The Effects of Machining Defects on the Lumber Quality of Cupressus lustanica (C. lusitanica) Grown in Arsi Forest Enterprise, Degaga, Ethiopia

Abstract

Machining defects are the important types of wood defects that reduce the lumber quality of most timber tree species. The purpose of this study was to evaluate the main machining defects of C. lusitanica grown in Arsi Forest Enterprise, Degaga District, and to recommend suitable harvesting age for the species based on the results obtained. Nine C. lusitanica logs representing 25, 30 and 35 years (3 trees from each age category) were used in the study. Sample trees with similar diameters (27-33 cm) at breast height and planted with an original similar stand spacing of 2.5m were collected. Sample discs obtained from bottom, middle and top portions were used to determine average initial tree moisture content (MC) and basic density. Then, the logs were transported to mobile saw mill of Arsi Forest Enterprise, Degaga and converted into 126 boards. The sawn boards were dried in the compartment kiln of the Forest Product Utilization and Research Center of Ethiopia by using seasoning schedule suggested for C. lusitanica. Thirty six boards were used for evaluation of machining defects from all the three age groups. Completely randomized design with factorial experiment was used to conduct this experiment. The statistical analyses were conducted considering three factors (3 age-groups, 3 heights and 2 tree diameter) to evaluate the effects of age, tree height and diameter on machining defects. The results showed that C. lusitanica lumber of all the age classes considered exhibit major machining defects like saw marks, chip marks, torn grain and woolly grain were observed on all age groups of lumber. Height variation (position from which the lumbers are taken along the stem) has significantly (P < 0.05) effected machining properties. On the other hand age variation also showed high significant (P < 0.01) effect on machining defects. In general, the machining properties, chip mark planing defects was high for the 25 year-old trees (4.66mm) than 30 and 35 year-old trees. Generally, the effects of age and height variation had high significant effects on the lumber quality of C. lusitanica. Based on the results harvest at 30 years of age is recommendable for the species to obtain the best lumber quality.

Keywords: Age variation, height variation, basic density, torn grain, chip mark, woolly grain.