Historic trees are trees that have been a witness to an historic event, or directly associated with a famous historic figure. Perhaps the tree was planted by Johnny Appleseed, or an important treaty was signed under it, or it is the subject of a famous painting, or photo.
Historic trees must be directly associated with a real event or person and are usually marked with a plaque noting the history behind the tree. Legends and apocryphal stories do not qualify.
Historic trees are not trees that are notable simply because of their size or age. Those trees should be listed in the Exceptional Trees category.
Also, "Moon Trees" are not historic per se and should be listed in the Moon Tree category. Trees planted in honor of an historic figure, or as a memorial also will not be considered for this category. There must be a direct association with an historic event or person.
Finally the descendents of historic trees (scion trees) are not eligible.