Abstract:

Nonlinear models were established for two species of poplar (Populus simonii and P.×beijingensis ) with the wood properties indices \[vessel element length (VEL) or wood fiber length (FL) or vessel lumen diameter (VLD)] as the dependent variables and the ring number from pith to bark as independent variable. Based on this, the mature wood age and the distribution of juvenile wood in tree stems were discussed. The models that predict the maturation age according to vessel length, fiber length or the diameter of the vessel lumen were established using the segmented regression analysis which begins with a quadratic part and then reaches a plateau. The square of the correlation coefficient ( r²) of nonlinear regression ranged from 0.857 to 0.991 and correlated significantly at 0.1% level in all cases. Using the fiber length as the wood property index, the models showed that variance of maturation age and the radius of juvenile wood existed between different species and different site conditions: for P.×beijingensis without irrigation, the maturation age and the radius of juvenile wood was about 6～10 a and 52 mm, while that for P. simonii without and with irrigation was 24～29 a and 90 mm, 13～15 a and 85 mm respectively.

Key words: poplar, wood property, juvenile wood, maturation age, model