Effects of biodegradation by brown-rot decay on selected wood properties in eastern white cedar (Thuja occidentalis L.)

• We investigated the changes in eastern white cedar wood properties due to brown rot decay.
• X-ray densitometry and scanning electron microscopy were used to detect and assess the wood decay.
• Changes in wood density due to decay were more prominent in earlywood than latewood.
• Brown rot decay destroys wood by selectively degrading the hemicelluloses and cellulose without removing lignin.
• An important reduction of mechanical strength occurs before significant weight loss due to hemicelluloses degradation.

The effects of decay on wood density, wood structure, chemical composition, and mechanical properties in eastern white cedar (Thuja occidentalis L.) were investigated. Decay stage was determined by X-ray densitometry and scanning electron microscopy (SEM). Chemical and mechanical properties of decayed and sound wood samples were also determined. SEM results showed that decay colonization varied among wood cell types and within individual cell wall layers. Growth of fungi causing brown rot decay was limited and slower in latewood than in earlywood due to the narrow cell lumen, thicker wall, and higher density of latewood. Decay-related changes in wood density were more prominent in earlywood than latewood tracheids. Brown-rot decay selectively removes structural carbohydrate components, increasing the higher lignin/carbohydrate ratio as decay progresses. The relationships between chemical composition, mechanical properties, and weight loss were highly significant, with 15% weight loss leading to 40% loss in modulus of rupture (MOR) and 30% loss in bending modulus of elasticity (MOE). The strength loss (MOR) was attributable to arabinan and galactan loss. The loss in wood stiffness was associated with cellulose (glucan) loss, and weight loss was associated with mannan and xylans losses.