthy now, but there's a certain leaf beetle coming our way, specifically the Viburnum leaf beetle (Pyrrhalta viburni). First noticed in the U.S. in 1994, it's a species from Europe and Asia that skeletonizes the leaves, exhausting the shrub's energy reserves after several years of defoliation. According to an information sheet prepared by Cornell (http://www.hort.cornell.edu/vlb/), the Arrowwood Viburnums are the most vulnerable. Mapleleaf Viburnums will be slower to succumb, and the other common native, blackhaw Viburnum, may show greater resistance. According to a comment on a Cornell University blog post, the beetle had already shown up at Duke Farms in 2011, just 15 miles north of Princeton.

This arrowwood Viburnum (lighter green foliage below is buttonbush and Virginia sweetspire) has reached ten feet high, along an ephemeral stream in the backyard. The mapleleaf Viburnums don't grow much past four feet in Princeton's woodlands.

As with the flowering dogwoods that have become more rare along the east coast due to an anthracnose disease introduced in the 1970s, the impact may be most felt by migrating birds that depend on the berries to fuel their flight south in the fall.

Knowing of the leaf beetle's imminent arrival at least gives us a chance to appreciate these shrubs while they can still spread a full array of leaves. It also deepens awareness of the importance of those who inspect plant material entering the country.

Towpath Nature Trail Loop in Late Spring

It's good to see a nature path well used and free of obstructions, which is the current state of the nature loop that winds through a wide section of the DR Canal State Park, just up the towpath from Harrison Street. (for posts showing the trail in different seasons, type the keyword "loop" into the searchbox for this blog) The whole area was being mowed until I convinced the state park folks to let the wildflowers grow, back in 2006. They then created a nature trail loop through the open woodland landscape between the canal and Carnegie Lake, and maintained it beautifully until a couple years ago, when they asked Princeton University to take over the mowing of the trail. PU actually owns the land, even though it's part of the state park, and they finally agreed to maintain the trail. I was out there with a chainsaw, doing what I could during the transition, given the tendency of trees to fall across the path.

As of June 2, the path was looking great, possibly due to university care, but thus far maintained more by foot traffic than anything else. Here's a plant-person's take on the interplay of native and non-native species to be found along the way.

Common milkweed is one of the few natives that can compete with the highly invasive mugwort. Both spread underground.

Bittersweet nightshade blooming on the shore of Lake Carnegie.

Blackberry flowers, with the green beginnings of the berry emerging as the petals fall.

Here, for comparison, is multflora rose, a nonnative shrub, more common than blackberry, with larger clusters of flowers, curved thorns, and lacking the linear grooves on the blackberry's stem.

Orchard grass blooming. Non-native but not very aggressive, often found as a single, erect clump here and there.

The orange-tinted remains of last year's broomsedge, which is not a sedge but instead a native grass, here lining the trail. Like other native prairie grasses, broomsedge is adapted for periodic fire, which its persistent stems encourage. A field of broomsedge can be very pretty after it turns color in the fall, though farmers associate it with poor soil.

Learn to recognize poison ivy in all its forms. It often looks glossier than other plants with three leaflets, reddish when young, with traces of red remaining in the stem later on. The pair of lower leaflets often show a "thumb" along the lower edge, a subtle version of which can be seen here in the mature leaf. People are surprised to learn that vines like poison ivy only bloom when they find a tree to climb up.

This is a hopeful sight for any lover of Joe-Pye-Weed, which will ornament the trail later in the summer in the patchwork of shade and sun beneath the scattered trees.

One of the dogbanes, which like milkweed will exude milky sap when you pluck a leaf.

Look closely at the photo below of Viburnum shrubs, and you'll see that the leaves of the one on the left are more distinctly toothed. That's the native arrowwood Viburnum (V. dentatum), while the shrub on the right is linden viburnum (V. dilatatum), a nonnative that has become surprisingly invasive in local preserves. As often happens, the native is seldom encountered, while the non-native is common, most likely due to deer preferring to eat natives.

