Graduate Thesis Or Dissertation
 

The development and use of breaking radius and impact bending tests for measuring wood strength loss caused by basidiomycetes isolated from air-seasoning Douglas-fir

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  • Douglas-fir utility poles are routinely air seasoned before treatment with chemical preservatives. Basidiomycetous fungi invade these poles and may cause strength loss during air seasoning or later if treatment temperatures are insufficient to kill the decay fungi. The purpose of this study was to develop a rapid test to asses the ability of these fungi to degrade wood. Two tests measuring wood toughness, the first mechanical property affected by decay fungi, were chosen. The breaking radius test measures the radius of curvature a specimen can withstand without failing. The impact bending test measures the amount of energy required to cause failure as a pendulum arm strikes the specimen. Variables affecting these tests such as specimen size, grain angle, moisture content and length of incubation with a suspect decay fungus were investigated. Methodologies were designed to reduce variability and give rapid results with each test. Douglas-fir test specimens (1.7mm x 9.4mm x 5.1cm) were incubated for 4 weeks with basidiomycetes isolated from air seasoning Douglas-fir poles. Sixteen specimens per fungal isolate were sampled oven dry for breaking radius and 12 were sampled above the fiber saturation point for impact bending. Between one and 16 isolates per species were tested. Twenty-three fungal species were ranked according to decay capacity and this information was related to isolation frequency. Two brown rot fungi, Poria placenta and Poria carbonica, degrade wood rapidly and are common in air seasoning Douglas-fir. Several white rot fungi including Haematostereum sanguinolentum and Peniohpora spp. are common in Douglas-fir poles, but much less damaging to the wood. Monokaryons and dikaryons of 15 species were compared by decay capacity and no consistent relationship was found. Isolates of each species were also compared to asses within species variability. Differences were found within species with high decay capacities. Large numbers of basidiomycetes invade air seasoning Douglas-fir poles, but most cause little strength loss. This information can be used in assessing when poles or other wood products may be at risk of strength loss and in need of chemical treatment.
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