Forgotten Fan Christopher Camastro: Girdling is a forestry practice to kill a tree, in this case to stop their spread into the meadow. That species is a black locust, I can tell by the bark, which is quite invasive. Dead trees left in grassy area provide prime nesting habitat for cavity seeking birds and mammals. I am assuming that was why that tree was girdled, they also used black locust for that path by Aurora Pond because it is hard as a rock and decays slowly.
Please don't assume this was for a noble purpose. This is the Parks Department we're talking about. Especially since I found this tidbit about Black Locust managment: "To kill a clone, cutting alone is ineffective."
Here's the original page: Douglaston, briefly