Grazing intensity impact on soil carbon sequestration and plant biomass in semi arid rangelands (Case study: Sisab rangelands of Bojnord)

Climate change and increase of global warming is one of the most important challenges in sustainable development, which is due to increase of concentration of greenhouse gasses in atmosphere. CO2 is the main part of greenhouse gasses. In order to mitigate atmospheric CO2 and create balance in greenhouse gasses, atmospheric carbon must be absorbed and sequestrated in different forms. Rangelands ecosystems have approximately half of the worlds land area and they store over third of trrestrial biospher carbon. In order to evaluate the effect of grazing intensity on content and distribution of soil carbon sequestration and plant biomass, a study was carried out at Sisab semiarid rangelands of North Khorasn province. After survey, three sampling area has been specified (reference, key and critical). The content of above ground and under ground biomass carbon, litter carbon and soil organic carbon (in two depths 0-15, 15-30 cm) was determined in three area. The result showed that the total carbon sequestration in reference area was 39. 79 ton/ha, in key area was 28. 97 ton/ha and in critical area was 24. 43 ton/ha. The results of carbon distribution showed that the soil organic carbon content was >97% of total carbon sequestration, In addition the carbon content in underground biomass was higher than above ground biomass. It was concluded that the grazing intensity cause to decrease of vegetation cover, content of plant biomass and decrease of carbon sequestration in soil and vegetation biomass, and soil is the most impotant sink for organic carbon storage in this rangelands.