Carbon Density Characteristics And Its Dynamics Of The Main Forest Types In Maoershan

Forest is the main component of terrestrial ecosystem and plays an important role in global carbon balance.In-depth understanding of forest carbon density dynamics and its influencing factors is of important for accurate evaluation and prediction of forest carbon sink functions.In this study,4 kinds of natural secondary forests(i.e.,hardwood stand,aspen-birch stand,mixed deciduous stand,and Mongolian oak stand)and two plantation stands(Dahurian larch stand and Korean pine stand)with similar ages but different site conditions at the Maoershan in Northeast of China,were selected as the research objects.Based on long-term positioning and monitoring data,the objective was to quantify the carbon density changes and explore their influencing factors.The main results showed that:(1)The vegetation carbon density of the six forest types showed an increasing trend,and the average increment was 35.75 t/ha.The carbon density increment(CDI)of dominant tree species with different succession stages were different with forest types.Except for aspen-birch stand,the increment of carbon density of pioneer species(0.19 t/ha/a ～ 0.99 t/ha/a)and later species(0.74 t/ha/a ～2.21 t/ha/a)was significantly different in other forest types.The average CDI of overstory was 35.55 t/ha in the six forest types,with accounts for 99% of the vegetation CDI,the CDI of understory varied with forest type.The vegetation carbon density was significantly positive correlated with stand DBH and soil phosphorus density,but negative correlated with average neighborhood comparison of DBH in the six forest types.(2)The coarse woody debris carbon density of the six forest types showed increased trend,and the increment ranged from 2.28 t/ha to 10.74 t/ha.Except for mixed deciduous stand,the CDI of total litter in other forest types ranged from 0.05 t/ha to 2.17 t/ha.The litterfall of each component had interannual dynamics,but the significance of the difference and fluctuation trend varied with the forest type.Litterfall was affected by temperature and soil moisture,but the sensitivity of its response varied with forest types and litterfall components.The litter decomposition coefficients of the six forest types ranged from 0.21 to 0.67.The decomposition coefficient was negatively correlated with soil phosphorus density in O layer,and positively correlated with litter nitrogen content.(3)In the past 15 years,the total carbon density showed slight decreasing in hardwood stand and mixed deciduous stand,while that of the other forest types showed an increasing trend(21.73 t/ha);The total carbon density was positively correlated with the stand DBH and soil water content.The contribution of soil,vegetation and plant debris to total carbon density was 47.74%,45.69% and 6.57%,respectively.There was no significant difference in soil carbon density between the six forest types in different years.The vegetation carbon density of hardwood stand,mixed deciduous stand,Mongolian oak stand and Korean pine stand showed a significant increase trend,and the increment ranged from 26.81 to 39.76 t/ha.The CDI of debris ranged from 2.52 to 20.85 t/ha in the six forest types.The above results show that stand factors and site conditions jointly affect the carbon density and carbon sequestration of forest ecosystems,the dominant tree species of late succession determines the carbon density and carbon sequestration of forest ecosystems.The research provides basic data and theoretical support for exploring the mechanism of carbon sink formation in forest ecosystem.