Aboveground Decay Resistance of Selected Canadian Softwoods at Four Test Sites after 10 Years of Exposure

Aboveground field performance data are needed to help users select appropriate materials, assist in the development of
evidence-based codes and standards, and support the development of new export markets. A review of the literature in the
early 2000s revealed that there was very little hard data on the performance of North American naturally durable wood
species, particularly for aboveground applications. Field tests of six Canadian wood species reputed to have moderate to high
natural durability were therefore installed in test out-of-ground contact in the autumn of 2004 and spring of 2005 at two test
sites in Canada and two in the United States. Decay results are reported after 10 years. The test site with the fastest
aboveground decay rate was in Hawaii. Above ground, yellow cedar (Callitropsis nootkatensis) and western red cedar (Thuja
plicata) were the most consistently durable at all four test sites. However, it would not have been possible to predict the
relative performance of naturally durable species in one climate and location from their relative performance in another
climate and location. The presence of sapwood was associated with more severe decay, although it was unclear whether the
presence of sapwood increased the risk of decay in the adjacent heartwood. There was no substantial difference between
decay in old-growth and second-growth samples above ground. The presence of a coating applied to decking had some
protective effect against decay at the less aggressive test sites.

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