Comparison of Carbon and Nitrogen Sequestration in Soils Under Plantations, Natural Forest and Agricultural Farm Land Uses in Arjan Plain in the Fars Province

The carbon sequestaration by plants and soil is one of the easiest and the most econimical ways to reduce atmosphere carbon. This study was conducted on the planted land use of Fraxinus rotundifolia, Cupressus arizonica, obinia pseudoacacia L., Elaeagnus angustifolia, Cedrus libani, and Quercus brantii (persica) in the Arjan plain of Fars province. For each plantation land use, there were three plots with 125 m2 area where 25 trees were planted with 2.5-meter distance. Also in the vicinity of these land uses, which were established about 50 years ago as a adaptation experiments, were a natural oak forest and a 10-year-old alfalfa farm land. In each plot, five soil samples were taken from 0–20 cm depth. Then simple soil samples from each plot were combined and a composite sample was prepared for each replicate. Totally three composite soil samples from each land use were transformed to the lab and organic carbon and total soil nitrogen were measured and carbon and nitrogen sequestration rate and their economic value were calculated. The total economic value of carbon sequestration in the soil under the cover of C. libani and Q. brantii natural forest was calculated to be $77571.43 and $69809.52, respectively. Each hectare of soil under the cover of these two species captured 387.9 and 348.6 tons of carbon dioxide, respectively. Unexpectedly, the values of carbon and nitrogen stock was higher under cedar trees, as non-native species, when compared with the other tree species. Therefore, these species can be considered as proper options for forest restoration plans. Transformation of natural forest to agriculture led to decreasing of soil carbon stock till 79.63%. According to the results of this study, it is recommended to avoid conversion of natural forest to agricultural lands and native trees like oak and non-native forest species adapted to climate conditions should be considerded to restore deforested forest lands.