EXTENDED ABSTRACT

Background and Objectives: Vegetation distribution in arid and semi-arid ecosystems is strongly influenced by soil physical and chemical properties, and variations in these properties can lead to the development of distinct plant communities even within relatively small spatial scales. Understanding the edaphic factors controlling vegetation distribution is essential for elucidating plant–soil relationships, managing desert ecosystems, and planning restoration and conservation programs. The Biabanak area, located in Sorkheh County, Semnan Province, Iran, represents a typical desert ecosystem that supports diverse vegetation types despite relatively uniform climatic conditions. This study aimed to investigate the relationships between vegetation types and soil physical and chemical characteristics and to identify the most important soil factors influencing vegetation differentiation in the Biabanak region.

Materials and Methods: The study was conducted within an area of approximately 2,000 ha. Vegetation sampling was carried out using a systematic-random approach, and a total of 31 plots (15 × 15 m) were established. Based on the dominant species, plots were classified into seven vegetation types, including Artemisia, Ephedra, Tamarix, Salsola, Suaeda, Halocnemum, and unvegetated sites (control). Soil samples were collected from the 0–15 cm depth in each plot. Several soil physical and chemical properties, including soil texture, bulk density, pH, electrical conductivity (EC), organic carbon, phosphorus, potassium, sodium, lime, and gypsum contents, were measured. Canonical Correspondence Analysis (CCA) was employed to examine relationships between vegetation types and environmental variables.

Results: Significant differences were observed among vegetation types for many soil physical and chemical properties. Sand content ranged from 53% to 69%, silt from 17% to 26%, and clay from 10% to 21%. Soil pH, electrical conductivity, organic matter, sodium, potassium, phosphorus, lime, and gypsum contents also differed significantly among vegetation types. The CCA results indicated that the first ordination axis was positively correlated with gypsum, sodium, electrical conductivity, and silt content, while showing a negative correlation with sand content. The second axis was primarily associated with soil lime content, whereas the third axis was mainly related to soil potassium. Ordination patterns revealed that the Halocnemum vegetation type was associated with soils characterized by the highest salinity and gypsum content, followed by the Salsola and Suaeda vegetation types along the same environmental gradient. In contrast, Artemisia and Ephedra were associated with less saline soils, lighter soil textures, and higher sand content. The Tamarix vegetation type was primarily related to silty soils with higher potassium concentrations.

Conclusion: Overall, the results demonstrated that variations in soil characteristics, particularly salinity, gypsum, sodium, soil texture, lime, and potassium, play a fundamental role in the differentiation and distribution of vegetation types in the Biabanak area. The findings highlight the importance of edaphic factors as the primary drivers of vegetation patterns in this desert ecosystem and suggest that these variables can serve as key indicators in desert management programs, including vegetation establishment, conservation, restoration, and rehabilitation efforts in arid and semi-arid environments.