4.1 Dynamics change in productivity and AGB stability from 1979 to 2017
Within the past several decades, land that is not conducive to farming has been converted from arable to woodland to recovery wood products and carbon store, including natural forest and plantation. Our results showed that unharvested planted forest had higher productivity than natural forest, which suggests that planted forests have high C uptake and C sequestration (Tong et al., 2020). However, natural forest stored large amounts of carbon and showed an apparent decline in productivity, natural forests in our study with mean stand age 80 years old, whose biomass may achieve a state of dynamic stability. Chazdon et al. (2016) also indicated that the mature natural forest’ s biomass has reached a climax state and their productivity declined. In addition, the AGB temporal stability in planted and natural forests decreased. As we know, AGB temporal stability in natural forest was more stability. In the following, we discussed possible causes underlying the observed trends and differences in AGB stability and productivity changes between the two forest types, and put forward corresponding management measures.