The relationship between species diversity and environmental factors in Chahar Bagh mountain rangelands

In order to properly manage rangeland ecosystems, it is necessary to study the relationship between ecological factors in nature such as elevation, climate and soil factors with vegetation and living organisms. In this regard, the present study was conducted to investigate the relationship between species diversity and environmental factors (Physical and chemical characteristics of soil, topographic and physiographic characteristics) in the mountain rangelands of Chahar Bagh Golestan.

 The study area of Chaharbagh Golestan mountain rangelands with an area of about 9,000 hectares is located 45 km southeast of Gorgan city. 6 plant types were identified, for sampling and measurement in each plant type, 3 transects of 300 meters were established and 10 plots along each transect and a total of 30 plots in each plant type were used. In each plot, the percentage of individual species coverage was estimated. Also, in each transect, soil samples were taken from the first and last plots according to the depth of the rooting of the dominant plants of the region. After sieving, soil samples were transferred to the laboratory to determine the physical and chemical properties of the soil, including soil texture, EC, pH, K, P, lime, saturated moisture, and the amount of organic matter. Also, slope, direction and height above sea level were measured at each soil sampling point, and average slope, modified direction and average height were measured for each plant type. In order to investigate the relationship between species diversity with topographic and physiographic characteristics and soil characteristics of types, classification methods were used. Based on the length of the gradient, the redundancy analysis method was used as a linear method to classify species diversity with environmental factors. All statistical calculations for classification were performed using Canoco software version 5 and calculations related to species diversity were performed using PAST software version 3.17.

The results of Margalf average (14.12) and Taxa (41) indices in type 1 (Ar au-St ba) are higher than other types. Also, the mean Shannon (3.306) and evenness (0.91) indices in type 6 (Ho vi-Cr ko-Ag in) are higher than other types. Ju po-On co-St ba type has the highest slope value (51.6%), on the other hand St ba-On co type has the lowest slope value (5.6%). The results showed that the values of Simpson evenness indices and Shannon-Wiener species diversity of types are also affected by slope, organic carbon content and electrical conductivity. The slope factor is the most important factor affecting Simpson evenness indices and Shannon-Weiner species diversity. The results of redundancy analysis showed that the relationship between the characteristics of the types and the indices of plant diversity is significant. The results showed that with increasing the amount of K and EC, the amount of evenness index also increases. The results also showed that with increasing lime and pH factors, the amount of Shannon index increases. Shannon indices are inversely related to directional slope and height factors. Also, according to the results, with increasing clay factors, saturation moisture and pebbles, the value of Margalf index increases. According to the results of Margalf index, it has an inverse relationship with sand factor.

 In general, physiographic and topographic characteristics have had the greatest impact on species richness, and soil chemical properties on the amount of evenness and species diversity of types. In general, the slope of the types is the most important environmental factor affecting the indicators of species diversity.  Therefore, according to the results of the present study, changes in species diversity indices can be used as an index to improve the condition of rangelands in the region and also in deciding on appropriate management programs.