A client was asking me the other day about a couple of ailing sugar maples in front of her house. The sidewalk next to them had been replaced last year, and this year the 14″ caliper trees were showing signs of stress — smaller leaves than usual, and fewer of them. I told her that it was likely the sidewalk work had damaged (or eliminated) significant root mass.
She pointed out that it was the leaves on the yard side of the trees that looked bad. How could that be? Well, many trees actually grow in a spiral fashion. Often, when you see crown problems on one side of a tree you’ll discover a girdling root gripping the trunk on the tree’s opposite side; conversely, if you find root problems on one side of a tree, you might find that foliage and limbs on the opposite side from the roots are showing signs of distress.
A couple of online resources discuss this phenomenon: in the journal Trees; Structure and Function, Hans Kubler writes about the spiral formation of tree grain as a way for the tree to distribute water and carbohydrates evenly through the tree, especially when one area in the root zone is dry.
Larry Gedney, writing in Alaska Science Forum, presents a couple of ideas from colleagues; one, that the Coriolis effect determines a tree’s spiral tendencies, and another, that prevailing wind loads combine with denser south-side foliage to twist a tree.
Hmm. We may never know — perhaps the spiral twist could be chalked up to some factor so far undiscovered — but Professor Kubler’s hypothesis seems to make sense. Looking at these two photos of the Catalpa tree outside the Lincoln, MA Public Library illustrates the plausibility of his concept: a sidewalk and road run right next to the tree, which would limit its rooting space and its ability to take up water on that side.
How might this spiralling tendency be exaggerated for use in a design? I could see a grove — or even just a trio — of trees like this as a setting for a dance performance.