The effect of spacing on quantitative and qualitative characteristics of black poplar (Populus nigra L.)

In this study we assessed the role of plantation spacing on the quantitative and qualitative characteristics of black poplar (Populous nigra L.) in three stands at 1/5×1, 1/5×irregular (0.44-1) and 3×1-meter planting intervals in the campus of Urmia University. The diameter at breast height (dbh) along with qualitative characteristics, including tree forking and vitality, crown and/or stem breakage and tree leaning of all individuals, were assessed in an area of 2500 m2 in each stand. To calculate form factor (F), 30 stems were chosen randomly in each stand (90 in total) and felled at 10-15 cm above ground. The diameter of all cut trees was measured at intervals of 0.1, 0.3, 0.5, 0.7 and 0.9 of tree length. A growth-ring disk (cross-section) was obtained from the stump of each tree to study the relationships between annual rings and plantation spacing. Furthermore, the standing volume of each stand was calculated using Huber, Hohenadel and simple (F=0.5) formulas. Results showed that the maximum dbh and height growth occurred in 1x3 m and 1x1/5 m planting intervals, respectively (α=5%). Also, the minimum mean volume was recorded for 1/5×irregular spacing. No significant differences were obtained for the amount of standing volume/ha using the three methods. Based on our results, the highest incidence of stem breakage and nearly 50% of tilted trees were observed in 1/5×1 m spacing.