Trees & Shrubs, so many trees and shrubs

9/13/14 Ashland Hockessin, DE

Overcast, cool

At the end of this trees and shrubs field trip, many of my classmates voiced what we were probably all feeling - our brains were full. It was not quite a three-hour walk, but we had seen a staggering number of plants, learning how to identify them, and in my case, forgetting most of them again. This will be an ongoing learning process, no question.

We actually spent a great deal of time at the beginning of the morning walking around the parking lot where we all met, finding a diverse collection of trees and shrubs, some planted, others that had sprouted naturally. Our instructor, John Harrod, earned his degree in horticulture, and I noticed that our discussion of plants, in addition to considering whether species are native or introduced and how they interact with the rest of the ecosystem, also occasionally touched on common uses for (or reasons to avoid) certain plants.

People have a unique and interesting relationship with wild plants that I haven’t thought too much about. Having only a small yard, which I have still managed to let go wild in a couple ways, I have tended to think of gardens and wild lands as very separate, but all of the plants we favor for landscaping and gardens came from the wild originally, even if they’ve been bred for certain traits since. And many of the plants we introduce for our gardens later escape to change the landscape around us.

Redbud

Early in our morning, before we’d really walked at all, really, we saw two adventive plants, ones that do not typically occur naturally in Delaware any more but are native elsewhere in the country and frequently planted here. Redbud (Cercis canadensis) is a smaller, understory tree in the pea family that moves from purple buds to pink flowers and has a zigzag stem that helps to distinguish it. Nearby we saw Mountain pepperbush (Clethra acuminata), which would typically occur further inland. Delaware is more commonly home to the Coastal pepperbush (Clethra alnifolia), but the hummingbird cultivar of the mountain pepperbush is popular as a landscape plant.

Another plant popular with people, dogwood also occurs naturally throughout the Piedmont, becoming more prevalent as one moves south. Two varieties around the parking lot, Silky dogwood (Cornus amomum) and Flowering dogwood (Cornus florida), helped us see the distinguishing characteristics of the genus. The veins in dogwood leaves grow out from the center, as in any leaf, but turn and run along the edge. The leaves also change color early in the fall, but the burgundy-colored leaves then hang on the branches for some time. Even after the leaves have fallen, dogwood trees have identifying traits. The twigs and some smaller branches show simpotal growth, in which the twig shows distinct curved sections that recur along its length, each bowed area representing a season or two of growth.

We came across two trees that grow fast on disturbed land, taking advantage of the sunlight before other, larger trees shade them out. Sweetgum (Liquidambar styraciflua) is sometimes mistaken for a maple with its five-pointed, serrated star of a leaf, but at least in our area, most people seem to universally know it as the monkey ball tree for the distinctive seed pods it drops. WIthout the seed pods, and if you aren’t sure about the leaves, you can tell a sweetgum from a maple because the sweetgum’s leaves are alternate while the maples are opposite - that is, growing directly across from each other on the twig. We learned in our class that in our area, there are relatively few kinds of trees and shrubs with opposite leaves - maples, ash, dogwood, horse chestnut and viburnums - so it can be a useful place to start an identification.

The Eastern red cedar (Juniperus virginiana) is a conifer that appears early in an area’s succession, like the sweetgum, intolerant of shade, favored by deer and susceptible to fire. That last trait may not matter so much in the relatively wet environment we have, but John mentioned there are many more of these trees in the Southwest now, after the extirpation of bison and a century of fire suppression.

A Blackgum (Nyssa sylvatica) by the shed at the end of the parking lot illustrated another impact the relative amount of sun can have on some trees. In the open, blackgums are dense, a tangle of branches and leaves, but they spread out in the shade of a healthy forest. Oaks, on the other hand, are known as large, spreading trees in the open, but grow straight and tall in the forest, concentrating branches and leaves on the canopy.

Under the blackgum was spicebush (Lindera benzoin), a common shrub in the area. Its name is appropriate, as the plant can be used as an alternative to allspice. Its red berries are high in lipids and valuable for birds beginning their migrations, and the Lenape used the plant for insect repellant and teeth cleaning, according to other teacher naturalists I have followed on Lenape programs. John’s commentary about the spicebush was more ecosystem-focused, though: spicebush has a noticeable yellow fall color, and sometimes a forest understory will be dominated by the hue. This is a sign that the forest is overgrazed by deer, because they will avoid the spicebush until there is nothing else to eat.

We noticed a black walnut (Juglans nigra) next, with its large, pinnately compound leaves and well-known fruit. Someone in the class asked whether it’s true that walnuts poison the soil and competitors, and John shared that they produce a chemical called juglone from their roots that does kill other plants. He also let us know, though, that it’s not an uncommon strategy among plants. Plants that chemically suppress competition are known as allelopathic. The chemicals they produce and the other plants those chemicals affect vary, however.

