Distribution characteristics of vegetation and soil carbon density of different forests in Ningxia

There are great uncertainties for the estimation of forest carbon density, due to their wide distribution, multiple types, natural and human disturbances. However, it is the foundation to better understand the dynamics and trends of terrestrial carbon cycle. Therefore, based on Ningxia Hui Autonomous Region forest resources inventory, a field investigation was carried out to study on the distribution characteristics of vegetation and soil carbon density of different forests in Ningxia. 9 sites were investigated and 4 typical natural forests were included: broadleaved deciduous forest, temperate coniferous forest, cold temperate coniferous forest and temperate mixed broadleaf-conifer forest. Vegetation biomass, vegetation carbon content, soil bulk density, and soil carbon content were determined, and carbon density of both vegetation and soil were calculated. The results showed that: 1) the mean biomass carbon density of different vegetation layer was: arbor layer(57.66 Mg/hm²)>fine root layer(8.39 Mg/hm²)>litter layer(8.34 Mg/hm²)>grass layer(0.23 Mg/hm²)>shrub layer(0.20 Mg/hm²), with the arbor layer accounted for 77.06%; 2) the mean soil carbon density ranged from 170.15 to 354.29 Mg/hm², with the highest in temperate mixed broadleaf-conifer forest in Luoshan(TCB2) and the lowest in cold temperate coniferous forest in Helanshan(CC1), while with regard to the vertical distribution, 50~100 cm accounted for 40% of the soil profile deep to 1 m; 3) the ecosystem carbon density was between 221.63 and 444.77 Mg/hm², with the highest in TCB2 and the lowest in temperate mixed broadleaf-conifer forest in Liupanshan(TCB1); 4) soil carbon density was 4.09 times larger than the biomass carbon density, and as the higher stability of soil carbon pool, the forest with higher soil carbon density(mixed broadleaf-conifer forest and coniferous forest) might have great potential to sequester C. Our study could have some implications for future forest culture and management in Ningxia Province.