Assessment of Different Methods of Form Factor Determination for Volume Estimation of Planted Populus deltoides and Taxodium distichum Trees (Klodeh Region- Mazandaran Province)

One of the most important factors in determining the volume of trees is selection of appropriate form factor. In the present study، four different methods of form factor calculation were evaluated for two rapid growth species including Populus deltoides and Taxodium distichum. For this purpose، in each stand، 12 trees per 4 diameter class ranging from 10 to 45 cm in DBH were randomly selected and diameter at breast height of all trees was measured. Then، using sectional measurement (cylindrical volume formula and Esmalyan) method، the actual volume of each tree was calculated. Also، Real (Fr)، Normal (F0. 1)، Artificial (F1. 3) and Hohenadl (Fh) form factors were measured. Analyses of variances were used to investigate any significant differences between the calculated coefficients. Dunnett''s test was used to explore significant differences between various methods of coefficient calculation and the real form factor coefficients. Results showed that for Populus deltoides، artificial form factor (0. 50) was closer to the real form factor (0. 51) while for Taxodium distichum، hohenadl form factor (0. 52) was closest to the real form factor (0. 50). In addition، natural and artificial form factors were related to DBH، but real and hohenadl form factors were not related to DBH. Artificial form factor can be used for both species in this study as a suitable and useful form factor.