Last year a snow plow really hit the big maple tree between the sidewalk and the road very hard. The grand old tree took the hit not seeming to be damaged too much. However, when we called a place that does tree pruning in Brooklyn NY to come out and trim it this summer, it was discovered that the hit by the plow damaged a large section of the layer just under the bark that transports the nutrients the tree needs to live. I thought the whole tree moved the sap. It turns out it is just a thin layer just under the bark that does it.
They told me that a tree can be killed by cutting into the layer around the tree. You essentially cut off its food supply. The plow damaged the layer that carried the nutrients for a large percentage of the tree’s circumference. It just could not keep up. It still had a full set of leaves this year, but they seemed to be smaller than the year before. We thought we were imagining it.
Unfortunately, the old maple was damaged beyond any capacity to repair it. Even heavy pruning could not make up for the nutrient loss. The arborist said it would likely die on its own, but then it would be a risk for toppling over in a storm. We chose to have it cut down. It was sad to see it cut down. However, we kept some slices of the wood to make clocks to give to neighbors who all liked the beauty of the old tree. I had them cut me a piece right across the trunk to make a large wall clock. It was so heavy the wall had to be reinforced to hold the brackets attached to its back. Now we have a small maple growing in its place.