a solitary tree amid remote or wide open landscape. Usually a witness tree has been around for many hundreds of years and is the only witness to the history in that area. This phrase can also refer to other objects that have stood the test of time to be the only witness in an area; for example a witness rock.
While driving through wide open prairie of South Dakota, we stopped to have a picnic under a witness tree.
Bob caught his limit of walleye while sitting on a witness rock at wolverine bend.