Stipa barbata

Abstract: The interaction among species is one of the most important factors influencing the distribution of plants in a given habitat. Vegetation of arid rangelands often appears patchy with many herbaceous species associated with shrub species. It was hypothesised that plant interactions among different life forms together with the effect of grazing preference generate this type of spatial distribution of plant species in the semi-arid rangelands of middle Iran. Spatial patterns and associations were quantitatively analysed using Hopkins' index and Chi-square tests to establish links between spatial relationships,plantlifeformsandpreferencebygrazersonthesouthfoothillsoftheTaleghanranges,AlborzProvince.Data were collected from three geographical sites with different dominant species and clumped patterns of plant spatial distributions for these species were detected. These spatial patterns were probably generated by the interplay of life form- dependentfacilitativeinteractionsamongplantsandthegrazingpressureonpreferredspeciesratherthanduetotheirintrinsic characters.Inthestudysites,grassspeciesweresignificantlymorefrequentlyobservedinthevicinityofnursespeciesthanin open areas. It was also found that plant-plant interactions may change in response to changes in environmental conditions, such as soil characters and the benefits achieved by the beneficiary species from being associated with nurse species. All preferred perennial species were spatially associated with shrub species (Astragalus gossypinus Fischer and Thymus kotschyanus Boiss & Hohen), while nurse species that just physically protect the beneficiary species from grazing (e.g. A. gossypinus) did not associate with non-preferred species (e.g. Stipa barbata Desf). Instead, these non-preferred species may positively aggregate with nurse plants showing other beneficial characteristics such as nitrogen fixation and improvement of soil conditions. Additional keywords: competition, facilitation, grass species, shrubs, spatial association, Taleghan.

Abstract: The rangelands, as one of the largest dynamic biomes in the world, have very capabilities. Regulation of greenhouse gases in the Earth's atmosphere, particularly carbon dioxide as the main greenhouse gases, is one of these cases. The attention to rangeland, as cheep and reachable resources to sequestrate the carbon dioxide, increases after the Industrial Revolution. Rangelands comprise the large parts of Iran as a steppic area. Rudshur (Saveh), as area index of steppic area, was selected under three sites including long-term exclosure, medium-term exclosure, and grazable area due to the capability of carbon dioxide's sequestration of dominated species. Canopy cover's percentage of two dominated species (Artemisia sieberi Besser and Stipa barbata Desf.) was determined via establishing of random 1 square meter plot. The sampling of above and below ground biomass style was obtained by complete random. After determination of ash percentage in the laboratory; conversion ratio of plant biomass to organic carbon was calculated by ignition method. Results of the paired t-test showed that the amount of carbon sequestration in above ground and underground biomass of Artemisia sieberi Besser and Stipa barbata Desf. is different in three regions. It, of course, has not any difference between under and surface ground's biomass of Artemisia sieberi Besser in long-term exclosure. The independent t-test results indicate differences between underground biomass corresponding each other in the studied sites. Carbon sequestration in the Stipa barbata Desf. was totally more than Artemisia sieberi Besser. Altogether, the average sequestration of the long- term exclosure was 5.842gr/m², the medium-term exclosure was 4.115gr/m², and grazable area was 5.975gr/m² so that there is not valuable statistical difference in terms of total amount of carbon sequestration to three sites.