EFFECT OF INITIAL SPACING ON GAS PERMEABILITY OF POPULUS NIGRA var. BETULIFOLIA

Initial spacing during planting affects growth rate of trees and consequently influences various properties of wood. Permeability is an important property of wood that determines many of its applications. The present study was therefore focused on the effect of initial spacing on gas permeability of Populus nigra var. betulifolia in connection with its vessel properties. Treatments included four initial spacings of the poplar cuttings at 3 × 4, 3 × 6.7, 3 × 8 and 3 × 10 m of 10-year-old poplar trees, intercropped with alfalfa. Specific gas permeability values were measured at breast height in longitudinal and radial directions. Maximum longitudinal permeability value was 1631.26 × 10^-13 m3 m-1 for the 3 × 10 m treatment where maximum vessel lumen diameter was found to be 67.09 μm. Minimum longitudinal permeability was in the 3 × 4 m treatment with a value of 1052.15 × 10^-13 m3 m-1 where minimum vessel lumen diameter was observed (63.17 μm). Vessel lumen area decreased by 10.2% as the initial spacing increased from 3 × 4 to 3 × 10 m but a clear positive relation was still found between initial spacing and gas permeability. Therefore, it can be concluded that vessel lumen diameter was more influential in the determination of gas permeability than percentage of vessel lumen area.