Fitting of Species Frequency Distribution Models in Woody Societies in Rangelands of Gouradarah, Gechigiran Ahar

     One of the important goals of natural resource management is to conserve plant diversity in the ecosystem so that sites are more productive and more ecologically stable at the various situations. Different diversity indices have been presented to study the species status of natural ecosystems. One of these indicators is the use of empirical distribution models that each of these models indicates the sustainability and health of plant communities. This research was carried out in Guyje bel woodlands of Gechigiran region in order to know about the extent of degradation and stability of plant communities in two levels of altitude. For this purpose, 50 samples were taken in two altitude levels; lower and upper than 1800 m above sea level. We recorded the percentage of shrubs and trees species in the plots. Parametric indicators including diversity grading curves and frequency distribution models (broken wands, logical norm, logarithmic series and geometric series) were used for graphical study of plant diversity and their fitting with experimental models of sustainability of plant communities. The results showed that, by examining the fitting of species abundance data, using the Chi-square fit test, the plant community of both altitude classes follows the logarithmic series model at the 5% level. Since the logarithmic series model represents unstable communities and the plant community has a relatively small number of species, it can be expected that these two sites were in a low diversity in terms of species diversity and stability. Both elevations had a significant fitting of 5% with the geometric series model. According to the results, the lower altitude (lower than 1800 m) had a lower diversity than the higher altitudes (above 1800 m). Therefore, it is suggested that management decisions should be made to increase species diversity in the mentioned areas.