عنوان مقاله [English]
In this trial, 24 Poplar clones (10 clones of Populus deltoides, P. euramericana and P. alba as wide crown species and 14 clones of P. nigra as narrow crown clones) were studied in Sanandaj, western Iran during 2001-2008. Planting of cuttings were accomplished on early March of 2000 and transplanting of saplings and planting were conducted on early April of 2001 with spacing of 4 m×4 m for Wide Crown Clones (WCC) and 3 m×3 m for Narrow Crown Clones (NCC) in 2 separated experiments with 3 replications. Each plot contained 25 saplings that were planted as 5×5 rows (9 saplings as main and 16 for buffer effect). In each year, some morphological traits were evaluated. Results showed that in terms of diameter at breast height (D), tree height (H) and wood volume per hectare (V) there were significant differences among years and also between WCC and NCC groups (P≤0.01). Although growth traits of tree diameter and volume during the period increased, but increasing rates in different years were different. Based on the mean comparisons of the years, there were no significant differences between the two consecutive years of growth (e.g., 2005 and 2006 etc.) in terms of the D and V traits in the NCC and WCC, but each year took place in a specific group for H in both NCC and WCC. P.a. Saghez in terms of D and V traits was different from others among WCC, but all clones of the NCC behaved almost the same from viewpoint of growth procedure. The growth rate of WCC was more than NCC, indicating the growth rate (diameter, height and volume) of WCC were higher than NCC. Based on the results and graphs of diameter (D) and wood volume (V) in both WCC and NCC, two stages of the rapid growth vs. three stages of slow growth were observed. This point indicates that the rates of diameter (D) and wood volume (V) growths are a periodic process in poplars (Populus spp.). In other words, diameter and volume growth traits had a periodic mode over the time. The phenomenon is a practical result to determine the time of cutting and harvesting of poplar trees. By calculating the growth years of trees, farmers can harvest them at the end of the rapid growth year and don’t need to remain the trees in the farm in the slow growth year. This reduces the costs of farm maintenance.