| With the continuous progress of global industry, the content of greenhouse gases in atmosphere is rising continuously, and global warming is more and more cause the attention of people. Forest ecosystems are the main component of terrestrial ecosystems, their function of carbon fixation and carbon sinks become more significant. Carbon storage in forest ecosystems including organic carbon storage in soil, organic carbon storage in vegetation and organic carbon storage in litter layer, is the major source of evaluating forest ecosystem's carbon dioxide absorption function. Cunninghamia lanceolata, Pinus massoniana, Phyllostachys edulis and Eucalyptus grandis are important forest resources in south of China with wide economic use, and they are the most widespread plantation ecosystems in Fujian province. This thesis use the method of combining field investigation and laboratory testing to study the plantation ecosystem's carbon density and spatial distribution of Cunninghamia lanceolata, Pinus massoniana, Phyllostachys edulis and Eucalyptus grandis in Fujian province. Based on the data, the least squares -support vector machine method is used to separately predict and estimate the plantations'organic carbon content and organic carbon density in soil and analyze the linear and nonlinear regression between organic carbon density in soil, and stand age, slope exposure, slope position. Therefore this thesis apply the multivariable linear regression model to predict the biomass of different plantation's various organs in tree layer and calculate the organic carbon content and organic carbon density of various organs in tree layer. In plantation ecosystems of Cunninghamia lanceolata, Pinus massoniana and Eucalyptus grandis, the canonical analysis research is carried out to analyze the relationships between each soil layer's organic carbon density and tree layer's trunk, branch, leaf and root, the herb layer, shrub layer and litter layer of undergrowth vegetation. Furthermore, the relationship between soil carbon density and aboveground carbon density is studied. Finally, the jackknife method, projection pursuit method, etc. are used to simulate the relationship between carbon density in the tree layer and DBH, tree height. The major research results are as follows:1 The characteristic of soil organic carbon content and carbon density's spatial distribution: organic carbon content and carbon density are all represented as the surface soil organic carbon content's decreasing along with soil depth's increasing in the vertical direction, in which the fastest decline is from the surface layer to second layer. In the horizontal direction, the order is followed as Phyllostachys edulis>Eucalyptus grandis>Cunninghamia lanceolata>Pinus massoniana, downgrade>mesoslope>upslope, sunnyslope>dark-slope. Cunninghamia lanceolata forest and Phyllostachys edulis forest's soil organic carbon content and organic carbon density represent the mutative characteristic of young forest>middle-aged forest>mature forest, but Pinus massoniana forest, Eucalyptus grandis forest at different developmental stages, the trend of soil organic carbon density is opposite, represent young forest Pinus massoniana forest> Phyllostachys edulis forest. The organic carbon density of various organs in different kinds of forest's tree layer all showed the trend of trunk> root> branch>leaf. In detail, on the part of trunks, the big to small order of organic carbon density is followed as: Pinus massoniana > Cunninghamia lanceolata > Eucalyptus grandis > Phyllostachys edulis. On the part of roots, the big to small order of organic carbon density is followed as: Cunninghamia lanceolata > Pinus massoniana > Phyllostachys edulis > Eucalyptus grandis. On the part of branches, the big to small order of organic carbon density is followed as: Cunninghamia lanceolata > Pinus massoniana > Phyllostachys edulis > Eucalyptus grandis. On the part of leaves, the big to small order of organic carbon density is followed as: Cunninghamia lanceolata > Pinus massoniana > Eucalyptus grandis > Phyllostachys edulis.8 The largest organic carbon density of understory vegetation in different forest is Pinus massoniana of 0.263 kg/m2, followed by Eucalyptus grandis, Cunninghamia lanceolata, Phyllostachys edulis. The carbon density of the vegetation under Phyllostachys edulis forest is the least of only 0.031 kg/m2. Underground vegetation in each layer, the carbon density of pinus massoniana in shrub layer and litter layer is the largest of 0.133 kg/m2 and 0.107 kg/m2, followed by Eucalyptus grandis and Cunninghamia lanceolata, Phyllostachys edulis is the least. And, the largest organic carbon content in herb layer is Cunninghamia lanceolata forest, followed by Eucalyptus grandis, Pinus massoniana and Phyllostachys edulis. Hence, in this study, the forest structure of Phyllostachys edulis is simple and seriously disturbed by human. Pinus massoniana and Cunninghamia lanceolata plantations are relatively rich in forest structure, understory plant species is diversity and the biodiversity is high.9 The carbon storage of four kinds of plantation's ecosystem is different, The organic carbon storage of Cunninghamia lanceolata plantation's ecosystem is the largest of 28.125 kg/m2, Pinus massoniana plantation is the second of 27.779 kg/m2. Phyllostachys edulis is the third of 22.884 kg/m2, and Eucalyptus grandis plantation is the smallest of 22.381 kg/m2.10 Forest ecosystem is an organic whole, each part of the organic carbon content not only influenced by environmental factors, but also there must be self-relevant. This thesis makes the sub-layer organic density of the soil h1, h2, h3 and h4 and 0-100cm's profile organic carbon density as the typical variable of first group x2, x3, x4, x5, and the tree layer of trunk, root, branch, leaf, herb layer, shrub layer and litter layer are the second group as y1, y2, y3, y4, y5, y6, y7. Canonical correlation analysis was carried out to discuss the effect of underground carbon density to aboveground carbon density and analyze the relationship between soil carbon density and aboveground carbon density. The results showed that the extent of relative effect of soil organic carbon density to u1 will successively reduce as the soil depth decline, and the order is the h1 layer (0 ~ 20 cm) >the h2 layer (20 ~ 40 cm) > the h3 layer (40 ~ 60 cm) >the h4 layer (60 ~ 100 cm) in which the role of the h1layer is the largest, the role of the h4 layer is little. The correlativity between v1 and the raw data of each layer's organic carbon density on the aboveground part is as follows: a significant positive correlation is existed between v1 and aerial parts of tree trunks, roots organic carbon density (yi).11 Based on the 64 survey materials of Cunninghamia lanceolata, Pinus massoniana, Phyllostachys edulis and Eucalyptus grandis in Yongan and Jianyang County, Fujian province the jackknife method was used to estimate the organic carbon density in tree layer of plantations. According to calculate results, the organic carbon density's estimated amount is 12.740 kg/m2 in plantation tree layer, and the estimated accuracy is 93.239%. Therefore, the result of estimating the organic carbon content of plantation tree layer is reliable by using the method of jackknife.12 Because the premise of establishing multiple regression models is that there is exactly exist the model's assumed correlation between the impact factor and predicting factor and the correlation between predictors is not consistent linear or nonlinear and show several related forms, projection pursuit regression model of soil organic carbon density is adaptable for simulating. This thesis introduced the idea of weighting and established the soil organic carbon density model in the constrained based constringent and optimized genetic algorithm.
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