Visiting the Arboretum: All members and visitors need to make a reservation in advance of their visit to the Minnesota Landscape Arboretum. We hope to see you soon!
By Liz Potasek
There was something special about the large bur oak that stood near the entrance to the Wilson Rose Garden. With it’s large, twisting branches and thick trunk, the tree preceded the Minnesota Landscape Arboretum’s founding in 1958, and the Arboretum grew up around it.
Unfortunately, the tree contracted Bur Oak Blight, and it was also impacted by road and garden construction, two-lined chestnut borer, and Armillaria root rot, a common soil-borne fungus, says Erin Buchholz, Arboretum integrated pest management specialist. “The combination of environmental and pest issues proved too much for our beloved tree,” she adds.
In August of 2020, a tree company was hired to cut the crown of the tree, leaving the trunk, as Arboretum staff explored the best way to honor this treasured member of our community in the long term.
On Wednesday, with guidance from Dan Griffin, a University of Minnesota dendrochronologist (a researcher who studies tree rings), Arboretum staff took down the trunk, which was starting to rot, and carefully carved a few sections from the tree to use for research and display.
The tree’s trunk tells its story. In addition to estimating its age by counting its rings, and finding scars that indicate damage to the trunk and marks where the tree was treated for bur oak blight, scientists can look at its growth patterns to learn more about the natural history of the area, noting wet periods as well as drought conditions. They can also make comparisons with other trees they’ve studied throughout the area to tell a broader story.
“It’s not as old as I expected,” Griffin says, after an initial look at the rings. “One of the things we’re trying to understand about bur oaks is sometimes they grow like weeds and sometimes they grow slow.” Some of the oldest trees aren’t necessarily the biggest, he adds, noting that they can grow slowly, suppressed below the canopy. To determine the exact age of the tree, Griffin will study the rings using a microscope to count rings during its first years of life.
While some of the trunk will be studied by Griffin, the Arboretum is keeping a cross-section of the trunk for display. The cross-section or “cookie” will be air-dried indoors with metal bands to minimize cracking for the next 1-2 years. A few wedges of the trunk were also preserved with the intention of drying them and using them for educational purposes and classes.