Carbon Sequestration Rate And Productivity Of Natural Secondary Quercus Liaotungensis Forests In The Loess Hilly Region

In recent years,a series of ecological and environmental problems caused by global climate change,including the increases in CO2 concentration and temperature,have made the carbon cycling of forest ecosystems drawing increasing attention.Loess hilly region is the key implementation area of natural forest protection project and Grain-for-Green project,being the potential area of carbon sink.The carbon sequestration of the forest ecosystem is one of the research hotspots in recent years.The estimation of the carbon sequestration status,rate and the gross primary productivity of the forest ecosystem in the region is essential to evaluating the role of vegetation restoration and ecosystem services.Based on multiple surveys of permanent plots,this study estimated the present situation of carbon sequestration,the distribution of ecosystem biomass and carbon density,and the change of primary productivity and carbon fixation rate of tree layer in time series in the natural secondary forest of Q.liaotungensis.The study would provide theoretical basis for assessing the forest ecosystem function and services in the region and for the estimation of carbon sequestration potential of Q.liaotungensis natural secondary forests.The main conclusions of this study are as follows:(1)In the Loess hilly region,the biomass of the arbor layer was 201.08 t·hm-2 in the natural secondary forest ecosystem of the Q.liaotungensis forests.The stem biomass accounted for 63.94% of the tree.The proportion of each other organ(branches,roots and leaves)of tree biomass was 19.91%,11.59% and 4.56%,respectively.The biomass of shrub was 7.25 t·hm-2,and the relevant proportion of each organ(leaves,branches and roots)of shrub biomass was 6.18%,66.07%,27.75 %.The biomass of herb layer was 0.19 t·hm-2,and the responding ratio of above-and underground was 22.16% and 77.84%.The biomass of litter was 8.06 t·hm-2,which was higher than that of shrub and herb layer.(2)The distribution of carbon density in the vegetation layer was similar with the biomass in the Q.liaotungensis forests.The carbon density of the arbor layer of Q.liaotungensis forests was 90.88 t·hm-2,as well the stem was the main contributor.The stem carbon density made up 65.25% of the tree.The ratio of other organs(branches,roots and leaves)of tree layer carbon density was 20.14%,9.65% and 4.96%,respectively.The carbon density of the shrub layer was 3.16 t·hm-2,and the separate proportion of each organ(leaves,branches and roots)carbon density in the shrub layer was 6.30%,69.91% and 23.79%.The carbon density of herb layer was 0.06 t·hm-2,and the ratio of herb aboveground and underground was 31.72% and 68.28 %.The carbon density of the litter layer was 2.06 t·hm-2,which was 35 times as many as that of the herb layer.(3)The distribution of carbon content and carbon density in each soil layer of the Q.liaotungensis forests was consistent with the previous studies.In Q.liaotungensis forests,the soil organic carbon contents decreased with the deepening of soil layer.It means the soil carbon content in the 0~10cm layer was the highest,and that in the 50~100cm layer was the lowest.The differences of the carbon contents between soil layers were much bigger in the surface soil layers.With the deepening of soil layer,the differences in carbon contents between soil layers were basically the same.The carbon density of the Q.liaotungensis forests was 79.51 t·hm-2,and the carbon density of 0~10cm surface soil was 27.32 t·hm-2,which accounted for 34.36% for the whole soil layer(0~100cm).The surface soil can effectively accumulate more organic carbon,which is an important contribution component of soil carbon pool.(4)The biomass of Q.liaotungensis forests ecosystem was 216.58 t·hm-2,the biomass distribution of the tree layer was the largest,which accounted for 92.84%.The proportion of the shrub,herb and litter was 3.35%,0.09% and 3.62%,respectively.The carbon density of Q.liaotungensis forests was 175.66 t·hm-2.The arbor layer and soil layer were the important components of the ecosystem carbon pool,and the total proportion of the two layers in Q.liaotungensis ecosystem carbon density was 97%.(5)The gross primary productivity of the Q.liaotungensis forests was 11.97±1.76 t·hm-2·a-1.The carbon sequestration rate of the Q.liaotungensis was the highest in the near-mature forest period,reaching 3.25 t·hm-2·a-1,and lowest in the middle age.When Q.liaotungensis forests reached maturity,the carbon sequestration rate began to decline.