Comparing Distance-based and Quadrate-based Methods to Identify Spatial Pattern of Saxaul Haloxylon ammodenderon C.A.Mey (Siah-Kooh Region, Yazd Province)

Investigation of spatial pattern in vegetative populations is an important part of forest ecology. Great areas in central deserts of Iran are covered with saxaul (Haloxylon spp.). Therefore، any research concerning this species has a great importance. Eight distance-based and five quadrate-based methods، including: nearest neighbor، Holgate، Pielou، Eberhardt، Hopkins، Johnson & Zimmer، C، Hines، Green، Morisita، Standardized Morisita، Index of Dispersion and Lioyd were used to determine spatial pattern of this species. Two districts each 30 hectares area which were representative of saxaul populations were selected. Coordinates for all shrubs were determined using distance and azimuth and finally a point map was created in ArcGIS. Then، 35 sample plots (each 0. 1 ha area) overlaid randomly on point map. Centers of these plots were used as random points for distance-based methods. In district I، Johnson and Zimmer، standardized Morisita and Index of dispersion indices showed clumped pattern for saxaul while other indices showed random pattern. In district II، all indices showed clumped pattern except for Johnson and Zimmer index. Overall spatial pattern of saxaul appraised random in flat areas and clumped in mountain-sides. Also T-square index (C) and Holgate were the best distance-based indices to identify pattern. Morisita index was the best one between quadrate-based indices.