Investigating the correlation between vegetation cover, soil elements and plant and soil organic carbon storage in mountain pastures under flooding and grazing (case study: Asadabad Pass, Hamadan)

The extent of rangeland is one of the most important characteristics of organic carbon uptake and storage in soil and plants. The present study investigates the indices of plant diversity and organic carbon storage in mountain pastures under grazing and 10-year enclosure in Asadabad. The rangeland is approximately 100 hectares and its rangelands are in good condition and are in the 2S class in terms of competence, which are grazed from mid-May to early September. The type of grazing livestock is mostly sheep and rarely goats. The plant type is Astragalus parrowianus, Bromus tomentellus and Festuca ovina. Vegetation and soil sampling was performed in both work units by random-systematic method and indices of diversity, uniformity, and richness were evaluated. The results showed the highest amount of plant diversity, richness and uniformity was in the exclosure so that the number of species in the grazed area was 127 and in the exclosure was 139. The highest amount of deposited carbon in vegetation and soil, with a significant difference, was observed in the exclosure zone. Livestock grazing significantly reduced the amount of soil organic carbon storage (from 83.13 to 74.35 tons per hectare from grazing area to grazing area) and organic carbon of vegetation (from 0.00273 to 0.00219 tons per hectare from the restricted area to the grazing area) at the level of 5%. There was no significant correlation between Shannon-Wiener, Simpson and Hill plant diversity indices with organic carbon storage in vegetation. In the area where the pasture was grazed, the vegetation and soil of a part of that area was severely damaged due to over-exploitation, so the amount of vegetation was significantly at the level of 5%, from / 6 67% in the enclosed area has decreased to 35.1% in the grazing area and as a result the percentage of bare soil has increased. In this study, the results of the average species richness using Manning and Margalf indices in the two protected areas were 2.555 and 3.8044, respectively, and under grazing 2.4499 and 3.55545, respectively. The effect of grazing management is on the amount of species richness because the grazing factor has reduced the richness or number of species in the area. Also, the amount of organic carbon of vegetation and soil organic carbon in the exclosure was 0.0273 and 83.132 tons per hectare, respectively, and in the grazing area were 0.0219 and 74.357 tons per hectare.