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Original Article

Determining Ecological Thresholds in Saline Habitats on Western Shore of Lake Urmia, Iran



In temporal and spatial patterns, the critical (ecological) thresholds have rapid changes in ecological gradient. Determination of thresholds along the environmental gradients can help to control destructive factors and therefore, the success in restoration projects can be guaranteed. This study was conducted to evaluate the trend of changes in functional and structural indices along soil salinity gradient and to determine the ecological thresholds in saline habitats of Uremia Lake, Iran, in the growing season of 2019 and 2020. Landscape Function Analyses (LFA) guideline was used to evaluate the sites. The values of the indices were fitted with the pattern diagrams (S-shaped curves). The habitat restoration process after five years of range management and development projects was evaluated and ecological thresholds were determined. The results showed that the values of the functional and structural indices decrease along the salinity gradient and the lowest values were observed at the end points of the gradient. As a result, the success of range development projects was lower at salinity center. The results of the S-shaped curve models showed that the regression relationship between landscape organization index and nutrient cycle with eleven soil indices along the salinity gradient was not significant and their determinant coefficients were less than 50 %. On the other hand, there was a strong relationship between the index of stability and permeability with the salinity gradient, with determinant coefficients of 83 and 63%, respectively so that the values of these two indices decreased significantly when approaching the salinity center.