In order to determine the best form factor equation for Loblolly Pine (Pinus taeda L.) plantations in Talesh (Western Guilan province-Iran), a number of 110 individual trees were selected based on diameter classes, from 12 to 34 cm (in a two cm diameter interval). First, several quantitative factors including diameter at breast height, diameter at 0.65 m of height, and diameter at stump were measured using a diameter tape, just before the trees being cut. Secondly After cutting the trees, their heights, and their diameter from breast height up to the height where diameter is 2 cm was measured using a diameter tape in a two meter interval. Finally, diameter at 0.1, 0.3, 0.5, 0.7, and 0.9 meter of the total height was measured for each tree. Consequently, each tree's volume was then precisely calculated based on the factors measured. it was used as the real volume. Next, the Real form factor ( ) was calculated for each tree and its average was compared statistically to the averages of Natural ( ), Artificial ( ), and Hohenadl’s ( ) form factors, using pair wise T-test. Results of the study showed that there is not a significant difference between the averages of real and Hohenadl’s form factors (at = 0.01 level). Furthermore, no significant difference was observed between the averages of real and artificial form factors. Hence, both artificial and Hohenadl’s form factors are capable to replace the real form factor of Loblolly Pine in the study area.
