Carbon Storage Of Typical Plantations In South Sub-Tropical Area

Climate change mitigation through afforestation and reforestation has become the generalconsensus of the international community. The south subtropical area of China is the priorityregion for afforestation and reforestation. In subtropical area of China,70%of the plantationsare composed of coniferous species. In view of low ecosystem service and ecologicalinstability of pure coniferous species, transforming conifer pure plantation by plantingindigenous and valuable broad-leaf tree species is being advocated as an effectiveclose-to-nature forest management in sub-tropical China. To native hardwood species, peopleoften pay more attention to their timber income, while litter information about their capabilityof carbon sequestration was focused. In Tropical Forestry Experimental Center of ChineseAcademy of Forestry Science, the following contents were studied:1) The biomass allometricequations of Castanopsis hystrix and Mytilaria laosensis were established, and the errors of thebiomass equations from different forms and independent variables were analyzed.2) Carbonstock and carbon sequestration of a beech (Castanopsis hystrix) chronosequence plantations insouth sub-tropical area were studied.3) Carbon storage and distribution feature of the Mytilarialaosensis plantation in south sub-tropical area were researched.4) The soil carbon storage ofCunninghamia lanceolata,Pinus massoniana,Castanopsi hystrix, Mytilaria laosensis,andCastanopsi hystrix*Pinus massoniana mixed plantations were compared,and its influencingfactors were analyzed.5) The carbon storage and distribution feature of plantations in TFECwere researched.6) The plantation carbon storage in TFEC was assessed with the AnalyticHierarchy and some advices for the forest management were proposed. The main results are asfollowing:1) The Power model fit well for the Castanopsi hystrix (R²=0.967±0.024,SE=0.042±0.021), Mytilaria laosensis(R²=0.955±0.062, SE=0.064±0.098), Cunninghamialanceolata(R²=0.960±0.035,SE=0.084±0.081)and Pinus massoniana (R²=0.982±0.01,SE=0.067±0.035)among seven models with D as the independent variabe. Accuracy can be slightly improved if H as a second independent variabe is included in a DBH based allomatricequations. Compared to DBH-only equations, the DBH-H combined equations increasd R²from-0.38%to1.40%.2)Carbon concentrations and stocks of different plant tissues, litters, soils, and theirspatial distributions of a beech (C. hystrix) chronosequence (10-,20-and27-year-old)plantations were investigated by biomass harvesting method in south sub-tropical area of China.Carbon concentrations in different organs of C. hystrix ranged from49.7%to57.9%. Thecarbon concentration of litter layer was40.8%-50.5%, and the fresh litter layer was higher thanthe humus layer. Carbon concentrations in the soil profile of0-60cm depth increased with thestand age, and decreased with the soil depth. The total carbon stocks in the beechchronosequence (10-,20-and27-year-old) were182.42,234.75,269.75t hm^-2, respectively.The proportions of the component carbon stock of the tree layer, litter layer and soil layer were19.8%,32.0%and32.8%ï¼›1.5%,1.6%and1.3%ï¼›78.7%,66.4%and65.9%. The stage of10～20years is the rapid development period for C. hystrix. The proportion of tree layer carbonstorage in the total carbon pool rapidly increased from19.9%to32.0%, while the proportion ofsoil layer was reduced from78.7%to66.4%. The component percentage of carbon storage in C.hystrix plantations from20～27years old is relatively stable. The proportion of the tree layerranged from32.0%to32.9%, and the soil layer ranged from65.9%to66.4%. The annual netcarbon sequestration of C.hystrix plantations of10,20, and27years old are4.70,5.64and5.18t hm^-2, respectively.3)The concentration, storage and allocation of carbon for the Mytilaria laosensisplantation were investigated through biomass harvesting. The carbon content of differentorgans varied from51.47%to57.38%. There are significant differences in carbon contentbetween different organs. Litter carbon content varied from49.87%to56.02%. Soil carboncontent varied from0.62%to2.91%for0-100cm. The carbon stocks of tree, litter, and soillayer were154.07,2.74, and174.80t/hm², respectively. The average annual net carbonsequestration of tree layer and litter layer were8.97t/hm²and0.91t/hm²respectively. 4)The soil carbon content of top soil (0²0cm) are significantly different among thefive plantations with Castanopsi hystrix*Pinus massoniana＞Mytilaria laosensis＞Castanopsihystrix＞Pinus massoniana＞Cunninghamia lanceolata. The soil carbon content of differentstands gradually decreased with soil depth increasing. For the40～60cm, no significantdifferences among different stands were found. The soil TN content for each soil layer is notsignificant differences among different stands. In0-60cm soil layer, both TN content and soilwater content was significantly correlated with soil organic carbon (P<0.01), correlationcoefficients were0.838and0.416, reflecting the coupling relationships among soil carbon,nitrogen and water content. In0～20cm soil layer,the soil carbon content was positivelycorrelated with TP,and negatively correlated with total K and hydrolyzable N. No significantcorrelations were found with other nutrients. The difference of soil carbon storage is similarwith soil carbon content.5)Based on forest resource inventory data, the carbon storage of plantations distributed inTFEC is411709.6t, and the biomass carbon density was30.93t/hm². Masson pine plantation inthe region accounted for a large proportion of carbon reserves, accounted for65.2%of the totalplantation carbon reserves. The carbon density of different plantations in the order as follows:native broadleaf species (35.38t/hm²)> Pinus massoniana (32.05t/hm²)> Cunninghamialanceolata (31.74t/hm²)> fast-growing eucalyptus (16.16t/hm²)> cash forest (14.55t/hm²).Amongst, middle-aged forest, near mature forest and mature forest accounted a largeproportion of carbon storage with39.40%,30.37%and17.96%. With the standing ageincreasing, the forest carbon density increased significantly from young forest to near matureforest (8.19t/hm²-49.52t/hm²), while from mature forest to overmature forest, carbon density isrelatively stable (55.64t/hm²ï½ž58.46t/hm²).6)Through the analytic hierarchy process of plantation carbon storage evaluation, theirweights are as follows: Coniferous and native broad-leaved mixed forest(0.3509), nativebroad-leaved forest (0.2643), coniferous forest (0.1864), fast-growing eucalyptus (0.1092) andcash forest (0.0892). The pure coniferous plantation should be converted into mixed forest and native broad-leaved forest through interplanting or repairing planting. The volume mature ageand carbon mature age of Pinus massoniana was22years old.