Visual identification, physical properties, ash composition, and water diffusion of wetwood in Gmelina arborea

Wetwood is commonly reported in temperate species but not so in tropical species. In an old Gmelina arborea Roxb. plantation, wetwood was identified by a darker colour compared with the rest of heartwood; by a higher moisture content (average 182%); and a lower specific gravity (0.34, compared with 0.38 for sapwood and heartwood). Tangential shrinkage was 3.7%, which was significantly higher than that of heartwood and sapwood. Radial shrinkage was not significantly different between wetwood and sapwood, but it was significantly greater (2.6%) in wetwood than in heartwood (1.8%). Wetwood had a significantly higher pH than normal wood, but ash composition was similar to that of normal wood, with the exception of the amounts of iron and potassium. Wetwood and sapwood were less decay resistant than heartwood. Wetwood required less time than heartwood to reach equilibrium moisture content, but more time than sapwood. The tangential and longitudinal diffusion coefficients of wetwood were significantly higher than those of heartwood and lower than those of sapwood. In the radial direction sapwood showed a faster drying rate than wetwood but there was no significant difference between wetwood and heartwood.