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Getting to the Core of Historic Trees

David Hewitt cores a tree

August 20, 2012

Lora Burns is an adult programs intern at the Academy, assisting with the institution’s Adult Field Studies program and Mega-Bad Movie Nights. Here, Lora recaps an Academy field study at the Woodlands Cemetery in Philadelphia’s University City.

On the morning of June 23, Academy Research Associate in Botany Dr. David Hewitt led a group of explorers through the Woodlands Cemetery in University City, Philadelphia. The group included local tree enthusiasts from as little as two blocks away to environmentalists who had traveled from the Poconos to take part. Everyone was talking about the chance to core a tree, a method by which researchers can gauge tree growth and age without damaging the plant.

The field study started in the Woodlands Mansion with an overview from Jessica Baumert, executive director at the Woodlands Cemetery. Baumert told us that the cemetery, which was founded in 1840, is comprised of 54 acres on the former estate of William Hamilton, who studied at the University of Pennsylvania and developed a passion for botany. Hamilton sought to model the grounds of his estate after the gardens and estates of Europe, and ultimately, he revamped the property to include more than 10,000 plants and trees, many of which he imported from abroad and raised in his greenhouse.

The group made its way outside, and the first tree Hewitt pointed out was a beautiful Caucasian zelkova, which was estimated to be about 90 years old. Hewitt remarked that this zelkova, a deciduous species native to Europe and Asia, was the only tree of its kind in Philadelphia and possibly in the entire region of the Delaware Valley. Hewitt said that this particular tree was likely a root sucker from a zelkova that had stood in its place or nearby up until about 90 years ago; the shoot may have developed at the base of a preexisting tree. The zelkova may have even descended from multiple root suckers that grafted together as they grew.

We paused for a moment at a massive mulberry tree, which had likely seeded in on its own, as mulberries have rarely been planted in the Philadelphia area for well over a century. Hewitt showed us a small hole in the side of the tree and told us that he and another group had cored the mulberry in that exact spot several months earlier. Based on the sample, they determined that the mulberry was likely about 100 years old. Hewitt said he would show us how it was done with another tree.

Hewitt selected a false cypress for the group to core. He gave us a sharp, hollow borer that we took turns twisting into the tree’s base until we hit the middle. The core we had bored was a pencil-sized section, which we then removed from the trunk using an extractor, called a “spoon.” With some help from the group, Hewitt twisted the borer out of the tree and finished the process.

We carefully took our sample in a plastic straw covering back into the mansion to examine its rings under a microscope, along with multiple other core samples that had been collected on a different day. The group left with an appreciation of the various species of extraordinary trees right here in Philadelphia, and we began to feel that every tree is entwined with history—and therefore has its own unique story.

Join the Academy for its next adults-only field study—this time in the New Jersey Pine Barrens. On this September 29 trip, you can help scientists Paul Overbeck and Rich Horwitz with actual Academy research involving the Pinelands’ stream ecology and migratory fish. If you want to catch and release wild fish populations in the area’s lake and river system, this excursion is for you! Click here to learn more about the Academy’s upcoming adult field studies; call 215-299-1060 for more information and to register.