If you know your plants, then you'll look at this small clump of leaves and feel happiness at all the yellow, cone-shaped flowers cutleaf coneflowers will produce later in the summer.

And even happier when you find a large congregation of cutleaf coneflower rising like a very slow-motion firework that will explode in color a month from now.

But knowing plants also allows you to foresee less auspicious trends, as the porcelainberry (NJ's kudzu wannabe) begins to grow up and over most everything in a smothering embrace. Persistent emails have yet to convince the university of the need to mow the field once a year in late winter, like state parks used to do. Annual mowing is the key to sustaining this open woodland of scattered trees lording over a vista of wildflowers.

There's a little parking just across the Harrison Street bridge. The trail loop is on the Princeton side of the towpath, just in from Harrison, with what looks like a birdhouse at the trailhead. Returning via the canal, I happened to see this yellow iris (I. pseudacorus), framed in the trees' reflection in the canal. The native iris sometimes seen is blue.

Red Berries in the Forest

There are lots of red berries in the woods right now. Consistent summer rains have made for a bumper crop. Here's some help in distinguishing between them all.

Asian photinia (Photinia villosa) is a robust exotic shrub that reaches twenty feet high and can be found singly or in dense stands. The leaves are "obovate", meaning they are often widest towards the tip. The berries are in terminal clusters.

Winterberry (Ilex vericillata) is a native shrub typically found in lowlands. At Mountain Lakes, its leaves are still showing a little green, and the berries are tight against the stem, rather than in terminal clusters.

Swamp rose (Rosa palustris) is another native, also found in lowlands. Its hips are larger than those of the exotic multiflora rose, and its thorns are not curved backwards like the fishhook-shaped thorns of multiflora rose. Also, the thorns of swamp rose are more dense towards the base--the opposite pattern found on multiflora.

I'm calling this Viburnum dilitatum, the linden Viburnum--an exotic shrub that is proving fairly invasive. It's leaves could be mistaken for the native Viburnum dentatum, but are wavier and less toothed along the edges.

September Nature Vignettes

 Encounters with nature and sustainability around Princeton in September.

One of my favorite corners in Princeton is near the middle school, at Guyot and Ewing. It's a small enclave, a triangle of sense, where the yards and the roofs of houses actually perform work, growing food and gathering energy. On one side is a small house with a small yard that the owner has turned into an orchard and vineyard, as might be more often encountered in Italy. 

Nearby is a house whose south-facing roof has been completely covered with solar panels for 20 years. 

When a house was torn down recently at the corner, I feared it would be replaced with something huge and unattractive, 

but instead, a one-story house with extra thick insulated walls and solar panels and interesting design is taking form. It was a real surprise to see a one-story house being replaced with another one-story house that is sensitive to the history of the site and seeking to fit in, while showing off a modern design that seeks to minimize energy consumption.

They even have a sign on the fence describing the project and what was there back in Princeton's agrarian era. 

Blooming along the fenceline next to the house are sunflowers and autumn clematis vine. Gorgeous as they are, thankfully generating color at a time when most flowers are spent, they are best not planted in a garden unless where the spread of their roots is limited by a house or pavement. Otherwise, given abundant sun to power their aggressively spreading roots, they will take over your garden.

Another common encounter in September is with late-flowering thoroughwort, which spreads not by roots but by seed. It can be weedy but also lovely and even elegant at times, and is great for pollinators. I couldn't get myself to pull this one out in our backyard, even though it has completely taken over a garden path.

At the Barden in Herrontown Woods, they are so plentiful that we don't feel too bad pulling out the ones that lean over the pathways.

The fight against invasive species has the side benefit of taking me to areas of a nature preserve where I wouldn't otherwise go. Recently, it led me to a patch of native diversity in Herrotown Woods that I hadn't noticed before.

Here is obedient plant, 

New York ironweed, 

and the post-flowering look of water hemlock. 

