فهرست مطالب zahra jaberolansar

Plant species diversity always implies ecosystem stability against environmental and biological disturbances. This study was conducted to investigate the effects of grazing management on diversity indices of plant species in grazed and exclosed rangeland sites of Hanna station- Semirom. Sampling was performed using 30 plots (1 m2) along four transects. Canopy area and density of species were recorded in sampling units, and the floristic list was provided in the whole area. Species richness, heterogeneity and evenness indices were calculated from density data and parametric diversity indices including log normal, geometric, and broken stick were fited in both exclosed and grazed areas. The Chi-Square test was used to examine the significance of measured traits. The results of numerical indices showed a higher species richness, evenness and species diversity indices in grazed than in the ungrazed site. The logarithmic diagram in the exclosed and grazed areas followed the broken stick model, indicating the presence of dominant species. The floristic lists of the study sites showed that the number of specific plant species in the grazed site was higher than that of exclosed site. Overall, the results showed that moderate grazing conditions in Hanna station improved plant species diversity indices and increased climax plant species.

Gavkhooni, registered in the Ramsar International Convention due to its ecological importance, is one of the important wetlands in the country, which is the outlet of Zayanderud basin. This wetland has various environmental functions such as: reducing the consequences of climate change, ecotourism, water and air filtration, ground water recharge, sand dune stabilization, forage production, biodiversity and wildlife habitat.
As a natural ecosystem, Gavkhooni is a fundamental reservoir for plant and animal species. There are 24 vegetation types in Gavkhooni and the largest area belongs to Salsola tomentosa- Artemisia sieberi and Calliganum commusum - Stipagrostis karelinii. This area is also the habitat of birds, mammals, reptiles, amphibians and fishes. Changes in quantity and quality of water have caused the dryness of a vast area of Gavkhooni in recent years as well as the loss of many valuable plant and animal species such as eluropuslittoralis, Halocnemumstrobilaceum,PhragmitesaustralisandSalicorniapersica. The conversion of this ecosystem in the central region of the country into the core of wind erosion crisis and dust storms is a threat for the residential and agricultural areas around it.