Effect Of Close-to-nature Management On Conmmunity Characteristics And Carbon Storage In Cunninghamia Lanceolata Plantations

Cunninghamia lanceolata plantation is a very important forest type in China and has large potential of carbon sink,also plays an important role for the carbon neutral.Pure plantation has many disadvatages include the limitation of forest carbon sink.Thus the pure plantation should be converted to the close-to-nature silviculture（CNS）for the sustainable forest and increment of carbon sinks.Forest carbon accumulation will change significantly after the coniferous pure planation transformed to uneven-aged mixed coniferous and broad-leaved forest.However,study on relationship between community succession and carbon accumulation and also changes of carbon allocation was not deep enough.In this study,uneven-aged mixed stand of Cunninghamia lanceolate,Castanopsis hystrix and Michelia hedyosperma（CCM）,uneven-aged mixed stand of Cunninghamia lanceolate,Quercus griffithii and Erythrophleum fordii（CQE）,and the unimproved monoculture of Cunninghamia lanceolate（MC）have been chosen as research objects.Field investigation combined with physical and chemical analysis were done.Specifically,the study include:（1）the impacts of CNS on forest vegetation community structure,（2）the impacts of CNS on carbon storage and carbon allocation in different ecosystem layers,（3）major impact factors of forest ecosystem carbon accumulation.Through comparative study on the changes of community structure,plant nutrients,soil physical and chemical properties,carbon storage and distribution of carbon pools in forests under different management,the study investigated the effects of CNS to forest carbon accumulation.Findings of this study provide scientific basis for sustainable development of forestry and management on forest carbon pool.Results are as follows:（1）The vegetation species composition in CNS stands is different from that in the unimproved pure plantation（the control）.Importance value of C.lanceolate in CCM and CQE reduced 37.25%and 40.63%respectively.The species composition of tree layer changed from single dominance of C.lanceolate to diversification.Number of shrub layer vegetation species in CCM and CQE increased 1 and 5 respectively.Number of herb layer vegetation species in CCM and CQE increased 2 and fell 4 respectively.The average individual number of shrub layer vegetation in CCM doubled and average individual number of herb layer vegetation in CQE was halved respectively（p<0.05）.CNS enhanced the value of the Simpson Index of tree layer（～50%,p<0.05）.Simpson Index of tree layer positively correlated with the size coefficient of variation（SCV）,negatively correlated with the mean diameter at breast height（DBH）,tree height and the basal area（p<0.01）.Topsoil（0～20cm）C:N ratio positively correlated with the Simpson Index of tree layer,and soil N:P&C:P negatively correlated with the diversity indexes of shrub layer,respectively（p<0.05）.（2）The individual carbon accumulation rate of Q.griffithii(15.01±2.24 kg C a^-1)was largely higher than that of other tree species（p<0.05）.Carbon storage of tree layer in CQE was more than that in CCM for about 62.03%.The litter layer carbon storage was in the order of CCM>CQE>MC（p<0.05）.The percentage of litter layer carbon storage that accounted for carbon storage of understory layers in CCM and CQE increased for 21.47%and 18.32%respectively.0～40cm soil carbon storage in CCM was 31.31%higher than that in the control forest（MC）.CNS also reduced percentage of easily oxidized organic carbon（EOC）accounted for soil organic carbon（SOC）content.The belowground carbon storage accounted for 77.80%,67.92%and 69.37%of total carbon storage in CCM,CQE and MC respectively.（3）Correlation analysis indicated that community indexes were major driving factors of ecosystem carbon accumulation.Impact of different community index on the carbon storage of each layer of ecosystem was different.Carbon accumulation was also influenced by soil properties.Litter layer carbon storage was positively correlated with the topsoil（0～20cm）carbon storage（p<0.05）.Topsoil C:N was in the order of CCM>CQE>MC（p<0.05）.Soil C:N was positively correlated with SOC content（p<0.01）and negatively correlated with EOC（p<0.05）.CNS accelerated community succession through changing tree sepcies compostition and community structure.This promoted tree layer diveristy and organic matter input from litter,enhanced soil carbon stability,facilitated soil carbon accumulation and increment of belowground carbon allocation.