چکیده:
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.
خلاصه ماشینی:
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.
Quantitative analysis, especially quantitative classification methods and ordination techniques, has been widely used to indicate the ecological relationships between vegetation and the environment (Jiang, 1994).
One of the most popular hierarchical divisive clustering techniques in community ecology is the Two- way Indicator Species Analysis (TWINSPAN) (Zhang and Oxley, 1994).
Canonical correspondence analysis (CCA) is introduced as a multivariate extension of weighted averaging ordination, which is a simple method for arranging species along environmental variables (ter Braak, 1987).
The Sørensen index was calculated as:vegetation groups and environmental factors, using DCA and CCA techniques.
The relationship between plant species variation and environmental variation was assessed using canonical correspondence analysis (CCA) (Ter Braak, 1986).
2. Ordination The relationship between plant species variation and environmental variation was assessed using canonical correspondence analysis (CCA).
5. Discussion and conclusion This paper presents a quantitative account of vegetation-environmental factor relationships in the Zirkouh rangelands of Qaen in Iran, using methods of TWINSPAN, DCA and CCA.
Soil moisture content has many effects on the distribution of vegetation groups and plant species.
In general, the most important ecological factors influencing vegetation groups in Zirkouh rangelands are soil texture, EC, soil saturation moisture, soil moisture content, slope and elevation.