When Your 188-Year-Old Tree Has Issues... Who You Gonna Call?
When the Haverford College Arboretum staff was concerned about one of their historic trees, they called the Morris Arboretum Urban Forestry Consultants for advice.
The 188-year-old Quercus macrocarpa (bur oak) planted in 1834 is one of Haverford College Arboretum’s unique and revered amenity trees planted as part of English gardener William Carvill’s original landscape design. The massive oak is highly valued and loved by faculty, staff, students, and alumni, and watchful eyes are always focused on this piece of the College’s history. Recently, it was noted that a mass fruiting of fungus was growing at the base.
The Morris Arboretum’s Urban Forestry’s Associate Director of Arboriculture Outreach, Mike LaMana and Urban Forestry Intern Eugenia Warnock conducted a series of visual and physical observations followed by resistance-drill testing of specific areas at the tree’s base. Resistance drilling is used to determine the amount and location of potential internal decay. Significant changes in drilling resistance mark internal cavities and decay, and the resistance is recorded on a graph. The results did not reflect decay and the trunk flare appeared sound for an oak of its age. The species of fungus previously seen at the base of the bur oak was determined to be Grifola frondosa, more commonly known as hen-of-the-woods. It is a common species of fungus which can cause a spongey, white rot condition that could impact structural roots. As this initial review and testing focused only on above ground portions of the tree, the Morris Arboretum staff suggested air excavation be conducted to reveal the condition of the structural roots.
In the field of arboriculture, air excavation utilizes a stream of highly pressurized air which removes layers of soil to expose tree roots for visual inspection without causing harm. With the bur oak, the process began with raking and removing the wood-chip mulch from the surfaces of the root zone to expose the mineral soil beneath. The air excavation, which was also observed by Consulting Arborist John Hosbach, Jr. of Rockwell Associates, was performed by staff from John B. Ward & Co. using the AirSpade tool and an air compressor. Fortunately, the majority of the structural roots observed were found to be in good biological and structural health, free of any signs of decay, and the soil was immediately reapplied to cover the roots. Going forward, the Morris Arboretum staff recommended monitoring the bur oak for signs of new fungal fruiting, observing how the tree responds to winds (i.e. any movement in the bottom ten to fifteen feet of the trunk such as rocking or leaning) and lastly, considering another air excavation assessment in the next three to five years regardless of potential new fungal growth.
These measures, combined with ongoing professional maintenance provided by the Haverford College Arboretum staff, should help assure that this magnificent and historic oak will have a long and useful life.