“Ooh, pretty.” That’s what most visitors to Tyler Arboretum say about the three acres of grasslands that come to life every summer. Few realize, though, that Pink Hill is a serpentine barren millions of years old, and the last of its kind in Delaware County. Enter Swarthmore College’s Roger Latham, an ecologist and conservation
biologist dedicated to preserving Pink Hill.
MLT: So, a serpentine barren is a winding stretch of fallow land?
RL: Quite the opposite. It’s filled with rare and endangered species of plants.
“Serpentine” is the layer of earth that was created half a billion years ago. It was the seafloor, and then the continents collided and it rose, filling with huge rocks and a mountainous surface. About 100 million years of erosion did away with that surface, exposing the soil beneath it. That soil is incredibly unique, as is what grows on it.
MLT: And the soil only exists in certain areas.
RL: Serpentine barrens are rare in the eastern United States, and most are located in Southeastern Pennsylvania. They are a point of pride. In my world, the serpentine barren is the equivalent of the Liberty Bell—but much, much older. John Bartram, the first American-born botanist, wrote about them, and they’ve fascinated people ever since.
MLT: How big was Pink Hill originally?
RL: We don’t know. The first aerial photos were taken in 1937. From those, we determined that Pink Hill was about 14 acres. It has shrunk to three. There were 17 barrens in Chester County, and now there are nine or 10. There were 11 barrens in Delaware County, and Pink Hill is the only one left. There are none in Montgomery County.
MLT: If barrens survived for millennia, why are they in danger?
RL: Two reasons: development and trees. The areas were not protected, so structures were built on them. As for trees, they lay down huge amounts of dead leaves that turn into humus. That allows more trees to grow, invading the barrens and crowding out their native plants. Also, tree shade is bad for the barren. Its plants need sunlight.
MLT: What’s your goal for Pink Hill?
RL: We want to preserve its three acres, and then expand it back to 12 acres—not just the barren itself, but also to protect the rare butterflies and birds that need it. We do that by changing the soil to make it a good habitat for plants that were native to the barren. We started in November by cutting down most of the trees that have come into the barren.
MLT: You’re killing trees?
RL: Yep. Trees belong in the forest. They’re not endangered. The barren is. —Melissa Jacobs