In the middle of the parking lot is a red maple (Acer rubrum), another familiar tree, but beneath it grew a couple of shrubs of interest. Arrowwood viburnum (Viburnum dentatum) grows in dense thickets and makes for good habitat. Growing next to the viburnum was aromatic sumac (Rhus aromatica), or gro-low sumac, which has leaves of three palmately compound leaflets, and while it is safe to touch, it is related to Poison Ivy, which has similar leaflet configuration. (The leaflets themselves are different shapes, and the leafstalks are all the same length on the sumac.)

Once out of the parking lot and onto the trail by Indian Rill we saw poison ivy (Toxicodendron radicans), which was demonstrating for us how variable it can be. This healthy plant had vined its way up a tree and sent its own branch out from the trunk, so while you could see the characteristically hairy vine, it was not as obvious that the leaves three feet away from the trunk were also actually poison ivy. Poison ivy can grow straight up itself if there’s nothing to climb, as well, so it can appear more shrub-like.

Throughout this first hour of the trip, spent entirely in and around the parking lot, we identified many species, some familiar and some I knew of but couldn’t identify previously. But even with the well-known trees there was often something interesting to learn. I know of sycamores (Platanus occidentalis), for instance, as water-loving, growing and thriving only near streams. But it turns out that while they only sprout naturally in such areas, they are also drought-tolerant, adapted to drop their leaves when it gets too dry. The sycamore we saw this morning was also suffering from a pathogen of some sort that was causing witches’ brooming, the condition of many weak stalks being sent up at the end of branches. Chestnut trees are known as a great loss of the Eastern forest because the chestnut blight prevents nearly all of them from reaching an advanced age. But the famous density of chestnuts in the region may have been the result of colonists’ intense clearing of the land, because the trees grow fast and therefore thrive in disturbed conditions, much like tulip trees, which are everywhere in our area. (Even for tulip trees, though, we got some new information: if you want to see the flowers, which occur in the canopy and are hard to see, they can be seen when crossing the Tyler-McConnell bridge on 141 by the experimental station.) Some of the information was quite practical, and while many in the group may have already known, I was happy to learn you shouldn’t plant silver maples (Acer saccharinum) near homes because they are known for falling apart.

We came across an identification puzzle as we continued on the trail where a green ash (Fraxinus pennsylvanica) and a box elder grew within a couple feet of one another. The box elder is also known as the ashleaf maple (Acer negundo), and they are similar enough John had to stop and compare to distinguish which was which. Both have opposite leaves, so while that’s usually a good way to start an identification, it’s no help telling these two apart. The box elder has fewer leaflets per leaf, usually three to five where the green ash has six or seven. It also has slight teeth on the leaflets, but the green ash leaflets are entire (uninterrupted around the edges). The underside of green ash leaves are soft, almost fuzzy, unlike ashleaf maples. And, this was honestly part of John’s identification, the green ash leaves are a darker green than the ashleaf maple - a trait perhaps only useful when the two trees are growing next to each other. Writing it out it sounds like there are lots of ways to tell the two apart, but it is more a case where you need all those differences to look for because at first glance they appear so similar.

Mapleleaf viburnum

The ashleaf maple is not alone in being one genus showing characteristics of another. Later on the hike we also saw two deceptive viburnums, mapleleaf viburnum (Viburnum acerifolium) and Viburnum prunifolium, the Latin name suggesting cherry-leafed viburnum, although it is commonly called smooth blackhaw. (The mapleleaf viburnum can be distinguished from young maple trees because the viburnum’s leaves are kind of fuzzy. The blackhaw can be seen not to be a cherry tree because its petiole - the section of leafstalk growing from the twig - is flat, which is unusual and not the case with cherry trees.)

Making our way towards the trail leading across Barley Mill Road, we took a short detour to see a thicket of common alder (Alnus serrulata), called smooth alder in my field guide. Alder is an attractive and small tree that people often plant in their yards, but in the moist soil conditions it favors it grows into impressively dense and exclusive thickets that homeowners can spend considerable and repeated times trying to cut back.

Alder thicket

We saw a number of additional trees on our way past the marsh, hearing a bit about them as we went, but it was once we were in the woods along treetop trail that we got an entirely new set of species. With drier soil and more shade, the forest gave us a chance to see oaks, beeches and hickories - the usual dominant species in an older secondary forest in our region - as well as many different shrubs. Beeches and oaks both show leaf persistence, meaning young trees and branches hang on to dead leaves through the winter, and in the forest both also provided examples of how they host other organisms. A white oak (Quercus alba) had flat patches on the bark of its trunk that were evidence of a fungus, and nearby American beech (Fagus grandifolia) trees had epiphages growing from their roots.

