CCA application for vegetation-environment relationships evaluation in arid environments (southern Khorasan rangelands).

Abstract

This paper presents a quantitative account of vegetation–environmental factor relationships in arid rangelands. Vegetation cover was recorded using Braun-Blanquet combined abundance-cover scale in each quadrat. Within each quadrat, one profile was dug and soil samples being taken at 0-20cm and 20-100cm depths. Under study physicalchemical characteristics included texture, lime, organic matter, soil moisture content, saturation moisture, EC and pH. Five vegetation groups were identified after the application of Two Way Indicator Species Analysis (TWINSPAN) and Detrended Correspondence Analysis (DCA) methods including: A: Salsola richteri-Aelorupes littoralis; B: Zygophyllum eurypterum-Haloxylon ammodendron; C: Artemisia sieberi-Zygophyllum eurypterum; D: Ammodendron persicum-Stipagrostis pennata; E: Artemisia aucheri-Amygdalus scoparia. Canonical Correspondence Analysis (CCA) was used in a direct gradient analysis of the vegetation with the environmental variables. The results of CCA showed that first axis represented a landscape and edaphic gradient; it was positively correlated to soil texture and soil saturation moisture; it was negatively correlated with elevation and slope. The second axis represented mainly a soil moisture-salinity gradient; it was positively correlated with EC and soil moisture content. The results showed that those environmental factors that affect water availability were the most effective environmental factors in the distribution of vegetation groups in arid rangelands.