Objective  Based on the estimation of ecosystem carbon density in broadleaved Korean pine forest disturbed by different logging intensities, the recovery status of the forest after 30 years of logging was discussed, and the relationship among logging intensity, composition of ecosystem carbon density, and stand structure was analyzed to provide a scientific basis for forest management, aiming at enhancing ecosystem carbon sink function and protecting species diversity.

  Method  The current study took the broadleaved Korean pine forest disturbed by different logging intensities in Wangqing Forestry Bureau, Jilin Province of northeastern China as the research object. The vegetation, litter and soil characteristics of different logging disturbance stands, unharvested, class Ⅰ (30%), class Ⅱ (40%), class Ⅲ (50%), class Ⅳ (above 60%) and class Ⅴ (clear cut), were investigated and analyzed, and the carbon densities of vegetation, litter and soil were systematically estimated, and their differences were also compared and analyzed, as well as their relationship with logging intensities and stand structure.

  Result  Although the broadleaved Korean pine forest disturbed by different logging intensities had been restored for 30 years, its vegetation carbon density was still significantly lower than that of the control sample plots due to the significant negative effect of logging, but the carbon density had recovered to no significant difference between different logging intensity sample plots, except for clear-cutting. The tree layer carbon densities of disturbed stands with different logging intensities increased to a certain extent in the small- and medium-small-diameter trees, but it still could not make up for the carbon density loss of the large-diameter trees above 40 cm. The carbon densities of young trees and herbs were not significantly affected by logging intensity, but the carbon density of shrub plants was significantly positively correlated with logging intensity and only the disturbance of clear cutting increased significantly. Clear-cutting disturbance significantly reduced the carbon density of litter and soil layer B, while the soil carbon densities of other logging intensities were generally close to or higher than that of control stands due to the increase of soil carbon density of layer B. Compared with the control groups, the ecosystem carbon densities disturbed by clear cutting, class Ⅰ and class Ⅱ logging intensities decreased significantly, while the ecosystem carbon densities disturbed by class Ⅲ and class Ⅳ logging intensities were close to and slightly higher than control, respectively. In the composition of ecosystem carbon density, the proportion of soil carbon density was the highest, and the total proportion of under-canopy vegetation and litter was less than 3%. The negative effects of logging intensities on tree height uniformity index, DBH Shannon index and DBH uniformity index were still significant, and the change of stand structure had a significant positive effect on carbon density of tree layer, but it had a significant negative effect on the carbon density of shrubs. Affected by the strong negative effect of logging, tree layer carbon density was significantly correlated with shrub carbon density, litter carbon density, and herb richness. Moreover, there were also significant correlations between litter carbon density and soil carbon density and herb richness.

  Conclusion  After 30 years of logging disturbance in broadleaved Korean pine forests, the carbon density of ecosystems has basically recovered or exceeded the level of unharvested stands, except for clear-cutting, and the recovery of carbon density is mainly due to the relatively rapid accumulation of soil carbon, while the loss of vegetation carbon density still needs more time to recover. The negative effect of logging causes the change of stand structure, leading to the linkage changes of arbor layer, under-canopy vegetation, litter and soil, therefore, there are significant correlations among logging intensities, ecosystem carbon density and stand structure.