|Agate Beach, Grand Marais, Michigan|
Bearing trees are a special kind of witness tree which the surveyors notched, blazed, and scribed in a standard way to facilitate the relocation of the survey corner should the wooden corner post or corner stone be lost or moved. The surveyor was required to note for each bearing tree: 1) its type (~species), 2) its diameter, 3) its distance to the corner, and 4) its azimuth or “bearing” from the corner and hence its applied name. These are the actual data associated with an individual bearing tree that ecologists use. Witness tree is a broader term that includes trees that were marked on line or near the corner, generally without the required distance and bearing notes required of a true bearing tree. Thus true bearing trees, line trees, and generic witness trees were distinguished in the field with appropriate inscriptions (BT, LT, WT respectively) and are distinguished in the notes as well. Bearing trees were required at both the standard corners of the rectangular survey grid and at points on the survey lines where the surveyors were forced to meander around impassable areas such as lakes . The NHIS Bearing Tree Database Contains only records of true bearing trees at the standard survey corners.
For the rest, go to the Minnesota site where I found the information above. Sorry I could not find anything directly bearing on Michigan's current data collection project.