11.1.2005

Reforesting the Yard

Savaged by insects, ravaged by disease and old age, the elms of Harvard Yard were much diminished by 1990 (see photographs, below), when Michael...

From The November-December 2005 Issue

Savaged by insects, ravaged by disease and old age, the elms of Harvard Yard were much diminished by 1990 (see photographs, below), when Michael Van Valkenburgh Associates began crafting a plan for an arboreal restoration. Van Valkenburgh’s idea, inspired by a lone red oak outside Holworthy Hall, was to replace the Ulmus americana monoculture with a diverse palette of tree species that would be trained to form an elm-like canopy. Fifteen years later, the trees are in late adolescence, and the Yard is a much greener place. Not that lessons weren’t learned along the way, says Van Valkenburgh, the Eliot professor of practice at the Graduate School of Design. Swamp white oaks, “the biggest delightful surprise,” he says, have thrived in the Yard’s heavy soils and areas with poor drainage, as have the pin oaks, which are particularly easy to “limb up” (remove the lowest branches). “Another great triumph is the hybrid hackberry,” which is both tough and “wonderfully elmlike” in shape. Among the biggest disappointments were the tulip poplars, which were fast growing, but couldn’t tolerate the Yard’s compacted soils and an especially cold winter two years ago. The willow oaks, which reach the northern edge of their natural range in Boston, died then, too, and are thought to have been killed by that same mid-winter arctic blast. Outside the main spaces, evergreens have flourished and Van Valkenburgh hopes to add more of these at the margins for their beauty in the winter landscape. Finally, he says, “An old adage proved true: Plant a small tree in a well-prepared hole.” Twelve years later, trees planted at just 3-inch caliper have surpassed trees that went in at two to three times that size.