The impact of thinning intensity on carbon storage in the mixed coniferous and broad-leaved forest ecosystem in Northeast China

Objective Thinning is an important forest management method to improve forest quality and optimize forest structure, which has a significant impact on regulating the carbon sequestration capacity of forest ecosystems. At present, there is no consensus on the response of carbon storage at the ecosystem level of natural mixed forests to different thinning intensities. The aim of this study is to explore the dynamic changes in carbon storage in coniferous and broad-leaved mixed forest ecosystems under different thinning intensities, providing a theoretical basis for rational selection of thinning intensities and enhancing forest carbon sequestration capacity.

Method In 2011, light thinning (intensity 17.3%), moderate thinning (intensity 34.7%), heavy thinning (intensity 51.9%) plots and control plots were established to calculate the carbon stocks of various components in the ecosystem in 2021. The dynamic changes in forest carbon stocks over the past 10 years after thinning were analyzed to reveal the response patterns of forest ecosystem carbon stocks to different thinning intensities.

Result After 10 years of thinning, the carbon storage of forest ecosystems showed an upward trend with increasing thinning intensity (333.72 t/hm² for light thinning, 358.48 t/hm² for moderate thinning, and 386.93 t/hm² for heavy thinning). There was no significant difference in forest ecosystem carbon storage among plots with different thinning intensities, but the carbon storage in the tree layer of the heavily logged plot was significantly lower than that of the control plot, while there was no significant difference between the lightly logged plot and the control plot (the carbon storage in the tree layer of the lightly logged plot was 1.09 times that of the control plot). The carbon storage of shrubs in moderate thinning plots was significantly higher than that in control plots (p < 0.05); The carbon storage of herbaceous plants was significantly lower in heavily logged plots than in control plots (p < 0.05). There is no significant difference in soil carbon storage under different thinning intensities, but it shows an upward trend with the increase of thinning intensity, which is one of the main reasons for the increasing trend of ecosystem carbon storage.

Conclusion A cultivation and logging intensity of less than 20% can not only achieve the goal of forest structure adjustment, but also promote the accumulation of carbon storage in the vegetation layer of the forest ecosystem. After 10 years of thinning, it has been restored to the level of the control plot. From the perspective of the ecosystem, if other carbon components such as soil are included, heavy thinning may actually promote the increase of carbon storage in the ecosystem. Therefore, it is necessary to comprehensively consider the restoration status of various components of the ecosystem and select the most suitable thinning intensity for nurturing. The time span of this study is 10 years, which is relatively short compared to the growth cycle of forests. Therefore, it is necessary to evaluate the changes in ecosystem carbon storage on a longer time scale in the future.