Determining the most suitable planting spacing for superior poplar clones in Markazi province based on wood production performance

The proper spacing for planting stands is of special importance in producing well-shaped, high-quality trees with straight trunks and few knots, as well as in meeting wood production needs. In this study, the wood production performance of five successful clones of Populus nigra L. was tested at different planting spacings. Initially, a sufficient number of cuttings were obtained from the clones, and seedlings were produced in the nursery. Then, 81 one-year-old seedlings from each clone were planted at three different spacings (2×3, 2×2, and 2×1 m) and in three replicates with a randomized complete block design as split plots. Vegetative characteristics such as diameter at breast height (DBH) and total height were measured annually, and the current and average annual increments of DBH, height, and volume were calculated. The damage caused by Phloeomyzus passerinii Sign., Paranthrene tabaniformis Rott., and Monosteria unicostata (Muls & Rey) attacks was also recorded. The results showed a statistically significant difference in vegetative variables of volume per ha and average production among the different planting spacings and clones. The P.n.62/154 clone had the greatest increment in volume per ha, and the highest average yield of wood production per ha after three years was at a spacing of 2×1 m and in the P.n.62/154 clone. The P. n.62/154 clone at 2×1 m spacing is recommended for short-term exploitation and at 2×2 m spacing for medium-term exploitation. Pest investigation showed that the P. n. betulifolia 17/13 clone had the greatest damage to pests at a spacing of 2×3 m, with an 18.52% frequency. The P. n.62/154 clone at a planting spacing of 2×1 m with an average wood production of 90.88 m3 ha-1yr-1 for short-term exploitation and at a planting spacing of 2×2 m with an average wood production of 44.36 m3 ha-1yr-1 for medium-term exploitation are recommended in Markazi Province.