Effects of site and tree size on wood density and bark properties of Lebombo ironwood (Androstachys johnsonii Prain)

Abstract

Background: Wood and bark are important renewable natural resources. Density is an important property that is used to describe wood and bark quality for a number of end uses. However, wood and bark density, bark proportion and dimensions vary with age and site, as well as among and within trees. The aim of this study was to investigate the effect of site, diameter class, and vertical position within the stem on the density of wood and bark, bark volume, bark dry-mass and thickness of Lebombo ironwood (Androstachys johnsonii Prain). Methods: The study was conducted on 93 Lemombo ironwood trees growing in Mozambique. Eight discs were sampled from each selected tree and diameter over and under bark was measured. Bark thickness, bark mass and bark density were determined along with the basic wood density of each disc. Results: The overall average whole-stem properties were estimated at: 786 kg m–3 wood density, 586 kg m–3 bark density, 19% bark volume, 19% bark dry-mass, and 9 mm bark thickness. Height level uniquely explained most of the variation in bark mass (97%), bark volume (95%) and wood density (86%). Diameter class explained most of the variation in bark density (51%) and bark thickness (51%). Site only explained a small proportion of the variation in all dependent variables. Conclusions: Overall, the patterns of variation of all wood and bark properties were highly dependent on tree diameter class and vertical position within the stem. Site differences were not a significant source of variation in the properties studied. Improved knowledge of the wood and bark properties of this species will aid its sustainable management and utilisation.