Journal of Rangeland Science (JRS) Evaluation of Distance and Quadratic Indices for Determination of Plant Species Distribution Pattern in Khoosef Rangelands, Birjand, Iran Volume 8 (2018) Issue 4, October 2018 2024 01 30 Evaluation of Distance and Quadratic Indices for Determination of Plant Species Distribution Pattern in Khoosef Rangelands, Birjand, Iran EN Reza Yari Assist. Prof., Faculty of Agriculture, University of Sarayan, Birjand, Iran. Atefeh Gholami PhD student, Institute of Atmospheric Physics, University of Chinese Academy of Sciences Masoud Jafari Shalamzari University of Chinese Academy of Sciences, Institute of Remote Sensing and Digital Earth (RADI), China, Beijing Gholam Ali Heshmati Range and Watershed management Faculty, Agriculture and Natural Resource University of Gorgan, IRAN. Journal Article 2024 01 30 One of the major issues examined in the quantitative ecology is the spatial distribution pattern of plant species. Knowledge of the spatial distribution patterns is essential to measure the level of uniformity in the surrounding environment, plant reproduction, and distribution of the seedlings, plant behavioral patterns, coexistence, allelopathic relations, and competition. Therefore, the aim of the present research is to select suitable indicators to determine the spatial distribution of three plant species namely Seidlitzia rosmarinus, Cornulaca monacantha and Stipagrostis plumosa and to evaluate their accuracy in arid and semi-arid rangelands of Birjand. Sampling was taken in the key area of ​​each site with four transects of 100 m using quadrates (with their size proportional to the vegetative form of the plant species) by a stratified random sampling technique in 2014-2015. At each point, the distance from the nearest neighbors, the closest species and species richness were recorded. S. plumosa and S. rosmarinus produced the largest and smallest values as 6.6 and 0.24 plant/m2, respectively. Our results suggested that S. rosmarinus, C. monacantha and S. plumosa follow regular and uniform distribution patterns. The results of the statistical analysis also showed the positive binomial distribution for these species, which further confirm our finding. In total, it has been found that quadratic indicators provide more accurate results regarding plant species distribution patterns as compared with the distance indicators.