Wikipedia
A Line Tree is a real estate term that refers to an actual tree which sits in the center line between two separate real properties or on the corner of several properties. Older deeds often refer to these trees as actual landmarks in their written descriptions, i.e.: "a northerly line extending approximately 3000 feet to the old oak...." As surveys and property deeds are updated, these line trees might remain but are often eliminated from written descriptions, to be replaced with modern metal and stone markers, or even longitudinal and latitudinal positions as determined by global positioning satellite systems.
Line Trees were especially important in historical deeds because at one time it was difficult, if not impossible, to carry or create enough long-lasting man-made markers for legal descriptions of land swaps in the wilderness. Historic court battles and documents are replete with the term. See: