| Global carbon cycle is a very important issue in the study of global climate change. Forest ecosystem carbon cycle is one of the important part of global carbon cycle, but at the present time there are considerable uncertainties in the research of global carbon cycle, which also exist in forest ecosystems carbon cycle research, especially in the estimation of carbon storage of region forest ecosystems and CO2 fluxes exchanging with other systems. Accurate estimation of the carbon storage and CO2 fluxes and reducing the estimation uncertainties for region forest ecosystems are the hot and difficult problems. As a case study with Quercus liaotungensis, Betulla platyphylla, Poplus davidiana, Pinus tabulaeformis and Larix, principis-rupprechtii in Northern China, several crucial issues have been studied, including the measurement of the tissues' carbon content of the main constructive arbor species and shrub species, the estimation methodologies of carbon storage and carbon sequestration abilities of region forest ecosystems and so on. The main results are as following:First, the tissues' carbon content had been measured on eight constructive arbor species and ten shrub species in Northern China by using the combustion method, and the mean tissues' carbon contents of these species were 0.4880, 0.4764. 0.5105, 0.5010, 0.5158, 0.5118, 0.4897 respectively in Quercus liaotungensis, Betulla platyphylla, Poplus davidiana, Tilia mongolica, Pinus tabulaeformis, Platycladus orientalis, Larix principis rupprechtii, Picea Koraiensis and ten shrub species(they are Corylus hrterophylla, Ostryopsis davidiana, Lespedeza bicolor, Spiraea pubescens, Rosa xanthina, Syringa oblata, Eleagnaceae umbellate, Lonicera maackii, Acer ginnala, and Hippophae rhamnoides). Based on the biomass data of stand sample plot, the mean carbon content of seven stands had been calculated, the result was 0.4761 in Quercus liaotungensis, 0.5008 in Betulla platyphylla, 0.4859 in Poplus davidiana, 0.5030 in Pinus tabulaeformis, 0.5053 in Platycladus orientalis, 0.5097 in Larix principis rupprechtii and 0.5111 in Picea Koraiensis. The variance ratio of the tissues' carbon content ranged from 1.49% to 6.32% inner species, and 2.15% to 7.48% between species. The mean tissues' carbon content of conifer species was higher than broadleaf species by 1.6%-3.4%, and the carbon content of conifer stands was also higher than broadleaf stands.Second, the study results show that the biomass expansion factors (BEF) for main forest types in Northern China were closely related with the ratio of stand total biomass to stem biomass (Wt/Ws] and also were closely related with the timber basic density(p). Theformula of BEF is BEF=p×(Wt/Ws). According to the changing values of Wt/Ws and p,the theory BEF for 5 main forest types have been calculated, and the theoretic value of BEF is rather consistent with the actual BEF value. Various models have been applied to study the relationship between BEF of the 5 forest types in Northern China and stand growing stock, and the results showed that by developing the regressive models concerning BEF and stand growing stock to estimate the stand biomass it was hard to achieve satisfying results.Third, there are close Correlations between stand each biomass component and growing stock volume in 5 main forest types in Northern China, the optimal correlation model is the form of W = a + bV for main forest types in Northern China.Fourth, based on the data of national forest survey, the compatible biomass estimation models on 5 main forest types in Northern China have been brought forward, and their parameters also have been estimated and examined. A great deal calculation and analysis results showed that using this kind of model to estimate the each biomass component of stand can get more precise estimation.Fifth, in the stand biomass estimation based on the data of national forest survey, the concept of coefficient of volume adjustment (CVA) for young stand growing stock has been firstly put forward, and the CVA models...
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