The response of carbon storage to the age of three forest plantations in the Loess Hilly Regions of China

- The biomass and age significantly impacted SOC storage in forest plantations.
- The plantations with large biomass had a high SOC for the three species investigated in this work.
- C storage (both biomass C and SOC) for the plantations did not decrease during the period from 9- to 26-years old.

The Grain for Green Project (GGP) has increased the area of forest plantations on the Loess plateau region of China, which has created a need to understand the potential for long-term carbon (C) sequestration. The objectives of this work were to investigate the response of biomass C and soil organic carbon (SOC) densities to the age of these forest plantations and to determine their contribution to the C sources/sink within these regional forest ecosystems. In this project three different species of plants, Caragana korshinskii Kom., Hippophae rhamnoides and Prunus davidiana (Carr.) Franch, were studied by selecting 3 plantation areas where each plant had grown for 9-years and 3 separate plantation areas where each plant had grown for 26-years. All three of these species were widely planted in the case study area. A total of 54 quadrants (2 m × 2 m) were randomly selected in 18 plots (3 plots for each species × 3 species × 2 stand ages) from these plantations for measuring the above- and below-ground biomass as well as the biomass C concentration and density of the three species. A bucket auger was used to collect soil samples from 0 to 100 cm soil depth to determine the SOC concentration and density in each plot. Biomass density, biomass C and SOC increased with growth between 9 and 26 years for all three plant species. The biomass densities for P. davidiana, C. korshinskii and H. rhamnoides increased from 27.3 ± 7.5 to 49.9 ± 11.9 Mg ha− 1, 16.6 ± 3.8 to 39.0 ± 18.2 MgC ha− 1, and 14.4 ± 4.4 to 23.7 ± 5.7 Mg ha− 1, respectively. The biomass C for P. davidiana, C. korshinskii and H. rhamnoides also increased during this time from 9.5 ± 2.6 to 18.7 ± 4.1 Mg ha− 1, 6.2 ± 1.1 to 14.6 ± 6.6 Mg ha− 1, and 6.2 ± 1.9 to 8.5 ± 2.0 Mg ha− 1, respectively. Similarly, the SOC for P. davidiana, C. korshinskii and H. rhamnoides during this time increased from 114.1 ± 13.9 to 185.4 ± 21.2 Mg ha− 1, 80.0 ± 9.0 to 93.3 ± 10.7 Mg ha− 1, and 62.4 ± 3.5 to 81.6 ± 15.4 Mg ha− 1, respectively. Significant differences (P < 0.05) were found for the biomass C and SOC densities between the 9- and 26-year old plantations, demonstrating that biomass production continued to significantly impact the SOC storage with increasing age of the forest plantations investigated. This work suggested that both the stored biomass C and SOC in these plantations did not decrease during the growth period from 9- to 26-years. The results of this study highlighted the importance of forest age in understanding the C storage of these forest plantations.