Graduate Thesis Or Dissertation
 

Environmental effects on heartwood extractive content and their consequences for natural durability in Douglas-fir and western redcedar

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  • Heartwood can have properties that are distinct from sapwood, including resistance to insect and microbial attack. Despite the practical importance of heartwood formation in trees, a review of the literature revealed that little was known about the effects of environmental factors on heartwood quality or how variations in heartwood properties may influence natural durability. Growth rate variations in six Douglas-fir trees coincided with variations in the extractive concentration in annual rings estimated to have become heartwood at the same time. An experiment to examine the mechanisms for this phenomenon involving thinning or pruning treatments with 30 young Douglas-fir trees produced no consistent relationships between environmental changes, growth rate and heartwood extractive content. An examination of the stable carbon isotope patterns in the acetone/water-soluble wood extractives and the cellulose of Douglas-fir wood indicated that some of the sapwood extractives within an annual ring were formed at the time the ring was formed. Extractives and cellulose δ¹³C values within annual rings were correlated (R²≈0.50) across the radius of six trees, which suggested that sapwood extractives were relatively immobile over time and made an important contribution to the heartwood extractives that were subsequently deposited in the same rings. This suggests that influence-s on a wood ring at the time of formation will affect heartwood properties many years later when the ring becomes heartwood. An analysis of 24 young western redcedar trees from a silvicultural trial that involving thinning and fertilization treatments found no consistent effect of increasing growth rate on heartwood quality, as represented by various measures of extractive content. Tests of the natural durability of western redcedar and Alaska cedar heartwood against termites and fungi revealed that methanotsoluble extractives were crucial for resistance; however, correlations among extractive components were weak and extractive concentrations explained relatively little of the variation in natural durability. These studies suggest a potential for influencing heartwood quality through silviculture, but considerable research will be needed to understand the relationships between environmental factors and heartwood formation, and between heartwood variability and natural durability.
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