In American history--specifically that of New England where Wharton's narrative is also set--the elm tree holds much significance. For, in Boston there was a large, tall elm tree which came to be referred to as the Liberty Tree. Under this tree, Boston radicals rallied, calling for home rule and the expulsion of controlling British troops. During the early part of the Revolutionary War, imperial troops cut the tree down, but it did grow back thus becoming the indomitable spirit of the Revolutionaries.
Additionally, the elm tree, which is typically very tall, was in pagan times a tree that was dedicated to the gods and signified wisdom. In Nordic mythology the first woman was believed to have been made from an elm tree. Ethan Frome's physical characteristics, tall, blue-eyed and blonde, suggest the Nordic.
In Chapter II, the elm tree is first mentioned as Ethan and Mattie walk home with arms linked. In a portentous moment, Mattie mentions a sledding couple that nearly killed themselves on the big elm at the bottom of the hill, Ethan assures her that she would be safe if he were steering the sled. This mention early in the narrative of the elm tree which serves as the agent of tragedy indicates Edith Wharton's motif of Determinism, reminiscent of the old Calvinists of New England as the town Starkfield also suggests. Yet, for Wharton, the backdrop of Puritanism is more for atmosphere than for moral instruction as it was for Hawthorne as the environment of Calvinistic determinism is the force that decides men's fates despite the symbolic meaning of the elm as liberty.