One of my favorite garden plants this time of year is stonecrop "Autumn Joy." 

A sedum, its disks of flowers go through a gradual enrichment of color from green to pink to deepening shades of red, then finally chocolate. Nonnative but noninvasive, it has the added benefit of being popular with pollinators. 

Pawpaw trees are becoming more common in Princeton. The patches planted in Herrontown Woods have yet to bear, but this one in my backyard reflects a growing interest in this unusual species native to the north yet with a tropical taste.

Native persimmons, likely once common in Princeton but often shaded out by larger trees in recent decades, are an attractive smaller tree that might actually bear edible fruit if you happen to get a female and harvest it just at the right time.

If the drought hasn't made the berries too dry, these blackhaw berries could make for some good picking after they darken. Blackhaw viburnum, Viburnum prunifolium, is the most common native viburnum in our woodlands.

Less generating of anticipation are the fruits of a female ginkgo tree, encountered growing near the Princeton Junction train station. The fruits have such an unappealing smell that people try to avoid planting female trees. 

Among inedible fruits, I call this the incredible shrinking pokeweed, because it initially grew to be seven feet tall--way too big to grow along a busy street. So I cut it down midsummer and thought that was that, only to have it sprout back as a smaller version of itself. You could try this technique with a number of perennial native wildflowers that get too tall for people's taste. Cut them down partway through the summer, then let them grow back in a miniature form. 

Though it dies down to the ground each year like a perennial wildflower, pokeweed looks more like a miniature tree, and in fact it has a close relative in Argentina. The ombu grows to the size of a large tree, yet lacks xylem. 

This shrub, too, needs to be cut back. It's an oak-leafed hydrangea I planted long ago in a little raingarden at the front of the Whole Earth Center. The landlord the store leases from must have a new landscape firm taking care of the grounds, because I stopped by recently to find that my native shrubs have been trimmed to look like bowling balls. Funny to see a native shrub and wildflower planting getting the bowling ball treatment. I'll have to take some loppers to restore light to the window next time I stop by to buy some beets or delicious bread.

Sometimes, frequently in fact, I find myself wishing I wasn't right. Take this ash tree for instance, planted by the people who landscaped the new parking lot that Westminster Choir College built about ten years ago. I told them they needed to remove the ash trees they had just planted. The emerald ash borers are coming, and the trees won't survive. They left the trees in. The trees survived longer than I expected, but are finally succumbing. 

Actually, if you were trying to make Princeton sustainable, you might want to "farm" Princeton with smaller, short-lived trees that provide shade but are less expensive to take down. The above ground portions could be periodically harvested as a local energy source, and the roots left in the ground would sequester carbon. Trees are a source of solar energy, since they draw their carbon not from underground but from the atmosphere all around them. Thus, no net increase in atmospheric carbon from their combustion.

The landscaping for the parking lot also called for a raingarden to be planted here in this hollow. After being planted, the young river birch trees soon began to wither for lack of water. I assumed they would die, and that the raingarden would be poorly maintained and ultimately be mowed down. I was only half right. The river birch trees survived.

Here's what looks like a bright white flower that isn't. The white is the puffy seeds that give the plant its name. The flower seems not to open but remain in what looks like a bud stage. It's pilewort, a native weed that can reach seven feet tall.

Finally, a grass encountered in fields and local rights of way. When its flowers open and display their golden anthers, this native member of the tallgrass prairies can be eye-catching. Indian grass, Sorghastrum nutans, reminds me of the midwest prairies I used to help manage, and a time long ago when prairie openings were common in the east as well.

