Modeling the effect of vegetation conversion and climate change on the dynamics of soil organic carbon stock in a complex ecosystem

The conversion of natural vegetation to other vegetation covers and climate change has had a major impact on the decomposition of soil organic carbon and eventually the emission of carbon dioxide (CO2) from the soil into the atmosphere. But so far in Iran, little researches have looked at the effect of the conversion of vegetation and climate change on the amount of soil organic carbon (SOC) stock as a key component in reducing the effects of climate change and global warming. To overcome the limitations of field studies, SOM models provide the best scientific understanding of the dynamics of SOM. RothC Carbon model is one of the most widely used models in soil carbon sequestration studies that has been used in many studies to study the effect of climate change on soil carbon stock. The purpose of present study, investigate the effect of converting native vegetation (rangeland) into four new vegetation (rangelands of cypress under-story, rangelands of almond under-story, cypress trees and almond trees), as well as the simulation of the effect of two climate scenarios (non-occurrence of climate change and the occurrence of climate change) on the dynamics of SOC stock in the five vegetation covers of the Shiraz Bajgah region for 36 years (2014-2050). In this study, 210 soil samples were collected to determine the soil organic carbon and soil texture as well as 420 samples for determining the soil bulk density. After measuring the parameters, SOC stock at 0-20 cm depth was calculated for each vegetation cover treatment. Finally, the effect of vegetation conversion and two climate scenarios on the amount of SOC stock using the RothC model was investigated in the five vegetation covers of Shiraz Bajgah region. The results showed that the increase of SOC stock due to planting of cypress trees after 15 years was higher than the amount increase of SOC stock due to the planting of almond trees after 30 years in Bajgah region. The simulation results of the RothC model also indicated that in comparison with 2014, the SOC stock in the 2050 in the rangeland, rangelands of almond under-story, rangelands of cypress under-story, cypress trees and almond trees treatments will be decreased by 12.19%, 12.14%, 12.11%, 10.37% and 10.49%, respectively due to climate change; and the amount of SOC stock in each of the treatments before and after climate change at 5% level (P <0.05) had significant difference.