Carbon Sequestration Of Main Forest Types At Huoditang Forest Region In The Qinling Mountains

Biomass in pure forests of Quercus aliena var. acuteserrata, Pinus armandi, Pinus tabulaeformis and Betula albo-sinensis, as well as a mixed forest between Quercus aliena var. acuteserrata and Pinus armandi at Huoditang forest region in the Qinling Mountains were determined. Meanwhile, carbon content rates and carbon density of dominant vegetation and litter layers in these forests were estimated. Finally, carbon density, carbon spatial distribution pattern and carbon variations of the forests above were analyzed. Conclusions are as follows:(1) The total biomass in pure forests of Q. aliena var. acuteserrata, P. armandi, P. tabulaeformis and B. albo-sinensis, as well as the mixed forest between Q. aliena var. acuteserrata and P. armandi at Huoditang forest region were236.958t·hm-2,198.422t·hm-2，224.950t·hm-2，179.591and210.820t-hm"2respectively; specifically, for arbor layers, the biomass were231.416t·hm-2，193.056t·hm-2,220.578t·hm-2,177.884t·hm-2and207.56t·hm-2respectively; for shrub layers, the biomass were4.621t·hm-2,3.331t·hm-2,4.517t·hm-2,2.882t·hm-2and2.149t·hm-2respectively; for herb layers, the biomass were0.588t·hm-2,0.342t·hm-2,0.600t·hm-2,0.522t·hm-2and0.718t·hm-2respectively; for litter layers, the biomass were0.334t·hm-2,0.513t·hm-2,0.441t·hm-2,1.707t·hm-2and0.394t·hm-2respectively.Aboveground biomass of the investigated forest types accounts for75%to90%in the total, while underground biomass accouts for10%-25%.(2) The average carbon content rates in arbor layers of pure forests of Q. aliena var. acuteserrata, P. armandii, P. tabulaeformis and B. albo-sinensis, as well as the mixed forest between Q. aliena var. acuteserrata and P. armandi were0.4712,0.4863,0.4977,0.4841and0.4671respectively; specifically, for shrub layers, average carbon content rates were0.4250,0.4419,0.4022,0.4132and0.4333respectively; for herb layers, average carbon content rates were0.3740,0.4017,0.3978,0.3926and0.3491respectively and for litter layers, average carbon content rates were0.3336,0.3409,0.3804,0.3450and0.3634. All the carbon content rates in shrub, herb and litter layers of the five forest types were lower than0.45. If0.45or0.50was used as average carbon content rate to compute the carbon stock in shrub, herb and litter layers, the results might be overvalued. In addition, the differences of carbon content rates of different components in the same shrub layers or the same component in different shrubs layers were much higher than that of arbors. For instance, for shoots and stems of shrubs, the carbon content rates ranged from0.3764to0.4978, and for leaves of shrubs, the carbon content rates ranged from0.3335to0.4857, and for roots of shrubs, the carbon content rates ranged from0.2640to0.5238. Moreover, average carbon content rate of weighted biomass in a cluster of shrub ranged from0.3623to0.4789, which confirmed that the carbon stock in shrub layers of forest community should be estimated based on the biomass and carbon stock of different organs in a cluster of shrub, rather than the average carbon content rate.(3) The carbon density in arbor layers of pure forests of Q. aliena var. acuteserrata, P. armandi, P. tabulaeformis and B. albo-sinensis, as well as mixed forests of Q. aliena var. acuteserrata and P. armandi were109.052t·hm2,93.878t·hm-2,109.773t·hm-2,86.111t·hm-2and96.955t·hm-2respectively; The carbon density in shrub layers were1.878t·hm-2,1.816t·hm-2,1.230t·hm-2,1.398t·hm-2and0.931t-hm"2respectively; the carbon density of aboveground parts took42.36%,62.43%,56.53%,50.30%and46.67%respectively; while the underground counterparts were57.64%,37.57%,43.47%,49.30%and53.33%respectively. In the herb layers of the investigated forest types, the carbon density were0.220t·hm-2,0.137t·hm-2,0.239t·hm-2,0.205t-hm"2and0.251t·hm-2respectively; the aboveground parts took46.68%,31.31%,27.78%and36.87%respectively, while the underground counterparts took53.32%,68.69%,72.22%and63.13%respectively. The carbon density in litter layers were0.112t·hm-2,0.175t·hm-2,0.168t·hm-2,0.589t-hm"2and0.143t·hm-2respectively.(4) Carbon stock increased with diameter classes, but this correlation was not significant, as a result of random emergence in individuals with large diameter classes.(5) The principal parts for carbon sink in the5forest types were all shoots and stems, accounting for66.59%-79.77%of the arbor layers. Though carbon sink of roots in these layers were also great, obvious differences of carbon sink among roots from different trees were found(7.50%-24.11%), indicating high complexity in root growth. In contrast, the leaves and bark had the least carbon stock(7.25%-16.73%).(6) From2006to2011, the average annual increase in the carbon density of pure forests of P. armandi, P. tabulaeformis and B. albo-sinensis were3.512t·hm-2,3.738t·hm-2and2.214t·hm-2respectively. The rise of carbon density might be caused by forest tending in the past several years. On the contrary, the carbon density in pure forest of Q. aliena var. acuteserrata was0.134t·hm-2. The cause of this decrease is still unknown and requires further research.