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.