The heygi competition index have been widely used in forestry, it was defined as :

Heygi=dj/(di*Lij)

where, di and dj are the diameter for reference tree i and its neighbor tree j, Lij is the distance between tree i and j.

Thus, I would like to ask how much the logical range of this index, and if there have some classification criterions when evaluated the competition status of trees in forestry.