Carbon Dynamic Of Betula Platyphylla Natural Secondary Forest In North Region Of Yanshan Mountain

Forest ecosystem plays an important role in carbon sequestration. The carbon sinkfunction of forest is a complicated dynamic process, which is influenced by various factors,such as intermediate cutting and rotation. A comprehensive understanding of its dynamicchange process and carbon sink function has important scientific and realistic significance.In this paper, biomass carbon, soil carbon, woody forest products carbon and carbondynamic of the betula platyphylla natural secondary forest in north region of Yanshanmountain were studied by using CO2FIX V.2model. At the same time, we also comparedwith the carbon dynamic of local larch plantation, in order to comprehensivelyunderstanding the carbon sinks function of natural secondary forest, provide reasonableadvice for the region forest management. The main results are as follow:（1） Under the current rotation system in Chengde region, carbon storage of biomass,soil, woody forest products in betula platyphylla natural secondary forest present periodicchanges, In each cycle, the biomass carbon storage show a fluctuant trend, ranged from0to50t hm^-2;Soil carbon storage first reduce, then increase fluctuantly and last return to theinitial level. Carbon storage of woody forest products is rapid increase in short-term andthen decrease slowly. According to the carbon storage value of different woody forestproducts carbon pools, the order is: long-term landfill> mid-term products> long-termproducts> energy （firewood）> dump>short-term products. The periodic change rule ofeach carbon pool in larch plantation is similar to betula platyphylla natural secondaryforest, the biomass carbon storage is higher than betula platyphylla forest, which is rangedfrom0to55t hm^-2, the carbon storage of long-term products and dump in woody forestproducts are larger than mid-term products and energy （firewood）.In a120-years simulation period, the soil carbon storage in two kinds of forests areboth gradually increasing with the extension of time, betula platyphylla natural secondaryforest ranged from79to106t hm^-2, larch plantation ranged from82to116t hm^-2, whichis a little higher. Woody forest products carbon storage of both forests are also graduallyincreasing with the extension of time in this period.（2） Total carbon storage of betula platyphylla natural secondary forest presents periodic changes, in each cycle, the total carbon storage showed a“reduce-increase-reduce” trend. In the simulation period, betula platyphylla forest showeda slow increase trend, ranged from80to150t hm^-2, larch plantation showed a increasetrend, ranged from90to166t hm^-2. In the simulation period, the contribution rates of eachcarbon pool in forest is constantly changing, the contribution rates of soil carbon storage,biomass carbon storage and woody forest products carbon storage in betula platyphyllaforest to the total were75%,22%and3%respectively, larch plantation were70%,22%and8%.（3） In the early and later stage of the stand, betula platyphylla natural secondaryforest performance as carbon source, among most of the time （about30years） performanceas carbon sink. The time of larch plantation performance as carbon sink is a little longer,about40years. From the annual net carbon balance point of view, both kinds of the forestsare obviously carbon source, annual net carbon balance of betula platyphylla forest andlarch plantation respectively is about0.5t hm^-2and0.9t hm^-2.（4） In this region,404t hm^-2carbon were sequestrated by the betula platyphyllanatural secondary forest in two rotations （100years）.84%of the carbon transfered into soilthrough the way of litter and logging slash, the other16%transfered into woody forestproducts. After the rotation, about80%（according to the forest carbon sequestration） of thecarbon released to the atmosphere through soil respiration,8%released to the atmospherethrough decomposition and energy burning. Then, the values are respectively as follow:biomass carbon storage0t,3%stored in soil carbon pool, about12.82t,8%stored inwoody forest products carbon pool, about35.26t.The NPP of larch plantation is about501t,70%of the carbon transfered into soilthrough the way of litter and logging slash, the other30%transfered into woody forestproducts. After the rotation, about66%（according to the forest carbon sequestration） of thecarbon released to the atmosphere through soil respiration,23%released to the atmospherethrough decomposition and energy burning. Then, the values are respectively as follow:biomass carbon storage0t,5%stored in soil carbon pool, about23.00t,7%stored inwoody forest products carbon pool, about33.19t.（5） Under different rotation （30a,40a,50a,60a and70a）, the total carbon storage andeach carbon pool carbon storage of betula platyphylla natural secondary forest are different:from the total carbon storage point of view, appropriate rotation length is about60a;Appropriate rotation length of biomass carbon storage is about60a; Appropriate rotationlength of soil carbon storage is about40a; short rotation is helpful to the carbonaccumulation in woody forest products. Whereas, appropriate rotation length of totalcarbon storage in larch plantation is about40a; Extension of rotation contribute to theincrease of biomass carbon storage; Appropriate rotation length of soil carbon storage isabout50a; short rotation is helpful to the carbon accumulation in woody forest products. Taken together, the current rotation length （50a） of two kinds of forests is more reasonable.（6） When temperature or rainfall increased, soil carbon storage of both betulaplatyphylla natural secondary forest and larch plantation would decrease while soilrespiration enhanced. Climate change such as the change of the temperature, precipitationand other factors, induced soil carbon storage and ecosystem by influencing the soilrespiration etc. We should pay more attention to these problems.