What is IV (Imp. Value) – how was it derived?
We generated importance values (IV) for each species as follows: IV(x) = 100*BA(x) / BA(all species) + 100*NS(x) / NS(all species) where x is a particular species on a plot, BA is basal area, and NS is number of stems (summed for overstory and understory trees). In monotypic stands, the IV would reach the maximum of 200. The IVs were rounded to decimal numbers with one exception. If the IV was greater than zero but less than one, it was assigned to one. This decision was taken since rounding would have falsely turned species-present counties to species-absent counties.
