Estimation of taper rates and volume of smaller-sized logs in spotted gum saw timber plantations in Southeast Queensland, Australia

Abstract

Spotted gum (Corymbia citriodora subspecies Variegata) is a popular tree species for hardwood saw timber plantations in Southeast Queensland (SEQ), Australia. In many parts of the world, logs up to 10 cm top diameter are considered to be merchantable logs and acceptable at sawmills. However, due to the higher handling costs of smaller size logs, sawmills in SEQ are only buying logs with a top diameter of 25 cm and larger. This necessitates the determination of the volume of logs with top diameters between 10 cm and 25 cm. This paper compares the taper rates of different sizes of spotted gum logs and estimates the stem volume of spotted gum logs between 10 and 24.94 cm diameter. Analysis showed that there is a statistically significant difference between the mean taper rates of bottom (30.5 - 64.2 cm diameter) and top parts of stems (10 - 24.94 cm diameter) at harvesting age. Using only the average taper rate of large diameter logs would underestimate the log volume of smaller diameter logs. The average length of spotted gum logs between 10 and 24.94 cm was found to be 19.27 m. Therefore, by the sawmill declining to use 10 to 24.94 cm diameter logs, approximately 0.55 m3 of log volume per tree at harvesting age would be lost.