Investigation of Environmental Factors Affecting the Distribution of Calligonum bungei Species in Rangelands of Kerman Province

The distribution and establishment of plant species are influenced by various environmental conditions. Calligonum bungei, a species of the genus Calligonum, is widely distributed in arid and semi-arid climates in Iran. This research aimed to investigate the environmental conditions governing the distribution of Calligonum bungei in the desert rangelands of Kerman province. The study focused on identifying different types of Calligonum bungei habitats, assessing canopy cover, density, and associated species, and examining the influence of environmental factors, such as climate, topography, and soil, on the species' distribution.

Four representative areas in Kerman province were selected to represent the dominant types of Calligonum bungei habitats. Geomorphological types were identified using satellite images and field visits. Environmental factors, including climate, topography, soil properties, and characteristics specific to the species (density, canopy cover, associated species), were evaluated in each habitat type. Vegetation studies were conducted along 300-meter transects, with plot sizes determined based on vegetation type and distribution (100 square meters). A total of 40 plots (10 plots per studied area) were investigated. Canopy cover was determined by measuring two perpendicular diameters of the plant canopy. Principal component analysis (PCA) using PC-ORD software was employed to analyze the relationship between environmental factors and species establishment in the study areas.

The results showed that Calligonum bungei was present in the altitude range of 1400-1750 meters, slopes ranging from 1% to 18.4%, and in all directions. The average annual rainfall in the areas varied from 55.5 to 163.4 mm, while the average annual temperature ranged from 16.7 to 26.4 degrees Celsius. The minimum and maximum absolute temperatures recorded were between -20.8 and 48.8 degrees Celsius, respectively. The average annual humidity ranged from 29.6% to 42.5%, and the length of the dry season varied from 8 to 12 months per year. Soil analysis revealed shallow soil with sandy-loamy to sandy-loamy texture, sand content between 67% and 84%, lime content between 8.5% and 20%, carbon content between 0.1% and 1.35%, nitrogen content between 0.0% and 0.7%, absorbable phosphorus between 9.5 and 13.5 milliequivalents, absorbable potassium between 200 and 217.5 milliequivalents, salinity between 0.36 and 1.02 decisimians, and pH values between 7.8 and 8.09. In terms of vegetation, Calligonum bungei was observed to be scattered in all studied areas, with densities ranging from 10 to 280 plants per hectare and canopy cover varying from 0.1% to 5.7%.

The principal component analysis revealed that the first component (annual temperature, humidity, sand, and silt) explained 46.9% of the variation, the second component (altitude, slope, annual rainfall, phosphorus, lime, and potassium) explained 35.3%, and the third component (clay, nitrogen, and salinity) explained 17.8%. Environmental factors influencing the establishment of Calligonum bungei varied among the studied areas. In Anar and Kerman regions, increasing sand content and decreasing annual temperature, humidity, and silt were significant factors. In the Bam region, increasing phosphorus and potassium content and decreasing altitude, slope, annual rainfall, and lime were influential. In the Jiroft region, reducing sand content and increasing annual temperature, humidity, and silt played a role. Overall, these findings indicate that the identified environmental factors act as limiting factors for the establishment of Calligonum bungei in the study areas.