Classification and determination of environmental factors affecting the distribution of plant communities in Niatak flood spreading area, Zabol

Considering the role and importance of environmental factors in the distribution and spread of vegetation, as well as the existence of wind of 120 days in the Sistan region, and the necessity and importance of vegetation and flood spreading in the region, this research was done to classification and ordination of plant communities in Niatak flood spreading area, Zabol. Vegetation types were determined by Braun-Blanquet's physiognomy-floristic method and cluster analysis based on species composition and soil characteristics were used to classify vegetation. In each plant type, soil and vegetation sampling was done. In the key area of each plant type, 3 transects of 30 m were established, and during each transect, all surface features were measured. In addition, in each transect, soil samples were taken and physical and chemical properties were determined. The results of the preliminary studies obtained from the initial typology by the physiognomy-floristic method in 17 investigated types led to the identification of five plant communities, such as Ta. stricta, Ta. aphylla, Ha. ammodendron, Ha. persicum and Pr. stephaniana. In addition, the classification of vegetation by cluster analysis method based on species composition and soil properties was identified as five and three plant communities, respectively. The ordination results showed that the first axis and the second axis together with 64% of the variance of the distribution of plant communities are the most important axes. Sand percentage has the most positive correlation and absorbable phosphorus (Pav) has the most negative correlation with axis 1. Sodium (Na) and exchange sodium percentage (ESP) have the most positive correlation with axis 2. Redundancy analysis (RDA) biplot shows that characteristics, such as sand and fine sand percentage have a positive correlation with Ta. aphylla and Ha.ammodendron communities, and factors such as Pav, absorbable potassium (Kav), and cation exchange capacity (CEC) cause the distribution of Ta. stricta community in the region. Electrical conductivity (EC) and sodium absorption ratio (SAR) cause the presence of Ta. aphylla and Ha. ammodendron communities. There was a special relationship between different plant communities and soil characteristics.