Contributed by Daniel Sax, 2018-19 Walter W. Root Endowed Arborist Intern

It is with a heavy heart that the Morris Arboretum’s Urban Forestry team must announce an imminent loss to the University of Pennsylvania tree-scape. After much scrutiny, it has been decided that one of campus’s most distinguished Japanese zelkova (Zelkova serrata) specimens will be pruned to its base this coming spring. The tree in question was planted in 1971 as part of John Collins’ firm, Collins and DuTots’, design for the Hi –Rise, or ‘Superblock,’ residential development complex from 38th to 40th Street Walnut to Spruce. Collins –known locally for his work on the Schuylkill River Park project as well as the creation of Temple University’s Landscape Architecture and Horticulture programs–was renowned for his ability to integrate place and community through landscape design. It comes as no surprise, then that his choice to highlight the zelkova as a focal point of the College House green has been so successful; not only for the experience of visitors, but for the tree itself. Since its planting, the zelkova has thrived: growing to a trunk diameter of 33 inches and asserting itself as a dominant presence both when in leaf and during the winter months. Recent years have proven difficult for the zelkova, however, and, regardless of its impressive stature and historical pedigree, the tree has started to present structural red flags that cannot be ignored. For safety reasons, the canopy of the zelkova will be removed during spring break when fewer people are on campus.

 
The original landscape planting plan is shown above. The zelkova that is being removed is shown in green. On the left is the original corresponding planting plan.

The landscape architect, John Collins
 

Due to the constant pressure of torsional wind load –powerful gusts that twist the tree and its branches –significant cracks have formed along the zelkova’s primary branch unions. Although trees can typically adapt to such forces, this specimen has failed to do so, and the observed fractures have spread downwards towards the base of the trunk. In addition to these signs of stress, subsidence cracks –long fissures that run through the center of lateral branches –riddle the tree’s crown and have brought the stability of the zelkova’s branches into question. In short, the risk to students, faculty, staff, and Penn Arboretum visitors is too great to leave this heritage tree in its current state; however, there is still hope for its future.

Rejuvenation is a common tactic employed by urban foresters to mitigate risk to the public without sacrificing the totality of ecological services that a long-lived tree provides. When reduced to its base, the zelkova will respond with rapid shoot growth to compensate for the loss of its crown. As these pseudo-saplings develop, the most vibrant members will be selected by Penn’s consulting arborists and allowed to grow without competition. In time, an entire new canopy will emerge, once again providing beauty and shade to the Gregory College House. In the meantime, be sure to stop by to watch as this experiment in arboriculture begins!