effects of topographical factors on distribution of plant communities in semi-steppe grasslands (case study: ghorkhud region, northern khorasan province, iran)

abstract. the purpose of this study was to investigate the effects of topographical factors on the classification of grassland plant communities in the rangelands of ghorkhud, northern khorasan province, iran. for sampling, land units were specified. a floristic list was prepared using minimal area method based on the nested plot (braun-blanquet method). 116 10m2 furrows were selected. within each furrow, the presence and cover percent were estimated. on the basis of braun-blanquet classification method, cover percent of each species was ranked and the representative matrix was established. vegetation was characterized by the means of braun-blanquet classification method using twinspan level 2. to determine the relationships between vegetation and effective topographic factors, a canonical correspondence analysis (cca) method was used. results showed that the region's vegetation was divided into four plant communities including stipa barbata-festuca ovina, festuca ovina-agropyron trichophorum, stipa hohenackeriana-festuca ovina and agropyron cristatum-stipa barbata, respectively. based on results of cca, the first and second axes (eigenvalue=0.39, 0.29 ) were accounted for 50.2 and 37.7% variations, respectively and totally, the first two axes were accounted as 82% of total variation concerning the environmental factors such as aspect with the first axis and elevation and slope with the second axis.