Effects of thinning on structural and compositional complexity, and carbon sequestration capacity in Chinese fir plantations

To detect the effects of thinning on the structural and compositional complexity, and carbon sequestration capacity in a Chinese fir plantation, to provide theoretical references for the management and conservation of forest ecosystems in the context of climate change.

Using a 19-year-old Cunninghamia lanceolata plantation at the Lishui forest farm in Nanjing as the research subject, four thinning intensities were randomly established (with 0%, 30%, 50%, and 70% of trees removed). Changes in structural and compositional diversity, as well as carbon storage and carbon sequestration rates, were measured three and six years after thinning.

Compared to the unthinned plots (0% reduction in trees), high intensity thinning (70% reduction in trees) reduced carbon storage of trees, and carbon storage of the shrubs and herbs significantly increased in the high intensity thinning and medium intensity thinning (50% reduction in trees). In contrast, aboveground carbon storage of stands was dependent on sampling time. With recovery time increasing after thinning, the carbon storage of trees, shrubs and herbs increased significantly. Carbon sequestration rate of the trees, shrubs, herbs and aboveground significantly increased with increasing thinning intensity. Effects of thinning on the structural and compositional complexity indices of Chinese fir plantation was dependent on the recovery time after thinning. Three years after thinning, DBH, Simpson index and species richness increased with thinning intensity, and both moderate and low intensity thinning significantly reduced Gini index of DBH and thinning had no significant effects on Shannon index and basal area of trees. Six years after thinning, DBH and Simpson indexes increased significantly with thinning intensity, and high intensity thinning decreased Gini_DBH index but increased Shannon index, while basal area and species richness did not change. Aboveground carbon sequestration rate was positively correlated with Simpson index, species richness and DBH, but negatively correlated with Gini index of DBH.

These results suggested that the relationship between the structural and compositional complexity and carbon sequestration capacity of Chinese fir plantation after thinning depends on the recovery time after thinning, so long-term research is necessary.