Effect of Transforming Pure Cunninghamia lanceolate Plantation to mixed Forest with Broad-leaf Tree Species on Organic Carbon Density

In Febuary 2007, transformation was carried out on cutting area of pure the first generation of Cunninghamia lanceolata plantation in Kaihua, Zhejiang Province. Afforestations were implemented on different sample plots namely of pure C. lanceolata suckers (CK), 2-year container seedlings of Betula luminifera, Schima superba and Houpoea officinalis with C. lanceolata suckers. In November 2022, investigation was made on different sample plots, with DBH, height and stand density. Biomass of sample trees in each plots, understorey vegetation was determined and soil organic carbon and soil bulk density was detected. The results showed that the organic carbon density of arbor layer in C. lanceolata suckers+S. superba and C. lanceolata suckers+H. officinalis was close to that in the control, but that in C. lanceolata suckers+B. luminifera was 25.8% lower than that in the control. There was no difference of organic carbon density of understory vegetation between the three mixed plantations and the control, but the organic carbon density of litter was lower than that of the control. The soil organic carbon density in the 0-50 cm soil layer of the three mixed plantations was 5.9%, 8.6% and 21.7% higher than that of the control. Compared with the control, the total organic carbon density of mixed C. lanceolata suckers +S. superba and C. lanceolata suckers + M. officinalis plantations increased by 5.7% and 15.3%, while that of C. lanceolata suckers+B . luminifera plantation decreased by 6.1%.