Species Richness, Evenness and Plant Community Stability 22 Years after Ploughing a Semiarid Rangeland

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Rangeland ploughing and cultivation using dry land farming crops may be amajor reason for the destruction of natural resources in the semiarid and sub-humid regionswhich may significantly change the composition and reduce the stability of the affectedcommunities. In present research, an abandoned ploughed site was compared with a nearbyreference site in the semiarid rangelands of Baharkish, Quchan, Iran in spring and summerof 2010. Frequency and canopy cover of all plant species were recorded within 40quadrates of 1m2 area. Simpson, Shannon-Weiner, Hill and Macintosh indices forbiodiversity, Margalof and Menhening for richness and Camargo, Simpson, Modified Nee,Smith and Wilson for evenness were used. Floristic composition, plant life forms, andimportant value of major plant species were compared with respect to the sites. Landploughing and subsequent abandonment had increased total number of plant species(richness) but decreased the species heterogeneity (evenness). It resulted to non-significantdifferences in species diversity between the ploughed and reference sites. Ploughing hadincreased (8%) the important values of respruting plant species. Therefore, patchydistribution of clonal plants had reduced species evenness within the abandoned site.Furthermore, there were some increases in number of therophytes (100%) buthemicryptophytes (24%), chamaephyte (33%) and phanerophyte (100%) species werereduced in the abandoned site. In conclusion, lower evenness and high proportion ofannual plants should make the abandoned site more fragile and sensitive against the futureenvironmental fluctuations.