Abstract: Stem analysis is the most fundamental technique in forest mensuration. The traditional method for measuring diameters of tree rings is to average two geomagnetic directions (southnorth and eastwest) passing through the pith, which are perpendicular to each other. Since disks are usually eccentric, biomass or section area estimated by diameters passing through the pith can be significantly underestimated in general, which has been ignored in the past. This oldstyle method has never been challenged in dealing with accuracy. A new method, tested by digital photo technology, for getting individual ring diameters more close to the real diameters, was proposed in this paper. The line representing diameter of a ring was not necessarily set through the pith, rather on a subtense close to the real diameter. The ring diameters of the disks were measured by using different methods for accuracy comparison. It is proved that this method is more accurate than the traditional one tested by circularity index and closeness index. The method is easier for operation compared with the traditional one, which is expected to reduce the uncertainty in the measurement of tree growth as well as forest productivity.

Key words: DCCA, environmental interpretation., TWINSPAN, plant community