通过对杨树各个年轮的容积密度、纤维长度的测定，将测定结果绘出每株树的年轮─—容积密度、年轮─—纤维长度的变化曲线图，从曲线图中可以看出材性表现不稳定的非成熟材（幼龄材）与材性表现相对稳定的成熟材。各选出５个不相同的无性系进行测定，其结果表明：容积密度及纤维长度自髓心向外都随着年轮的增加而逐渐变大，到第７、８年轮左右达到最大值后，基本保持稳定。 According to the determination of the bulk density and fiber length of each annual ring of poplar, the results of the measurement are plotted as the annual ring-volume density, annual ring-fiber length of each tree, and as can be seen from the graph Imperfect material performance instability (young material) and the material performance is relatively stable mature wood. The results showed that the bulk density and fiber length gradually increased with the increase of annual rings from the medullary center to the maximum at the seventh and eighth rounds After the basic remained stable.