Quickbeam's "people" are rowan trees. Our word rowan is ultimately derived from Old Norse, but in Old English the tree was called cwic-beam. In that case, "cwic" means "live, living," as in the phrase "the quick and the dead." Whatever. The startling thing is, "Quickbeam" is just the modern spelling of cwic-beam. So the rowan-like ent is named "rowan" in OE. One more example of how Tolkien used his academic specialty in his story-telling, and one more example of the unusual depth of his created world.
I first read LOTR over fifty years ago, and I'm still finding new details in it, like this ent whose name is an OE-based pun.