The Trees of Bryn Mawr

So many magnificent trees thrive on campus. The Bulletin unearths their stories.

The fair green hill

“In the very beginning, Bryn Mawr was favored by its situation, for it stands on the top and extends down the sides of a fair green hill conspicuous for its beauty,” wrote Helen Flexner (Class of 1893) in the January 1908 issue of the Bryn Mawr Alumnae Quarterly.

Flexner went on to describe the architectural beauty of the campus—the “harmonious color and line” of its distinguished buildings—and its educational program and “standard of scholarship.”

Yet throughout, she pays homage as well to the natural beauty of the campus and particularly to the trees of Bryn Mawr—the “great forest trees,” “old apple trees, gnarled chestnuts, and maples that turn golden in the autumn,” and “Japanese cherry trees whose shower of pink blossoms looks so particularly pleasing in the spring time.”

There are 1,298 large trees on the main campus—more than 3,000 when the Graduate School of Social Work and Social Research and Morris Woods are added into the count.

More than 100 years after Flexner’s time, many of the species she so admired are still here. Back then, Asian varieties were much prized, and many such specimens—and not just the cherry trees—made their way to campus early on. When Dawn DiGiovanni, associate director of facilities for grounds who started her career at the U.S. Forestry Service, first arrived on campus, some of those specimens had her stumped.

“We try to mix in the new with the old,” she says, “but the mindset has changed, and people want more native specimens. They survive better. We don’t even want to go too far from Pennsylvania to buy them. We’ve found that trees grown in this area survive in this area. They’re adapted to the local climate, soil type, and wildlife.”

DiGiovanni’s first priority is health and maintenance. “My biggest job is to keep the trees as long as I possibly can. I’m constantly walking campus to monitor how they’re doing.” Still some won’t make it: bad storms, wind shear, rot, and disease can all damage, and eventually kill, a tree.

When a tree is lost, a tree is planted. “When our beautiful old linden had to be taken down, we put in a large-leafed magnolia,” DiGiovanni says. “We replaced a weeping hemlock over at Taylor recently, and when Park Science was being renovated, we transplanted five trees—a dawn redwood, a crepe myrtle, and three Japanese maples—over near Gateway. I try to rescue as many trees as I possibly can.”

the wood wide web

It may seem a romantic notion—that trees communicate with one another—but it turns out that, much like Mawrters, they like to talk.

Over the past few decades, scientists have identified a complex system that facilitates communication among trees in the form of an underground fungal network that connects them to one another. It’s being called the Wood Wide Web.

More formally known as mycorrhizal networks, these webs are formed by a system of mycelia (the threadlike, vegetative part of fungi) that sprawls underground and links the roots of plants. For the fungi in this association, the plants provide food (i.e., carbohydrates). In return, the fungi provide nutrients such as phosphorus and nitrogen, help the trees absorb water, and boost their immune system.

What’s more, these mycorrhizal networks enable trees to network with one another, share water and nutrients, and perhaps send distress signals about drought, disease, or infestation. Some scientists believe that certain hub trees perform a kind of nurturing role, particularly toward younger trees. One study reported that saplings growing in shaded areas received more carbon from donor trees than those with abundant access to sunlight—and hence the ability to photosynthesize.

Plant a Billion Trees

Using data from 1.2 million forest tree plots in more than 70 countries, an international team of scientists recently mapped the Wood Wide Web, and what they found has some serious implications for climate change.

Their research showed that certain types of fungi—those that support carbon stores in the soil—are being replaced by fungi that release carbon into the Earth’s atmosphere.

Significantly, that carbon hog, called ectomycorrhiza (EM) fungi, prefers cooler climes, while its carbon-spewing cousin, arbuscular mycorrhiza (AM) fungi, dominates in tropical regions.

This map of the world’s fungal networks reveals that more than 60 percent of the world’s trees are connected by EM fungi—the good guys that lock up carbon. But with rising temperatures, scientists predict a decline in EM fungi and a consequent flourishing of AM fungi.

While not exactly good news, these results have spurred on reforestation efforts. For one, the UN’s Trillion Tree Campaign has planted, to date, more than 13.6 million trees in a global campaign as a response to climate change.

A Living Campus

For Earth Week 2019, a Class Year Tree Planting event found members of each current class, including McBrides, selecting and planting specimens: cherry trees near the hammocks, crabapples by the Campus Center, and a magnolia next to Radnor.

Rachel Hertzberg ’19, who helped plant the senior class cherry tree, reported that the work, while harder than expected, was worth the effort: “After all the trees were planted,” she blogged, “we talked about coming back to Bryn Mawr someday and seeing how tall they had grown. One day they will be as tall and strong as the trees along Senior Row, but for now they are just barely twigs.”

Like Hertzberg, DiGiovanni looks to the future: She hopes to continue Earth Week class plantings and to do more with the Morris Woods. “A lot of people don’t even know it exists,” she says, “And the trees have been there for so long—they were there when the Vaux family owned the Russian House—and nobody has touched them.”

In the meantime, she’s thrilled by Living Campus, a new interactive map that features the most significant trees on campus along with sculpture and benches (as of this writing, still a work in progress; check back for more!). Available online, the map was developed by a team that included DiGiovanni, Kate Fernandez (Alumnae/i Relations and Development), Alicia Peaker (Library and Information Technology), and Robin Parks and Christian Zavisca (Communications).

For more about its development, see “Living Campus.” To visit, go to digitalscholarship.brynmawr.edu/livingcampus.