This past weekend, we came across the little, round fruits of a sycamore along the banks of the Ohio River on the North Shore of Pittsburgh, next to the Carnegie Science Center. It was pretty windy, but we had some time to kill before meeting my parents inside. The February weather was too nasty for any bird watching except for one lonely duck, so we turned our attention to some trees along the river. They looked as cold as we felt, no leaves for shelter from the gray, stormy sky and the bases of their trunks were unceremoniously caked in mud from the recent flooding from the yet another winter rain storm. Yet, they still stood along the riverbank, maybe hoping that stupid groundhog had been right about warmer days coming.
Now I’m not much good at identifying trees. Sure, I know what an evergreen is, and I can tell the difference between oaks and maples, but I often get confused beyond that. (And to muddy the water even more, there is the rare maple-leaved oak, Quercus acerifolia, of the Ozarks…) However, one of the first trees that Maria had me learn was the sycamore tree, also called the American planetree (Platanus occidentalis). It’s a good one to spot from a distance with its white peeling bark. Beyond that, being a strong, broad tree near water makes it’s a favorite nesting tree for the resurgent bald eagles in our area.
According to our Audubon Field Guide to Trees, this is one of the largest eastern hardwood trees. Once Maria got me to watch for them, they’re not hard to spot. However, from a distance I often confuse the tree with the sweetgum (Liquidambar styraciflua), which is in the witch-hazel family. They both have a round fruit about half an inch smaller than a golf ball. The sycamore’s fruit is an outside of densely-packed hairy tufts attached to nutlets. These balls come apart in winter to disperse the seeds to make new sycamores. Sweetgums have a round fruit the same size but instead the ball is surrounded with sharp points. Not something you’d want to step on in bare feet! Both trees like soil with moisture and can be found near water. They also both act as pioneering species and can be found as the newer inhabitants of recently cleared land.
Up close, the bark is a dead give-away between the two species. Sweetgums have a gray bark with deep ridges. Instead, the sycamore has a unique light brown, green, or gray color that peels off in patches to reveal a smooth, light undercoat. In winter when there aren’t leaves to block your view, the white bark is quite dramatic. It seems that the bark peels because it’s thinner and cracks as the tree grows. But why is it thinner? It doesn’t seem like there is a definite answer, but an article in the NYC Parks dept newsletter, “The Daily Plant” (btw, good pun) offers a few possibilities. It could be to encourage moisture and gas to easily move into and out of the tree. It could also be a way to shed parasites, fungi, and mosses from its trunk. A third possibility is for photosynthesis. According to biologist, John A. Keslick, Jr., sycamores can actually turn sunlight into sugar using only it’s trunk and branches, before leaves have even opened. It doesn’t seem that anyone knows the correct answer to why sycamores have such thin bark, but still interesting to think about.
There’s another tree that confuses me when I see it. The London planetree (Platanus x acerifolia) is a hybrid of the sycamore and the Oriental planetree (Platanus orientalis), and it’s a popular cultivar since it’s more resistant to a fungal disease. It’s often planted in parks, cities, and our front yards, generally places away from the wet stream bottoms where the sycamore is often found. The hybrid’s bark has the same mottled look, with the peeling top layer. The fruit is ball-shaped as well, although it usually has two per stem compared to the sycamore’s one per stem. The hybrid also has differently shaped leaves, can you guess the shape? Hint look at the 2nd part of its scientific name, acerifolia (check out the name also from the maple-leaved oak above). Acers are the maple family which gives you a good idea about the London planetree’s leaves. The sycamore also has lobed simple leaves, meaning that parts of the leaf project out. And “simple” in the case of leaves doesn’t mean easy or humble. Here it means that the leaf is not divided into multiple leaflets all attached to the same stalk (think of the leaves of a black walnut or sumac with their many long, leaflets).
A few fun sycamore tidbits…
Chimney Swifts’ Historic Home
John James Audubon estimated about 9000 swifts had been staying in a hollow sycamore back in 1808 near Louisville, KY. I often forget that there was a time before large houses, factories, and other buildings dominated our North American landscape. Before they had the chimneys to nest in, they used hollowed-out trees. Unfortunately, now with few brick chimneys, the energetic, insect devouring birds are having a harder time finding nesting sites. At least in Pennsylvania, with large trees, like 8-foot-wide sycamores, also harder to come by, conservation efforts have focused on artificial “chimneys” for the swifts. Learn more here!
Though bald eagles will build a nest in just about any tree that is strong enough to hold their impressive stick mansions, sycamores are a frequent favorite since they are often found along rivers—exactly where a fish specialist like bald eagles might like to live! (Well, to clarify, they may be expert fishers, but bald eagles are most interested in whatever dinner is quickest, be it small animals or roadkill!) If you’re a Pittsburgher who fell in love with our pairs of eagles in Hays and Harmar, you probably already noticed that the Harmar pair doesn’t have a camera on their nest currently. The birds recently moved nest sites, from one sycamore to another sycamore about half a mile away.
Just another reminder that there’s cool stuff out there, even if it’s a common tree on a windy February day!
Field Guide to Trees, Eastern Region, North America, National Audubon Society, Alfred A Knopf, 2016, New York