| Biomass and carbon storage of tree plantations in China have been increased continuallyin recent decades, and play a more and more significant role in the global atmospheric carboncycle. Eucalypt is the main plantation species in southern China, and total eucalypt plantationarea in China is the third in the world. Therefore, studying biomass and carbon storage ofeucalypt plantations in China will be very helpful to understand its important role in mitigatingglobal climate change. Only isolated studies were reported until now to characterize biomassand carbon pools of the above-ground components of eucalypt plantations in China, and studieswith the spatial and temporal heterogeneity of carbon storage in eucalypt plantations are scarce.Moreover, there is no study to quantify the amount and distribution of biomass and carbonstorage of eucalypt plantation ecosystems in Hainan province.Field experiments were conducted at northern wet area, middle mountainous area,southeastern high wet area, west Semi-humid semiarid area in Hainan, China. Chronosequenceapproach was employed to select a series of different age stands which represented the variousdevelopment stages of an individual stand. An age series of6stands (aged1,2,3,4,5and6years) were selected to study temporal and spatial biomass and carbon storage patterns ineucalypt plantation ecosystems at the four sites. The results can provide an academic referencefor budget of biomass and carbon storage of plantations, and valuable information for decisionmakers in forestry carbon sequestration programs. The main results of this thesis study asfollows:(1) Dry weights of tree components (stemwood, stembark, branches, foliage, stump androots) and above-ground biomass, below-ground biomass and total biomass of eucalypt trees inHainan were estimated as a function of diameter at breast height (DBH), tree height (H),standage and a combination of these three factors. The regression models were found to be bettermodels when DBH or H was used as the single predictor, based on R2, p-values, AIC, andresiduals. However, the advantage of such models based solely on DBH as an independent variable was that they were practically easy to construct and did not require time-consumingheight measurements in the field so that the inventory of total and component biomass wereeffective, while still being sufficiently accurate. Therefore, a complete set of equations usedDBH as the only one explanatory variable were employed to predict the individual biomass ofeach tree and the results of these equations were then pooled to obtain the total and componentbiomass per area.(2) Total biomass of eucalypt plantations increased along the age series at four sites. Totalbiomass increased from2.32t·hm-2 at a stand age of1year to114.18t·hm-2at6years atQiongzhong, varied from3.12to93.73t·hm-2at Lingao, ranged from1.40to86.98t·hm-2atDanzhou and rose from5.00to87.4486.98t·hm-2at Wanqiong. Above-ground biomass wassignificantly higher than the below-ground biomass in all plantations. Regarding componentcontribution to stand biomass, clearly, the most important component of biomass yield in anage-sequence of eucalypt plantations was the stemwood.(3) This study revealed an increasing trend in undergrowth biomass with stand age series.Undergrowth biomass at Qiongzhong ranged from1.57t·hm-2at1-year-old to7.48t·hm-2at6-year-old. Similar trends were found from0.27to7.28t·hm-2for Lingao, from1.01to6.50t·hm-2for Danzhou and from0.45to4.23t·hm-2for Wanqiong. In this study, herb biomass washigher than the shrub biomass along a chronosequence. While the proportions of herb biomassin the undergrowth biomass decreased progressively with stand age, but those of shrub biomassincreased.(4) Litterfall observed in eucalypt plantations from four sites ascended firstly and thendeclined later from1-year-old to6-year-old, and the lowest at an age of1year, the highest atan age of4or5years. The corresponding trend for eucalypt plantations at Qiongzhong variedfrom0.97to8.47t·hm-2, from1.13to6.73t·hm-2at Lingao, from1.31to17.08t·hm-2atDanzhou and from0.64to16.47t·hm-2at Wanqiong. Litterfall allocated a higher proportion ofbiomass in the undecomposed litterfall compared to that in semi-decomposed and decomposedlitterfall in the early growing period, but was opposite in the last the proportion. (5) There was an increasing in soil carbon storage of eucalypt plantations at0～100cmsoil layer with stand age. Soil carbon storage at Qionzhong varied from67.55to233.51t·hm-2according to the age gradient,63.58to148.41t·hm-2at Lingao,39.75to76.39t·hm-2atDanzhou and36.91to62.45t·hm-2at Wanqiong. In all eucalypt plantations there was a declinein soil carbon storage from0～20cm soil layer to80～100cm soil layer, and the ranges offour sites were63.50to8.96t·hm-2,34.98to9.38t·hm-2,17.48to7.73t·hm-2and13.94to6.66t·hm-2, respectively.(6) Carbon storage of eucalypt plantations at four sites in Hainan varied from40.77to294.18t·hm-2, and it increased from69.84t·hm-2at1year of age to294.18t·hm-2at6years ofage for Qiongzhong, from65.77to200.77t·hm-2for Lingao, from41.48to128.16t·hm-2forDanzhou and from40.77to113.28t·hm-2for Wanqiong. At all eucalypt plantation ecosystems,carbon storage was more concentrated in soil and trees. When tree age increased, theproportion of carbon storage allocated to the soil decreased, whereas the proportion allocated totrees increased.(7) Carbon accumulation rate of eucalypt plantation ecosystems was decreased with age.Annual net carbon sequestration of arbor layer generally graded in the fallowing order:Qiongzhong>Lingao>Wanqiong>Danzhou. Annual net carbon sequestration of eucalyptplantations at four sites was similar, ranging from10.34t·hm-2·yr-1to11.80t·hm-2·yr-1.Eucalypt plantations sequencing carbon dioxide from atmosphere reached38.28t·hm-2·yr-1forQiongzhong,38.68t·hm-2·yr-1for Lingao,37.96t·hm-2·yr-1for Danzhou and43.27t·hm-2·yr-1for Wanqiong.
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