Hundreds of years of human history haunt Arlington National Cemetery. Atop the hill, alongside a mansion with panoramic views of the national capital below, are the graves of Union dead deliberately dug around what had been General Robert E. Lee’s home. Downhill, in Section 60, where soldiers of the Iraq and Afghanistan wars come to be buried, a wide muddy trench pierced by car tracks is evidence enough of all the transit. Partway in between burns John F. Kennedy’s “eternal flame,” while a famous post oak — named the Arlington oak — hangs overhead.

Like the Arlington oak, many of the cemetery’s eight thousand trees, dotting 652 acres, stand inseparable from those buried beneath. The giant urban oaks, the oldest the three-hundred-year-old white “Taft oak” by the former president’s grave; the cedar of Lebanon honoring the victims of the bombing of the Marine Corps barracks in Beirut in 1983; and the conspicuous flowering dogwoods, the memorial tree most often requested by families, all serve as dynamic headstones for the dead. Here, human history entangles with the roots of trees.

“We probably have the finest collection of old trees that you’ll find in any urban area, certainly the mid-Atlantic,” says Erik Dihle, division chief for grounds, burial operations, and ceremonial support at Arlington National Cemetery. A horticulturist by trade, he estimates the cemetery boasts about six hundred trees over age one hundred, with a sizeable number over two hundred, too.

The age of the trees is all the more remarkable, Dihle says, given the constant digging at the cemetery and the corresponding risk of damage to tree roots. Arlington is home to twenty-eight to thirty funerals each day.

At Arlington, staff block off locations specifically for trees between and among the hundreds of thousands of headstones. But sometimes tree roots outgrow their allocated spaces — a particularly acute problem when it comes to burying the next of kin in sites that have long been undisturbed. Dihle has seen dramatic cases, like that of the widow of a World War II soldier who died fifty years after her husband. In the intervening period, a lovely black cherry tree had grown up and out near the gravesite, the roots spreading laterally underground. “Well, what do we do? We don’t bat an eye. We dig that grave so she can join her husband,” says Dihle.

But, he adds, “We’re going to do the least damage we can to that cherry tree.”

Stephen Van Hoven, the cemetery’s urban forester, describes the desperate measures unleashed in those rare cases where roots infringe upon space needed for a gravesite: how landscapers prune the sprawling roots with a circular blade they pierce through the soil, blindly dragging it along the tree’s extremities, cutting the roots cleanly so they can regenerate.

He tells how landscapers take an extra step with the most vulnerable of trees — angling an “air spade” and blasting soil away supersonically — then making selective, precise root cuts before the gravedigger starts digging. As long as it’s a clean slice, the tree stands a chance. But when a backhoe snags and yanks at the roots, leaving them ragged, the tree is less likely to ever recover.

There are post-traumatic treatments too. Whenever roots threaten to tango with a backhoe, Van Hoven types a note in his master database. After the funeral procession retreats, the endangered trees receive extra watering, fertilization, or treatment with Cambistat, a chemical that stimulates root growth by rerouting the energy a tree typically devotes to stretching its shoots.

All of this doesn’t come up often. With approximately forty-one hundred burials at Arlington National Cemetery each year, the tension arises just twenty-five times or so. In his just over twenty-five years at the cemetery, Dihle says he can count on one hand the number of times he thought a tree was situated too close to a burial plot. And though a Kentucky coffee tree that, until recently, grew in Section 42 is a notable exception, only rarely, Dihle says, do they lose a tree for a grave.