Changes of vegetation indices in arable lands with different years of abandonment in Shirmard rangelands, Chaharmahal va Bakhtiari province

Abandonment of arable lands is the starting point of vegetation succession. The trajectory and speed of succession can be different according to the time of abandonment. The aim of this study is to assess the effect of abandonment periods on species richness, diversity and functional groups in shrublands and grasslands of Shirmard rangelands in Chaharmahal va Bakhtiri, Iran. A total of 96 abondoned arable lands were selected and grouped according to the abandonment periods (less than 5, 5-15, 15-25 and more than 25 years). 24 patches around abondoned arable lands were chosen as control sites. Cover of all species was estimated in 4 m2 plot (10 plots in each patches). Data were analyzed using one-way ANOVA. The results of this study indicated that the lowest values of Shannon-Wiener and Margalef indices in both vegetation types belonged to area with less than 5 years abondonment. The greatest Shannon-Wiener and Margalef indices in shrubland (1.85 and 3.83 respectively) were found in 15-25 years but in grassland (1.93 and 4.39 respectively) it happened in 5-15 years. In both vegetation types we found that the average canopy covers of functional groups such as annual plants, annual grasses, Poaceae and Cruciferae families significantly decreased as the time of abandonment incraesed. In contrast, a significant increase was found for perennial plants, shrubs, trees and Papilionaceae family. Therefore, this study showed that vegetation indices improved during natural succession of vegetation in abandoned arable lands but the reversibility of vegetation indices varied according to the kind of index and vegetation type.