JapanSociety ofForest Planning 59 Article Estimationof Carbon Stock in using X-ray Fagus crenata Densitometry SecondaryForest Ybshihiro Nobori'L, HiromichiOnodera'2,Masato Noda"3 and 'ferutaka Katoh'À BSTRACT Global warming due to increase in the atmespheric carbon dioxide level is a matter oi grewing concern and the carbon-absorbing function of the forest is now an issue gathering public attention. Under $uch conditions, it is necessary to calculate carbon stock in tree stems, and understand

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... e details of the bulk density of stems. Ihe aim of this study is te estimate the carbon stock in the forest with guaranteed accuracy by stem analysis and soft X-ray densitometry, using a Stem Density Analyzer (SDA). Samples of beech CFZIgus crenata) were collected at Kaminagawa Experimenta1 Forest, Yamagata University [[len trees were selected from the standing trees in the investigation area. The wood disks were obtained from the stem at a 1-m interval starting from the height of O.2m. Frem each di$k, four blocks were cut out in the feur directions, and a 1.4mm-thick strip was prepared from each block using a doubletoothed circular saw. Annual ring width and bulk density were measured by soft X-ray densitometry Each 1-m-long stem segment was regarded as a cone trapezoid, and using the average of annual ring widths in four directions, wood volume fer each year was calculated. The calculated value was multiplied by average of bulk density to obtain wood dry weight for each year, and it was cenverted to carbon stock by multiplying by the rate of carbon. SDA was used for these calculations. The distributien of bulk density in the $tem was variable in the same individual, and even the average bulk density of each individual varied with the individual, even though the bulk density was measured for the individual$ with similar ages and under simi!ar environmental cenditions. 'Ihese results indicate that the examination of bulk density is impertant for the calculation of carbon stocks. 1[he diarneter at breast height (DBH) of trees was found to have a close correlation with the carbon stock. Iherefore, we estimated carbon stock per unit area using the correlatien formula between DBH and carben stock in each tree in the investigation area. Ihe estirnated carben stock per unit area in the stand was 44% greater than that estimatecl by the method currently proposed by IPCC method. Carbon stock can be estimated with high accuracy using the correlation formula between DBH and carbon stock.