It is a tree-ring, a type of designed feature found on many Irish estate landscapes, in which a circular enclosure defined by a fosse (a shallow ditch) was planted with trees to create a formal grove. The effect is somewhere between ornament and screen, adding visual punctuation to an estate that was shaped as much for appearance as for agriculture.

The earliest cartographic evidence for this particular feature comes from the first edition of the Ordnance Survey six-inch map, published in 1840, where it appears simply as a small grove of trees. By the time the second edition was produced in 1903, the fosse had become distinct enough to record as a defining feature, giving the enclosure the clear circular outline that links it to several other tree-rings documented across the Dundrum demesne. The feature was later identified in aerial photography, which allowed the earthwork's form to be read as a whole from above in a way that ground-level survey cannot always achieve. That multiple examples of this form survive across the same demesne suggests a deliberate programme of landscape design rather than any incidental planting.