Abundance and dominance are two aspects of the plant species diversity dynamics, often considered interchangeably together with frequency and density to estimate Importance Value Index (IVI). The importance of the use of abundance or dominance for IVI has been explored through an investigation of abundance-dominance directed species dynamics on Gandhamardan hill of western Odisha in the altitudinal range 340-960m. In total 232 plant species were documented. Large number of species have higher abundance guided IVI (A-IVI) compared to dominance guided IVI (D-IVI). Whole vegetation, Tree-1(>15cm GBH), Tree-2(<15cm GBH), Shrub, LTC (Lianas, Twinner, Climber), Herb/Grass and Seedling community, with 93.53%, 81.40%, 89.66%, 100%, 100%, 100% and 99.01% species showing contiguous distribution, respectively, justify this finding. The values of Shannon-Wiener and Simpson’s diversity indices and Evenness index are higher in case of A-IVI compared to D-IVI. The R2 values for A-IVI based Whittaker plot of top twenty species in Tree-2, Shrub, LTC, Herb/Grass and Seedling communities are higher than that of D-IVI based plot except in Tree-1 and Whole vegetation. In these communities the evenness of top twenty species is more expressed by A-IVI than D-IVI. The mean R2 value for A-IVI and D-IVI based plots are 0.64 and 0.56, respectively, indicating that the species evenness is explainable at 64% level by A-IVI, in contrast to 56% level by D-IVI. There are number of species common to the Abundance and Dominance based groups of top twenty five species in each community and this commonness follows the order ‘LTC>Shrub>Seedling>Tree-2>Tree-1>Herb/Grass>Whole vegetation. For A-IVI and D-IVI based groups of top twenty species, the order is ‘Shrub>LTC=Tree-2>Tree-1=Seedling>Herb/Grass>Whole vegetation’. In the two orders, ‘whole vegetation’ is placed at the end with 8% and 45% common species, suggesting that abundance and dominance have high discriminating ability when the whole vegetation is considered as a unit. In this community, nine species are observed to be common amongst top twenty species for A-IVI and D-IVI groups, out of which five are tree species; top twenty species in A-IVI and D-IVI based groups consists of six and sixteen tree species, respectively. Out of top twenty five plant species in whole plant community based on abundance, 19 are herbs/grasses (76%), while on dominance, 24 are trees (96%). Thus, abundance is a factor in vegetation survey, which reveals, promotes and prioritizes communities other than trees. Dominance is justified for tree community as the individuals of tree species are available in higher girths. Therefore, importance value index of species belonging to tree and other communities should be evaluated based on dominance and abundance separately.