Shrubs and Vines to Cut Back Along Nature Trails

Without volunteers wielding clippers and loppers, most trails in Princeton would quickly become overgrown. Some preserves, like Mountain Lakes, Herrontown Woods and Autumn Hill Reservation, have more organized maintenance, but in some others it's catch as catch can. In May and June, that first flush of growth begins reaching out over trails, and so a pair of clippers is handy to keep in the back pocket during a hike. Cutting back anything that overhangs a trail is useful, but as a botanist I'm also identifying as I go along. Most of the shrubs that grow out into trails are invasive species that we'd want to cut wherever they are growing, but especially along trails. There are also some natives, but I'll start with the non-natives, which are so numerous mostly because the deer won't eat them. 

Privet -- A shrub that people plant as hedges, but which has spread into nature preserves, establishing dense stands. In low, wet, shaded areas, there can be thousands and thousands of these, claiming all the space. Most don't bloom because they are too shaded.

Here's a typical branch of privet growing out over a trail. 

Linden Viburnum has become highly invasive, forming dense stands. It has attractive flowers and fall color, but is just way too aggressive. It looks a lot like the native arrowwood Viburnum (V. dentatum), which is relatively rare and has more deeply toothed leaves. 

We commonly call this shrub Photinia, after its latin name. You can identify it by its distinctive obovate leaves, meaning the leaf is wider towards the tip. Names can get complicated in botany. The common name, which I just learned, is Christmas berry. The latin name was Photinia villosa, but that got changed to Pourthiaea villosa. Can you say "Pourthiaea"? Neither can I. In any case, it is another way-too aggressive nonnative shrub that we cut back or down.

This shrub, winged Euonymus, is super easy to identify. Just look for the "wings" on the stem (those brown ribs that run along the stem). It, too, is a nonnative that forms dense stands and often obscures what would otherwise be lovely vistas from the trail. If you see a nice vista from the trail, oftentimes it's because we've been cutting these shrubs down to open up the view. 

A common story about native plants in the wild: there's a native Euonymus, called Hearts-a-Bustin', but it's rarely seen because the deer love to eat it. We've nurtured a few specimens of it to show off at the Barden.

Bush honeysuckle -- Honeysuckle comes in the form of a vine (Japanese honeysuckle) and several species of shrub. it is frequently found along the edges of people's backyards--a sort of default vegetation that moves in on its own. It can also be numerous in some of Princeton's preserves.

Wineberry is an asian species of bramble with distinctively hairy reddish stems. It has tasty berries, but we often cut or pull it, given its lanky, thorny growth.

Autumn olive has a distinctive silver sheen on the underside of the leaves. While many invasive shrubs thrive in shade, autumn olive prefers sun, and so is infrequently encountered along our wooded trails.

Multiflora rose is an introduced species that has made many a forest impenetrable with its curved "fishhook" thorns. Multiflora means many flowers clustered together, as opposed to the single flowers that many roses have. We definitely cut this one back, or down to the ground, to keep hikers from getting snagged. 

Our native roses--at Herrontown Woods, that would be the very rarely encountered swamp rose--have single pink flowers, as opposed to the multiflora's clusters of white.

If you forgot your clippers, it's possible to avoid the thorns while carefully bending a young sprig like this one back on itself with your fingers until it snaps.

Two nonnative vines we pull out along trails are the Japanese honeysuckle 

and oriental bittersweet. Both are easily pulled out. For more success in pulling them out, grab low and pull slow. 

There are native versions of vine honeysuckle and bittersweet, but never encountered, as far as I know, in Herrontown Woods.

A common native along trails is sweetgum, which can grow into a statuesque tree but which we tend to cut or pull along trails, since its seedlings are so numerous.

The most common native shrub is blackhaw Viburnum, which has tasty berries in the fall. Sometimes it can be distinguished from other shrubs by its pairs of tiny leaves tucked in among the larger leaves, growing tight against the stems.

Another common native shrub is the spicebush, which has very fragrant, citrony leaves. 

Hickories are common as well. This is a photo of one leaf with five leaflets. 

I always feel some remorse while cutting native species back, but it has to be done if the trails are to remain clear.

Related post: Portrait of Sidewalk Neglect -- A post about plants that are growing over a neglected sidewalk.