The effect of water availability on growth strain in Eucalyptus grandis-urophylla trees

Abstract

The Eucalyptus genus is the most widely planted hardwood worldwide. It is, however, mostly used for low value products as a result of various wood quality problems. Splitting and distortion of wood due to growth stresses is arguably the most critical quality issue for this genus. In this research, the effect of water availability on the peripheral and internal longitudinal growth strain of 7-year-old Eucalyptus grandis-urophylla trees was investigated. A new method using a custom modified digital dial gauge was developed for measuring the internal growth strain variability in standing trees – the first such method according to the best of our knowledge. Growth strain was measured on three sites with different water availability. The results showed that not only peripheral but also internal longitudinal growth strain was significantly affected by the water availability. Trees from the wet site showed higher surface and internal growth strain, while the trees planted on the dry site indicated lower and more uniform growth strain distribution inside their stems. Apart from the water availability, the direction of the prevailing wind was found as another influencing factor on growth strain. Both the radial and longitudinal patterns of longitudinal growth strains were determined and the results showed that growth strain decreased with height and that the neutral points of strain for all sites were between 8 and 9 tenths of the diameter from the pith. Growth strain was also measured destructively on logs and it was found that there was a significant difference between the growth strains of the logs from the same height but from different sites. The results also showed that, on the same log, the end split length per area of log cross section occurring during cross cutting could be modelled moderately well with a linear regression equation (R2 = 0.67). The model included the variables maximum compressive strain over the radius, the maximum difference of compressive and tensile strain (between south and east directions) and the sum of strain difference over the radius between adjacent points divided by the diameter.