H. Siroosi - GORGAN UNI
G.A. Heshmati - GORGAN UNI
H.R. Naseri - TEHRAN UNI

Identification of ecosystem thresholds is a way to predict future changes and taking the bestmanagement practices in restoration processes. Thresholds are an integral part of nonlinearresponses of ecosystems to disturbances such as climate change or human activities. In thisstudy, structural threshold of the total patch area and mean patch width in a grazinggradient were identified using the nonlinear function and the concept of threshold ofpotential concern. Other structural features including number of grass, shrub and forbpatches were also measured. The result showed that three-parametric sigmoid functions hadthe highest ability to predict structural changes in ecosystem structure within a grazinggradient radiating out from the livestock stock night corral (camp). The result also showedthat 1 to 2 Km radius from the livestock camp is the critical threshold in ecosystemstructure based on total patch area, landscape organization index and mean patch widthfitting to a sigmoid function. Generally, the area within 2 Km from the camp needed toreceive emergency remedial management actions. The present study showed that theconcept of threshold of potential concern is a useful and early way to predict the thresholdsin the ecosystem for management actions. Also, the present study revealed that threeparametersigmoid function provides a much better fit to structural data than other nonlinearfunctions.

Ecosystem, Structure, threshold, concern, sigmoid