Introducing new indices for weed flora studies

ABSTRACT: Field surveys were conducted during 2010-2012 to determine the dominance of weeds in alfalfa fields of Tabriz-Iran. A total 65 weed species belonging to 25 families were recorded. The major families were Asteraceae, Poaceae, and Brassicaceae with 67.54, 65.41, and 41.13FDI (Family Dominance Index), respectively. Bromus tectorum, Crepis sancta, and Tragopogon graminifolius with 30.25, 25.56.and 22.16 RD (Relative Dominance) were the most important weeds in Tabriz alfalfa fields. The objective of this study was to improve the Relative Abundance (RA) and Abundance Index (AI) methods and introducing of Relative Dominance Index (RD) to describe the ranking of weed species, and introducing of FDI (Family Dominance Index) instead of FIV (Family Important Value) for plant family ranking in weed communities. In RD method, we used four quantitative measures including relative frequency, relative uniformity, relative density, and relative coverage. In RA, the mean density had a significant role and in AI, the frequency and uniformity had a higher value than the mean field density. In both of them, the role of vegetation cover percentage has been taken in to consideration. FIV combined of two parameters (relative diversity and elative density), and lake of relative coverage in this index is highlight. In weed flora surveys, in case of some parasitic weeds like dodder, perennial rhizomatous weeds like bindweed, bermudagrass, johnsongrass and etc, winter weeds compare with summer weeds, and grasses compare with broadleaves, only the density could not be sufficient. By adding vegetation coverage to RA and FIV parameters we suggested RD for weed species ranking and FDI for family ranking in weed flora surveys.