Research On Cabon Density And Carbon Sequestrarion Capacity Of Secondary Quercus Variabilis Forest In The Karst Area Of Xichuan County Henan Province

This paper makes a research in the karst area of Xichuan County,Which is the water source of the Middle Route South-to-North Water Transfer Project and the northernmost karst area in Southwest China.with different fixed number of year of the recovery（20a,35a,40a,28a,and 53a,70a）the Quercus variabilis forest as the research object,based on“the space instead of time”method,through combination of field survey and indoor experiment,analysis the different recovery duration of Quercus variabilis forest community structure characteristics,and the tree layer are calculated by use of a standard tree modeling method of biomass,the full harvest method is adopted for bringing,litter biomass directly,combination with the determination of the biological carbon content and soil carbon content,The carbon density of the secondary forest community of Quercus variabilis in different restoration years was calculated to determine the carbon density and distribution pattern of different levels of Joe-irrigation-grass in the community plant carbon pool,root,stem,branch,leaf and soil carbon pool,and to estimate the carbon sequestration capacity of the secondary forest community of Quercus variabilis in karst area.The results of this study provide scientific basis for the management of stony desertification and the operation and management of increased accumulation and emission reduction of Quercus variabilis forest in karst area of Xichuan County.The main research conclusions are as follows:1、The results of plant community survey showed that there were 63 species of vascular plants belonging to 40 families and 58 genera.On the whole,the species composition is relatively simple and the richness is at a low level.With the increase of the recovery years,the species richness increased,but most of the species were single family,single genus and single species.The diversity index of species at all levels in the plot showed different characteristics with the increase of recovery years,and the overall change trend was slowly rising.The 6communities with different recovery years were very dissimilar and the species composition was very different.2、The results of community biomass calculation showed that the biomass of secondary forest of Quercus variabilis was the highest at 306.08t/hm²after 70 years of restoration,and the biomass of community restored at 20 years was the lowest at 128t/hm².The compatible biomass model was used to calculate the biomass of trees,and the results showed that the indexes of the binary model with DBH and tree height as variables were better than those of the unary model.The biomass of the shrub layer increased first and then decreased with the increase of the recovery time.The biomass of the herb layer decreased gradually with the increase of the time.There was no obvious rule of the litter layer biomass.3、The calculation results of vegetation carbon density showed that the vegetation carbon density in the community was closely related to biomass and increased with the increase of vegetation restoration years.The carbon density of the arbor layer ranged from 87.53%to94.68%,and the carbon density of the understory vegetation ranged from 5.32%to 12.47%,represented by the shrub layer,>litter layer,>herb layer.The analysis of the carbon density distribution pattern of the arbor layer shows that the proportion of the aboveground carbon density in the total carbon density is between 73.66%and 78.42%,and that of the underground carbon density is between 21.58%and 26.34%.In the aboveground part,the proportion of trunk was the largest,57.99%-59.76%.The second is the branch,and the proportion of carbon density is 16.49%-21.14%.It is bark again,and the proportion of carbon density on the area is between 15.30%and 18.20%.Leaves accounted for the smallest proportion（5.54%-5.57%）,with little change over time.4、The average carbon content（0-30cm）of the soil in the secondary forest of Quercus variabilis in karst area of Xichun County is 54.69g/kg,of which the carbon content in the soil in sample 40a of the restoration period is the highest（69.58g/kg）,and that in sample 20a of the restoration period is the lowest（43.26g/kg）.The soil carbon content of 0-10cm in different recovery years was 19.62g/kg-41.81g/kg（average 28.59g/kg）,and the soil organic carbon density was 25.31t/hm²-45.57t/hm²（average 32.35 t/hm²）,which was comparable to the soil organic carbon density of 33.10t/hm²in the karst forests of southwest China.Soil carbon density of Quercus variabilis secondary forest in Karst area of Xichuan County is similar to that in karst area of southwest China and lower than that in non-karst area.5、The carbon density of the secondary forest community of Quercus variabilis in karst area of Xichuan County was 112.23t/hm²-197.09t/hm²,with an average of 146.19t/hm².With the increase of recovery years,the carbon density of Quercus variabilis community showed an increasing trend.Among them,the carbon density of vegetation layer accounted for50.28%-68.19%of the community carbon density,and the proportion showed a gradual increasing trend with the increase of recovery years.The proportion of carbon density in the soil layer decreases gradually.The analysis of community carbon sequestration capacity showed that the annual carbon sequestration of soil in the secondary forest of Quercus variabilis in karst area was lower than that of vegetation.The annual carbon sequestration rate of vegetation and soil decreased with the increase of recovery time,and the annual carbon sequestration rate of soil decreased faster than that of vegetation,and the gap increased with the increase of recovery time.On the whole,the karst area has a good growth condition and great carbon sequestration capacity,which plays an important role in reducing atmospheric CO₂emission,and is suitable to be promoted as the main afforestation tree species for the control of rocky desertification in Xichuan County and even the whole southwest Karst area.