A Song of Ice and Fire: Blood and Stone
When the Andals invaded and claimed all of Westeros south of The Neck, nearly all Weirwoods in the south were burned to make way for a new religion, the Faith of the Seven. House Tallystan resisted the Andal offensive, however, remaining one of the last bastions of First Men traditions south of The Neck. The House still holds many First Men traditions dear to them, and chief amongst those is an adherance to the old gods.
Outside of the Isle of Faces, Hammerstone is home to what may be the only weirwood south of the neck. Nestled in a small grove behind the walls of the great castle, the grove is an important place of worship for the lords of Hammerstone, although the First Men traditions gradually wear away with each new generation of Tallystans.