The Effects of Plot Shape and Size on Determining the Distribution Pattern of Astragalus verus Olivier

The distribution pattern of plants is an important characteristic of plant communities, being of critical importance in ecological studies and sampling plans. This study was designed to investigate the efficiency of different shapes and sizes of quadrants to delineate the spatial patterns of Astragalus verus Olivier by using dispersion indices. At Mayan Rangeland (Khorasan Razavi), a digital camera and R software were used to locate the coordinates of individual plants and to demarcate the boundary of the study area. We used plots of different shapes, square, wide rectangular and long rectangular, with the areas of 1, 2, 4, and 8 m2, for a total of 12 combinations of shapes and sizes. The distribution indices used included Green, Lioyd, Morisita, and the Standardized Index of Morisita. The results of the study showed that the standard Morisita's index and Morisita’s index had the same distribution patterns in all shapes and sizes of plots. These two indices were not affected by plot size and shape in displaying the distribution pattern. The current study alsoshowed that Morisita’s and standard Morisita’s indices were more precise in comporison with Green and Lioyd indeces.