RELATIONSHIP BETWEEN INCIPIENT DECAY, STRENGTH, AND CHEMICAL-COMPOSITION OF DOUGLAS-FIR HEARTWOOD

A new laboratory technique to simulate the initiation of wood decay an d to assess the effects of incipient decay on material properties is d escribed. Douglas-fir heartwood specimens were exposed to brown-rot (P ostia placenta and Gloeophyllum trabeum) fungi for various periods. Be nding properties were determined by nondestructive and destructive tes ts, and chemical composition of specimens was analyzed. Weight losses of 1 to 18% were linearly related to strength losses of 5 to 70%. Wood strength loss by brown-rot fungi was also closely related to degradat ion of hemicellulose components. Hemicellulose sidechains, such as amb inose and plactose, were degraded in the earliest stages of decay; mai n-chain hemicellulose carbohydrates, such as mannose and xylose, were degraded in the later stages. Changes in glucose content, a measure of residual cellulose, were minimal. Our technique was effective for est ablishing and assessing brown-rot decay.