Extended summed dominace ratio, E-SDR, for comparison of grassland vegetation

Abstract

The summed dominance ratio, SDR, has been used to explain the species dominance in grassland community studies. The SDR_2 for a given species is defined as the average of the following two quantities : (1) relative coverage and (2) relative plant height of each species to the respective maximum values in one community. Then, the SDR_2 takes a value between 100 and 0. Since this index cannot be used for comparing the vegetation among various communities, a new index, the extended summed dominance ratio, E-SDR_2, was developed and described in this paper. In the new index, the range for the selection of the maximum coverage or height in calculating the SDR_2 is extended from one community to all the related communities. We selected, as an example, a comparison between the E-SDR_2 and the SDR_2 calculated using date which had been accumulated in a semi-natural grassland with four different treatments in the Tohoku Area for 11 years. All the values of the SDR_2 for Miscanthus sinensis were 100 in every treatment in all the years, which the values of the E -SDR_2 for M. sinensis varied with the treatments or years and all were lower than 100. We concluded that the E-SDR was the available index for comparing the vegeattion among various communities which were calculated from the plural quantities like the SDR.