Effects of spacing on yield of various clones of Populus nigra L.

In order to determine the optimal spacing in respect to maximum wood production in unit area, an experiment was conducted in 1993 at West Paper Industries Co. site (West Iran), using a number of high yield exotic poplars under statistical design of factorial with three replicates. The factors consisted of spacing at four levels (1×2, 2×2, 2×3 and 2×4 m.) and Populus nigra with four clones (exotics: 62/172, 62/154 and 63/135 and native (control): 42/78). Every plot contained 25 seedlings of one year old root and stem. The growth parameters consisted of height, breast height diameter and volume which were measured and recorded annually, up to eight years. The best poplar clones in respect to maximum wood volume production at each spacing treatment were as follows: 1×2 m. spacing: P. nigra 63/135 with 54 m3/ha/y and 11.3 cm DBH 2×2 m. spacing: P. nigra 63/135 with 34.3 m3/ha/y and 13 cm DBH. 2×3 m. spacing: P. nigra 62/154 with 29 m3/ha/y 13.9 cm DBH. 2×4 m. spacing: P. nigra 63/135 with 25 m3/ha/y and 15.2 cm DBH