Strength reduction in slash pine (Pinus elliotii) wood caused by decay fungi
Small wood specimens selected from slash pine (Pinus elliotii )trees at three growth rates (fast, medium, and slow) were inoculated with brown-rot and white-rot fungi and then evaluated for work to maximum load (WML), modulus of rupture (MOR), and modulus of elasticity (MOE). The experimental variables studied included a brown-rot fungus (Gloeophyllum trabeum) and a white-rot fungus (Trametes versicolor) and six exposure periods (2, 4, 6, 8, 10, and 12 weeks) in which weight loss measurements were recorded. All samples were tested for nondestructive MOE (MOEsw) prior to static bending and the results were compared via regression analyses. There were significant differences in weight loss, WML, MOR, and MOE reductions due to tree growth rate and decay periods. The weight loss, WML, MOR, and MOE losses of all three growth rate classes treated with brown-rot fungi were greater than those exposed to white-rot fungi with the exception of very early decay (i.e., 2 weeks after inoculation). The mechanical property reduction was greater for fast grown wood than that of slow grown wood. As expected, strength decreased as exposure time to the fungi increased. The specimens exposed to brown-rot decay showed most of the strength reduction in the initial 6 weeks and after 10 weeks. The samples inoculated with the white-rot fungi showed a continual slight strength reduction for the entire 12 weeks. The results showed that the ratio of the loss in mechanical properties compared to weight loss were 7.2: 1 for WML, 6.4: 1 for MOR, and 3.8: 1 for MOE, for slash pine sapwood exposed to G. trabeum, and that of wood specimens exposed to T. versicolor were 3.0: 1 for WML, 2.2: 1 for MOR, and 4.1: 1 for MOE. Regression analysis indicated good correlations between MOEsw and static bending MOE after the 12 week exposure period.