White oak with fungus-caused flat patches of bark

Among the shrubs we saw was common witch-hazel (Hamamelis virginiana), which blooms with long yellow flowers in the fall. Further south, a related but distinct species of witch-hazel blooms in the spring. Like jewelweed and bloodroot, witch-hazel seed pods explode when ripe to disperse the seeds.

We continued on, furiously taking notes, starting to give up and relax about not getting everything written down, given how much we were seeing: highbush blueberry; mountain laurel; American Holly; ironwood, with its distinctive muscled trunk. Bending to look at bushes and reaching up to pull down branches to examine trees, scribbling away in our notebooks, my classmates and I had become quite focused on trying to record and absorb the information John was sharing. But as we made our way up the trail, a pileated woodpecker calling seemed to cut through to everyone, and I heard one of my classmates remark it “sounds like the jungle,” which is a pretty good description for the sound and feeling, at least for someone from the Mid-Atlantic with minimal experience of actual jungle.

Slippery elm leaf

There were a couple more trees for us to see on the hillside, although we turned around soon after. John quizzed the class on Slippery elm (Ulmus rubra), and it’s a good thing it wasn’t up to me to answer. But he explained elms are marked by the base of the leaves, where they join the petiole, coming in unevenly. Most leaves have the edges head off from the leafstalk symmetrically, but in elms, one side starts further up the stalk then the other. Slippery elm got its common name from the bark, which slips off and reveals an inner bark that was once chewed or eaten to prevent scurvy.

As we left the forest, we passed an elderberry bush, where we paused to see they have opposite, pinnately compound leaves and that the blue-black berries are tasty when ripe (poisonous when not, and the red ones are always poisonous). Mostly, though, the bush just reminded a number of us about Elderberry beer from Magic Hat, which was perhaps not very educational but a nice moment of class bonding. It also may have been we were getting hungry towards the end of the morning. After a quick walk through the marsh noting burr cucumber, blackhaw, oriental bittersweet, the different jewelweeds (see my last post) and a couple of other plants, we wrapped up in the picnic area talking about other shrubs and trees good for berries: porcelain berry, bayberry and serviceberry, if you can get the fruit before the catbirds.

Species list

Red Oak (Quercus rubra)

Sweetgum (Liquidambar styraciflua)

Black Cherry (Prunus serotina)

Mountain Pepperbush (Clethra acuminata)

Redbud (Cercis canadensis)

Virginia sweetspire (Itea virginica)

Silky Dogwood (Cornus amomum)

Sassafras (Sassafras albidum)

Flowering dogwood (Cornus florida)

Eastern red cedar (Juniperus virginiana)

American strawberry bush (Euonymous americana)

Blackgum (Nyssa sylvatica)

Spicebush (Lindera benzoin)

Black walnut (Juglans nigra)

Red maple (Acer rubrum)

Aromatic sumac (Rhus aromatica)

Arrowwood viburnum (Viburnum dentatum)

Sycamore (Platanus occidentalis)

Tulip tree (Liriodendron tulipifera)

River birch (Betula nigra)

Hemlock (Tsuga canadensis)

Bur oak (Quercus macrocarpa)

grape vine

Common alder (Alnus serrulata)

Silver maple (Acer saccharinum)

Poison ivy (Toxicodendron radicans)

Green ash (Fraxinus pennsylvanica)

Box elder (Acer negundo)

Wineberry (Rubus phoenicolasius)

Raspberry

White oak (Quercus alba)

Black willow (Salix nigra)

Oriental cherry

Privet

Norway maple (Acer platanoides)

American beech (Fagus grandifolia)

Mapleleaf viburnum (Viburnum acerifolium)

Highbush blueberry (Vaccinium corymbosum)

Mountain laurel (Kalmia latifolia)

Witch hazel  (Hamamelis virginiana)

Ironwood (Carpinus caroliniana)

American holly (Ilex americana)

Burning bush (Euonymus atropurpureus)

Slippery elm (Ulmus rubra)

Shagbark hickory (Carya ovata)

Elderberry (Sambucus canadensis)

Chestnut oak (Quercus montana)

Bur cucumber (Sicyos spp.)

Spotted jewelweed (Impatiens capensis)

Pale jewelweed (Impatiens pallida)

Smooth blackhaw (Viburnum prunifolium)

Oriental bittersweet (Celastrus orbiculatus)

Sweetbay Magnolia (Magnolia virginiana)

Sweet birch (Betula lenta)