Carbon Pools In The Typical Forest Ecosystems In Hilly Loess Region

In this paper, to estimate carbon density of Robinia pseudoacacia, Pinus tabulaeformisplantation and Quercus liaotungensis natural forest ecosystems for different stand ages moreaccurately, we tracked8-,18-,28-, and37-year-old Robinia,9-,23-,33-and47-year-old Pinusand20-,45-,75-, and105-year-old Quercus forests in Hilly Loess Region in China, throughfield investigation, laboratory analysis and data processing analysis, studying the boimass andcarbon content in plant organs, litter and soil, as well as the carbon storage and its allocation indifferent layers. The main results were as follows.(1) The biomass of the arbor layer of Robinia, Pinus and Quercus increased with stand age.The arbor layer biomass of Robinia, Pinus and Quercus were in the range of18.76—134.86t/hm2,1.83—134.00t/hm2and24.79—52.52t/hm2. In most cases, the orders of biomass ofdifferent arbor organs were obvious. The biomass distribution ratios of different arbor organschanged with different tree ages. The proportion of ground and underground decreased withincreasing tree age, and the proportions of Robinia and Pinus were lower than Quercus. Thebiomass of shrub were in the order of branches> roots> leaves. The biomass of shrub brancheswere significantly higher than roots and leaves. Herb was shown as aboveground biomass wassignificantly larger than the underground part. The total biomass of Robinia, Pinus and Quercusforests with increasing stand age showed an increasing trend. Average biomass in the differentcomponents of the studied forest ecosystems were in the order of: arbor layer> litter layer>undergrowth vegetation layer. Arbor layer biomass of the three species and the total communitybiomass had a significant positive correlation. Arbor layer as the main body of forests taked thelargest biomass proportion of vegetation, and directly determined the trend of the total biomassof vegetation.(2) By analysis of variance, the carbon content was significantly different in organs of thesame age forests. The carbon content of same organ was significantly different in Robinia, Pinusand Quercus, too. The average carbon content of various organs of Robinia, Pinus and Quercuswere in the range of38.9%—43.6%,47.3%—53.3%and39.9%—45.9%, respectively. Carboncontent of Robinia, Pinus and Quercus calculated with biomass weight were41.89%,50.83%and44.55%, respectively. Shrub carbon content of various organs was in the order of branches>leaves> root. The carbon content of herbs was greater in the above-ground portion than in theunderground portion. The general performance of the average carbon content of the forest layers were shrub> herb> litter, and significantly lower than the tree layer carbon content. The organiccarbon content of Robinia, Pinus and Quercus soil (0í100cm) was between0.51%3.61%,0.30%2.70%and0.33%2.68%, respectively. Robinia deep soil organic carbon content wassignificantly higher than that of Pinus and Quercus, and gradually increased with stand age. Soilorganic carbon content also existed significant difference of different forest ages in the same soillayer. The soil organic carbon content in different soil layers of the same age forests weresignificantly different. The forests soil organic carbon content had an obvious verticaldistribution characteristic: the surface soil layer had a higher organic carbon content and organiccarbon content gradually decreased as soil depth increased.(3) The carbon density in arbor layers of Robinia, Pinus and Quercus increased withincreasing stand age significantly. The carbon density in arbor layers of Robinia, Pinus andQuercus were in the range of7.6557.15,0.9060.20and10.6323.62t/hm2,respectively.The soil layer carbon density of Robinia increased with increasing stand age, and inthe range of7.6557.15t/hm2. The soil layer carbon density of Pinus and Quercus firstincreased and then decreased with increasing stand age, and in the range of65.05100.73t/hm2and88.47—112.03t/hm2, respectively. The proportion of vegetation carbon density increasedwith increasing tree age continually, whereas that of soil carbon density had the opposite pattern.Forest age was a dominant factor affecting the carbon density of the forest communities. Carbondensity in different components of the studied forest ecosystems was in the order of: soil layer>vegetation layer> litter layer.