Carbon Accumulation And Distribution In Eucalyptus Urophylla×E.Grandis, Acacia Grasscarpa And Their Mistrure Plantation Ecosystems

The forest is the main body of terrestrial ecosystem and it plays an impotant role in the global canbon cycle.With the nature forest resource decreased,artificial forest continuously increased,and the carbon sink of artificial forest are being more and more concerned. After the Kyoto Protocal was signed and put into effect,finding ways to control or reduce carbon release must be the urgent impotant problem to be solved for countries all over the world at present and from now on. It is no doubt an impotant way to improve carbon fixiation of terrestrial ecosystem and slow down the carbon accumulation rate in the atomosphere by afforestation and reafforestation,which will be one of the main development derection of China forestry.Guangxi province was the first region to carry out the forest carbon sink project for clean development mechanism,which may play a very important part in the grobal practice of forest carbon sink.So the carbon sink of artifficial forest of Guangxi must be immidiately test to provide basic data for making regional forest carbon sink standard.For this two common short-term rotated industrial timber plantations(Eucalyptus urophylla×E.grandis and Acacia grasscarpa)and their mixture plantation were chosen to sdudy the carbon accumulation and distribution of their ecosystems by using data continuously investigated from permanent sampling plots.The main results are as follows:There were differences of carbon content of different component of Eucalyptus urophylla×E.grandis,Acacia grasscarpa and their mixture plantations among different tree species and different organs.The sequence of mean carbon content of arboreous layer of 1.5,2.5,3.5 and 4.5-year-old tree species was Acacia grasscarpa＞Eucalyptus urophylla×E.grandis.The sequence of carbon content of different organs of arboreous layer was leaf＞branch and stem＞root＞bark. The sequence of mean carbon content of different component of was arboreous layer＞ground litter＞Herb layer＞Shurb layer.Soil carbon content and the differences between them decreased with soil depth increased.Mean carbon content of the same soil layer were all in sequence of mixture plantation＞pure artificial Acacia grasscarpa forest＞pure artificial Eucalyptus urophylla×E.grandis forest.The carbon storage of Eucalyptus urophylla×E.grandis,Acacia grasscarpa and their mixture plantation ecosystems of 1.5,2.5,3.5 and 4.5-year-old were 90.75,111.56,124.10 and 137.18 t·hm^-2,73.04, 86.11,97.02 and 118.76 t·hm^-2,83.42,109.03,130.39 and 145.45 t·hm^-2,respectively.The carbon storage increased with stand age,but mainly in arboreous layer.There were differences among carbon storage of the three plantation ecosystems.The caobon storage was in sequence of pure artificial Eucalyptus urophylla×E.grandis forest＞mixture plantation＞pure artificial Acacia grasscarpa forest in 1.5-year-old and 2.5-year-old plantations,and in sequence of mixture plantation＞pure artificial Eucalyptus urophylla×E.grandis forest＞pure artificial Acacia grasscarpa forest in 3.5-year-old and 4.5-year-old plantations.Mixture plantation enhanced the increase of carbon storage in arboreous layer and soil.The carbon distribution of Eucalyptus urophylla×E.grandis,Acacia grasscarpa and their mixture plantation ecosystems was in sequence of soil＞arboreous layer＞underground vegetation.Carbon mainly accumulated in the soil and especially in the 0～20cm layer.Over 50 percent of the total carbon storage of soil was in the 0～20cm layer of the three plantations.The annual net carbon fixiation of 1.5,2.5,3.5 and 4.5-year-old plantation of Eucalyptus urophylla×E.grandis,Acacia grasscarpa and their mixture plantation were 14.84,20.65,12.07 and 11.69 t·hm^-2.a^-1(amounted CO₂ to 54.42,75.72,44.26 and 42.87 t·hm^-2·a^-1),3.89, 11.45,10.05 and 20.03 t·hm^-2·a^-1(amounted CO₂ to 14.26,41.98, 36.85 and 73.44 t·hm^-2·a^-1),9.77,22.62,19.21 and 13.79 t·hm^-2·a^-1(amounted CO₂ to 35.82,82.94,70.44 and 50.56 t·hm^-2·a^-1)。The percentage of annual carbon return through litter to annual net carbon fixiation were below 33.37%.The potential of the three plantations are still very large.