Forest harvest practice is essential in influencing forest carbon density. Different logging methods, logging intensity, recovery methods, and recovery time have a profound impact on the forest ecosystem carbon density. Mixed broadleaf Korean pine (Pinus koraiensis) forest is an important component of temperate forest in China. Recent years, with the increase of forest harvest practice in broadleaved Korean pine forest, it is necessary to the study the impact of logging on broadleaved Korean pine forest ecosystem carbon density.
We established 1 hm²×11 permanent sites from 2007 to 2009 including primary and secondary broadleaved-Korean pine mixed forests after logging based on different logging intensity and recovery time on Changbai mountains, northeast China and use the method of replacement between time and space to find out the impacts of logging intensity and recovery time on forest ecosystem carbon density. We investigate aboveground vegetation (DBH>2cm), collect litter layer and sampled soil samples of each site. We use ailometric equation and transforming relationship between biomass and carbon content to estimate aboveground vegetation carbon density, use dry matter per unit area of litter layer and carbon content to estimate the litter layer carbon density and use soil bulk density, per unit mass of carbon content to estimate soil carbon density.
Our results show that carbon density of vegetation and soil declined after logging, and the impact of logging on vegetation carbon density is mainly reflected in the main forest layer(DBH>20cm), and in the soil surface (0-20cm). We also found an increase in both vegetation (30% logging intensity: y=2.17x+64.01, R²=0.801, P<0.01; 40% logging intensity: y=2.46x+37.87, R²=0.783, P<0.01) and soil carbon density (y=2.34x+76.91, R²=0.847, P<0.01) with recovery time increasing. There is no significant impact of logging intensity or recovery time on litter layer carbon density, but different recovery methods has a significant impact on litter carbon density(larch plantation> Mixed broadleaf Korean pine forest>birch forest). There is a negative linear correlation between vegetation carbon density and logging intensity (y=-0.9x+91.17, R²=0.626, P<0.01).
These results imply that although deforestation causes the reduction of forest ecosystem carbon density, the appropriate logging intensity and recovery time may solve the contradiction of timber production and carbon sequestration. Base on the relationship between carbon density and recovery time and logging intensity, we believe 30% logging intensity and 45 years' rotation are better for forest ecological recovery, timber production and carbon fixing.