| Sichuan alder(Alnus cremastogyne)is one of the most important species and it has become a important kinds of forestation trees which consisted of the shelter belts of the plain region in the Yangtze River valley,the forest for water and soil conservation in the hilly area and base of short-rotation industrial plantation.Moreover, The Alnus cremastogyne is a specie of warm-temperature, humidity, water proof and barren tolerance, whose bole is upright and orbicular, and it is suitable for de-farming and reafforestation and ecological construction projects in Hunan province.Study on density, storage and distribution of Carbon in Alnus cremastogyne plantation ecosystem could provide some correct and basic data for making a further thorough study on carbon cycling in forest ecosystems by region scale or nation scale, or even by globe scale, and provide some references for correctly estimating ecological benefits of forest. The main results of the research are as follows:Used permanent sampling plots data investigated the carbon content of a Alnus cremastogyne plantation ecosystem. The results showed that the average foliar carbon densities in the vertical canopy profile varied from 0.5340gC/g to 0.5531gC/g, decreasing from the top to the bottom of the canopy and the average carbon density of branches in the vertical canopy profile varied from 0.5167gC/g to 0.5432gC/g in the following orde:middle canopy>lower>upper canopy.The carbon contents of different organs varied form 0.3955gC/g to 0.5199gC/g for the 3-year-old plantation, form 0.4199gC/g to 0.5435gC/g for the 5-year-old stands, form 0.4337gC/g to 0.5453gC/g for the 8-year-old stands, and 0.4250gC/g to 0.5513gC/g for the 14-year-old plantation. The variation coefficient ranged form 0.25% to 9.58%. The carbon densities of different organs varied in the following order: stems>branches>leaves>roots>bark. The arithmetic average carbon density of different organs was 0.4613gC/g for the 3 years old Alnus cremastogynes,0.4788gC/g for the 5-year-old Alnus cremastogynes,0.4857gC/g for the 8-year-old Alnus cremastogynes,and 0.4958 gC/g for the 14 years old Alnus cremastogynes.The arithmetic average carbon density of different organs of the same age Alnus cremastogyne in Huayuan area and Miluo area are 0.4788gC/g and 0.5397gC/g, The carbon densities of different organs varied in the following order in Miluo assay fields as:stems> leaves> bark> branches> roots.No obvious trends were detected for the carbon content in different groups of under-storey of plants or the duff layer as the forest aged. The carbon content in the whole canopy profile of a stand varied in the following order:over-storey trees>plants>floors.The soil organic density inceeased Along with the increase of age while decreased as the depth increased in the different age classes Alnus cremastogyne plantation. The diversity of soil organic carbon density in different layers displayed as: the 0～15cm soil layer>the 15～30cm soil layer>the 30-60cm soil layer in the different age and different assay fields Alnus cremastogyne plantation.Soil carbon contents of different layers in Alnus cremastogyne plantation was positive linear correlation with the soil pH value, and had a significant positive relationship with total nitrogen and C/N ratio.Carbon storage of Alnus cremastogyne plantation ecosystem mainly consisted of three sections, that was the trees, the litter and the soil at Huitong, Hunan, and the order of whose carbon storage could be ranked as follow:the soil>the trees>the litter. Carbon storage of the 5-year-old Alnus cremastogyne plantation, the 8-year-old Alnus cremastogyne plantation and the 14-year-old Alnus cremastogyne plantation was 95.89,120.82 and 130.75t/hm2. Superiority of carbon storage in the trees gradually strengthen with the forest stands age growth, carbon storage of the trees had gone up from 25.88 t/hm2 in the 5-year-old to 49.63t/hm2 in the 14-year-old, carbon storage of the trees in the 5-year-old, the 8-year-old and the 14-year-old occupied 26.99%, 29.73% and 37.96% of total carbon storage in the whole ecosystem.Carbon storage in forestlands soil layer (0～60cm) was a considerable figure, soil carbon storage in the 3-year-old,5-year-old, the 8-year-old and the 14-year-old Alnus cremastogyne forestlands was up to 68.24,68.61,83.55 and 77.69t/hm2, respectively, accounting for more than 59.42% of carbon storage in the whole ecosystem. In the soil layer, carbon storage of the surface soil (0～15cm) layer in the 3-year-old, the 5-year-old, the 8-year-old and the 14-year-old Alnus cremastogyne forestlands held 41.08%,38.71%,34.63% and 46.87%, of that in the soil layer (0～60cm), respectively, and that of the soil layer (0～30cm) in the 3-year-old,5-year-old, the 8-year-old and the 14-year-old Alnus cremastogyne forestlands took up 69.03%, 61.72%,61.68% and 66.55% of that in the soil layer (0-60cm), respectively. The ratio of carbon storage of aboveground to that of underground in the 5-year-old, the 8-year-old and the 14-year-old Alnus cremastogyne plantation ecosystem was 1:2.50, 1:2.24 and 1:1.46, respectively, and deceased as the Alnus cremastogyne forest age growth.Carbon storage of Huayuan assay fields Alnus cremastogyne plantation, and Miluo assay fields Alnus cremastogyne plantation was 95.89 t/hm2 and 104.91t/hm2,while soil carbon storage in Huayuan and Miluo assay fields Alnus cremastogyne plantation was respectively 68.61t/hm2 and 75.07 t/hm2, accounting for 71.55% and 71.56% of carbon storage in the whole ecosystem. The ratio of carbon storage of aboveground to that of underground in Huayuan and Miluo assay fields Alnus cremastogyne plantation ecosystem was 1:2.51 and 1:2.52.Soil carbon storage decreased as the soil depth increased,while the ratio in different layers(0-15cm,15～30cm and 30-60cm) was similar, carbon storage of soil layer in Huayuan Alnus cremastogyne forestlands held 38.71%,23.01% and 38.28%, respectively, and that of the soil layer in Miluo Alnus cremastogyne forestlands took up 38.70%,22.43% and 38.37%, respectively.The annual net primary production of the 5-year-old, the 8-year-old and the 14-year-old Alnus cremastogyne plantation was respectively 11.93,11.62 and 13.11 t/hm2-a, while their annual carbon amount was up to 5.84,5.20 and 6.08 t/hm2-a, respectively, respectively, the annual carbon amount in the litter-fall was respectively 0.66,0.71 and 1.29 t/hm2-a. Extant carbon storage and potential carbon storage of Alnus cremastogyne forest vegetation in Hunan Province was 2.2641×106t and 4.7658×106t, respectively, extant carbon storage was accounting for 47.51% of potential carbon storage.
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