Comparison of Whittaker and Modified-Whittaker plots to estimate species richness in semi-arid grassland and shrubland

Biological diversity and species richness have been declined throughout the world as a result of human activities. Measuring species richness is important in rangeland conservation to evaluate the status and trends of native plant species, detecting non-native species invasion and monitoring rare species. However, heterogeneity in plant distribution makes inventories difficult. In this study two methods of measuring species richness, Whittaker and Modified-Whittaker plots, were compared to see how well they captured the species diversity. This was carried out on grassland and shrubland vegetation types using three replicates in Salook National Park in Esfaraien, Iran. The result of this study showed that there is a significant difference between the two methods in estimating species richness for both vegetation types where greater species richness was found in Modified-Whittaker plot. The regression model for species-area relationship was significant for both methods in each vegetation type but explaining more variation (91%) in Modified-Whittaker plot. There was no significant difference between the two methods according to the sampling time except for 1 m2 sub-plots; however, the Modified-Whittaker plot is more convenient for establishing and measuring in the field.